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%bookinfo;
]>
FreeBSD Developers' HandbookThe FreeBSD Documentation Projectdoc@FreeBSD.orgAugust 20002000The FreeBSD Documentation Project
&bookinfo.legalnotice;
Welcome to the Developers' Handbook.IntroductionDeveloping on FreeBSDThis will need to discuss FreeBSD as a development
platform, the vision of BSD, architectural overview, layout of
/usr/src, history, etc.Thank you for considering FreeBSD as your development
platform! We hope it will not let you down.The BSD VisionArchitectural OverviewThe Layout of /usr/srcThe complete source code to FreeBSD is available from our
public CVS repository. The source code is normally installed in
/usr/src which contains the
following subdirectories.DirectoryDescriptionbin/Source for files in
/bincontrib/Source for files from contribued software.crypto/DES sourceetc/Source for files in /etcgames/Source for files in /usr/gamesgnu/Utilities covered by the GNU Public Licenseinclude/Source for files in /usr/includekerberosIV/Source for Kerbereros version IVkerberos5/Source for Kerbereros version 5lib/Source for files in /usr/liblibexec/Source for files in /usr/libexecrelease/Files required to produce a FreeBSD releasesbin/Source for files in /sbinsecure/FreeSec sourcesshare/Source for files in /sbinsys/Kernel source filestools/Tools used for maintenance and testing of
FreeBSDusr.bin/Source for files in /usr/binusr.sbin/Source for files in /usr/sbinBasics
-
- Compilation
+
+ Programming Tools
- This will include things like: compilation, makefiles, .mk
- files, basic debugging, linking, secure programming
- guidelines, style(9), CVS, diff, patch, etc.
+ This chapter was written by James Raynard.
+ Modifications for the Developer's Handbook by Murray Stokely.
+
+
+ Synopsis
+
+ This document is an introduction to using some of the
+ programming tools supplied with FreeBSD, although much of it
+ will be applicable to many other versions of Unix. It does
+ not attempt to describe coding in any
+ detail. Most of the document assumes little or no previous
+ programming knowledge, although it is hoped that most
+ programmers will find something of value in it
+
+
+
+ Introduction
+
+ FreeBSD offers an excellent development environment.
+ Compilers for C, C++, and Fortran and an assembler come with the
+ basic system, not to mention a Perl interpreter and classic Unix
+ tools such as sed and awk.
+ If that is not enough, there are many more compilers and
+ interpreters in the Ports collection. FreeBSD is very
+ compatible with standards such as POSIX and
+ ANSI C, as well with its own BSD heritage, so
+ it is possible to write applications that will compile and run
+ with little or no modification on a wide range of
+ platforms.
+
+ However, all this power can be rather overwhelming at
+ first if you've never written programs on a Unix platform
+ before. This document aims to help you get up and running,
+ without getting too deeply into more advanced topics. The
+ intention is that this document should give you enough of the
+ basics to be able to make some sense of the
+ documentation.
+
+ Most of the document requires little or no knowledge of
+ programming, although it does assume a basic competence with
+ using Unix and a willingness to learn!
+
+
+
+
+ Introduction to Programming
+
+ A program is a set of instructions that tell the computer
+ to do various things; sometimes the instruction it has to
+ perform depends on what happened when it performed a previous
+ instruction. This section gives an overview of the two main
+ ways in which you can give these instructions, or
+ commands as they are usually called. One way
+ uses an interpreter, the other a
+ compiler. As human languages are too
+ difficult for a computer to understand in an unambiguous way,
+ commands are usually written in one or other languages specially
+ designed for the purpose.
+
+
+ Interpreters
+
+ With an interpreter, the language comes as an environment,
+ where you type in commands at a prompt and the environment
+ executes them for you. For more complicated programs, you can
+ type the commands into a file and get the interpreter to load
+ the file and execute the commands in it. If anything goes
+ wrong, many interpreters will drop you into a debugger to help
+ you track down the problem.
+
+ The advantage of this is that you can see the results of
+ your commands immediately, and mistakes can be corrected
+ readily. The biggest disadvantage comes when you want to
+ share your programs with someone. They must have the same
+ interpreter, or you must have some way of giving it to them,
+ and they need to understand how to use it. Also users may not
+ appreciate being thrown into a debugger if they press the
+ wrong key! From a performance point of view, interpreters can
+ use up a lot of memory, and generally do not generate code as
+ efficiently as compilers.
+
+ In my opinion, interpreted languages are the best way to
+ start if you have not done any programming before. This kind
+ of environment is typically found with languages like Lisp,
+ Smalltalk, Perl and Basic. It could also be argued that the
+ Unix shell (sh, csh) is itself an
+ interpreter, and many people do in fact write shell
+ scripts to help with various
+ housekeeping tasks on their machine. Indeed, part
+ of the original Unix philosophy was to provide lots of small
+ utility programs that could be linked together in shell
+ scripts to perform useful tasks.
+
+
+
+ Interpreters available with FreeBSD
+
+ Here is a list of interpreters that are available as
+ FreeBSD
+ packages, with a brief discussion of some of the
+ more popular interpreted languages.
+
+ To get one of these packages, all you need to do is to
+ click on the hotlink for the package, then run
+
+ &prompt.root; pkg_add package name
+
+
+ as root. Obviously, you will need to have a fully
+ functional FreeBSD 2.1.0 or later system for the package to
+ work!
+
+
+
+ BASIC
+
+
+ Short for Beginner's All-purpose Symbolic
+ Instruction Code. Developed in the 1950s for teaching
+ University students to program and provided with every
+ self-respecting personal computer in the 1980s,
+ BASIC has been the first programming
+ language for many programmers. It's also the foundation
+ for Visual Basic.
+
+ The Bywater
+ Basic Interpreter and the Phil
+ Cockroft's Basic Interpreter (formerly Rabbit
+ Basic) are available as FreeBSD FreeBSD
+ packages
+
+
+
+
+ Lisp
+
+
+ A language that was developed in the late 1950s as
+ an alternative to the number-crunching
+ languages that were popular at the time. Instead of
+ being based on numbers, Lisp is based on lists; in fact
+ the name is short for List Processing.
+ Very popular in AI (Artificial Intelligence)
+ circles.
+
+ Lisp is an extremely powerful and sophisticated
+ language, but can be rather large and unwieldy.
+
+ FreeBSD has GNU
+ Common Lisp available as a package.
+
+
+
+
+ Perl
+
+
+ Very popular with system administrators for writing
+ scripts; also often used on World Wide Web servers for
+ writing CGI scripts.
+
+ The latest version (version 5) comes with FreeBSD.
+
+
+
+
+ Scheme
+
+
+ A dialect of Lisp that is rather more compact and
+ cleaner than Common Lisp. Popular in Universities as it
+ is simple enough to teach to undergraduates as a first
+ language, while it has a high enough level of
+ abstraction to be used in research work.
+
+ FreeBSD has packages of the Elk
+ Scheme Interpreter, the MIT
+ Scheme Interpreter and the SCM
+ Scheme Interpreter.
+
+
+
+
+ Icon
+
+
+ The
+ Icon Programming Language.
+
+
+
+
+ Logo
+
+
+ Brian
+ Harvey's LOGO Interpreter.
+
+
+
+
+ Python
+
+
+ The
+ Python Object-Oriented Programming
+ Language
+
+
+
+
+
+
+ Compilers
+
+ Compilers are rather different. First of all, you write
+ your code in a file (or files) using an editor. You then run
+ the compiler and see if it accepts your program. If it did
+ not compile, grit your teeth and go back to the editor; if it
+ did compile and gave you a program, you can run it either at a
+ shell command prompt or in a debugger to see if it works
+ properly.
+
+
+ If you run it in the shell, you may get a core
+ dump.
+
+
+ Obviously, this is not quite as direct as using an
+ interpreter. However it allows you to do a lot of things
+ which are very difficult or even impossible with an
+ interpreter, such as writing code which interacts closely with
+ the operating system—or even writing your own operating
+ system! It's also useful if you need to write very efficient
+ code, as the compiler can take its time and optimise the code,
+ which would not be acceptable in an interpreter. And
+ distributing a program written for a compiler is usually more
+ straightforward than one written for an interpreter—you
+ can just give them a copy of the executable, assuming they
+ have the same operating system as you.
+
+ Compiled languages include Pascal, C and C++. C and C++
+ are rather unforgiving languages, and best suited to more
+ experienced programmers; Pascal, on the other hand, was
+ designed as an educational language, and is quite a good
+ language to start with. Unfortunately, FreeBSD doesn't have
+ any Pascal support, except for a Pascal-to-C converter in the
+ ports.
+
+ As the edit-compile-run-debug cycle is rather tedious when
+ using separate programs, many commercial compiler makers have
+ produced Integrated Development Environments
+
+ (IDEs for short). FreeBSD does not have an
+ IDE as such; however it is possible to use Emacs
+ for this purpose. This is discussed in .
+
+
+
+
+
+
+
+ Compiling with <command>cc</command>
+
+ This section deals only with the GNU compiler for C and C++,
+ since that comes with the base FreeBSD system. It can be
+ invoked by either cc or gcc. The
+ details of producing a program with an interpreter vary
+ considerably between interpreters, and are usually well covered
+ in the documentation and on-line help for the
+ interpreter.
+
+ Once you've written your masterpiece, the next step is to
+ convert it into something that will (hopefully!) run on FreeBSD.
+ This usually involves several steps, each of which is done by a
+ separate program.
+
+
+
+ Pre-process your source code to remove comments and do
+ other tricks like expanding macros in C.
+
+
+
+ Check the syntax of your code to see if you have obeyed
+ the rules of the language. If you have not, it will
+ complain!
+
+
+
+ Convert the source code into assembly
+ language—this is very close to machine code, but still
+ understandable by humans. Allegedly.
+
+
+ To be strictly accurate, cc converts the
+ source code into its own, machine-independent
+ p-code instead of assembly language at
+ this stage.
+
+
+
+
+ Convert the assembly language into machine
+ code—yep, we are talking bits and bytes, ones and
+ zeros here.
+
+
+
+ Check that you have used things like functions and
+ global variables in a consistent way. For example, if you
+ have called a non-existent function, it will
+ complain.
+
+
+
+ If you are trying to produce an executable from several
+ source code files, work out how to fit them all
+ together.
+
+
+
+ Work out how to produce something that the system's
+ run-time loader will be able to load into memory and
+ run.
+
+
+
+ Finally, write the executable on the file system.
+
+
+
+ The word compiling is often used to refer to
+ just steps 1 to 4—the others are referred to as
+ linking. Sometimes step 1 is referred to as
+ pre-processing and steps 3-4 as
+ assembling.
+
+ Fortunately, almost all this detail is hidden from you, as
+ cc is a front end that manages calling all these
+ programs with the right arguments for you; simply typing
+
+ &prompt.user; cc foobar.c
+
+
+ will cause foobar.c to be compiled by all the
+ steps above. If you have more than one file to compile, just do
+ something like
+
+ &prompt.user; cc foo.c bar.c
+
+
+ Note that the syntax checking is just that—checking
+ the syntax. It will not check for any logical mistakes you may
+ have made, like putting the program into an infinite loop, or
+ using a bubble sort when you meant to use a binary
+ sort.
+
+
+ In case you didn't know, a binary sort is an efficient
+ way of sorting things into order and a bubble sort
+ isn't.
+
+
+ There are lots and lots of options for cc, which
+ are all in the man page. Here are a few of the most important
+ ones, with examples of how to use them.
+
+
+
+
+
+
+ The output name of the file. If you do not use this
+ option, cc will produce an executable called
+ a.out.
+
+
+ The reasons for this are buried in the mists of
+ history.
+
+
+
+ &prompt.user; cc foobar.c executable is a.out
+&prompt.user; cc -o foobar foobar.c executable is foobar
+
+
+
+
+
+
+
+
+
+ Just compile the file, do not link it. Useful for toy
+ programs where you just want to check the syntax, or if
+ you are using a Makefile.
+
+
+ &prompt.user; cc -c foobar.c
+
+
+
+ This will produce an object file (not an
+ executable) called foobar.o. This
+ can be linked together with other object files into an
+ executable.
+
+
+
+
+
+
+
+ Create a debug version of the executable. This makes
+ the compiler put information into the executable about
+ which line of which source file corresponds to which
+ function call. A debugger can use this information to show
+ the source code as you step through the program, which is
+ very useful; the disadvantage is that
+ all this extra information makes the program much bigger.
+ Normally, you compile with while you
+ are developing a program and then compile a release
+ version without when you're
+ satisfied it works properly.
+
+
+ &prompt.user; cc -g foobar.c
+
+
+
+ This will produce a debug version of the
+ program.
+
+
+ Note, we didn't use the flag
+ to specify the executable name, so we will get an
+ executable called a.out.
+ Producing a debug version called
+ foobar is left as an exercise for
+ the reader!
+
+
+
+
+
+
+
+
+ Create an optimised version of the executable. The
+ compiler performs various clever tricks to try and produce
+ an executable that runs faster than normal. You can add a
+ number after the to specify a higher
+ level of optimisation, but this often exposes bugs in the
+ compiler's optimiser. For instance, the version of
+ cc that comes with the 2.1.0 release of
+ FreeBSD is known to produce bad code with the
+ option in some circumstances.
+
+ Optimisation is usually only turned on when compiling
+ a release version.
+
+
+ &prompt.user; cc -O -o foobar foobar.c
+
+
+
+ This will produce an optimised version of
+ foobar.
+
+
+
+
+ The following three flags will force cc
+ to check that your code complies to the relevant international
+ standard, often referred to as the ANSI
+ standard, though strictly speaking it is an
+ ISO standard.
+
+
+
+
+
+
+ Enable all the warnings which the authors of
+ cc believe are worthwhile. Despite the
+ name, it will not enable all the warnings
+ cc is capable of.
+
+
+
+
+
+
+
+ Turn off most, but not all, of the
+ non-ANSI C features provided by
+ cc. Despite the name, it does not
+ guarantee strictly that your code will comply to the
+ standard.
+
+
+
+
+
+
+
+ Turn off all
+ cc's non-ANSI C
+ features.
+
+
+
+
+ Without these flags, cc will allow you to
+ use some of its non-standard extensions to the standard. Some
+ of these are very useful, but will not work with other
+ compilers—in fact, one of the main aims of the standard is
+ to allow people to write code that will work with any compiler
+ on any system. This is known as portable
+ code.
+
+ Generally, you should try to make your code as portable as
+ possible, as otherwise you may have to completely re-write the
+ program later to get it to work somewhere else—and who
+ knows what you may be using in a few years time?
+
+
+ &prompt.user; cc -Wall -ansi -pedantic -o foobar foobar.c
+
+
+
+ This will produce an executable foobar
+ after checking foobar.c for standard
+ compliance.
+
+
+
+
+
+
+ Specify a function library to be used during when
+ linking.
+
+ The most common example of this is when compiling a
+ program that uses some of the mathematical functions in C.
+ Unlike most other platforms, these are in a separate
+ library from the standard C one and you have to tell the
+ compiler to add it.
+
+ The rule is that if the library is called
+ libsomething.a,
+ you give cc the argument
+ .
+ For example, the math library is
+ libm.a, so you give
+ cc the argument .
+ A common gotcha with the math library is
+ that it has to be the last library on the command
+ line.
+
+
+ &prompt.user; cc -o foobar foobar.c -lm
+
+
+
+ This will link the math library functions into
+ foobar.
+
+ If you are compiling C++ code, you need to add
+ , or if
+ you are using FreeBSD 2.2 or later, to the command line
+ argument to link the C++ library functions.
+ Alternatively, you can run c++ instead
+ of cc, which does this for you.
+ c++ can also be invoked as
+ g++ on FreeBSD.
+
+
+ &prompt.user; cc -o foobar foobar.cc -lg++For FreeBSD 2.1.6 and earlier
+&prompt.user; cc -o foobar foobar.cc -lstdc++For FreeBSD 2.2 and later
+&prompt.user; c++ -o foobar foobar.cc
+
+
+
+ Each of these will both produce an executable
+ foobar from the C++ source file
+ foobar.cc. Note that, on Unix
+ systems, C++ source files traditionally end in
+ .C, .cxx or
+ .cc, rather than the
+ MS-DOS style
+ .cpp (which was already used for
+ something else). gcc used to rely on
+ this to work out what kind of compiler to use on the
+ source file; however, this restriction no longer applies,
+ so you may now call your C++ files
+ .cpp with impunity!
+
+
+
+
+
+ Common <command>cc</command> Queries and Problems
+
+
+
+
+ I am trying to write a program which uses the
+ sin() function and I get an error
+ like this. What does it mean?
+
+
+ /var/tmp/cc0143941.o: Undefined symbol `_sin' referenced from text segment
+
+
+
+
+
+ When using mathematical functions like
+ sin(), you have to tell
+ cc to link in the math library, like
+ so:
+
+
+ &prompt.user; cc -o foobar foobar.c -lm
+
+
+
+
+
+
+
+ All right, I wrote this simple program to practice
+ using . All it does is raise 2.1 to
+ the power of 6.
+
+
+ #include <stdio.h>
+
+int main() {
+ float f;
+
+ f = pow(2.1, 6);
+ printf("2.1 ^ 6 = %f\n", f);
+ return 0;
+}
+
+
+
+ and I compiled it as:
+
+
+ &prompt.user; cc temp.c -lm
+
+
+
+ like you said I should, but I get this when I run
+ it:
+
+
+ &prompt.user; ./a.out
+2.1 ^ 6 = 1023.000000
+
+
+
+ This is not the right answer!
+ What is going on?
+
+
+
+ When the compiler sees you call a function, it
+ checks if it has already seen a prototype for it. If it
+ has not, it assumes the function returns an
+ int, which is definitely not what you want
+ here.
+
+
+
+
+
+ So how do I fix this?
+
+
+
+ The prototypes for the mathematical functions are in
+ math.h. If you include this file,
+ the compiler will be able to find the prototype and it
+ will stop doing strange things to your
+ calculation!
+
+
+ #include <math.h>
+#include <stdio.h>
+
+int main() {
+...
+
+
+
+ After recompiling it as you did before, run
+ it:
+
+
+ &prompt.user; ./a.out
+2.1 ^ 6 = 85.766121
+
+
+
+ If you are using any of the mathematical functions,
+ always include
+ math.h and remember to link in the
+ math library.
+
+
+
+
+
+ I compiled a file called
+ foobar.c and I cannot find an
+ executable called foobar. Where's
+ it gone?
+
+
+
+ Remember, cc will call the
+ executable a.out unless you tell it
+ differently. Use the
+
+ option:
+
+
+ &prompt.user; cc -o foobar foobar.c
+
+
+
+
+
+
+
+ OK, I have an executable called
+ foobar, I can see it when I run
+ ls, but when I type in
+ foobar at the command prompt it tells
+ me there is no such file. Why can it not find
+ it?
+
+
+
+ Unlike MS-DOS, Unix does not
+ look in the current directory when it is trying to find
+ out which executable you want it to run, unless you tell
+ it to. Either type ./foobar, which
+ means run the file called
+ foobar in the current
+ directory, or change your PATH environment
+ variable so that it looks something like
+
+
+ bin:/usr/bin:/usr/local/bin:.
+
+
+
+ The dot at the end means look in the current
+ directory if it is not in any of the
+ others.
+
+
+
+
+
+ I called my executable test,
+ but nothing happens when I run it. What is going
+ on?
+
+
+
+ Most Unix systems have a program called
+ test in /usr/bin
+ and the shell is picking that one up before it gets to
+ checking the current directory. Either type:
+
+
+ &prompt.user; ./test
+
+
+
+ or choose a better name for your program!
+
+
+
+
+
+ I compiled my program and it seemed to run all right
+ at first, then there was an error and it said something
+ about core dumped. What does that
+ mean?
+
+
+
+ The name core dump dates back
+ to the very early days of Unix, when the machines used
+ core memory for storing data. Basically, if the program
+ failed under certain conditions, the system would write
+ the contents of core memory to disk in a file called
+ core, which the programmer could
+ then pore over to find out what went wrong.
+
+
+
+
+
+ Fascinating stuff, but what I am supposed to do
+ now?
+
+
+
+ Use gdb to analyse the core (see
+ ).
+
+
+
+
+
+ When my program dumped core, it said something about
+ a segmentation fault. What's
+ that?
+
+
+
+ This basically means that your program tried to
+ perform some sort of illegal operation on memory; Unix
+ is designed to protect the operating system and other
+ programs from rogue programs.
+
+ Common causes for this are:
+
+
+
+ Trying to write to a NULL
+ pointer, eg
+
+ char *foo = NULL;
+strcpy(foo, "bang!");
+
+
+
+
+ Using a pointer that hasn't been initialised,
+ eg
+
+ char *foo;
+strcpy(foo, "bang!");
+
+
+ The pointer will have some random value that,
+ with luck, will point into an area of memory that
+ isn't available to your program and the kernel will
+ kill your program before it can do any damage. If
+ you're unlucky, it'll point somewhere inside your
+ own program and corrupt one of your data structures,
+ causing the program to fail mysteriously.
+
+
+
+ Trying to access past the end of an array,
+ eg
+
+ int bar[20];
+bar[27] = 6;
+
+
+
+
+ Trying to store something in read-only memory,
+ eg
+
+ char *foo = "My string";
+strcpy(foo, "bang!");
+
+
+ Unix compilers often put string literals like
+ "My string" into read-only areas
+ of memory.
+
+
+
+ Doing naughty things with
+ malloc() and
+ free(), eg
+
+ char bar[80];
+free(bar);
+
+
+ or
+
+ char *foo = malloc(27);
+free(foo);
+free(foo);
+
+
+
+
+ Making one of these mistakes will not always lead to
+ an error, but they are always bad practice. Some
+ systems and compilers are more tolerant than others,
+ which is why programs that ran well on one system can
+ crash when you try them on an another.
+
+
+
+
+
+ Sometimes when I get a core dump it says
+ bus error. It says in my Unix
+ book that this means a hardware problem, but the
+ computer still seems to be working. Is this
+ true?
+
+
+
+ No, fortunately not (unless of course you really do
+ have a hardware problem…). This is usually
+ another way of saying that you accessed memory in a way
+ you shouldn't have.
+
+
+
+
+
+ This dumping core business sounds as though it could
+ be quite useful, if I can make it happen when I want to.
+ Can I do this, or do I have to wait until there's an
+ error?
+
+
+
+ Yes, just go to another console or xterm, do
+
+ &prompt.user; ps
+
+
+ to find out the process ID of your program, and
+ do
+
+ &prompt.user; kill -ABRT pid
+
+
+ where
+ pid is
+ the process ID you looked up.
+
+ This is useful if your program has got stuck in an
+ infinite loop, for instance. If your program happens to
+ trap SIGABRT, there are several other
+ signals which have a similar effect.
+
+
+
+
+
+
+
+ Make
+
+
+ What is <command>make</command>?
+
+ When you're working on a simple program with only one or
+ two source files, typing in
+
+ &prompt.user; cc file1.c file2.c
+
+
+ is not too bad, but it quickly becomes very tedious when
+ there are several files—and it can take a while to
+ compile, too.
+
+ One way to get around this is to use object files and only
+ recompile the source file if the source code has changed. So
+ we could have something like:
+
+ &prompt.user; cc file1.o file2.o … file37.c &hellip
+
+
+ if we'd changed file37.c, but not any
+ of the others, since the last time we compiled. This may
+ speed up the compilation quite a bit, but doesn't solve the
+ typing problem.
+
+ Or we could write a shell script to solve the typing
+ problem, but it would have to re-compile everything, making it
+ very inefficient on a large project.
+
+ What happens if we have hundreds of source files lying
+ about? What if we're working in a team with other people who
+ forget to tell us when they've changed one of their source
+ files that we use?
+
+ Perhaps we could put the two solutions together and write
+ something like a shell script that would contain some kind of
+ magic rule saying when a source file needs compiling. Now all
+ we need now is a program that can understand these rules, as
+ it's a bit too complicated for the shell.
+
+ This program is called make. It reads
+ in a file, called a makefile, that
+ tells it how different files depend on each other, and works
+ out which files need to be re-compiled and which ones don't.
+ For example, a rule could say something like if
+ fromboz.o is older than
+ fromboz.c, that means someone must have
+ changed fromboz.c, so it needs to be
+ re-compiled. The makefile also has rules telling
+ make how to re-compile the source file,
+ making it a much more powerful tool.
+
+ Makefiles are typically kept in the same directory as the
+ source they apply to, and can be called
+ makefile, Makefile
+ or MAKEFILE. Most programmers use the
+ name Makefile, as this puts it near the
+ top of a directory listing, where it can easily be
+ seen.
+
+
+ They don't use the MAKEFILE form
+ as block capitals are often used for documentation files
+ like README.
+
+
+
+
+ Example of using <command>make</command>
+
+ Here's a very simple make file:
+
+ foo: foo.c
+ cc -o foo foo.c
+
+
+ It consists of two lines, a dependency line and a creation
+ line.
+
+ The dependency line here consists of the name of the
+ program (known as the target), followed
+ by a colon, then whitespace, then the name of the source file.
+ When make reads this line, it looks to see
+ if foo exists; if it exists, it compares
+ the time foo was last modified to the
+ time foo.c was last modified. If
+ foo does not exist, or is older than
+ foo.c, it then looks at the creation line
+ to find out what to do. In other words, this is the rule for
+ working out when foo.c needs to be
+ re-compiled.
+
+ The creation line starts with a tab (press
+ the tab key) and then the command you would
+ type to create foo if you were doing it
+ at a command prompt. If foo is out of
+ date, or does not exist, make then executes
+ this command to create it. In other words, this is the rule
+ which tells make how to re-compile
+ foo.c.
+
+ So, when you type make, it will
+ make sure that foo is up to date with
+ respect to your latest changes to foo.c.
+ This principle can be extended to
+ Makefiles with hundreds of
+ targets—in fact, on FreeBSD, it is possible to compile
+ the entire operating system just by typing make
+ world in the appropriate directory!
+
+ Another useful property of makefiles is that the targets
+ don't have to be programs. For instance, we could have a make
+ file that looks like this:
+
+ foo: foo.c
+ cc -o foo foo.c
+
+install:
+ cp foo /home/me
+
+
+ We can tell make which target we want to make by
+ typing:
+
+ &prompt.user; make target
+
+
+ make will then only look at that target
+ and ignore any others. For example, if we type
+ make foo with the makefile above, make
+ will ignore the install target.
+
+ If we just type make on its own,
+ make will always look at the first target and then stop
+ without looking at any others. So if we typed
+ make here, it will just go to the
+ foo target, re-compile
+ foo if necessary, and then stop without
+ going on to the install target.
+
+ Notice that the install target doesn't
+ actually depend on anything! This means that the command on
+ the following line is always executed when we try to make that
+ target by typing make install. In this
+ case, it will copy foo into the user's
+ home directory. This is often used by application makefiles,
+ so that the application can be installed in the correct
+ directory when it has been correctly compiled.
+
+ This is a slightly confusing subject to try and explain.
+ If you don't quite understand how make
+ works, the best thing to do is to write a simple program like
+ hello world and a make file like the one above
+ and experiment. Then progress to using more than one source
+ file, or having the source file include a header file. The
+ touch command is very useful here—it
+ changes the date on a file without you having to edit
+ it.
+
+
+
+ FreeBSD Makefiles
+
+ Makefiles can be rather complicated to write. Fortunately,
+ BSD-based systems like FreeBSD come with some very powerful
+ ones as part of the system. One very good example of this is
+ the FreeBSD ports system. Here's the essential part of a
+ typical ports Makefile:
+
+ MASTER_SITES= ftp://freefall.cdrom.com/pub/FreeBSD/LOCAL_PORTS/
+DISTFILES= scheme-microcode+dist-7.3-freebsd.tgz
+
+.include <bsd.port.mk>
+
+
+ Now, if we go to the directory for this port and type
+ make, the following happens:
+
+
+
+ A check is made to see if the source code for this
+ port is already on the system.
+
+
+
+ If it isn't, an FTP connection to the URL in
+ MASTER_SITES is set up to download the
+ source.
+
+
+
+ The checksum for the source is calculated and compared
+ it with one for a known, good, copy of the source. This
+ is to make sure that the source was not corrupted while in
+ transit.
+
+
+
+ Any changes required to make the source work on
+ FreeBSD are applied—this is known as
+ patching.
+
+
+
+ Any special configuration needed for the source is
+ done. (Many Unix program distributions try to work out
+ which version of Unix they are being compiled on and which
+ optional Unix features are present—this is where
+ they are given the information in the FreeBSD ports
+ scenario).
+
+
+
+ The source code for the program is compiled. In
+ effect, we change to the directory where the source was
+ unpacked and do make—the
+ program's own make file has the necessary information to
+ build the program.
+
+
+
+ We now have a compiled version of the program. If we
+ wish, we can test it now; when we feel confident about the
+ program, we can type make install.
+ This will cause the program and any supporting files it
+ needs to be copied into the correct location; an entry is
+ also made into a package database, so
+ that the port can easily be uninstalled later if we change
+ our mind about it.
+
+
+
+ Now I think you'll agree that's rather impressive for a
+ four line script!
+
+ The secret lies in the last line, which tells
+ make to look in the system makefile called
+ bsd.port.mk. It's easy to overlook this
+ line, but this is where all the clever stuff comes
+ from—someone has written a makefile that tells
+ make to do all the things above (plus a
+ couple of other things I didn't mention, including handling
+ any errors that may occur) and anyone can get access to that
+ just by putting a single line in their own make file!
+
+ If you want to have a look at these system makefiles,
+ they're in /usr/share/mk, but it's
+ probably best to wait until you've had a bit of practice with
+ makefiles, as they are very complicated (and if you do look at
+ them, make sure you have a flask of strong coffee
+ handy!)
+
+
+
+ More advanced uses of <command>make</command>
+
+ Make is a very powerful tool, and can
+ do much more than the simple example above shows.
+ Unfortunately, there are several different versions of
+ make, and they all differ considerably.
+ The best way to learn what they can do is probably to read the
+ documentation—hopefully this introduction will have
+ given you a base from which you can do this.
+
+ The version of make that comes with FreeBSD is the
+ Berkeley make; there is a tutorial
+ for it in /usr/share/doc/psd/12.make. To
+ view it, do
+
+ &prompt.user; zmore paper.ascii.gz
+
+
+ in that directory.
+
+ Many applications in the ports use GNU
+ make, which has a very good set of
+ info pages. If you have installed any of these
+ ports, GNU make will automatically
+ have been installed as gmake. It's also
+ available as a port and package in its own right.
+
+ To view the info pages for GNU
+ make, you will have to edit the
+ dir file in the
+ /usr/local/info directory to add an entry
+ for it. This involves adding a line like
+
+ * Make: (make). The GNU Make utility.
+
+
+ to the file. Once you have done this, you can type
+ info and then select
+ make from the menu (or in
+ Emacs, do C-h
+ i).
+
+
+
+
+ Debugging
+
+
+ The Debugger
+
+ The debugger that comes with FreeBSD is called
+ gdb (GNU
+ debugger). You start it up by typing
+
+ &prompt.user; gdb progname
+
+
+ although most people prefer to run it inside
+ Emacs. You can do this by:
+
+ M-x gdb RET progname RET
+
+
+ Using a debugger allows you to run the program under more
+ controlled circumstances. Typically, you can step through the
+ program a line at a time, inspect the value of variables,
+ change them, tell the debugger to run up to a certain point
+ and then stop, and so on. You can even attach to a program
+ that's already running, or load a core file to investigate why
+ the program crashed. It's even possible to debug the kernel,
+ though that's a little trickier than the user applications
+ we'll be discussing in this section.
+
+ gdb has quite good on-line help, as
+ well as a set of info pages, so this section will concentrate
+ on a few of the basic commands.
+
+ Finally, if you find its text-based command-prompt style
+ off-putting, there's a graphical front-end for it xxgdb in the ports
+ collection.
+
+ This section is intended to be an introduction to using
+ gdb and does not cover specialised topics
+ such as debugging the kernel.
+
+
+
+ Running a program in the debugger
+
+ You'll need to have compiled the program with the
+ option to get the most out of using
+ gdb. It will work without, but you'll only
+ see the name of the function you're in, instead of the source
+ code. If you see a line like:
+
+ … (no debugging symbols found) …
+
+
+ when gdb starts up, you'll know that
+ the program wasn't compiled with the
+ option.
+
+ At the gdb prompt, type
+ break main. This will tell the
+ debugger to skip over the preliminary set-up code in the
+ program and start at the beginning of your code. Now type
+ run to start the program—it will
+ start at the beginning of the set-up code and then get stopped
+ by the debugger when it calls main().
+ (If you've ever wondered where main()
+ gets called from, now you know!).
+
+ You can now step through the program, a line at a time, by
+ pressing n. If you get to a function call,
+ you can step into it by pressing s. Once
+ you're in a function call, you can return from stepping into a
+ function call by pressing f. You can also
+ use up and down to take
+ a quick look at the caller.
+
+ Here's a simple example of how to spot a mistake in a
+ program with gdb. This is our program
+ (with a deliberate mistake):
+
+ #include <stdio.h>
+
+int bazz(int anint);
+
+main() {
+ int i;
+
+ printf("This is my program\n");
+ bazz(i);
+ return 0;
+}
+
+int bazz(int anint) {
+ printf("You gave me %d\n", anint);
+ return anint;
+}
+
+
+ This program sets i to be
+ 5 and passes it to a function
+ bazz() which prints out the number we
+ gave it.
+
+ When we compile and run the program we get
+
+ &prompt.user; cc -g -o temp temp.c
+&prompt.user; ./temp
+This is my program
+anint = 4231
+
+
+ That wasn't what we expected! Time to see what's going
+ on!
+
+ &prompt.user; gdb temp
+GDB is free software and you are welcome to distribute copies of it
+ under certain conditions; type "show copying" to see the conditions.
+There is absolutely no warranty for GDB; type "show warranty" for details.
+GDB 4.13 (i386-unknown-freebsd), Copyright 1994 Free Software Foundation, Inc.
+(gdb) break main Skip the set-up code
+Breakpoint 1 at 0x160f: file temp.c, line 9. gdb puts breakpoint at main()
+(gdb) run Run as far as main()
+Starting program: /home/james/tmp/temp Program starts running
+
+Breakpoint 1, main () at temp.c:9 gdb stops at main()
+(gdb) n Go to next line
+This is my program Program prints out
+(gdb) s step into bazz()
+bazz (anint=4231) at temp.c:17 gdb displays stack frame
+(gdb)
+
+
+ Hang on a minute! How did anint get to be
+ 4231? Didn't we set it to be
+ 5 in main()? Let's
+ move up to main() and have a look.
+
+ (gdb) up Move up call stack
+#1 0x1625 in main () at temp.c:11 gdb displays stack frame
+(gdb) p i Show us the value of i
+$1 = 4231 gdb displays 4231
+
+
+ Oh dear! Looking at the code, we forgot to initialise
+ i. We meant to put
+
+ …
+main() {
+ int i;
+
+ i = 5;
+ printf("This is my program\n");
+&hellip
+
+
+ but we left the i=5; line out. As we
+ didn't initialise i, it had whatever number
+ happened to be in that area of memory when the program ran,
+ which in this case happened to be
+ 4231.
+
+
+ gdb displays the stack frame every
+ time we go into or out of a function, even if we're using
+ up and down to move
+ around the call stack. This shows the name of the function
+ and the values of its arguments, which helps us keep track
+ of where we are and what's going on. (The stack is a
+ storage area where the program stores information about the
+ arguments passed to functions and where to go when it
+ returns from a function call).
+
+
+
+
+ Examining a core file
+
+ A core file is basically a file which contains the
+ complete state of the process when it crashed. In the
+ good old days, programmers had to print out hex
+ listings of core files and sweat over machine code manuals,
+ but now life is a bit easier. Incidentally, under FreeBSD and
+ other 4.4BSD systems, a core file is called
+ progname.core instead of just
+ core, to make it clearer which program a
+ core file belongs to.
+
+ To examine a core file, start up gdb in
+ the usual way. Instead of typing break or
+ run, type
+
+ (gdb) core progname.core
+
+
+ If you're not in the same directory as the core file,
+ you'll have to do dir
+ /path/to/core/file first.
+
+ You should see something like this:
+
+ &prompt.user; gdb a.out
+GDB is free software and you are welcome to distribute copies of it
+ under certain conditions; type "show copying" to see the conditions.
+There is absolutely no warranty for GDB; type "show warranty" for details.
+GDB 4.13 (i386-unknown-freebsd), Copyright 1994 Free Software Foundation, Inc.
+(gdb) core a.out.core
+Core was generated by `a.out'.
+Program terminated with signal 11, Segmentation fault.
+Cannot access memory at address 0x7020796d.
+#0 0x164a in bazz (anint=0x5) at temp.c:17
+(gdb)
+
+
+ In this case, the program was called
+ a.out, so the core file is called
+ a.out.core. We can see that the program
+ crashed due to trying to access an area in memory that was not
+ available to it in a function called
+ bazz.
+
+ Sometimes it's useful to be able to see how a function was
+ called, as the problem could have occurred a long way up the
+ call stack in a complex program. The bt
+ command causes gdb to print out a
+ back-trace of the call stack:
+
+ (gdb) bt
+#0 0x164a in bazz (anint=0x5) at temp.c:17
+#1 0xefbfd888 in end ()
+#2 0x162c in main () at temp.c:11
+(gdb)
+
+
+ The end() function is called when a
+ program crashes; in this case, the bazz()
+ function was called from main().
+
+
+
+ Attaching to a running program
+
+ One of the neatest features about gdb
+ is that it can attach to a program that's already running. Of
+ course, that assumes you have sufficient permissions to do so.
+ A common problem is when you are stepping through a program
+ that forks, and you want to trace the child, but the debugger
+ will only let you trace the parent.
+
+ What you do is start up another gdb,
+ use ps to find the process ID for the
+ child, and do
+
+ (gdb) attach pid
+
+
+ in gdb, and then debug as usual.
+
+ That's all very well, you're probably
+ thinking, but by the time I've done that, the child
+ process will be over the hill and far away. Fear
+ not, gentle reader, here's how to do it (courtesy of the
+ gdb info pages):
+
+ &hellip
+if ((pid = fork()) < 0) /* _Always_ check this */
+ error();
+else if (pid == 0) { /* child */
+ int PauseMode = 1;
+
+ while (PauseMode)
+ sleep(10); /* Wait until someone attaches to us */
+ &hellip
+} else { /* parent */
+ &hellip
+
+
+ Now all you have to do is attach to the child, set
+ PauseMode to 0, and wait
+ for the sleep() call to return!
+
+
+
+
+ Using Emacs as a Development Environment
+
+
+ Emacs
+
+ Unfortunately, Unix systems don't come with the kind of
+ everything-you-ever-wanted-and-lots-more-you-didn't-in-one-gigantic-package
+ integrated development environments that other systems
+ have.
+
+
+ At least, not unless you pay out very large sums of
+ money.
+
+
+ However, it is possible to set up your own environment. It
+ may not be as pretty, and it may not be quite as integrated,
+ but you can set it up the way you want it. And it's free.
+ And you have the source to it.
+
+ The key to it all is Emacs. Now there are some people who
+ loathe it, but many who love it. If you're one of the former,
+ I'm afraid this section will hold little of interest to you.
+ Also, you'll need a fair amount of memory to run it—I'd
+ recommend 8MB in text mode and 16MB in X as the bare minimum
+ to get reasonable performance.
+
+ Emacs is basically a highly customisable
+ editor—indeed, it has been customised to the point where
+ it's more like an operating system than an editor! Many
+ developers and sysadmins do in fact spend practically all
+ their time working inside Emacs, leaving it only to log
+ out.
+
+ It's impossible even to summarise everything Emacs can do
+ here, but here are some of the features of interest to
+ developers:
+
+
+
+ Very powerful editor, allowing search-and-replace on
+ both strings and regular expressions (patterns), jumping
+ to start/end of block expression, etc, etc.
+
+
+
+ Pull-down menus and online help.
+
+
+
+ Language-dependent syntax highlighting and
+ indentation.
+
+
+
+ Completely customisable.
+
+
+
+ You can compile and debug programs within
+ Emacs.
+
+
+
+ On a compilation error, you can jump to the offending
+ line of source code.
+
+
+
+ Friendly-ish front-end to the info
+ program used for reading GNU hypertext documentation,
+ including the documentation on Emacs itself.
+
+
+
+ Friendly front-end to gdb, allowing
+ you to look at the source code as you step through your
+ program.
+
+
+
+ You can read Usenet news and mail while your program
+ is compiling.
+
+
+
+ And doubtless many more that I've overlooked.
+
+ Emacs can be installed on FreeBSD using the Emacs
+ port.
+
+ Once it's installed, start it up and do C-h
+ t to read an Emacs tutorial—that means
+ hold down the control key, press
+ h, let go of the control
+ key, and then press t. (Alternatively, you
+ can you use the mouse to select Emacs
+ Tutorial from the Help
+ menu).
+
+ Although Emacs does have menus, it's well worth learning
+ the key bindings, as it's much quicker when you're editing
+ something to press a couple of keys than to try and find the
+ mouse and then click on the right place. And, when you're
+ talking to seasoned Emacs users, you'll find they often
+ casually throw around expressions like M-x
+ replace-s RET foo RET bar RET so it's
+ useful to know what they mean. And in any case, Emacs has far
+ too many useful functions for them to all fit on the menu
+ bars.
+
+ Fortunately, it's quite easy to pick up the key-bindings,
+ as they're displayed next to the menu item. My advice is to
+ use the menu item for, say, opening a file until you
+ understand how it works and feel confident with it, then try
+ doing C-x C-f. When you're happy with that, move on to
+ another menu command.
+
+ If you can't remember what a particular combination of
+ keys does, select Describe Key from
+ the Help menu and type it in—Emacs
+ will tell you what it does. You can also use the
+ Command Apropos menu item to find
+ out all the commands which contain a particular word in them,
+ with the key binding next to it.
+
+ By the way, the expression above means hold down the
+ Meta key, press x, release
+ the Meta key, type
+ replace-s (short for
+ replace-string—another feature of
+ Emacs is that you can abbreviate commands), press the
+ return key, type foo
+ (the string you want replaced), press the
+ return key, type bar (the string you want to
+ replace foo with) and press
+ return again. Emacs will then do the
+ search-and-replace operation you've just requested.
+
+ If you're wondering what on earth the
+ Meta key is, it's a special key that many
+ Unix workstations have. Unfortunately, PC's don't have one,
+ so it's usually the alt key (or if you're
+ unlucky, the escape key).
+
+ Oh, and to get out of Emacs, do C-x C-c
+ (that means hold down the control key, press
+ x, press c and release the
+ control key). If you have any unsaved files
+ open, Emacs will ask you if you want to save them. (Ignore
+ the bit in the documentation where it says
+ C-z is the usual way to leave
+ Emacs—that leaves Emacs hanging around in the
+ background, and is only really useful if you're on a system
+ which doesn't have virtual terminals).
+
+
+
+ Configuring Emacs
+
+ Emacs does many wonderful things; some of them are built
+ in, some of them need to be configured.
+
+ Instead of using a proprietary macro language for
+ configuration, Emacs uses a version of Lisp specially adapted
+ for editors, known as Emacs Lisp. This can be quite useful if
+ you want to go on and learn something like Common Lisp, as
+ it's considerably smaller than Common Lisp (although still
+ quite big!).
+
+ The best way to learn Emacs Lisp is to download the Emacs
+ Tutorial
+
+ However, there's no need to actually know any Lisp to get
+ started with configuring Emacs, as I've included a sample
+ .emacs file, which should be enough to
+ get you started. Just copy it into your home directory and
+ restart Emacs if it's already running; it will read the
+ commands from the file and (hopefully) give you a useful basic
+ setup.
+
+
+
+ A sample <filename>.emacs</filename> file
+
+ Unfortunately, there's far too much here to explain it in
+ detail; however there are one or two points worth
+ mentioning.
+
+
+
+ Everything beginning with a ; is a comment
+ and is ignored by Emacs.
+
+
+
+ In the first line, the
+ -*- Emacs-Lisp -*- is so that
+ we can edit the .emacs file itself
+ within Emacs and get all the fancy features for editing
+ Emacs Lisp. Emacs usually tries to guess this based on
+ the filename, and may not get it right for
+ .emacs.
+
+
+
+ The tab key is bound to an
+ indentation function in some modes, so when you press the
+ tab key, it will indent the current line of code. If you
+ want to put a tab character in whatever
+ you're writing, hold the control key down
+ while you're pressing the tab key.
+
+
+
+ This file supports syntax highlighting for C, C++,
+ Perl, Lisp and Scheme, by guessing the language from the
+ filename.
+
+
+
+ Emacs already has a pre-defined function called
+ next-error. In a compilation output
+ window, this allows you to move from one compilation error
+ to the next by doing M-n; we define a
+ complementary function,
+ previous-error, that allows you to go
+ to a previous error by doing M-p. The
+ nicest feature of all is that C-c C-c
+ will open up the source file in which the error occurred
+ and jump to the appropriate line.
+
+
+
+ We enable Emacs's ability to act as a server, so that
+ if you're doing something outside Emacs and you want to
+ edit a file, you can just type in
+
+ &prompt.user; emacsclient filename
+
+
+ and then you can edit the file in your
+ Emacs!
+
+
+ Many Emacs users set their EDITOR environment to
+ emacsclient so this happens every
+ time they need to edit a file.
+
+
+
+
+
+ A sample <filename>.emacs</filename> file
+
+ ;; -*-Emacs-Lisp-*-
+
+;; This file is designed to be re-evaled; use the variable first-time
+;; to avoid any problems with this.
+(defvar first-time t
+ "Flag signifying this is the first time that .emacs has been evaled")
+
+;; Meta
+(global-set-key "\M- " 'set-mark-command)
+(global-set-key "\M-\C-h" 'backward-kill-word)
+(global-set-key "\M-\C-r" 'query-replace)
+(global-set-key "\M-r" 'replace-string)
+(global-set-key "\M-g" 'goto-line)
+(global-set-key "\M-h" 'help-command)
+
+;; Function keys
+(global-set-key [f1] 'manual-entry)
+(global-set-key [f2] 'info)
+(global-set-key [f3] 'repeat-complex-command)
+(global-set-key [f4] 'advertised-undo)
+(global-set-key [f5] 'eval-current-buffer)
+(global-set-key [f6] 'buffer-menu)
+(global-set-key [f7] 'other-window)
+(global-set-key [f8] 'find-file)
+(global-set-key [f9] 'save-buffer)
+(global-set-key [f10] 'next-error)
+(global-set-key [f11] 'compile)
+(global-set-key [f12] 'grep)
+(global-set-key [C-f1] 'compile)
+(global-set-key [C-f2] 'grep)
+(global-set-key [C-f3] 'next-error)
+(global-set-key [C-f4] 'previous-error)
+(global-set-key [C-f5] 'display-faces)
+(global-set-key [C-f8] 'dired)
+(global-set-key [C-f10] 'kill-compilation)
+
+;; Keypad bindings
+(global-set-key [up] "\C-p")
+(global-set-key [down] "\C-n")
+(global-set-key [left] "\C-b")
+(global-set-key [right] "\C-f")
+(global-set-key [home] "\C-a")
+(global-set-key [end] "\C-e")
+(global-set-key [prior] "\M-v")
+(global-set-key [next] "\C-v")
+(global-set-key [C-up] "\M-\C-b")
+(global-set-key [C-down] "\M-\C-f")
+(global-set-key [C-left] "\M-b")
+(global-set-key [C-right] "\M-f")
+(global-set-key [C-home] "\M-<")
+(global-set-key [C-end] "\M->")
+(global-set-key [C-prior] "\M-<")
+(global-set-key [C-next] "\M->")
+
+;; Mouse
+(global-set-key [mouse-3] 'imenu)
+
+;; Misc
+(global-set-key [C-tab] "\C-q\t") ; Control tab quotes a tab.
+(setq backup-by-copying-when-mismatch t)
+
+;; Treat 'y' or <CR> as yes, 'n' as no.
+(fset 'yes-or-no-p 'y-or-n-p)
+ (define-key query-replace-map [return] 'act)
+ (define-key query-replace-map [?\C-m] 'act)
+
+;; Load packages
+(require 'desktop)
+(require 'tar-mode)
+
+;; Pretty diff mode
+(autoload 'ediff-buffers "ediff" "Intelligent Emacs interface to diff" t)
+(autoload 'ediff-files "ediff" "Intelligent Emacs interface to diff" t)
+(autoload 'ediff-files-remote "ediff"
+ "Intelligent Emacs interface to diff")
+
+(if first-time
+ (setq auto-mode-alist
+ (append '(("\\.cpp$" . c++-mode)
+ ("\\.hpp$" . c++-mode)
+ ("\\.lsp$" . lisp-mode)
+ ("\\.scm$" . scheme-mode)
+ ("\\.pl$" . perl-mode)
+ ) auto-mode-alist)))
+
+;; Auto font lock mode
+(defvar font-lock-auto-mode-list
+ (list 'c-mode 'c++-mode 'c++-c-mode 'emacs-lisp-mode 'lisp-mode 'perl-mode 'scheme-mode)
+ "List of modes to always start in font-lock-mode")
+
+(defvar font-lock-mode-keyword-alist
+ '((c++-c-mode . c-font-lock-keywords)
+ (perl-mode . perl-font-lock-keywords))
+ "Associations between modes and keywords")
+
+(defun font-lock-auto-mode-select ()
+ "Automatically select font-lock-mode if the current major mode is
+in font-lock-auto-mode-list"
+ (if (memq major-mode font-lock-auto-mode-list)
+ (progn
+ (font-lock-mode t))
+ )
+ )
+
+(global-set-key [M-f1] 'font-lock-fontify-buffer)
+
+;; New dabbrev stuff
+;(require 'new-dabbrev)
+(setq dabbrev-always-check-other-buffers t)
+(setq dabbrev-abbrev-char-regexp "\\sw\\|\\s_")
+(add-hook 'emacs-lisp-mode-hook
+ '(lambda ()
+ (set (make-local-variable 'dabbrev-case-fold-search) nil)
+ (set (make-local-variable 'dabbrev-case-replace) nil)))
+(add-hook 'c-mode-hook
+ '(lambda ()
+ (set (make-local-variable 'dabbrev-case-fold-search) nil)
+ (set (make-local-variable 'dabbrev-case-replace) nil)))
+(add-hook 'text-mode-hook
+ '(lambda ()
+ (set (make-local-variable 'dabbrev-case-fold-search) t)
+ (set (make-local-variable 'dabbrev-case-replace) t)))
+
+;; C++ and C mode...
+(defun my-c++-mode-hook ()
+ (setq tab-width 4)
+ (define-key c++-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (define-key c++-mode-map "\C-ce" 'c-comment-edit)
+ (setq c++-auto-hungry-initial-state 'none)
+ (setq c++-delete-function 'backward-delete-char)
+ (setq c++-tab-always-indent t)
+ (setq c-indent-level 4)
+ (setq c-continued-statement-offset 4)
+ (setq c++-empty-arglist-indent 4))
+
+(defun my-c-mode-hook ()
+ (setq tab-width 4)
+ (define-key c-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (define-key c-mode-map "\C-ce" 'c-comment-edit)
+ (setq c-auto-hungry-initial-state 'none)
+ (setq c-delete-function 'backward-delete-char)
+ (setq c-tab-always-indent t)
+;; BSD-ish indentation style
+ (setq c-indent-level 4)
+ (setq c-continued-statement-offset 4)
+ (setq c-brace-offset -4)
+ (setq c-argdecl-indent 0)
+ (setq c-label-offset -4))
+
+;; Perl mode
+(defun my-perl-mode-hook ()
+ (setq tab-width 4)
+ (define-key c++-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (setq perl-indent-level 4)
+ (setq perl-continued-statement-offset 4))
+
+;; Scheme mode...
+(defun my-scheme-mode-hook ()
+ (define-key scheme-mode-map "\C-m" 'reindent-then-newline-and-indent))
+
+;; Emacs-Lisp mode...
+(defun my-lisp-mode-hook ()
+ (define-key lisp-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (define-key lisp-mode-map "\C-i" 'lisp-indent-line)
+ (define-key lisp-mode-map "\C-j" 'eval-print-last-sexp))
+
+;; Add all of the hooks...
+(add-hook 'c++-mode-hook 'my-c++-mode-hook)
+(add-hook 'c-mode-hook 'my-c-mode-hook)
+(add-hook 'scheme-mode-hook 'my-scheme-mode-hook)
+(add-hook 'emacs-lisp-mode-hook 'my-lisp-mode-hook)
+(add-hook 'lisp-mode-hook 'my-lisp-mode-hook)
+(add-hook 'perl-mode-hook 'my-perl-mode-hook)
+
+;; Complement to next-error
+(defun previous-error (n)
+ "Visit previous compilation error message and corresponding source code."
+ (interactive "p")
+ (next-error (- n)))
+
+;; Misc...
+(transient-mark-mode 1)
+(setq mark-even-if-inactive t)
+(setq visible-bell nil)
+(setq next-line-add-newlines nil)
+(setq compile-command "make")
+(setq suggest-key-bindings nil)
+(put 'eval-expression 'disabled nil)
+(put 'narrow-to-region 'disabled nil)
+(put 'set-goal-column 'disabled nil)
+
+;; Elisp archive searching
+(autoload 'format-lisp-code-directory "lispdir" nil t)
+(autoload 'lisp-dir-apropos "lispdir" nil t)
+(autoload 'lisp-dir-retrieve "lispdir" nil t)
+(autoload 'lisp-dir-verify "lispdir" nil t)
+
+;; Font lock mode
+(defun my-make-face (face colour &optional bold)
+ "Create a face from a colour and optionally make it bold"
+ (make-face face)
+ (copy-face 'default face)
+ (set-face-foreground face colour)
+ (if bold (make-face-bold face))
+ )
+
+(if (eq window-system 'x)
+ (progn
+ (my-make-face 'blue "blue")
+ (my-make-face 'red "red")
+ (my-make-face 'green "dark green")
+ (setq font-lock-comment-face 'blue)
+ (setq font-lock-string-face 'bold)
+ (setq font-lock-type-face 'bold)
+ (setq font-lock-keyword-face 'bold)
+ (setq font-lock-function-name-face 'red)
+ (setq font-lock-doc-string-face 'green)
+ (add-hook 'find-file-hooks 'font-lock-auto-mode-select)
+
+ (setq baud-rate 1000000)
+ (global-set-key "\C-cmm" 'menu-bar-mode)
+ (global-set-key "\C-cms" 'scroll-bar-mode)
+ (global-set-key [backspace] 'backward-delete-char)
+ ; (global-set-key [delete] 'delete-char)
+ (standard-display-european t)
+ (load-library "iso-transl")))
+
+;; X11 or PC using direct screen writes
+(if window-system
+ (progn
+ ;; (global-set-key [M-f1] 'hilit-repaint-command)
+ ;; (global-set-key [M-f2] [?\C-u M-f1])
+ (setq hilit-mode-enable-list
+ '(not text-mode c-mode c++-mode emacs-lisp-mode lisp-mode
+ scheme-mode)
+ hilit-auto-highlight nil
+ hilit-auto-rehighlight 'visible
+ hilit-inhibit-hooks nil
+ hilit-inhibit-rebinding t)
+ (require 'hilit19)
+ (require 'paren))
+ (setq baud-rate 2400) ; For slow serial connections
+ )
+
+;; TTY type terminal
+(if (and (not window-system)
+ (not (equal system-type 'ms-dos)))
+ (progn
+ (if first-time
+ (progn
+ (keyboard-translate ?\C-h ?\C-?)
+ (keyboard-translate ?\C-? ?\C-h)))))
+
+;; Under UNIX
+(if (not (equal system-type 'ms-dos))
+ (progn
+ (if first-time
+ (server-start))))
+
+;; Add any face changes here
+(add-hook 'term-setup-hook 'my-term-setup-hook)
+(defun my-term-setup-hook ()
+ (if (eq window-system 'pc)
+ (progn
+;; (set-face-background 'default "red")
+ )))
+
+;; Restore the "desktop" - do this as late as possible
+(if first-time
+ (progn
+ (desktop-load-default)
+ (desktop-read)))
+
+;; Indicate that this file has been read at least once
+(setq first-time nil)
+
+;; No need to debug anything now
+(setq debug-on-error nil)
+
+;; All done
+(message "All done, %s%s" (user-login-name) ".")
+
+
+
+
+
+ Extending the Range of Languages Emacs Understands
+
+ Now, this is all very well if you only want to program in
+ the languages already catered for in the
+ .emacs file (C, C++, Perl, Lisp and
+ Scheme), but what happens if a new language called
+ whizbang comes out, full of exciting
+ features?
+
+ The first thing to do is find out if whizbang comes with
+ any files that tell Emacs about the language. These usually
+ end in .el, short for Emacs
+ Lisp. For example, if whizbang is a FreeBSD port, we
+ can locate these files by doing
+
+ &prompt.user; find /usr/ports/lang/whizbang -name "*.el" -print
+
+
+ and install them by copying them into the Emacs site Lisp
+ directory. On FreeBSD 2.1.0-RELEASE, this is
+ /usr/local/share/emacs/site-lisp.
+
+ So for example, if the output from the find command
+ was
+
+ /usr/ports/lang/whizbang/work/misc/whizbang.el
+
+
+ we would do
+
+ &prompt.root; cp /usr/ports/lang/whizbang/work/misc/whizbang.el /usr/local/share/emacs/site-lisp
+
+
+ Next, we need to decide what extension whizbang source
+ files have. Let's say for the sake of argument that they all
+ end in .wiz. We need to add an entry to
+ our .emacs file to make sure Emacs will
+ be able to use the information in
+ whizbang.el.
+
+ Find the auto-mode-alist entry in
+ .emacs and add a line for whizbang, such
+ as:
+
+ …
+("\\.lsp$" . lisp-mode)
+("\\.wiz$" . whizbang-mode)
+("\\.scm$" . scheme-mode)
+…
+
+
+ This means that Emacs will automatically go into
+ whizbang-mode when you edit a file ending
+ in .wiz.
+
+ Just below this, you'll find the
+ font-lock-auto-mode-list entry. Add
+ whizbang-mode to it like so:
+
+ ;; Auto font lock mode
+(defvar font-lock-auto-mode-list
+ (list 'c-mode 'c++-mode 'c++-c-mode 'emacs-lisp-mode 'whizbang-mode 'lisp-mode 'perl-mode 'scheme-mode)
+ "List of modes to always start in font-lock-mode")
+
+
+ This means that Emacs will always enable
+ font-lock-mode (ie syntax highlighting)
+ when editing a .wiz file.
+
+ And that's all that's needed. If there's anything else
+ you want done automatically when you open up a
+ .wiz file, you can add a
+ whizbang-mode hook (see
+ my-scheme-mode-hook for a simple example
+ that adds auto-indent).
+
+
+
+
+ Further Reading
+
+
+
+ Brian Harvey and Matthew Wright
+ Simply Scheme
+ MIT 1994.
+ ISBN 0-262-08226-8
+
+
+
+ Randall Schwartz
+ Learning Perl
+ O'Reilly 1993
+ ISBN 1-56592-042-2
+
+
+
+ Patrick Henry Winston and Berthold Klaus Paul Horn
+ Lisp (3rd Edition)
+ Addison-Wesley 1989
+ ISBN 0-201-08319-1
+
+
+
+ Brian W. Kernighan and Rob Pike
+ The Unix Programming Environment
+ Prentice-Hall 1984
+ ISBN 0-13-937681-X
+
+
+
+ Brian W. Kernighan and Dennis M. Ritchie
+ The C Programming Language (2nd Edition)
+ Prentice-Hall 1988
+ ISBN 0-13-110362-8
+
+
+
+ Bjarne Stroustrup
+ The C++ Programming Language
+ Addison-Wesley 1991
+ ISBN 0-201-53992-6
+
+
+
+ W. Richard Stevens
+ Advanced Programming in the Unix Environment
+ Addison-Wesley 1992
+ ISBN 0-201-56317-7
+
+
+
+ W. Richard Stevens
+ Unix Network Programming
+ Prentice-Hall 1990
+ ISBN 0-13-949876-1
+
+
+
- Secure ProgrammingThis chapter was written by Murray Stokely.SynopsisThis chapter describes some of the security issues that
have plagued Unix programmers for decades and some of the new
tools available to help programmers avoid writing exploitable
code.Secure Design
MethodologyWriting secure applications takes a very scrutinous and
pessimistic outlook on life. Applications should be run with
the principle of least privilege so that no
process is ever running than more with the bare minimum access
that it needs to accomplish its function. Previously tested
code should be reused whenever possible to avoid common
mistakes that others may have already fixed.One of the pitfalls of the Unix environment is how easy it
is to make assumptions about the sanity of the environment.
Applications should never trust user input (in all its forms),
system resources, inter-process communication, or the timing of
events. Unix processes do not execute synchronously so logical
operations are rarely atomic.Buffer OverflowsBuffer Overflows have been around since the very
beginnings of the Von-Neuman architecture.
They first gained widespread notoriety in 1988 with the Moorse
Internet worm. Unfortunately, the same basic attack remains
effective today. Of the 17 CERT security advisories of 1999, 10
of them were directly caused by buffer-overflow software bugs.
By far the most common type of buffer overflow attack is based
on corrupting the stack.Most modern computer systems use a stack to pass arguments
to procedures and to store local variables. A stack is a last
in first out (LIFO) buffer in the high memory area of a process
image. When a program invokes a function a new "stack frame" is
created. This stack frame consists of the arguments passed to
the function as well as a dynamic amount of local variable
space. The "stack pointer" is a register that holds the current
location of the top of the stack. Since this value is
constantly changing as new values are pushed onto the top of the
stack, many implementations also provide a "frame pointer" that
is located near the beginning of a stack frame so that local
variables can more easily be addressed relative to this
value. The return address for function
calls is also stored on the stack, and this is the cause of
stack-overflow exploits since overflowing a local variable in a
function can overwrite the return address of that function,
potentially allowing a malicious user to execute any code he or
she wants.Although stack-based attacks are by far the most common,
it would also be possible to overrun the stack with a heap-based
(malloc/free) attack.The C programming language does not perform automatic
bounds checking on arrays or pointers as many other languages
do. In addition, the standard C library is filled with a
handful of very dangerous functions.strcpy(char *dest, const char
*src)May overflow the dest bufferstrcat(char *dest, const char
*src)May overflow the dest buffergetwd(char *buf)May overflow the buf buffergets(char *s)May overflow the s buffer[vf]scanf(const char *format,
...)May overflow its arguments.realpath(char *path, char
resolved_path[])May overflow the path buffer[v]sprintf(char *str, const char
*format, ...)May overflow the str buffer.Example Buffer OverflowThe following example code contains a buffer overflow
designed to overwrite the return address and skip the
instruction immediately following the function call. (Inspired
by )
#include stdio.h
void manipulate(char *buffer) {
char newbuffer[80];
strcpy(newbuffer,buffer);
}
int main() {
char ch,buffer[4096];
int i=0;
while ((buffer[i++] = getchar()) != '\n') {};
i=1;
manipulate(buffer);
i=2;
printf("The value of i is : %d\n",i);
return 0;
}
Let us examine what the memory image of this process would
look like if we were to input 160 spaces into our little program
before hitting return.[XXX figure here!]Obviously more malicious input can be devised to execute
actual compiled instructions (such as exec(/bin/sh)).Avoiding Buffer OverflowsThe most straightforward solution to the problem of
stack-overflows is to always use length restricted memory and
string copy functions. strncpy and
strncat are part of the standard C library.
These functions accept a length value as a parameter which
should be no larger than the size of the destination buffer.
These functions will then copy up to `length' bytes from the
source to the destination. However there are a number of
problems with these functions. Neither function guarantees NUL
termination if the size of the input buffer is as large as the
destination. The length parameter is also used inconsistently
between strncpy and strncat so it is easy for programmers to get
confused as to their proper usage. There is also a significant
performance loss compared to strcpy when
copying a short string into a large buffer since
strncpy NUL fills up the the size
specified.In OpenBSD, another memory copy implementation has been
created to get around these problem. The
strlcpy and strlcat
functions guarantee that they will always null terminate the
destination string when given a non-zero length argument. For
more information about these functions see . The OpenBSD strlcpy and
strlcat instructions have been in FreeBSD
since 3.5.Compiler based run-time bounds checkingUnfortunately there is still a very large assortment of
code in public use which blindly copies memory around without
using any of the bounded copy routines we just discussed.
Fortunately, there is another solution. Several compiler
add-ons and libraries exist to do Run-time bounds checking in
C/C++.StackGuard is one such add-on that is implemented as a
small patch to the gcc code generator. From the StackGuard
website, http://immunix.org/stackguard.html :
"StackGuard detects and defeats stack
smashing attacks by protecting the return address on the stack
from being altered. StackGuard places a "canary" word next to
the return address when a function is called. If the canary
word has been altered when the function returns, then a stack
smashing attack has been attempted, and the program responds
by emitting an intruder alert into syslog, and then
halts."
"StackGuard is implemented as a small patch
to the gcc code generator, specifically the function_prolog()
and function_epilog() routines. function_prolog() has been
enhanced to lay down canaries on the stack when functions
start, and function_epilog() checks canary integrity when the
function exits. Any attempt at corrupting the return address
is thus detected before the function
returns."
Recompiling your application with StackGuard is an
effective means of stopping most buffer-overflow attacks, but
it can still be compromised.Library based run-time bounds checkingCompiler-based mechanisms are completely useless for
binary-only software for which you cannot recompile. For
these situations there are a number of libraries which
re-implement the unsafe functions of the C-library
(strcpy, fscanf,
getwd, etc..) and ensure that these
functions can never write past the stack pointer.libsafelibverifylibparnoiaUnfortunately these library-based defenses have a number
of shortcomings. These libraries only protect against a very
small set of security related issues and they neglect to fix
the actual problem. These defenses may fail if the
application was compiled with -fomit-frame-pointer. Also, the
LD_PRELOAD and LD_LIBRARY_PATH environment variables can be
overwritten/unset by the user.SetUID issuesThere are at least 6 different IDs associated with any
given process. Because of this you have to be very careful with
the access that your process has at any given time. In
particular, all seteuid applications should give up their
privileges as soon as it is no longer required.The real user ID can only be changed by a superuser
process. The login program sets this
when a user initially logs in and it is seldom changed.The effective user ID is set by the
exec() functions if a program has its
seteuid bit set. An application can call
seteuid() at any time to set the effective
user ID to either the real user ID or the saved set-user-ID.
When the effective user ID is set by exec()
functions, the previous value is saved in the saved set-user-ID.Limiting your program's environmentThe traditional method of restricting access to a process
is with the chroot() system call. This
system call changes the root directory from which all other
paths are referenced for a process and any child processes. For
this call to succeed the process must have execute (search)
permission on the directory being referenced. The new
environment does not actually take affect until you
chdir() into your new environment. It
should also be noted that a process can easily break out of a
chroot environment if it has root privilege. This could be
accomplished by creating device nodes to read kernel memory,
attaching a debugger to a process outside of the jail, or in
many other creative ways.The behavior of the chroot() system
call can be controlled somewhat with the
kern.chroot_allow_open_directories sysctl
variable. When this value is set to 0,
chroot() will fail with EPERM if there are
any directories open. If set to the default value of 1, then
chroot() will fail with EPERM if there are
any directories open and the process is already subject to a
chroot() call. For any other value, the
check for open directories will be bypassed completely.FreeBSD's jail functionalityThe concept of a Jail extends upon the
chroot() by limiting the powers of the
superuser to create a true `virtual server'. Once a prison is
setup all network communication must take place through the
specified IP address, and the power of "root privilege" in this
jail is severely constrained.While in a prison, any tests of superuser power within the
kernel using the suser() call will fail.
However, some calls to suser() have been
changed to a new interface suser_xxx().
This function is responsible for recognizing or denying access
to superuser power for imprisoned processes.A superuser process within a jailed environment has the
power to : Manipulate credential with
setuid, seteuid,
setgid, setegid,
setgroups, setreuid,
setregid, setloginSet resource limits with setrlimitModify some sysctl nodes
(kern.hostname)chroot()Set flags on a vnode:
chflags,
fchflagsSet attributes of a vnode such as file
permission, owner, group, size, access time, and modification
time.Bind to privileged ports in the Internet
domain (ports < 1024)Jail is a very useful tool for
running applications in a secure environment but it does have
some shortcomings. Currently, the IPC mechanisms have not been
converted to the suser_xxx so applications
such as MySQL can not be run within a jail. Superuser access
may have a very limited meaning within a jail, but there is
no way to specify exactly what "very limited" means.POSIX.1e Process CapabilitiesPosix has released a working draft that adds event
auditing, access control lists, fine grained privileges,
information labeling, and mandatory access control.This is a work in progress and is the focus of the TrustedBSD project. Some
of the initial work has been committed to FreeBSD-current
(cap_set_proc(3)).TrustAn application should never assume that anything about the
users environment is sane. This includes (but is certainly not
limited to) : user input, signals, environment variables,
resources, IPC, mmaps, the file system working directory, file
descriptors, the # of open files, etc.You should never assume that you can catch all forms of
invalid input that a user might supply. Instead, your
application should use positive filtering to only allow a
specific subset of inputs that you deem safe. Improper data
validation has been the cause of many exploits, especially with
CGI scripts on the world wide web. For filenames you need to be
extra careful about paths ("../", "/"), symbolic links, and
shell escape characters.Perl has a really cool feature called "Taint" mode which
can be used to prevent scripts for using data derived outside
the program in an unsafe way. This mode will check command line
arguments, environment variables, locale information, the
results of certain syscalls (readdir(),
readlink(),
getpwxxx(), and all file input.Race ConditionsA race condition is anomalous behavior caused by the
unexpected dependence on the relative timing of events. In
other words, a programmer incorrectly assumed that a particular
event would always happen before another.Some of the common causes of race conditions are signals,
access checks, and file opens. Signals are asynchronous events
by nature so special care must be taken in dealing with them.
Checking access with access(2) then
open(2) is clearly non-atomic. Users can
move files in between the two calls. Instead, privileged
applications should seteuid() and then call
open() directly. Along the same lines, an
application should always set a proper umask before
open() to obviate the need for spurious
chmod() calls.KernelHistory of the Unix KernelSome history of the Unix/BSD kernel, system calls, how do
processes work, blocking, scheduling, threads (kernel),
context switching, signals, interrupts, modules, etc.Memory and Virtual MemoryVirtual MemoryVM, paging, swapping, allocating memory, testing for
memory leaks, mmap, vnodes, etc.I/O SystemUFSUFS, FFS, Ext2FS, JFS, inodes, buffer cache, labeling,
locking, metadata, soft-updates, LFS, portalfs, procfs,
vnodes, memory sharing, memory objects, TLBs, cachingInterprocess CommunicationSignalsSignals, pipes, semaphores, message queues, shared memory,
ports, sockets, doorsNetworkingSocketsSockets, bpf, IP, TCP, UDP, ICMP, OSI, bridging,
firewalling, NAT, switching, etcNetwork FilesystemsAFSAFS, NFS, SANs etc]Terminal HandlingSysconsSyscons, tty, PCVT, serial console, screen savers,
etcSoundOSSOSS, waveforms, etcDevice DriversWriting FreeBSD Device DriversThis chapter was written by Murray Stokely with selections from
a variety of sources including the intro(4) man page by Joerg
Wunsch.Introduction
This chapter provides a brief introduction to writing device
drivers for FreeBSD. A device in this context is a term used
mostly for hardware-related stuff that belongs to the system,
like disks, printers, or a graphics display with its keyboard.
A device driver is the software component of the operating
system that controls a specific device. There are also
so-called pseudo-devices where a device driver emulates the
behaviour of a device in software without any particular
underlying hardware. Device drivers can be compiled into the
system statically or loaded on demand through the dynamic
kernel linker facility `kld'.Most devices in a Unix-like operating system are
accessed through device-nodes, sometimes also called special
files. These files are usually located under the directory
/dev in the file system hierarchy. Until
devfs is fully integrated into FreeBSD, each device node must
be created statically and independent of the existence of the
associated device driver. Most device nodes on the system are
created by running MAKEDEV.Device drivers can roughly be broken down into three
categories; character (unbuffered), block (buffered), and
network drivers.Dynamic Kernel Linker Facility - KLDThe kld interface allows system administrators to
dynamically add and remove functionality from a running
system. This allows device driver writers to load their new
changes into a running kernel without constantly rebooting to
test changes.The kld interface is used through the following
administrator commands :
kldload - loads a new kernel
modulekldunload - unloads a kernel
modulekldstat - lists the currently loadded
modulesSkeleton Layout of a kernel module
/*
* KLD Skeleton
* Inspired by Andrew Reiter's Daemonnews article
*/
#include <sys/types.h>
#include <sys/module.h>
#include <sys/systm.h> /* uprintf */
#include <sys/errno.h>
#include <sys/param.h> /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
/*
* Load handler that deals with the loading and unloading of a KLD.
*/
static int
skel_loader(struct module *m, int what, void *arg)
{
int err = 0;
switch (what) {
case MOD_LOAD: /* kldload */
uprintf("Skeleton KLD loaded.\n");
break;
case MOD_UNLOAD:
uprintf("Skeleton KLD unloaded.\n");
break;
default:
err = EINVAL;
break;
}
return(err);
}
/* Declare this module to the rest of the kernel */
DECLARE_MODULE(skeleton, skel_loader, SI_SUB_KLD, SI_ORDER_ANY);
MakefileFreeBSD provides a makefile include that you can use
to quickly compile your kernel addition.
SRCS=skeleton.c
KMOD=skeleton
.include <bsd.kmod.mk>
Simply running make with
this makefile will create a file
skeleton.ko that can be loaded into
your system by typing :
&prompt.root kldload -v ./skeleton.ko
Accessing a device driverUnix provides a common set of system calls for user
applications to use. The upper layers of the kernel dispatch
these calls to the corresponding device driver when a user
accesses a device node. The /dev/MAKEDEV
script makes most of the device nodes for your system but if
you are doing your own driver development it may be necessary
to create your own device nodes with mknodCreating static device nodesThe mknod command requires four
arguments to create a device node. You must specify the
name of this device node, the type of device, the major number
of the device, and the minor number of the device.Dynamic device nodesThe device filesystem, or devfs, provides access to the
kernel's device namespace in the global filesystem namespace.
This eliminates the problems of potentially having a device
driver without a static device node, or a device node without
an installed device driver. Unfortunately, devfs is still a
work in progress.Character DevicesA character device driver is one that transfers data
directly to and from a user process. This is the most common
type of device driver and there are plenty of simple examples
in the source tree.This simple example pseudo-device remembers whatever values you write
to it and can then supply them back to you when you read from
it.
/*
* Simple `echo' pseudo-device KLD
*
* Murray Stokely
*/
#define MIN(a,b) (((a) < (b)) ? (a) : (b))
#include <sys/types.h>
#include <sys/module.h>
#include <sys/systm.h> /* uprintf */
#include <sys/errno.h>
#include <sys/param.h> /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
#include <sys/conf.h> /* cdevsw struct */
#include <sys/uio.h> /* uio struct */
#include <sys/malloc.h>
#define BUFFERSIZE 256
/* Function prototypes */
d_open_t echo_open;
d_close_t echo_close;
d_read_t echo_read;
d_write_t echo_write;
/* Character device entry points */
static struct cdevsw echo_cdevsw = {
echo_open,
echo_close,
echo_read,
echo_write,
noioctl,
nopoll,
nommap,
nostrategy,
"echo",
33, /* reserved for lkms - /usr/src/sys/conf/majors */
nodump,
nopsize,
D_TTY,
-1
};
typedef struct s_echo {
char msg[BUFFERSIZE];
int len;
} t_echo;
/* vars */
static dev_t sdev;
static int len;
static int count;
static t_echo *echomsg;
MALLOC_DECLARE(M_ECHOBUF);
MALLOC_DEFINE(M_ECHOBUF, "echobuffer", "buffer for echo module");
/*
* This function acts is called by the kld[un]load(2) system calls to
* determine what actions to take when a module is loaded or unloaded.
*/
static int
echo_loader(struct module *m, int what, void *arg)
{
int err = 0;
switch (what) {
case MOD_LOAD: /* kldload */
sdev = make_dev(&echo_cdevsw,
0,
UID_ROOT,
GID_WHEEL,
0600,
"echo");
/* kmalloc memory for use by this driver */
/* malloc(256,M_ECHOBUF,M_WAITOK); */
MALLOC(echomsg, t_echo *, sizeof(t_echo), M_ECHOBUF, M_WAITOK);
printf("Echo device loaded.\n");
break;
case MOD_UNLOAD:
destroy_dev(sdev);
FREE(echomsg,M_ECHOBUF);
printf("Echo device unloaded.\n");
break;
default:
err = EINVAL;
break;
}
return(err);
}
int
echo_open(dev_t dev, int oflags, int devtype, struct proc *p)
{
int err = 0;
uprintf("Opened device \"echo\" successfully.\n");
return(err);
}
int
echo_close(dev_t dev, int fflag, int devtype, struct proc *p)
{
uprintf("Closing device \"echo.\"\n");
return(0);
}
/*
* The read function just takes the buf that was saved via
* echo_write() and returns it to userland for accessing.
* uio(9)
*/
int
echo_read(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
int amt;
/* How big is this read operation? Either as big as the user wants,
or as big as the remaining data */
amt = MIN(uio->uio_resid, (echomsg->len - uio->uio_offset > 0) ? echomsg->len - uio->uio_offset : 0);
if ((err = uiomove(echomsg->msg + uio->uio_offset,amt,uio)) != 0) {
uprintf("uiomove failed!\n");
}
return err;
}
/*
* echo_write takes in a character string and saves it
* to buf for later accessing.
*/
int
echo_write(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
/* Copy the string in from user memory to kernel memory */
err = copyin(uio->uio_iov->iov_base, echomsg->msg, MIN(uio->uio_iov->iov_len,BUFFERSIZE));
/* Now we need to null terminate */
*(echomsg->msg + MIN(uio->uio_iov->iov_len,BUFFERSIZE)) = 0;
/* Record the length */
echomsg->len = MIN(uio->uio_iov->iov_len,BUFFERSIZE);
if (err != 0) {
uprintf("Write failed: bad address!\n");
}
count++;
return(err);
}
DEV_MODULE(echo,echo_loader,NULL);
To install this driver you will first need to make a node on
your filesystem with a command such as :
&prompt.root mknod /dev/echo c 33 0
With this driver loaded you should now be able to type something
like :
&prompt.root echo -n "Test Data" > /dev/echo
&prompt.root cat /dev/echo
Test Data
Real hardware devices in the next chapter..Additional Resources
Dynamic
Kernel Linker (KLD) Facility Programming Tutorial -
Daemonnews October 2000How
to Write Kernel Drivers with NEWBUS - Daemonnews July
2000Block DevicesA block device driver transfers data to and from the
operating system's buffer cache. They are solely intended to
layer a file system on top of them. For this reason they are
normally implemented for disks and disk-like devices only.Example test data generator ... Example ramdisk device ... Real hardware devices in the next chapter..Network DriversDrivers for network devices do not use device nodes in
ord to be accessed. Their selection is based on other
decisions made inside the kernel and instead of calling
open(), use of a network device is generally introduced by
using the system call socket(2).man ifnet(), loopback device, Bill Pauls drivers, etc..PCI DevicesThis chapter will talk about the FreeBSD mechanisms for
writing a device driver for a device on a PCI bus.Probe and AttachInformation here about how the PCI bus code iterates
through the unattached devices and see if a newly loaded kld
will attach to any of them.
/*
* Simple KLD to play with the PCI functions.
*
* Murray Stokely
*/
#define MIN(a,b) (((a) < (b)) ? (a) : (b))
#include <sys/types.h>
#include <sys/module.h>
#include <sys/systm.h> /* uprintf */
#include <sys/errno.h>
#include <sys/param.h> /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
#include <sys/conf.h> /* cdevsw struct */
#include <sys/uio.h> /* uio struct */
#include <sys/malloc.h>
#include <sys/bus.h> /* structs, prototypes for pci bus stuff */
#include <pci/pcivar.h> /* For get_pci macros! */
/* Function prototypes */
d_open_t mypci_open;
d_close_t mypci_close;
d_read_t mypci_read;
d_write_t mypci_write;
/* Character device entry points */
static struct cdevsw mypci_cdevsw = {
mypci_open,
mypci_close,
mypci_read,
mypci_write,
noioctl,
nopoll,
nommap,
nostrategy,
"mypci",
36, /* reserved for lkms - /usr/src/sys/conf/majors */
nodump,
nopsize,
D_TTY,
-1
};
/* vars */
static dev_t sdev;
/* We're more interested in probe/attach than with
open/close/read/write at this point */
int
mypci_open(dev_t dev, int oflags, int devtype, struct proc *p)
{
int err = 0;
uprintf("Opened device \"mypci\" successfully.\n");
return(err);
}
int
mypci_close(dev_t dev, int fflag, int devtype, struct proc *p)
{
int err=0;
uprintf("Closing device \"mypci.\"\n");
return(err);
}
int
mypci_read(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
uprintf("mypci read!\n");
return err;
}
int
mypci_write(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
uprintf("mypci write!\n");
return(err);
}
/* PCI Support Functions */
/*
* Return identification string if this is device is ours.
*/
static int
mypci_probe(device_t dev)
{
uprintf("MyPCI Probe\n"
"Vendor ID : 0x%x\n"
"Device ID : 0x%x\n",pci_get_vendor(dev),pci_get_device(dev));
if (pci_get_vendor(dev) == 0x11c1) {
uprintf("We've got the Winmodem, probe successful!\n");
return 0;
}
return ENXIO;
}
/* Attach function is only called if the probe is successful */
static int
mypci_attach(device_t dev)
{
uprintf("MyPCI Attach for : deviceID : 0x%x\n",pci_get_vendor(dev));
sdev = make_dev(&mypci_cdevsw,
0,
UID_ROOT,
GID_WHEEL,
0600,
"mypci");
uprintf("Mypci device loaded.\n");
return ENXIO;
}
/* Detach device. */
static int
mypci_detach(device_t dev)
{
uprintf("Mypci detach!\n");
return 0;
}
/* Called during system shutdown after sync. */
static int
mypci_shutdown(device_t dev)
{
uprintf("Mypci shutdown!\n");
return 0;
}
/*
* Device suspend routine.
*/
static int
mypci_suspend(device_t dev)
{
uprintf("Mypci suspend!\n");
return 0;
}
/*
* Device resume routine.
*/
static int
mypci_resume(device_t dev)
{
uprintf("Mypci resume!\n");
return 0;
}
static device_method_t mypci_methods[] = {
/* Device interface */
DEVMETHOD(device_probe, mypci_probe),
DEVMETHOD(device_attach, mypci_attach),
DEVMETHOD(device_detach, mypci_detach),
DEVMETHOD(device_shutdown, mypci_shutdown),
DEVMETHOD(device_suspend, mypci_suspend),
DEVMETHOD(device_resume, mypci_resume),
{ 0, 0 }
};
static driver_t mypci_driver = {
"mypci",
mypci_methods,
0,
/* sizeof(struct mypci_softc), */
};
static devclass_t mypci_devclass;
DRIVER_MODULE(mypci, pci, mypci_driver, mypci_devclass, 0, 0);
Additional Resources
PCI Special Interest
GroupPCI System Architecture, Fourth Edition by
Tom Shanley, et al.USB DevicesThis chapter will talk about the FreeBSD mechanisms for
writing a device driver for a device on a USB bus.NewBusThis chapter will talk about the FreeBSD NewBus
architecture.ArchitecturesIA-32Talk about the architectural specifics of FreeBSD/x86.AlphaTalk about the architectural specifics of
FreeBSD/alpha.Explanation of allignment errors, how to fix, how to
ignore.Example assembly language code for FreeBSD/alpha.IA-64Talk about the architectural specifics of
FreeBSD/ia64.
-
+ DebuggingTrussvarious descriptions on how to debug certain aspects of
the system using truss, ktrace, gdb, kgdb, etcCompatibility LayersLinuxLinux, SVR4, etcAppendicesDaveAPattersonJohnLHennessy1998Morgan Kaufmann Publishers,
Inc.1-55860-428-6Morgan Kaufmann Publishers, Inc.Computer Organization and DesignThe Hardware / Software Interface1-2W.RichardStevens1993Addison Wesley Longman,
Inc.0-201-56317-7Addison Wesley Longman, Inc.Advanced Programming in the Unix Environment1-2MarshallKirkMcKusickKeithBosticMichaelJKarelsJohnSQuarterman1996Addison-Wesley Publishing Company,
Inc.0-201-54979-4Addison-Wesley Publishing Company, Inc.The Design and Implementation of the 4.4 BSD Operating System1-2AlephOnePhrack 49; "Smashing the Stack for Fun and Profit"ChrispinCowanCaltonPuDaveMaierStackGuard; Automatic Adaptive Detection and Prevention of
Buffer-Overflow AttacksToddMillerTheode Raadtstrlcpy and strlcat -- consistent, safe string copy and
concatenation.
diff --git a/en_US.ISO8859-1/books/developers-handbook/book.sgml b/en_US.ISO8859-1/books/developers-handbook/book.sgml
index 8aacd1d42a..bd58d4a25a 100644
--- a/en_US.ISO8859-1/books/developers-handbook/book.sgml
+++ b/en_US.ISO8859-1/books/developers-handbook/book.sgml
@@ -1,1510 +1,3751 @@
%bookinfo;
]>
FreeBSD Developers' HandbookThe FreeBSD Documentation Projectdoc@FreeBSD.orgAugust 20002000The FreeBSD Documentation Project
&bookinfo.legalnotice;
Welcome to the Developers' Handbook.IntroductionDeveloping on FreeBSDThis will need to discuss FreeBSD as a development
platform, the vision of BSD, architectural overview, layout of
/usr/src, history, etc.Thank you for considering FreeBSD as your development
platform! We hope it will not let you down.The BSD VisionArchitectural OverviewThe Layout of /usr/srcThe complete source code to FreeBSD is available from our
public CVS repository. The source code is normally installed in
/usr/src which contains the
following subdirectories.DirectoryDescriptionbin/Source for files in
/bincontrib/Source for files from contribued software.crypto/DES sourceetc/Source for files in /etcgames/Source for files in /usr/gamesgnu/Utilities covered by the GNU Public Licenseinclude/Source for files in /usr/includekerberosIV/Source for Kerbereros version IVkerberos5/Source for Kerbereros version 5lib/Source for files in /usr/liblibexec/Source for files in /usr/libexecrelease/Files required to produce a FreeBSD releasesbin/Source for files in /sbinsecure/FreeSec sourcesshare/Source for files in /sbinsys/Kernel source filestools/Tools used for maintenance and testing of
FreeBSDusr.bin/Source for files in /usr/binusr.sbin/Source for files in /usr/sbinBasics
-
- Compilation
+
+ Programming Tools
- This will include things like: compilation, makefiles, .mk
- files, basic debugging, linking, secure programming
- guidelines, style(9), CVS, diff, patch, etc.
+ This chapter was written by James Raynard.
+ Modifications for the Developer's Handbook by Murray Stokely.
+
+
+ Synopsis
+
+ This document is an introduction to using some of the
+ programming tools supplied with FreeBSD, although much of it
+ will be applicable to many other versions of Unix. It does
+ not attempt to describe coding in any
+ detail. Most of the document assumes little or no previous
+ programming knowledge, although it is hoped that most
+ programmers will find something of value in it
+
+
+
+ Introduction
+
+ FreeBSD offers an excellent development environment.
+ Compilers for C, C++, and Fortran and an assembler come with the
+ basic system, not to mention a Perl interpreter and classic Unix
+ tools such as sed and awk.
+ If that is not enough, there are many more compilers and
+ interpreters in the Ports collection. FreeBSD is very
+ compatible with standards such as POSIX and
+ ANSI C, as well with its own BSD heritage, so
+ it is possible to write applications that will compile and run
+ with little or no modification on a wide range of
+ platforms.
+
+ However, all this power can be rather overwhelming at
+ first if you've never written programs on a Unix platform
+ before. This document aims to help you get up and running,
+ without getting too deeply into more advanced topics. The
+ intention is that this document should give you enough of the
+ basics to be able to make some sense of the
+ documentation.
+
+ Most of the document requires little or no knowledge of
+ programming, although it does assume a basic competence with
+ using Unix and a willingness to learn!
+
+
+
+
+ Introduction to Programming
+
+ A program is a set of instructions that tell the computer
+ to do various things; sometimes the instruction it has to
+ perform depends on what happened when it performed a previous
+ instruction. This section gives an overview of the two main
+ ways in which you can give these instructions, or
+ commands as they are usually called. One way
+ uses an interpreter, the other a
+ compiler. As human languages are too
+ difficult for a computer to understand in an unambiguous way,
+ commands are usually written in one or other languages specially
+ designed for the purpose.
+
+
+ Interpreters
+
+ With an interpreter, the language comes as an environment,
+ where you type in commands at a prompt and the environment
+ executes them for you. For more complicated programs, you can
+ type the commands into a file and get the interpreter to load
+ the file and execute the commands in it. If anything goes
+ wrong, many interpreters will drop you into a debugger to help
+ you track down the problem.
+
+ The advantage of this is that you can see the results of
+ your commands immediately, and mistakes can be corrected
+ readily. The biggest disadvantage comes when you want to
+ share your programs with someone. They must have the same
+ interpreter, or you must have some way of giving it to them,
+ and they need to understand how to use it. Also users may not
+ appreciate being thrown into a debugger if they press the
+ wrong key! From a performance point of view, interpreters can
+ use up a lot of memory, and generally do not generate code as
+ efficiently as compilers.
+
+ In my opinion, interpreted languages are the best way to
+ start if you have not done any programming before. This kind
+ of environment is typically found with languages like Lisp,
+ Smalltalk, Perl and Basic. It could also be argued that the
+ Unix shell (sh, csh) is itself an
+ interpreter, and many people do in fact write shell
+ scripts to help with various
+ housekeeping tasks on their machine. Indeed, part
+ of the original Unix philosophy was to provide lots of small
+ utility programs that could be linked together in shell
+ scripts to perform useful tasks.
+
+
+
+ Interpreters available with FreeBSD
+
+ Here is a list of interpreters that are available as
+ FreeBSD
+ packages, with a brief discussion of some of the
+ more popular interpreted languages.
+
+ To get one of these packages, all you need to do is to
+ click on the hotlink for the package, then run
+
+ &prompt.root; pkg_add package name
+
+
+ as root. Obviously, you will need to have a fully
+ functional FreeBSD 2.1.0 or later system for the package to
+ work!
+
+
+
+ BASIC
+
+
+ Short for Beginner's All-purpose Symbolic
+ Instruction Code. Developed in the 1950s for teaching
+ University students to program and provided with every
+ self-respecting personal computer in the 1980s,
+ BASIC has been the first programming
+ language for many programmers. It's also the foundation
+ for Visual Basic.
+
+ The Bywater
+ Basic Interpreter and the Phil
+ Cockroft's Basic Interpreter (formerly Rabbit
+ Basic) are available as FreeBSD FreeBSD
+ packages
+
+
+
+
+ Lisp
+
+
+ A language that was developed in the late 1950s as
+ an alternative to the number-crunching
+ languages that were popular at the time. Instead of
+ being based on numbers, Lisp is based on lists; in fact
+ the name is short for List Processing.
+ Very popular in AI (Artificial Intelligence)
+ circles.
+
+ Lisp is an extremely powerful and sophisticated
+ language, but can be rather large and unwieldy.
+
+ FreeBSD has GNU
+ Common Lisp available as a package.
+
+
+
+
+ Perl
+
+
+ Very popular with system administrators for writing
+ scripts; also often used on World Wide Web servers for
+ writing CGI scripts.
+
+ The latest version (version 5) comes with FreeBSD.
+
+
+
+
+ Scheme
+
+
+ A dialect of Lisp that is rather more compact and
+ cleaner than Common Lisp. Popular in Universities as it
+ is simple enough to teach to undergraduates as a first
+ language, while it has a high enough level of
+ abstraction to be used in research work.
+
+ FreeBSD has packages of the Elk
+ Scheme Interpreter, the MIT
+ Scheme Interpreter and the SCM
+ Scheme Interpreter.
+
+
+
+
+ Icon
+
+
+ The
+ Icon Programming Language.
+
+
+
+
+ Logo
+
+
+ Brian
+ Harvey's LOGO Interpreter.
+
+
+
+
+ Python
+
+
+ The
+ Python Object-Oriented Programming
+ Language
+
+
+
+
+
+
+ Compilers
+
+ Compilers are rather different. First of all, you write
+ your code in a file (or files) using an editor. You then run
+ the compiler and see if it accepts your program. If it did
+ not compile, grit your teeth and go back to the editor; if it
+ did compile and gave you a program, you can run it either at a
+ shell command prompt or in a debugger to see if it works
+ properly.
+
+
+ If you run it in the shell, you may get a core
+ dump.
+
+
+ Obviously, this is not quite as direct as using an
+ interpreter. However it allows you to do a lot of things
+ which are very difficult or even impossible with an
+ interpreter, such as writing code which interacts closely with
+ the operating system—or even writing your own operating
+ system! It's also useful if you need to write very efficient
+ code, as the compiler can take its time and optimise the code,
+ which would not be acceptable in an interpreter. And
+ distributing a program written for a compiler is usually more
+ straightforward than one written for an interpreter—you
+ can just give them a copy of the executable, assuming they
+ have the same operating system as you.
+
+ Compiled languages include Pascal, C and C++. C and C++
+ are rather unforgiving languages, and best suited to more
+ experienced programmers; Pascal, on the other hand, was
+ designed as an educational language, and is quite a good
+ language to start with. Unfortunately, FreeBSD doesn't have
+ any Pascal support, except for a Pascal-to-C converter in the
+ ports.
+
+ As the edit-compile-run-debug cycle is rather tedious when
+ using separate programs, many commercial compiler makers have
+ produced Integrated Development Environments
+
+ (IDEs for short). FreeBSD does not have an
+ IDE as such; however it is possible to use Emacs
+ for this purpose. This is discussed in .
+
+
+
+
+
+
+
+ Compiling with <command>cc</command>
+
+ This section deals only with the GNU compiler for C and C++,
+ since that comes with the base FreeBSD system. It can be
+ invoked by either cc or gcc. The
+ details of producing a program with an interpreter vary
+ considerably between interpreters, and are usually well covered
+ in the documentation and on-line help for the
+ interpreter.
+
+ Once you've written your masterpiece, the next step is to
+ convert it into something that will (hopefully!) run on FreeBSD.
+ This usually involves several steps, each of which is done by a
+ separate program.
+
+
+
+ Pre-process your source code to remove comments and do
+ other tricks like expanding macros in C.
+
+
+
+ Check the syntax of your code to see if you have obeyed
+ the rules of the language. If you have not, it will
+ complain!
+
+
+
+ Convert the source code into assembly
+ language—this is very close to machine code, but still
+ understandable by humans. Allegedly.
+
+
+ To be strictly accurate, cc converts the
+ source code into its own, machine-independent
+ p-code instead of assembly language at
+ this stage.
+
+
+
+
+ Convert the assembly language into machine
+ code—yep, we are talking bits and bytes, ones and
+ zeros here.
+
+
+
+ Check that you have used things like functions and
+ global variables in a consistent way. For example, if you
+ have called a non-existent function, it will
+ complain.
+
+
+
+ If you are trying to produce an executable from several
+ source code files, work out how to fit them all
+ together.
+
+
+
+ Work out how to produce something that the system's
+ run-time loader will be able to load into memory and
+ run.
+
+
+
+ Finally, write the executable on the file system.
+
+
+
+ The word compiling is often used to refer to
+ just steps 1 to 4—the others are referred to as
+ linking. Sometimes step 1 is referred to as
+ pre-processing and steps 3-4 as
+ assembling.
+
+ Fortunately, almost all this detail is hidden from you, as
+ cc is a front end that manages calling all these
+ programs with the right arguments for you; simply typing
+
+ &prompt.user; cc foobar.c
+
+
+ will cause foobar.c to be compiled by all the
+ steps above. If you have more than one file to compile, just do
+ something like
+
+ &prompt.user; cc foo.c bar.c
+
+
+ Note that the syntax checking is just that—checking
+ the syntax. It will not check for any logical mistakes you may
+ have made, like putting the program into an infinite loop, or
+ using a bubble sort when you meant to use a binary
+ sort.
+
+
+ In case you didn't know, a binary sort is an efficient
+ way of sorting things into order and a bubble sort
+ isn't.
+
+
+ There are lots and lots of options for cc, which
+ are all in the man page. Here are a few of the most important
+ ones, with examples of how to use them.
+
+
+
+
+
+
+ The output name of the file. If you do not use this
+ option, cc will produce an executable called
+ a.out.
+
+
+ The reasons for this are buried in the mists of
+ history.
+
+
+
+ &prompt.user; cc foobar.c executable is a.out
+&prompt.user; cc -o foobar foobar.c executable is foobar
+
+
+
+
+
+
+
+
+
+ Just compile the file, do not link it. Useful for toy
+ programs where you just want to check the syntax, or if
+ you are using a Makefile.
+
+
+ &prompt.user; cc -c foobar.c
+
+
+
+ This will produce an object file (not an
+ executable) called foobar.o. This
+ can be linked together with other object files into an
+ executable.
+
+
+
+
+
+
+
+ Create a debug version of the executable. This makes
+ the compiler put information into the executable about
+ which line of which source file corresponds to which
+ function call. A debugger can use this information to show
+ the source code as you step through the program, which is
+ very useful; the disadvantage is that
+ all this extra information makes the program much bigger.
+ Normally, you compile with while you
+ are developing a program and then compile a release
+ version without when you're
+ satisfied it works properly.
+
+
+ &prompt.user; cc -g foobar.c
+
+
+
+ This will produce a debug version of the
+ program.
+
+
+ Note, we didn't use the flag
+ to specify the executable name, so we will get an
+ executable called a.out.
+ Producing a debug version called
+ foobar is left as an exercise for
+ the reader!
+
+
+
+
+
+
+
+
+ Create an optimised version of the executable. The
+ compiler performs various clever tricks to try and produce
+ an executable that runs faster than normal. You can add a
+ number after the to specify a higher
+ level of optimisation, but this often exposes bugs in the
+ compiler's optimiser. For instance, the version of
+ cc that comes with the 2.1.0 release of
+ FreeBSD is known to produce bad code with the
+ option in some circumstances.
+
+ Optimisation is usually only turned on when compiling
+ a release version.
+
+
+ &prompt.user; cc -O -o foobar foobar.c
+
+
+
+ This will produce an optimised version of
+ foobar.
+
+
+
+
+ The following three flags will force cc
+ to check that your code complies to the relevant international
+ standard, often referred to as the ANSI
+ standard, though strictly speaking it is an
+ ISO standard.
+
+
+
+
+
+
+ Enable all the warnings which the authors of
+ cc believe are worthwhile. Despite the
+ name, it will not enable all the warnings
+ cc is capable of.
+
+
+
+
+
+
+
+ Turn off most, but not all, of the
+ non-ANSI C features provided by
+ cc. Despite the name, it does not
+ guarantee strictly that your code will comply to the
+ standard.
+
+
+
+
+
+
+
+ Turn off all
+ cc's non-ANSI C
+ features.
+
+
+
+
+ Without these flags, cc will allow you to
+ use some of its non-standard extensions to the standard. Some
+ of these are very useful, but will not work with other
+ compilers—in fact, one of the main aims of the standard is
+ to allow people to write code that will work with any compiler
+ on any system. This is known as portable
+ code.
+
+ Generally, you should try to make your code as portable as
+ possible, as otherwise you may have to completely re-write the
+ program later to get it to work somewhere else—and who
+ knows what you may be using in a few years time?
+
+
+ &prompt.user; cc -Wall -ansi -pedantic -o foobar foobar.c
+
+
+
+ This will produce an executable foobar
+ after checking foobar.c for standard
+ compliance.
+
+
+
+
+
+
+ Specify a function library to be used during when
+ linking.
+
+ The most common example of this is when compiling a
+ program that uses some of the mathematical functions in C.
+ Unlike most other platforms, these are in a separate
+ library from the standard C one and you have to tell the
+ compiler to add it.
+
+ The rule is that if the library is called
+ libsomething.a,
+ you give cc the argument
+ .
+ For example, the math library is
+ libm.a, so you give
+ cc the argument .
+ A common gotcha with the math library is
+ that it has to be the last library on the command
+ line.
+
+
+ &prompt.user; cc -o foobar foobar.c -lm
+
+
+
+ This will link the math library functions into
+ foobar.
+
+ If you are compiling C++ code, you need to add
+ , or if
+ you are using FreeBSD 2.2 or later, to the command line
+ argument to link the C++ library functions.
+ Alternatively, you can run c++ instead
+ of cc, which does this for you.
+ c++ can also be invoked as
+ g++ on FreeBSD.
+
+
+ &prompt.user; cc -o foobar foobar.cc -lg++For FreeBSD 2.1.6 and earlier
+&prompt.user; cc -o foobar foobar.cc -lstdc++For FreeBSD 2.2 and later
+&prompt.user; c++ -o foobar foobar.cc
+
+
+
+ Each of these will both produce an executable
+ foobar from the C++ source file
+ foobar.cc. Note that, on Unix
+ systems, C++ source files traditionally end in
+ .C, .cxx or
+ .cc, rather than the
+ MS-DOS style
+ .cpp (which was already used for
+ something else). gcc used to rely on
+ this to work out what kind of compiler to use on the
+ source file; however, this restriction no longer applies,
+ so you may now call your C++ files
+ .cpp with impunity!
+
+
+
+
+
+ Common <command>cc</command> Queries and Problems
+
+
+
+
+ I am trying to write a program which uses the
+ sin() function and I get an error
+ like this. What does it mean?
+
+
+ /var/tmp/cc0143941.o: Undefined symbol `_sin' referenced from text segment
+
+
+
+
+
+ When using mathematical functions like
+ sin(), you have to tell
+ cc to link in the math library, like
+ so:
+
+
+ &prompt.user; cc -o foobar foobar.c -lm
+
+
+
+
+
+
+
+ All right, I wrote this simple program to practice
+ using . All it does is raise 2.1 to
+ the power of 6.
+
+
+ #include <stdio.h>
+
+int main() {
+ float f;
+
+ f = pow(2.1, 6);
+ printf("2.1 ^ 6 = %f\n", f);
+ return 0;
+}
+
+
+
+ and I compiled it as:
+
+
+ &prompt.user; cc temp.c -lm
+
+
+
+ like you said I should, but I get this when I run
+ it:
+
+
+ &prompt.user; ./a.out
+2.1 ^ 6 = 1023.000000
+
+
+
+ This is not the right answer!
+ What is going on?
+
+
+
+ When the compiler sees you call a function, it
+ checks if it has already seen a prototype for it. If it
+ has not, it assumes the function returns an
+ int, which is definitely not what you want
+ here.
+
+
+
+
+
+ So how do I fix this?
+
+
+
+ The prototypes for the mathematical functions are in
+ math.h. If you include this file,
+ the compiler will be able to find the prototype and it
+ will stop doing strange things to your
+ calculation!
+
+
+ #include <math.h>
+#include <stdio.h>
+
+int main() {
+...
+
+
+
+ After recompiling it as you did before, run
+ it:
+
+
+ &prompt.user; ./a.out
+2.1 ^ 6 = 85.766121
+
+
+
+ If you are using any of the mathematical functions,
+ always include
+ math.h and remember to link in the
+ math library.
+
+
+
+
+
+ I compiled a file called
+ foobar.c and I cannot find an
+ executable called foobar. Where's
+ it gone?
+
+
+
+ Remember, cc will call the
+ executable a.out unless you tell it
+ differently. Use the
+
+ option:
+
+
+ &prompt.user; cc -o foobar foobar.c
+
+
+
+
+
+
+
+ OK, I have an executable called
+ foobar, I can see it when I run
+ ls, but when I type in
+ foobar at the command prompt it tells
+ me there is no such file. Why can it not find
+ it?
+
+
+
+ Unlike MS-DOS, Unix does not
+ look in the current directory when it is trying to find
+ out which executable you want it to run, unless you tell
+ it to. Either type ./foobar, which
+ means run the file called
+ foobar in the current
+ directory, or change your PATH environment
+ variable so that it looks something like
+
+
+ bin:/usr/bin:/usr/local/bin:.
+
+
+
+ The dot at the end means look in the current
+ directory if it is not in any of the
+ others.
+
+
+
+
+
+ I called my executable test,
+ but nothing happens when I run it. What is going
+ on?
+
+
+
+ Most Unix systems have a program called
+ test in /usr/bin
+ and the shell is picking that one up before it gets to
+ checking the current directory. Either type:
+
+
+ &prompt.user; ./test
+
+
+
+ or choose a better name for your program!
+
+
+
+
+
+ I compiled my program and it seemed to run all right
+ at first, then there was an error and it said something
+ about core dumped. What does that
+ mean?
+
+
+
+ The name core dump dates back
+ to the very early days of Unix, when the machines used
+ core memory for storing data. Basically, if the program
+ failed under certain conditions, the system would write
+ the contents of core memory to disk in a file called
+ core, which the programmer could
+ then pore over to find out what went wrong.
+
+
+
+
+
+ Fascinating stuff, but what I am supposed to do
+ now?
+
+
+
+ Use gdb to analyse the core (see
+ ).
+
+
+
+
+
+ When my program dumped core, it said something about
+ a segmentation fault. What's
+ that?
+
+
+
+ This basically means that your program tried to
+ perform some sort of illegal operation on memory; Unix
+ is designed to protect the operating system and other
+ programs from rogue programs.
+
+ Common causes for this are:
+
+
+
+ Trying to write to a NULL
+ pointer, eg
+
+ char *foo = NULL;
+strcpy(foo, "bang!");
+
+
+
+
+ Using a pointer that hasn't been initialised,
+ eg
+
+ char *foo;
+strcpy(foo, "bang!");
+
+
+ The pointer will have some random value that,
+ with luck, will point into an area of memory that
+ isn't available to your program and the kernel will
+ kill your program before it can do any damage. If
+ you're unlucky, it'll point somewhere inside your
+ own program and corrupt one of your data structures,
+ causing the program to fail mysteriously.
+
+
+
+ Trying to access past the end of an array,
+ eg
+
+ int bar[20];
+bar[27] = 6;
+
+
+
+
+ Trying to store something in read-only memory,
+ eg
+
+ char *foo = "My string";
+strcpy(foo, "bang!");
+
+
+ Unix compilers often put string literals like
+ "My string" into read-only areas
+ of memory.
+
+
+
+ Doing naughty things with
+ malloc() and
+ free(), eg
+
+ char bar[80];
+free(bar);
+
+
+ or
+
+ char *foo = malloc(27);
+free(foo);
+free(foo);
+
+
+
+
+ Making one of these mistakes will not always lead to
+ an error, but they are always bad practice. Some
+ systems and compilers are more tolerant than others,
+ which is why programs that ran well on one system can
+ crash when you try them on an another.
+
+
+
+
+
+ Sometimes when I get a core dump it says
+ bus error. It says in my Unix
+ book that this means a hardware problem, but the
+ computer still seems to be working. Is this
+ true?
+
+
+
+ No, fortunately not (unless of course you really do
+ have a hardware problem…). This is usually
+ another way of saying that you accessed memory in a way
+ you shouldn't have.
+
+
+
+
+
+ This dumping core business sounds as though it could
+ be quite useful, if I can make it happen when I want to.
+ Can I do this, or do I have to wait until there's an
+ error?
+
+
+
+ Yes, just go to another console or xterm, do
+
+ &prompt.user; ps
+
+
+ to find out the process ID of your program, and
+ do
+
+ &prompt.user; kill -ABRT pid
+
+
+ where
+ pid is
+ the process ID you looked up.
+
+ This is useful if your program has got stuck in an
+ infinite loop, for instance. If your program happens to
+ trap SIGABRT, there are several other
+ signals which have a similar effect.
+
+
+
+
+
+
+
+ Make
+
+
+ What is <command>make</command>?
+
+ When you're working on a simple program with only one or
+ two source files, typing in
+
+ &prompt.user; cc file1.c file2.c
+
+
+ is not too bad, but it quickly becomes very tedious when
+ there are several files—and it can take a while to
+ compile, too.
+
+ One way to get around this is to use object files and only
+ recompile the source file if the source code has changed. So
+ we could have something like:
+
+ &prompt.user; cc file1.o file2.o … file37.c &hellip
+
+
+ if we'd changed file37.c, but not any
+ of the others, since the last time we compiled. This may
+ speed up the compilation quite a bit, but doesn't solve the
+ typing problem.
+
+ Or we could write a shell script to solve the typing
+ problem, but it would have to re-compile everything, making it
+ very inefficient on a large project.
+
+ What happens if we have hundreds of source files lying
+ about? What if we're working in a team with other people who
+ forget to tell us when they've changed one of their source
+ files that we use?
+
+ Perhaps we could put the two solutions together and write
+ something like a shell script that would contain some kind of
+ magic rule saying when a source file needs compiling. Now all
+ we need now is a program that can understand these rules, as
+ it's a bit too complicated for the shell.
+
+ This program is called make. It reads
+ in a file, called a makefile, that
+ tells it how different files depend on each other, and works
+ out which files need to be re-compiled and which ones don't.
+ For example, a rule could say something like if
+ fromboz.o is older than
+ fromboz.c, that means someone must have
+ changed fromboz.c, so it needs to be
+ re-compiled. The makefile also has rules telling
+ make how to re-compile the source file,
+ making it a much more powerful tool.
+
+ Makefiles are typically kept in the same directory as the
+ source they apply to, and can be called
+ makefile, Makefile
+ or MAKEFILE. Most programmers use the
+ name Makefile, as this puts it near the
+ top of a directory listing, where it can easily be
+ seen.
+
+
+ They don't use the MAKEFILE form
+ as block capitals are often used for documentation files
+ like README.
+
+
+
+
+ Example of using <command>make</command>
+
+ Here's a very simple make file:
+
+ foo: foo.c
+ cc -o foo foo.c
+
+
+ It consists of two lines, a dependency line and a creation
+ line.
+
+ The dependency line here consists of the name of the
+ program (known as the target), followed
+ by a colon, then whitespace, then the name of the source file.
+ When make reads this line, it looks to see
+ if foo exists; if it exists, it compares
+ the time foo was last modified to the
+ time foo.c was last modified. If
+ foo does not exist, or is older than
+ foo.c, it then looks at the creation line
+ to find out what to do. In other words, this is the rule for
+ working out when foo.c needs to be
+ re-compiled.
+
+ The creation line starts with a tab (press
+ the tab key) and then the command you would
+ type to create foo if you were doing it
+ at a command prompt. If foo is out of
+ date, or does not exist, make then executes
+ this command to create it. In other words, this is the rule
+ which tells make how to re-compile
+ foo.c.
+
+ So, when you type make, it will
+ make sure that foo is up to date with
+ respect to your latest changes to foo.c.
+ This principle can be extended to
+ Makefiles with hundreds of
+ targets—in fact, on FreeBSD, it is possible to compile
+ the entire operating system just by typing make
+ world in the appropriate directory!
+
+ Another useful property of makefiles is that the targets
+ don't have to be programs. For instance, we could have a make
+ file that looks like this:
+
+ foo: foo.c
+ cc -o foo foo.c
+
+install:
+ cp foo /home/me
+
+
+ We can tell make which target we want to make by
+ typing:
+
+ &prompt.user; make target
+
+
+ make will then only look at that target
+ and ignore any others. For example, if we type
+ make foo with the makefile above, make
+ will ignore the install target.
+
+ If we just type make on its own,
+ make will always look at the first target and then stop
+ without looking at any others. So if we typed
+ make here, it will just go to the
+ foo target, re-compile
+ foo if necessary, and then stop without
+ going on to the install target.
+
+ Notice that the install target doesn't
+ actually depend on anything! This means that the command on
+ the following line is always executed when we try to make that
+ target by typing make install. In this
+ case, it will copy foo into the user's
+ home directory. This is often used by application makefiles,
+ so that the application can be installed in the correct
+ directory when it has been correctly compiled.
+
+ This is a slightly confusing subject to try and explain.
+ If you don't quite understand how make
+ works, the best thing to do is to write a simple program like
+ hello world and a make file like the one above
+ and experiment. Then progress to using more than one source
+ file, or having the source file include a header file. The
+ touch command is very useful here—it
+ changes the date on a file without you having to edit
+ it.
+
+
+
+ FreeBSD Makefiles
+
+ Makefiles can be rather complicated to write. Fortunately,
+ BSD-based systems like FreeBSD come with some very powerful
+ ones as part of the system. One very good example of this is
+ the FreeBSD ports system. Here's the essential part of a
+ typical ports Makefile:
+
+ MASTER_SITES= ftp://freefall.cdrom.com/pub/FreeBSD/LOCAL_PORTS/
+DISTFILES= scheme-microcode+dist-7.3-freebsd.tgz
+
+.include <bsd.port.mk>
+
+
+ Now, if we go to the directory for this port and type
+ make, the following happens:
+
+
+
+ A check is made to see if the source code for this
+ port is already on the system.
+
+
+
+ If it isn't, an FTP connection to the URL in
+ MASTER_SITES is set up to download the
+ source.
+
+
+
+ The checksum for the source is calculated and compared
+ it with one for a known, good, copy of the source. This
+ is to make sure that the source was not corrupted while in
+ transit.
+
+
+
+ Any changes required to make the source work on
+ FreeBSD are applied—this is known as
+ patching.
+
+
+
+ Any special configuration needed for the source is
+ done. (Many Unix program distributions try to work out
+ which version of Unix they are being compiled on and which
+ optional Unix features are present—this is where
+ they are given the information in the FreeBSD ports
+ scenario).
+
+
+
+ The source code for the program is compiled. In
+ effect, we change to the directory where the source was
+ unpacked and do make—the
+ program's own make file has the necessary information to
+ build the program.
+
+
+
+ We now have a compiled version of the program. If we
+ wish, we can test it now; when we feel confident about the
+ program, we can type make install.
+ This will cause the program and any supporting files it
+ needs to be copied into the correct location; an entry is
+ also made into a package database, so
+ that the port can easily be uninstalled later if we change
+ our mind about it.
+
+
+
+ Now I think you'll agree that's rather impressive for a
+ four line script!
+
+ The secret lies in the last line, which tells
+ make to look in the system makefile called
+ bsd.port.mk. It's easy to overlook this
+ line, but this is where all the clever stuff comes
+ from—someone has written a makefile that tells
+ make to do all the things above (plus a
+ couple of other things I didn't mention, including handling
+ any errors that may occur) and anyone can get access to that
+ just by putting a single line in their own make file!
+
+ If you want to have a look at these system makefiles,
+ they're in /usr/share/mk, but it's
+ probably best to wait until you've had a bit of practice with
+ makefiles, as they are very complicated (and if you do look at
+ them, make sure you have a flask of strong coffee
+ handy!)
+
+
+
+ More advanced uses of <command>make</command>
+
+ Make is a very powerful tool, and can
+ do much more than the simple example above shows.
+ Unfortunately, there are several different versions of
+ make, and they all differ considerably.
+ The best way to learn what they can do is probably to read the
+ documentation—hopefully this introduction will have
+ given you a base from which you can do this.
+
+ The version of make that comes with FreeBSD is the
+ Berkeley make; there is a tutorial
+ for it in /usr/share/doc/psd/12.make. To
+ view it, do
+
+ &prompt.user; zmore paper.ascii.gz
+
+
+ in that directory.
+
+ Many applications in the ports use GNU
+ make, which has a very good set of
+ info pages. If you have installed any of these
+ ports, GNU make will automatically
+ have been installed as gmake. It's also
+ available as a port and package in its own right.
+
+ To view the info pages for GNU
+ make, you will have to edit the
+ dir file in the
+ /usr/local/info directory to add an entry
+ for it. This involves adding a line like
+
+ * Make: (make). The GNU Make utility.
+
+
+ to the file. Once you have done this, you can type
+ info and then select
+ make from the menu (or in
+ Emacs, do C-h
+ i).
+
+
+
+
+ Debugging
+
+
+ The Debugger
+
+ The debugger that comes with FreeBSD is called
+ gdb (GNU
+ debugger). You start it up by typing
+
+ &prompt.user; gdb progname
+
+
+ although most people prefer to run it inside
+ Emacs. You can do this by:
+
+ M-x gdb RET progname RET
+
+
+ Using a debugger allows you to run the program under more
+ controlled circumstances. Typically, you can step through the
+ program a line at a time, inspect the value of variables,
+ change them, tell the debugger to run up to a certain point
+ and then stop, and so on. You can even attach to a program
+ that's already running, or load a core file to investigate why
+ the program crashed. It's even possible to debug the kernel,
+ though that's a little trickier than the user applications
+ we'll be discussing in this section.
+
+ gdb has quite good on-line help, as
+ well as a set of info pages, so this section will concentrate
+ on a few of the basic commands.
+
+ Finally, if you find its text-based command-prompt style
+ off-putting, there's a graphical front-end for it xxgdb in the ports
+ collection.
+
+ This section is intended to be an introduction to using
+ gdb and does not cover specialised topics
+ such as debugging the kernel.
+
+
+
+ Running a program in the debugger
+
+ You'll need to have compiled the program with the
+ option to get the most out of using
+ gdb. It will work without, but you'll only
+ see the name of the function you're in, instead of the source
+ code. If you see a line like:
+
+ … (no debugging symbols found) …
+
+
+ when gdb starts up, you'll know that
+ the program wasn't compiled with the
+ option.
+
+ At the gdb prompt, type
+ break main. This will tell the
+ debugger to skip over the preliminary set-up code in the
+ program and start at the beginning of your code. Now type
+ run to start the program—it will
+ start at the beginning of the set-up code and then get stopped
+ by the debugger when it calls main().
+ (If you've ever wondered where main()
+ gets called from, now you know!).
+
+ You can now step through the program, a line at a time, by
+ pressing n. If you get to a function call,
+ you can step into it by pressing s. Once
+ you're in a function call, you can return from stepping into a
+ function call by pressing f. You can also
+ use up and down to take
+ a quick look at the caller.
+
+ Here's a simple example of how to spot a mistake in a
+ program with gdb. This is our program
+ (with a deliberate mistake):
+
+ #include <stdio.h>
+
+int bazz(int anint);
+
+main() {
+ int i;
+
+ printf("This is my program\n");
+ bazz(i);
+ return 0;
+}
+
+int bazz(int anint) {
+ printf("You gave me %d\n", anint);
+ return anint;
+}
+
+
+ This program sets i to be
+ 5 and passes it to a function
+ bazz() which prints out the number we
+ gave it.
+
+ When we compile and run the program we get
+
+ &prompt.user; cc -g -o temp temp.c
+&prompt.user; ./temp
+This is my program
+anint = 4231
+
+
+ That wasn't what we expected! Time to see what's going
+ on!
+
+ &prompt.user; gdb temp
+GDB is free software and you are welcome to distribute copies of it
+ under certain conditions; type "show copying" to see the conditions.
+There is absolutely no warranty for GDB; type "show warranty" for details.
+GDB 4.13 (i386-unknown-freebsd), Copyright 1994 Free Software Foundation, Inc.
+(gdb) break main Skip the set-up code
+Breakpoint 1 at 0x160f: file temp.c, line 9. gdb puts breakpoint at main()
+(gdb) run Run as far as main()
+Starting program: /home/james/tmp/temp Program starts running
+
+Breakpoint 1, main () at temp.c:9 gdb stops at main()
+(gdb) n Go to next line
+This is my program Program prints out
+(gdb) s step into bazz()
+bazz (anint=4231) at temp.c:17 gdb displays stack frame
+(gdb)
+
+
+ Hang on a minute! How did anint get to be
+ 4231? Didn't we set it to be
+ 5 in main()? Let's
+ move up to main() and have a look.
+
+ (gdb) up Move up call stack
+#1 0x1625 in main () at temp.c:11 gdb displays stack frame
+(gdb) p i Show us the value of i
+$1 = 4231 gdb displays 4231
+
+
+ Oh dear! Looking at the code, we forgot to initialise
+ i. We meant to put
+
+ …
+main() {
+ int i;
+
+ i = 5;
+ printf("This is my program\n");
+&hellip
+
+
+ but we left the i=5; line out. As we
+ didn't initialise i, it had whatever number
+ happened to be in that area of memory when the program ran,
+ which in this case happened to be
+ 4231.
+
+
+ gdb displays the stack frame every
+ time we go into or out of a function, even if we're using
+ up and down to move
+ around the call stack. This shows the name of the function
+ and the values of its arguments, which helps us keep track
+ of where we are and what's going on. (The stack is a
+ storage area where the program stores information about the
+ arguments passed to functions and where to go when it
+ returns from a function call).
+
+
+
+
+ Examining a core file
+
+ A core file is basically a file which contains the
+ complete state of the process when it crashed. In the
+ good old days, programmers had to print out hex
+ listings of core files and sweat over machine code manuals,
+ but now life is a bit easier. Incidentally, under FreeBSD and
+ other 4.4BSD systems, a core file is called
+ progname.core instead of just
+ core, to make it clearer which program a
+ core file belongs to.
+
+ To examine a core file, start up gdb in
+ the usual way. Instead of typing break or
+ run, type
+
+ (gdb) core progname.core
+
+
+ If you're not in the same directory as the core file,
+ you'll have to do dir
+ /path/to/core/file first.
+
+ You should see something like this:
+
+ &prompt.user; gdb a.out
+GDB is free software and you are welcome to distribute copies of it
+ under certain conditions; type "show copying" to see the conditions.
+There is absolutely no warranty for GDB; type "show warranty" for details.
+GDB 4.13 (i386-unknown-freebsd), Copyright 1994 Free Software Foundation, Inc.
+(gdb) core a.out.core
+Core was generated by `a.out'.
+Program terminated with signal 11, Segmentation fault.
+Cannot access memory at address 0x7020796d.
+#0 0x164a in bazz (anint=0x5) at temp.c:17
+(gdb)
+
+
+ In this case, the program was called
+ a.out, so the core file is called
+ a.out.core. We can see that the program
+ crashed due to trying to access an area in memory that was not
+ available to it in a function called
+ bazz.
+
+ Sometimes it's useful to be able to see how a function was
+ called, as the problem could have occurred a long way up the
+ call stack in a complex program. The bt
+ command causes gdb to print out a
+ back-trace of the call stack:
+
+ (gdb) bt
+#0 0x164a in bazz (anint=0x5) at temp.c:17
+#1 0xefbfd888 in end ()
+#2 0x162c in main () at temp.c:11
+(gdb)
+
+
+ The end() function is called when a
+ program crashes; in this case, the bazz()
+ function was called from main().
+
+
+
+ Attaching to a running program
+
+ One of the neatest features about gdb
+ is that it can attach to a program that's already running. Of
+ course, that assumes you have sufficient permissions to do so.
+ A common problem is when you are stepping through a program
+ that forks, and you want to trace the child, but the debugger
+ will only let you trace the parent.
+
+ What you do is start up another gdb,
+ use ps to find the process ID for the
+ child, and do
+
+ (gdb) attach pid
+
+
+ in gdb, and then debug as usual.
+
+ That's all very well, you're probably
+ thinking, but by the time I've done that, the child
+ process will be over the hill and far away. Fear
+ not, gentle reader, here's how to do it (courtesy of the
+ gdb info pages):
+
+ &hellip
+if ((pid = fork()) < 0) /* _Always_ check this */
+ error();
+else if (pid == 0) { /* child */
+ int PauseMode = 1;
+
+ while (PauseMode)
+ sleep(10); /* Wait until someone attaches to us */
+ &hellip
+} else { /* parent */
+ &hellip
+
+
+ Now all you have to do is attach to the child, set
+ PauseMode to 0, and wait
+ for the sleep() call to return!
+
+
+
+
+ Using Emacs as a Development Environment
+
+
+ Emacs
+
+ Unfortunately, Unix systems don't come with the kind of
+ everything-you-ever-wanted-and-lots-more-you-didn't-in-one-gigantic-package
+ integrated development environments that other systems
+ have.
+
+
+ At least, not unless you pay out very large sums of
+ money.
+
+
+ However, it is possible to set up your own environment. It
+ may not be as pretty, and it may not be quite as integrated,
+ but you can set it up the way you want it. And it's free.
+ And you have the source to it.
+
+ The key to it all is Emacs. Now there are some people who
+ loathe it, but many who love it. If you're one of the former,
+ I'm afraid this section will hold little of interest to you.
+ Also, you'll need a fair amount of memory to run it—I'd
+ recommend 8MB in text mode and 16MB in X as the bare minimum
+ to get reasonable performance.
+
+ Emacs is basically a highly customisable
+ editor—indeed, it has been customised to the point where
+ it's more like an operating system than an editor! Many
+ developers and sysadmins do in fact spend practically all
+ their time working inside Emacs, leaving it only to log
+ out.
+
+ It's impossible even to summarise everything Emacs can do
+ here, but here are some of the features of interest to
+ developers:
+
+
+
+ Very powerful editor, allowing search-and-replace on
+ both strings and regular expressions (patterns), jumping
+ to start/end of block expression, etc, etc.
+
+
+
+ Pull-down menus and online help.
+
+
+
+ Language-dependent syntax highlighting and
+ indentation.
+
+
+
+ Completely customisable.
+
+
+
+ You can compile and debug programs within
+ Emacs.
+
+
+
+ On a compilation error, you can jump to the offending
+ line of source code.
+
+
+
+ Friendly-ish front-end to the info
+ program used for reading GNU hypertext documentation,
+ including the documentation on Emacs itself.
+
+
+
+ Friendly front-end to gdb, allowing
+ you to look at the source code as you step through your
+ program.
+
+
+
+ You can read Usenet news and mail while your program
+ is compiling.
+
+
+
+ And doubtless many more that I've overlooked.
+
+ Emacs can be installed on FreeBSD using the Emacs
+ port.
+
+ Once it's installed, start it up and do C-h
+ t to read an Emacs tutorial—that means
+ hold down the control key, press
+ h, let go of the control
+ key, and then press t. (Alternatively, you
+ can you use the mouse to select Emacs
+ Tutorial from the Help
+ menu).
+
+ Although Emacs does have menus, it's well worth learning
+ the key bindings, as it's much quicker when you're editing
+ something to press a couple of keys than to try and find the
+ mouse and then click on the right place. And, when you're
+ talking to seasoned Emacs users, you'll find they often
+ casually throw around expressions like M-x
+ replace-s RET foo RET bar RET so it's
+ useful to know what they mean. And in any case, Emacs has far
+ too many useful functions for them to all fit on the menu
+ bars.
+
+ Fortunately, it's quite easy to pick up the key-bindings,
+ as they're displayed next to the menu item. My advice is to
+ use the menu item for, say, opening a file until you
+ understand how it works and feel confident with it, then try
+ doing C-x C-f. When you're happy with that, move on to
+ another menu command.
+
+ If you can't remember what a particular combination of
+ keys does, select Describe Key from
+ the Help menu and type it in—Emacs
+ will tell you what it does. You can also use the
+ Command Apropos menu item to find
+ out all the commands which contain a particular word in them,
+ with the key binding next to it.
+
+ By the way, the expression above means hold down the
+ Meta key, press x, release
+ the Meta key, type
+ replace-s (short for
+ replace-string—another feature of
+ Emacs is that you can abbreviate commands), press the
+ return key, type foo
+ (the string you want replaced), press the
+ return key, type bar (the string you want to
+ replace foo with) and press
+ return again. Emacs will then do the
+ search-and-replace operation you've just requested.
+
+ If you're wondering what on earth the
+ Meta key is, it's a special key that many
+ Unix workstations have. Unfortunately, PC's don't have one,
+ so it's usually the alt key (or if you're
+ unlucky, the escape key).
+
+ Oh, and to get out of Emacs, do C-x C-c
+ (that means hold down the control key, press
+ x, press c and release the
+ control key). If you have any unsaved files
+ open, Emacs will ask you if you want to save them. (Ignore
+ the bit in the documentation where it says
+ C-z is the usual way to leave
+ Emacs—that leaves Emacs hanging around in the
+ background, and is only really useful if you're on a system
+ which doesn't have virtual terminals).
+
+
+
+ Configuring Emacs
+
+ Emacs does many wonderful things; some of them are built
+ in, some of them need to be configured.
+
+ Instead of using a proprietary macro language for
+ configuration, Emacs uses a version of Lisp specially adapted
+ for editors, known as Emacs Lisp. This can be quite useful if
+ you want to go on and learn something like Common Lisp, as
+ it's considerably smaller than Common Lisp (although still
+ quite big!).
+
+ The best way to learn Emacs Lisp is to download the Emacs
+ Tutorial
+
+ However, there's no need to actually know any Lisp to get
+ started with configuring Emacs, as I've included a sample
+ .emacs file, which should be enough to
+ get you started. Just copy it into your home directory and
+ restart Emacs if it's already running; it will read the
+ commands from the file and (hopefully) give you a useful basic
+ setup.
+
+
+
+ A sample <filename>.emacs</filename> file
+
+ Unfortunately, there's far too much here to explain it in
+ detail; however there are one or two points worth
+ mentioning.
+
+
+
+ Everything beginning with a ; is a comment
+ and is ignored by Emacs.
+
+
+
+ In the first line, the
+ -*- Emacs-Lisp -*- is so that
+ we can edit the .emacs file itself
+ within Emacs and get all the fancy features for editing
+ Emacs Lisp. Emacs usually tries to guess this based on
+ the filename, and may not get it right for
+ .emacs.
+
+
+
+ The tab key is bound to an
+ indentation function in some modes, so when you press the
+ tab key, it will indent the current line of code. If you
+ want to put a tab character in whatever
+ you're writing, hold the control key down
+ while you're pressing the tab key.
+
+
+
+ This file supports syntax highlighting for C, C++,
+ Perl, Lisp and Scheme, by guessing the language from the
+ filename.
+
+
+
+ Emacs already has a pre-defined function called
+ next-error. In a compilation output
+ window, this allows you to move from one compilation error
+ to the next by doing M-n; we define a
+ complementary function,
+ previous-error, that allows you to go
+ to a previous error by doing M-p. The
+ nicest feature of all is that C-c C-c
+ will open up the source file in which the error occurred
+ and jump to the appropriate line.
+
+
+
+ We enable Emacs's ability to act as a server, so that
+ if you're doing something outside Emacs and you want to
+ edit a file, you can just type in
+
+ &prompt.user; emacsclient filename
+
+
+ and then you can edit the file in your
+ Emacs!
+
+
+ Many Emacs users set their EDITOR environment to
+ emacsclient so this happens every
+ time they need to edit a file.
+
+
+
+
+
+ A sample <filename>.emacs</filename> file
+
+ ;; -*-Emacs-Lisp-*-
+
+;; This file is designed to be re-evaled; use the variable first-time
+;; to avoid any problems with this.
+(defvar first-time t
+ "Flag signifying this is the first time that .emacs has been evaled")
+
+;; Meta
+(global-set-key "\M- " 'set-mark-command)
+(global-set-key "\M-\C-h" 'backward-kill-word)
+(global-set-key "\M-\C-r" 'query-replace)
+(global-set-key "\M-r" 'replace-string)
+(global-set-key "\M-g" 'goto-line)
+(global-set-key "\M-h" 'help-command)
+
+;; Function keys
+(global-set-key [f1] 'manual-entry)
+(global-set-key [f2] 'info)
+(global-set-key [f3] 'repeat-complex-command)
+(global-set-key [f4] 'advertised-undo)
+(global-set-key [f5] 'eval-current-buffer)
+(global-set-key [f6] 'buffer-menu)
+(global-set-key [f7] 'other-window)
+(global-set-key [f8] 'find-file)
+(global-set-key [f9] 'save-buffer)
+(global-set-key [f10] 'next-error)
+(global-set-key [f11] 'compile)
+(global-set-key [f12] 'grep)
+(global-set-key [C-f1] 'compile)
+(global-set-key [C-f2] 'grep)
+(global-set-key [C-f3] 'next-error)
+(global-set-key [C-f4] 'previous-error)
+(global-set-key [C-f5] 'display-faces)
+(global-set-key [C-f8] 'dired)
+(global-set-key [C-f10] 'kill-compilation)
+
+;; Keypad bindings
+(global-set-key [up] "\C-p")
+(global-set-key [down] "\C-n")
+(global-set-key [left] "\C-b")
+(global-set-key [right] "\C-f")
+(global-set-key [home] "\C-a")
+(global-set-key [end] "\C-e")
+(global-set-key [prior] "\M-v")
+(global-set-key [next] "\C-v")
+(global-set-key [C-up] "\M-\C-b")
+(global-set-key [C-down] "\M-\C-f")
+(global-set-key [C-left] "\M-b")
+(global-set-key [C-right] "\M-f")
+(global-set-key [C-home] "\M-<")
+(global-set-key [C-end] "\M->")
+(global-set-key [C-prior] "\M-<")
+(global-set-key [C-next] "\M->")
+
+;; Mouse
+(global-set-key [mouse-3] 'imenu)
+
+;; Misc
+(global-set-key [C-tab] "\C-q\t") ; Control tab quotes a tab.
+(setq backup-by-copying-when-mismatch t)
+
+;; Treat 'y' or <CR> as yes, 'n' as no.
+(fset 'yes-or-no-p 'y-or-n-p)
+ (define-key query-replace-map [return] 'act)
+ (define-key query-replace-map [?\C-m] 'act)
+
+;; Load packages
+(require 'desktop)
+(require 'tar-mode)
+
+;; Pretty diff mode
+(autoload 'ediff-buffers "ediff" "Intelligent Emacs interface to diff" t)
+(autoload 'ediff-files "ediff" "Intelligent Emacs interface to diff" t)
+(autoload 'ediff-files-remote "ediff"
+ "Intelligent Emacs interface to diff")
+
+(if first-time
+ (setq auto-mode-alist
+ (append '(("\\.cpp$" . c++-mode)
+ ("\\.hpp$" . c++-mode)
+ ("\\.lsp$" . lisp-mode)
+ ("\\.scm$" . scheme-mode)
+ ("\\.pl$" . perl-mode)
+ ) auto-mode-alist)))
+
+;; Auto font lock mode
+(defvar font-lock-auto-mode-list
+ (list 'c-mode 'c++-mode 'c++-c-mode 'emacs-lisp-mode 'lisp-mode 'perl-mode 'scheme-mode)
+ "List of modes to always start in font-lock-mode")
+
+(defvar font-lock-mode-keyword-alist
+ '((c++-c-mode . c-font-lock-keywords)
+ (perl-mode . perl-font-lock-keywords))
+ "Associations between modes and keywords")
+
+(defun font-lock-auto-mode-select ()
+ "Automatically select font-lock-mode if the current major mode is
+in font-lock-auto-mode-list"
+ (if (memq major-mode font-lock-auto-mode-list)
+ (progn
+ (font-lock-mode t))
+ )
+ )
+
+(global-set-key [M-f1] 'font-lock-fontify-buffer)
+
+;; New dabbrev stuff
+;(require 'new-dabbrev)
+(setq dabbrev-always-check-other-buffers t)
+(setq dabbrev-abbrev-char-regexp "\\sw\\|\\s_")
+(add-hook 'emacs-lisp-mode-hook
+ '(lambda ()
+ (set (make-local-variable 'dabbrev-case-fold-search) nil)
+ (set (make-local-variable 'dabbrev-case-replace) nil)))
+(add-hook 'c-mode-hook
+ '(lambda ()
+ (set (make-local-variable 'dabbrev-case-fold-search) nil)
+ (set (make-local-variable 'dabbrev-case-replace) nil)))
+(add-hook 'text-mode-hook
+ '(lambda ()
+ (set (make-local-variable 'dabbrev-case-fold-search) t)
+ (set (make-local-variable 'dabbrev-case-replace) t)))
+
+;; C++ and C mode...
+(defun my-c++-mode-hook ()
+ (setq tab-width 4)
+ (define-key c++-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (define-key c++-mode-map "\C-ce" 'c-comment-edit)
+ (setq c++-auto-hungry-initial-state 'none)
+ (setq c++-delete-function 'backward-delete-char)
+ (setq c++-tab-always-indent t)
+ (setq c-indent-level 4)
+ (setq c-continued-statement-offset 4)
+ (setq c++-empty-arglist-indent 4))
+
+(defun my-c-mode-hook ()
+ (setq tab-width 4)
+ (define-key c-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (define-key c-mode-map "\C-ce" 'c-comment-edit)
+ (setq c-auto-hungry-initial-state 'none)
+ (setq c-delete-function 'backward-delete-char)
+ (setq c-tab-always-indent t)
+;; BSD-ish indentation style
+ (setq c-indent-level 4)
+ (setq c-continued-statement-offset 4)
+ (setq c-brace-offset -4)
+ (setq c-argdecl-indent 0)
+ (setq c-label-offset -4))
+
+;; Perl mode
+(defun my-perl-mode-hook ()
+ (setq tab-width 4)
+ (define-key c++-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (setq perl-indent-level 4)
+ (setq perl-continued-statement-offset 4))
+
+;; Scheme mode...
+(defun my-scheme-mode-hook ()
+ (define-key scheme-mode-map "\C-m" 'reindent-then-newline-and-indent))
+
+;; Emacs-Lisp mode...
+(defun my-lisp-mode-hook ()
+ (define-key lisp-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (define-key lisp-mode-map "\C-i" 'lisp-indent-line)
+ (define-key lisp-mode-map "\C-j" 'eval-print-last-sexp))
+
+;; Add all of the hooks...
+(add-hook 'c++-mode-hook 'my-c++-mode-hook)
+(add-hook 'c-mode-hook 'my-c-mode-hook)
+(add-hook 'scheme-mode-hook 'my-scheme-mode-hook)
+(add-hook 'emacs-lisp-mode-hook 'my-lisp-mode-hook)
+(add-hook 'lisp-mode-hook 'my-lisp-mode-hook)
+(add-hook 'perl-mode-hook 'my-perl-mode-hook)
+
+;; Complement to next-error
+(defun previous-error (n)
+ "Visit previous compilation error message and corresponding source code."
+ (interactive "p")
+ (next-error (- n)))
+
+;; Misc...
+(transient-mark-mode 1)
+(setq mark-even-if-inactive t)
+(setq visible-bell nil)
+(setq next-line-add-newlines nil)
+(setq compile-command "make")
+(setq suggest-key-bindings nil)
+(put 'eval-expression 'disabled nil)
+(put 'narrow-to-region 'disabled nil)
+(put 'set-goal-column 'disabled nil)
+
+;; Elisp archive searching
+(autoload 'format-lisp-code-directory "lispdir" nil t)
+(autoload 'lisp-dir-apropos "lispdir" nil t)
+(autoload 'lisp-dir-retrieve "lispdir" nil t)
+(autoload 'lisp-dir-verify "lispdir" nil t)
+
+;; Font lock mode
+(defun my-make-face (face colour &optional bold)
+ "Create a face from a colour and optionally make it bold"
+ (make-face face)
+ (copy-face 'default face)
+ (set-face-foreground face colour)
+ (if bold (make-face-bold face))
+ )
+
+(if (eq window-system 'x)
+ (progn
+ (my-make-face 'blue "blue")
+ (my-make-face 'red "red")
+ (my-make-face 'green "dark green")
+ (setq font-lock-comment-face 'blue)
+ (setq font-lock-string-face 'bold)
+ (setq font-lock-type-face 'bold)
+ (setq font-lock-keyword-face 'bold)
+ (setq font-lock-function-name-face 'red)
+ (setq font-lock-doc-string-face 'green)
+ (add-hook 'find-file-hooks 'font-lock-auto-mode-select)
+
+ (setq baud-rate 1000000)
+ (global-set-key "\C-cmm" 'menu-bar-mode)
+ (global-set-key "\C-cms" 'scroll-bar-mode)
+ (global-set-key [backspace] 'backward-delete-char)
+ ; (global-set-key [delete] 'delete-char)
+ (standard-display-european t)
+ (load-library "iso-transl")))
+
+;; X11 or PC using direct screen writes
+(if window-system
+ (progn
+ ;; (global-set-key [M-f1] 'hilit-repaint-command)
+ ;; (global-set-key [M-f2] [?\C-u M-f1])
+ (setq hilit-mode-enable-list
+ '(not text-mode c-mode c++-mode emacs-lisp-mode lisp-mode
+ scheme-mode)
+ hilit-auto-highlight nil
+ hilit-auto-rehighlight 'visible
+ hilit-inhibit-hooks nil
+ hilit-inhibit-rebinding t)
+ (require 'hilit19)
+ (require 'paren))
+ (setq baud-rate 2400) ; For slow serial connections
+ )
+
+;; TTY type terminal
+(if (and (not window-system)
+ (not (equal system-type 'ms-dos)))
+ (progn
+ (if first-time
+ (progn
+ (keyboard-translate ?\C-h ?\C-?)
+ (keyboard-translate ?\C-? ?\C-h)))))
+
+;; Under UNIX
+(if (not (equal system-type 'ms-dos))
+ (progn
+ (if first-time
+ (server-start))))
+
+;; Add any face changes here
+(add-hook 'term-setup-hook 'my-term-setup-hook)
+(defun my-term-setup-hook ()
+ (if (eq window-system 'pc)
+ (progn
+;; (set-face-background 'default "red")
+ )))
+
+;; Restore the "desktop" - do this as late as possible
+(if first-time
+ (progn
+ (desktop-load-default)
+ (desktop-read)))
+
+;; Indicate that this file has been read at least once
+(setq first-time nil)
+
+;; No need to debug anything now
+(setq debug-on-error nil)
+
+;; All done
+(message "All done, %s%s" (user-login-name) ".")
+
+
+
+
+
+ Extending the Range of Languages Emacs Understands
+
+ Now, this is all very well if you only want to program in
+ the languages already catered for in the
+ .emacs file (C, C++, Perl, Lisp and
+ Scheme), but what happens if a new language called
+ whizbang comes out, full of exciting
+ features?
+
+ The first thing to do is find out if whizbang comes with
+ any files that tell Emacs about the language. These usually
+ end in .el, short for Emacs
+ Lisp. For example, if whizbang is a FreeBSD port, we
+ can locate these files by doing
+
+ &prompt.user; find /usr/ports/lang/whizbang -name "*.el" -print
+
+
+ and install them by copying them into the Emacs site Lisp
+ directory. On FreeBSD 2.1.0-RELEASE, this is
+ /usr/local/share/emacs/site-lisp.
+
+ So for example, if the output from the find command
+ was
+
+ /usr/ports/lang/whizbang/work/misc/whizbang.el
+
+
+ we would do
+
+ &prompt.root; cp /usr/ports/lang/whizbang/work/misc/whizbang.el /usr/local/share/emacs/site-lisp
+
+
+ Next, we need to decide what extension whizbang source
+ files have. Let's say for the sake of argument that they all
+ end in .wiz. We need to add an entry to
+ our .emacs file to make sure Emacs will
+ be able to use the information in
+ whizbang.el.
+
+ Find the auto-mode-alist entry in
+ .emacs and add a line for whizbang, such
+ as:
+
+ …
+("\\.lsp$" . lisp-mode)
+("\\.wiz$" . whizbang-mode)
+("\\.scm$" . scheme-mode)
+…
+
+
+ This means that Emacs will automatically go into
+ whizbang-mode when you edit a file ending
+ in .wiz.
+
+ Just below this, you'll find the
+ font-lock-auto-mode-list entry. Add
+ whizbang-mode to it like so:
+
+ ;; Auto font lock mode
+(defvar font-lock-auto-mode-list
+ (list 'c-mode 'c++-mode 'c++-c-mode 'emacs-lisp-mode 'whizbang-mode 'lisp-mode 'perl-mode 'scheme-mode)
+ "List of modes to always start in font-lock-mode")
+
+
+ This means that Emacs will always enable
+ font-lock-mode (ie syntax highlighting)
+ when editing a .wiz file.
+
+ And that's all that's needed. If there's anything else
+ you want done automatically when you open up a
+ .wiz file, you can add a
+ whizbang-mode hook (see
+ my-scheme-mode-hook for a simple example
+ that adds auto-indent).
+
+
+
+
+ Further Reading
+
+
+
+ Brian Harvey and Matthew Wright
+ Simply Scheme
+ MIT 1994.
+ ISBN 0-262-08226-8
+
+
+
+ Randall Schwartz
+ Learning Perl
+ O'Reilly 1993
+ ISBN 1-56592-042-2
+
+
+
+ Patrick Henry Winston and Berthold Klaus Paul Horn
+ Lisp (3rd Edition)
+ Addison-Wesley 1989
+ ISBN 0-201-08319-1
+
+
+
+ Brian W. Kernighan and Rob Pike
+ The Unix Programming Environment
+ Prentice-Hall 1984
+ ISBN 0-13-937681-X
+
+
+
+ Brian W. Kernighan and Dennis M. Ritchie
+ The C Programming Language (2nd Edition)
+ Prentice-Hall 1988
+ ISBN 0-13-110362-8
+
+
+
+ Bjarne Stroustrup
+ The C++ Programming Language
+ Addison-Wesley 1991
+ ISBN 0-201-53992-6
+
+
+
+ W. Richard Stevens
+ Advanced Programming in the Unix Environment
+ Addison-Wesley 1992
+ ISBN 0-201-56317-7
+
+
+
+ W. Richard Stevens
+ Unix Network Programming
+ Prentice-Hall 1990
+ ISBN 0-13-949876-1
+
+
+
- Secure ProgrammingThis chapter was written by Murray Stokely.SynopsisThis chapter describes some of the security issues that
have plagued Unix programmers for decades and some of the new
tools available to help programmers avoid writing exploitable
code.Secure Design
MethodologyWriting secure applications takes a very scrutinous and
pessimistic outlook on life. Applications should be run with
the principle of least privilege so that no
process is ever running than more with the bare minimum access
that it needs to accomplish its function. Previously tested
code should be reused whenever possible to avoid common
mistakes that others may have already fixed.One of the pitfalls of the Unix environment is how easy it
is to make assumptions about the sanity of the environment.
Applications should never trust user input (in all its forms),
system resources, inter-process communication, or the timing of
events. Unix processes do not execute synchronously so logical
operations are rarely atomic.Buffer OverflowsBuffer Overflows have been around since the very
beginnings of the Von-Neuman architecture.
They first gained widespread notoriety in 1988 with the Moorse
Internet worm. Unfortunately, the same basic attack remains
effective today. Of the 17 CERT security advisories of 1999, 10
of them were directly caused by buffer-overflow software bugs.
By far the most common type of buffer overflow attack is based
on corrupting the stack.Most modern computer systems use a stack to pass arguments
to procedures and to store local variables. A stack is a last
in first out (LIFO) buffer in the high memory area of a process
image. When a program invokes a function a new "stack frame" is
created. This stack frame consists of the arguments passed to
the function as well as a dynamic amount of local variable
space. The "stack pointer" is a register that holds the current
location of the top of the stack. Since this value is
constantly changing as new values are pushed onto the top of the
stack, many implementations also provide a "frame pointer" that
is located near the beginning of a stack frame so that local
variables can more easily be addressed relative to this
value. The return address for function
calls is also stored on the stack, and this is the cause of
stack-overflow exploits since overflowing a local variable in a
function can overwrite the return address of that function,
potentially allowing a malicious user to execute any code he or
she wants.Although stack-based attacks are by far the most common,
it would also be possible to overrun the stack with a heap-based
(malloc/free) attack.The C programming language does not perform automatic
bounds checking on arrays or pointers as many other languages
do. In addition, the standard C library is filled with a
handful of very dangerous functions.strcpy(char *dest, const char
*src)May overflow the dest bufferstrcat(char *dest, const char
*src)May overflow the dest buffergetwd(char *buf)May overflow the buf buffergets(char *s)May overflow the s buffer[vf]scanf(const char *format,
...)May overflow its arguments.realpath(char *path, char
resolved_path[])May overflow the path buffer[v]sprintf(char *str, const char
*format, ...)May overflow the str buffer.Example Buffer OverflowThe following example code contains a buffer overflow
designed to overwrite the return address and skip the
instruction immediately following the function call. (Inspired
by )
#include stdio.h
void manipulate(char *buffer) {
char newbuffer[80];
strcpy(newbuffer,buffer);
}
int main() {
char ch,buffer[4096];
int i=0;
while ((buffer[i++] = getchar()) != '\n') {};
i=1;
manipulate(buffer);
i=2;
printf("The value of i is : %d\n",i);
return 0;
}
Let us examine what the memory image of this process would
look like if we were to input 160 spaces into our little program
before hitting return.[XXX figure here!]Obviously more malicious input can be devised to execute
actual compiled instructions (such as exec(/bin/sh)).Avoiding Buffer OverflowsThe most straightforward solution to the problem of
stack-overflows is to always use length restricted memory and
string copy functions. strncpy and
strncat are part of the standard C library.
These functions accept a length value as a parameter which
should be no larger than the size of the destination buffer.
These functions will then copy up to `length' bytes from the
source to the destination. However there are a number of
problems with these functions. Neither function guarantees NUL
termination if the size of the input buffer is as large as the
destination. The length parameter is also used inconsistently
between strncpy and strncat so it is easy for programmers to get
confused as to their proper usage. There is also a significant
performance loss compared to strcpy when
copying a short string into a large buffer since
strncpy NUL fills up the the size
specified.In OpenBSD, another memory copy implementation has been
created to get around these problem. The
strlcpy and strlcat
functions guarantee that they will always null terminate the
destination string when given a non-zero length argument. For
more information about these functions see . The OpenBSD strlcpy and
strlcat instructions have been in FreeBSD
since 3.5.Compiler based run-time bounds checkingUnfortunately there is still a very large assortment of
code in public use which blindly copies memory around without
using any of the bounded copy routines we just discussed.
Fortunately, there is another solution. Several compiler
add-ons and libraries exist to do Run-time bounds checking in
C/C++.StackGuard is one such add-on that is implemented as a
small patch to the gcc code generator. From the StackGuard
website, http://immunix.org/stackguard.html :
"StackGuard detects and defeats stack
smashing attacks by protecting the return address on the stack
from being altered. StackGuard places a "canary" word next to
the return address when a function is called. If the canary
word has been altered when the function returns, then a stack
smashing attack has been attempted, and the program responds
by emitting an intruder alert into syslog, and then
halts."
"StackGuard is implemented as a small patch
to the gcc code generator, specifically the function_prolog()
and function_epilog() routines. function_prolog() has been
enhanced to lay down canaries on the stack when functions
start, and function_epilog() checks canary integrity when the
function exits. Any attempt at corrupting the return address
is thus detected before the function
returns."
Recompiling your application with StackGuard is an
effective means of stopping most buffer-overflow attacks, but
it can still be compromised.Library based run-time bounds checkingCompiler-based mechanisms are completely useless for
binary-only software for which you cannot recompile. For
these situations there are a number of libraries which
re-implement the unsafe functions of the C-library
(strcpy, fscanf,
getwd, etc..) and ensure that these
functions can never write past the stack pointer.libsafelibverifylibparnoiaUnfortunately these library-based defenses have a number
of shortcomings. These libraries only protect against a very
small set of security related issues and they neglect to fix
the actual problem. These defenses may fail if the
application was compiled with -fomit-frame-pointer. Also, the
LD_PRELOAD and LD_LIBRARY_PATH environment variables can be
overwritten/unset by the user.SetUID issuesThere are at least 6 different IDs associated with any
given process. Because of this you have to be very careful with
the access that your process has at any given time. In
particular, all seteuid applications should give up their
privileges as soon as it is no longer required.The real user ID can only be changed by a superuser
process. The login program sets this
when a user initially logs in and it is seldom changed.The effective user ID is set by the
exec() functions if a program has its
seteuid bit set. An application can call
seteuid() at any time to set the effective
user ID to either the real user ID or the saved set-user-ID.
When the effective user ID is set by exec()
functions, the previous value is saved in the saved set-user-ID.Limiting your program's environmentThe traditional method of restricting access to a process
is with the chroot() system call. This
system call changes the root directory from which all other
paths are referenced for a process and any child processes. For
this call to succeed the process must have execute (search)
permission on the directory being referenced. The new
environment does not actually take affect until you
chdir() into your new environment. It
should also be noted that a process can easily break out of a
chroot environment if it has root privilege. This could be
accomplished by creating device nodes to read kernel memory,
attaching a debugger to a process outside of the jail, or in
many other creative ways.The behavior of the chroot() system
call can be controlled somewhat with the
kern.chroot_allow_open_directories sysctl
variable. When this value is set to 0,
chroot() will fail with EPERM if there are
any directories open. If set to the default value of 1, then
chroot() will fail with EPERM if there are
any directories open and the process is already subject to a
chroot() call. For any other value, the
check for open directories will be bypassed completely.FreeBSD's jail functionalityThe concept of a Jail extends upon the
chroot() by limiting the powers of the
superuser to create a true `virtual server'. Once a prison is
setup all network communication must take place through the
specified IP address, and the power of "root privilege" in this
jail is severely constrained.While in a prison, any tests of superuser power within the
kernel using the suser() call will fail.
However, some calls to suser() have been
changed to a new interface suser_xxx().
This function is responsible for recognizing or denying access
to superuser power for imprisoned processes.A superuser process within a jailed environment has the
power to : Manipulate credential with
setuid, seteuid,
setgid, setegid,
setgroups, setreuid,
setregid, setloginSet resource limits with setrlimitModify some sysctl nodes
(kern.hostname)chroot()Set flags on a vnode:
chflags,
fchflagsSet attributes of a vnode such as file
permission, owner, group, size, access time, and modification
time.Bind to privileged ports in the Internet
domain (ports < 1024)Jail is a very useful tool for
running applications in a secure environment but it does have
some shortcomings. Currently, the IPC mechanisms have not been
converted to the suser_xxx so applications
such as MySQL can not be run within a jail. Superuser access
may have a very limited meaning within a jail, but there is
no way to specify exactly what "very limited" means.POSIX.1e Process CapabilitiesPosix has released a working draft that adds event
auditing, access control lists, fine grained privileges,
information labeling, and mandatory access control.This is a work in progress and is the focus of the TrustedBSD project. Some
of the initial work has been committed to FreeBSD-current
(cap_set_proc(3)).TrustAn application should never assume that anything about the
users environment is sane. This includes (but is certainly not
limited to) : user input, signals, environment variables,
resources, IPC, mmaps, the file system working directory, file
descriptors, the # of open files, etc.You should never assume that you can catch all forms of
invalid input that a user might supply. Instead, your
application should use positive filtering to only allow a
specific subset of inputs that you deem safe. Improper data
validation has been the cause of many exploits, especially with
CGI scripts on the world wide web. For filenames you need to be
extra careful about paths ("../", "/"), symbolic links, and
shell escape characters.Perl has a really cool feature called "Taint" mode which
can be used to prevent scripts for using data derived outside
the program in an unsafe way. This mode will check command line
arguments, environment variables, locale information, the
results of certain syscalls (readdir(),
readlink(),
getpwxxx(), and all file input.Race ConditionsA race condition is anomalous behavior caused by the
unexpected dependence on the relative timing of events. In
other words, a programmer incorrectly assumed that a particular
event would always happen before another.Some of the common causes of race conditions are signals,
access checks, and file opens. Signals are asynchronous events
by nature so special care must be taken in dealing with them.
Checking access with access(2) then
open(2) is clearly non-atomic. Users can
move files in between the two calls. Instead, privileged
applications should seteuid() and then call
open() directly. Along the same lines, an
application should always set a proper umask before
open() to obviate the need for spurious
chmod() calls.KernelHistory of the Unix KernelSome history of the Unix/BSD kernel, system calls, how do
processes work, blocking, scheduling, threads (kernel),
context switching, signals, interrupts, modules, etc.Memory and Virtual MemoryVirtual MemoryVM, paging, swapping, allocating memory, testing for
memory leaks, mmap, vnodes, etc.I/O SystemUFSUFS, FFS, Ext2FS, JFS, inodes, buffer cache, labeling,
locking, metadata, soft-updates, LFS, portalfs, procfs,
vnodes, memory sharing, memory objects, TLBs, cachingInterprocess CommunicationSignalsSignals, pipes, semaphores, message queues, shared memory,
ports, sockets, doorsNetworkingSocketsSockets, bpf, IP, TCP, UDP, ICMP, OSI, bridging,
firewalling, NAT, switching, etcNetwork FilesystemsAFSAFS, NFS, SANs etc]Terminal HandlingSysconsSyscons, tty, PCVT, serial console, screen savers,
etcSoundOSSOSS, waveforms, etcDevice DriversWriting FreeBSD Device DriversThis chapter was written by Murray Stokely with selections from
a variety of sources including the intro(4) man page by Joerg
Wunsch.Introduction
This chapter provides a brief introduction to writing device
drivers for FreeBSD. A device in this context is a term used
mostly for hardware-related stuff that belongs to the system,
like disks, printers, or a graphics display with its keyboard.
A device driver is the software component of the operating
system that controls a specific device. There are also
so-called pseudo-devices where a device driver emulates the
behaviour of a device in software without any particular
underlying hardware. Device drivers can be compiled into the
system statically or loaded on demand through the dynamic
kernel linker facility `kld'.Most devices in a Unix-like operating system are
accessed through device-nodes, sometimes also called special
files. These files are usually located under the directory
/dev in the file system hierarchy. Until
devfs is fully integrated into FreeBSD, each device node must
be created statically and independent of the existence of the
associated device driver. Most device nodes on the system are
created by running MAKEDEV.Device drivers can roughly be broken down into three
categories; character (unbuffered), block (buffered), and
network drivers.Dynamic Kernel Linker Facility - KLDThe kld interface allows system administrators to
dynamically add and remove functionality from a running
system. This allows device driver writers to load their new
changes into a running kernel without constantly rebooting to
test changes.The kld interface is used through the following
administrator commands :
kldload - loads a new kernel
modulekldunload - unloads a kernel
modulekldstat - lists the currently loadded
modulesSkeleton Layout of a kernel module
/*
* KLD Skeleton
* Inspired by Andrew Reiter's Daemonnews article
*/
#include <sys/types.h>
#include <sys/module.h>
#include <sys/systm.h> /* uprintf */
#include <sys/errno.h>
#include <sys/param.h> /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
/*
* Load handler that deals with the loading and unloading of a KLD.
*/
static int
skel_loader(struct module *m, int what, void *arg)
{
int err = 0;
switch (what) {
case MOD_LOAD: /* kldload */
uprintf("Skeleton KLD loaded.\n");
break;
case MOD_UNLOAD:
uprintf("Skeleton KLD unloaded.\n");
break;
default:
err = EINVAL;
break;
}
return(err);
}
/* Declare this module to the rest of the kernel */
DECLARE_MODULE(skeleton, skel_loader, SI_SUB_KLD, SI_ORDER_ANY);
MakefileFreeBSD provides a makefile include that you can use
to quickly compile your kernel addition.
SRCS=skeleton.c
KMOD=skeleton
.include <bsd.kmod.mk>
Simply running make with
this makefile will create a file
skeleton.ko that can be loaded into
your system by typing :
&prompt.root kldload -v ./skeleton.ko
Accessing a device driverUnix provides a common set of system calls for user
applications to use. The upper layers of the kernel dispatch
these calls to the corresponding device driver when a user
accesses a device node. The /dev/MAKEDEV
script makes most of the device nodes for your system but if
you are doing your own driver development it may be necessary
to create your own device nodes with mknodCreating static device nodesThe mknod command requires four
arguments to create a device node. You must specify the
name of this device node, the type of device, the major number
of the device, and the minor number of the device.Dynamic device nodesThe device filesystem, or devfs, provides access to the
kernel's device namespace in the global filesystem namespace.
This eliminates the problems of potentially having a device
driver without a static device node, or a device node without
an installed device driver. Unfortunately, devfs is still a
work in progress.Character DevicesA character device driver is one that transfers data
directly to and from a user process. This is the most common
type of device driver and there are plenty of simple examples
in the source tree.This simple example pseudo-device remembers whatever values you write
to it and can then supply them back to you when you read from
it.
/*
* Simple `echo' pseudo-device KLD
*
* Murray Stokely
*/
#define MIN(a,b) (((a) < (b)) ? (a) : (b))
#include <sys/types.h>
#include <sys/module.h>
#include <sys/systm.h> /* uprintf */
#include <sys/errno.h>
#include <sys/param.h> /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
#include <sys/conf.h> /* cdevsw struct */
#include <sys/uio.h> /* uio struct */
#include <sys/malloc.h>
#define BUFFERSIZE 256
/* Function prototypes */
d_open_t echo_open;
d_close_t echo_close;
d_read_t echo_read;
d_write_t echo_write;
/* Character device entry points */
static struct cdevsw echo_cdevsw = {
echo_open,
echo_close,
echo_read,
echo_write,
noioctl,
nopoll,
nommap,
nostrategy,
"echo",
33, /* reserved for lkms - /usr/src/sys/conf/majors */
nodump,
nopsize,
D_TTY,
-1
};
typedef struct s_echo {
char msg[BUFFERSIZE];
int len;
} t_echo;
/* vars */
static dev_t sdev;
static int len;
static int count;
static t_echo *echomsg;
MALLOC_DECLARE(M_ECHOBUF);
MALLOC_DEFINE(M_ECHOBUF, "echobuffer", "buffer for echo module");
/*
* This function acts is called by the kld[un]load(2) system calls to
* determine what actions to take when a module is loaded or unloaded.
*/
static int
echo_loader(struct module *m, int what, void *arg)
{
int err = 0;
switch (what) {
case MOD_LOAD: /* kldload */
sdev = make_dev(&echo_cdevsw,
0,
UID_ROOT,
GID_WHEEL,
0600,
"echo");
/* kmalloc memory for use by this driver */
/* malloc(256,M_ECHOBUF,M_WAITOK); */
MALLOC(echomsg, t_echo *, sizeof(t_echo), M_ECHOBUF, M_WAITOK);
printf("Echo device loaded.\n");
break;
case MOD_UNLOAD:
destroy_dev(sdev);
FREE(echomsg,M_ECHOBUF);
printf("Echo device unloaded.\n");
break;
default:
err = EINVAL;
break;
}
return(err);
}
int
echo_open(dev_t dev, int oflags, int devtype, struct proc *p)
{
int err = 0;
uprintf("Opened device \"echo\" successfully.\n");
return(err);
}
int
echo_close(dev_t dev, int fflag, int devtype, struct proc *p)
{
uprintf("Closing device \"echo.\"\n");
return(0);
}
/*
* The read function just takes the buf that was saved via
* echo_write() and returns it to userland for accessing.
* uio(9)
*/
int
echo_read(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
int amt;
/* How big is this read operation? Either as big as the user wants,
or as big as the remaining data */
amt = MIN(uio->uio_resid, (echomsg->len - uio->uio_offset > 0) ? echomsg->len - uio->uio_offset : 0);
if ((err = uiomove(echomsg->msg + uio->uio_offset,amt,uio)) != 0) {
uprintf("uiomove failed!\n");
}
return err;
}
/*
* echo_write takes in a character string and saves it
* to buf for later accessing.
*/
int
echo_write(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
/* Copy the string in from user memory to kernel memory */
err = copyin(uio->uio_iov->iov_base, echomsg->msg, MIN(uio->uio_iov->iov_len,BUFFERSIZE));
/* Now we need to null terminate */
*(echomsg->msg + MIN(uio->uio_iov->iov_len,BUFFERSIZE)) = 0;
/* Record the length */
echomsg->len = MIN(uio->uio_iov->iov_len,BUFFERSIZE);
if (err != 0) {
uprintf("Write failed: bad address!\n");
}
count++;
return(err);
}
DEV_MODULE(echo,echo_loader,NULL);
To install this driver you will first need to make a node on
your filesystem with a command such as :
&prompt.root mknod /dev/echo c 33 0
With this driver loaded you should now be able to type something
like :
&prompt.root echo -n "Test Data" > /dev/echo
&prompt.root cat /dev/echo
Test Data
Real hardware devices in the next chapter..Additional Resources
Dynamic
Kernel Linker (KLD) Facility Programming Tutorial -
Daemonnews October 2000How
to Write Kernel Drivers with NEWBUS - Daemonnews July
2000Block DevicesA block device driver transfers data to and from the
operating system's buffer cache. They are solely intended to
layer a file system on top of them. For this reason they are
normally implemented for disks and disk-like devices only.Example test data generator ... Example ramdisk device ... Real hardware devices in the next chapter..Network DriversDrivers for network devices do not use device nodes in
ord to be accessed. Their selection is based on other
decisions made inside the kernel and instead of calling
open(), use of a network device is generally introduced by
using the system call socket(2).man ifnet(), loopback device, Bill Pauls drivers, etc..PCI DevicesThis chapter will talk about the FreeBSD mechanisms for
writing a device driver for a device on a PCI bus.Probe and AttachInformation here about how the PCI bus code iterates
through the unattached devices and see if a newly loaded kld
will attach to any of them.
/*
* Simple KLD to play with the PCI functions.
*
* Murray Stokely
*/
#define MIN(a,b) (((a) < (b)) ? (a) : (b))
#include <sys/types.h>
#include <sys/module.h>
#include <sys/systm.h> /* uprintf */
#include <sys/errno.h>
#include <sys/param.h> /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
#include <sys/conf.h> /* cdevsw struct */
#include <sys/uio.h> /* uio struct */
#include <sys/malloc.h>
#include <sys/bus.h> /* structs, prototypes for pci bus stuff */
#include <pci/pcivar.h> /* For get_pci macros! */
/* Function prototypes */
d_open_t mypci_open;
d_close_t mypci_close;
d_read_t mypci_read;
d_write_t mypci_write;
/* Character device entry points */
static struct cdevsw mypci_cdevsw = {
mypci_open,
mypci_close,
mypci_read,
mypci_write,
noioctl,
nopoll,
nommap,
nostrategy,
"mypci",
36, /* reserved for lkms - /usr/src/sys/conf/majors */
nodump,
nopsize,
D_TTY,
-1
};
/* vars */
static dev_t sdev;
/* We're more interested in probe/attach than with
open/close/read/write at this point */
int
mypci_open(dev_t dev, int oflags, int devtype, struct proc *p)
{
int err = 0;
uprintf("Opened device \"mypci\" successfully.\n");
return(err);
}
int
mypci_close(dev_t dev, int fflag, int devtype, struct proc *p)
{
int err=0;
uprintf("Closing device \"mypci.\"\n");
return(err);
}
int
mypci_read(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
uprintf("mypci read!\n");
return err;
}
int
mypci_write(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
uprintf("mypci write!\n");
return(err);
}
/* PCI Support Functions */
/*
* Return identification string if this is device is ours.
*/
static int
mypci_probe(device_t dev)
{
uprintf("MyPCI Probe\n"
"Vendor ID : 0x%x\n"
"Device ID : 0x%x\n",pci_get_vendor(dev),pci_get_device(dev));
if (pci_get_vendor(dev) == 0x11c1) {
uprintf("We've got the Winmodem, probe successful!\n");
return 0;
}
return ENXIO;
}
/* Attach function is only called if the probe is successful */
static int
mypci_attach(device_t dev)
{
uprintf("MyPCI Attach for : deviceID : 0x%x\n",pci_get_vendor(dev));
sdev = make_dev(&mypci_cdevsw,
0,
UID_ROOT,
GID_WHEEL,
0600,
"mypci");
uprintf("Mypci device loaded.\n");
return ENXIO;
}
/* Detach device. */
static int
mypci_detach(device_t dev)
{
uprintf("Mypci detach!\n");
return 0;
}
/* Called during system shutdown after sync. */
static int
mypci_shutdown(device_t dev)
{
uprintf("Mypci shutdown!\n");
return 0;
}
/*
* Device suspend routine.
*/
static int
mypci_suspend(device_t dev)
{
uprintf("Mypci suspend!\n");
return 0;
}
/*
* Device resume routine.
*/
static int
mypci_resume(device_t dev)
{
uprintf("Mypci resume!\n");
return 0;
}
static device_method_t mypci_methods[] = {
/* Device interface */
DEVMETHOD(device_probe, mypci_probe),
DEVMETHOD(device_attach, mypci_attach),
DEVMETHOD(device_detach, mypci_detach),
DEVMETHOD(device_shutdown, mypci_shutdown),
DEVMETHOD(device_suspend, mypci_suspend),
DEVMETHOD(device_resume, mypci_resume),
{ 0, 0 }
};
static driver_t mypci_driver = {
"mypci",
mypci_methods,
0,
/* sizeof(struct mypci_softc), */
};
static devclass_t mypci_devclass;
DRIVER_MODULE(mypci, pci, mypci_driver, mypci_devclass, 0, 0);
Additional Resources
PCI Special Interest
GroupPCI System Architecture, Fourth Edition by
Tom Shanley, et al.USB DevicesThis chapter will talk about the FreeBSD mechanisms for
writing a device driver for a device on a USB bus.NewBusThis chapter will talk about the FreeBSD NewBus
architecture.ArchitecturesIA-32Talk about the architectural specifics of FreeBSD/x86.AlphaTalk about the architectural specifics of
FreeBSD/alpha.Explanation of allignment errors, how to fix, how to
ignore.Example assembly language code for FreeBSD/alpha.IA-64Talk about the architectural specifics of
FreeBSD/ia64.
-
+ DebuggingTrussvarious descriptions on how to debug certain aspects of
the system using truss, ktrace, gdb, kgdb, etcCompatibility LayersLinuxLinux, SVR4, etcAppendicesDaveAPattersonJohnLHennessy1998Morgan Kaufmann Publishers,
Inc.1-55860-428-6Morgan Kaufmann Publishers, Inc.Computer Organization and DesignThe Hardware / Software Interface1-2W.RichardStevens1993Addison Wesley Longman,
Inc.0-201-56317-7Addison Wesley Longman, Inc.Advanced Programming in the Unix Environment1-2MarshallKirkMcKusickKeithBosticMichaelJKarelsJohnSQuarterman1996Addison-Wesley Publishing Company,
Inc.0-201-54979-4Addison-Wesley Publishing Company, Inc.The Design and Implementation of the 4.4 BSD Operating System1-2AlephOnePhrack 49; "Smashing the Stack for Fun and Profit"ChrispinCowanCaltonPuDaveMaierStackGuard; Automatic Adaptive Detection and Prevention of
Buffer-Overflow AttacksToddMillerTheode Raadtstrlcpy and strlcat -- consistent, safe string copy and
concatenation.
diff --git a/en_US.ISO_8859-1/books/developers-handbook/book.sgml b/en_US.ISO_8859-1/books/developers-handbook/book.sgml
index 8aacd1d42a..bd58d4a25a 100644
--- a/en_US.ISO_8859-1/books/developers-handbook/book.sgml
+++ b/en_US.ISO_8859-1/books/developers-handbook/book.sgml
@@ -1,1510 +1,3751 @@
%bookinfo;
]>
FreeBSD Developers' HandbookThe FreeBSD Documentation Projectdoc@FreeBSD.orgAugust 20002000The FreeBSD Documentation Project
&bookinfo.legalnotice;
Welcome to the Developers' Handbook.IntroductionDeveloping on FreeBSDThis will need to discuss FreeBSD as a development
platform, the vision of BSD, architectural overview, layout of
/usr/src, history, etc.Thank you for considering FreeBSD as your development
platform! We hope it will not let you down.The BSD VisionArchitectural OverviewThe Layout of /usr/srcThe complete source code to FreeBSD is available from our
public CVS repository. The source code is normally installed in
/usr/src which contains the
following subdirectories.DirectoryDescriptionbin/Source for files in
/bincontrib/Source for files from contribued software.crypto/DES sourceetc/Source for files in /etcgames/Source for files in /usr/gamesgnu/Utilities covered by the GNU Public Licenseinclude/Source for files in /usr/includekerberosIV/Source for Kerbereros version IVkerberos5/Source for Kerbereros version 5lib/Source for files in /usr/liblibexec/Source for files in /usr/libexecrelease/Files required to produce a FreeBSD releasesbin/Source for files in /sbinsecure/FreeSec sourcesshare/Source for files in /sbinsys/Kernel source filestools/Tools used for maintenance and testing of
FreeBSDusr.bin/Source for files in /usr/binusr.sbin/Source for files in /usr/sbinBasics
-
- Compilation
+
+ Programming Tools
- This will include things like: compilation, makefiles, .mk
- files, basic debugging, linking, secure programming
- guidelines, style(9), CVS, diff, patch, etc.
+ This chapter was written by James Raynard.
+ Modifications for the Developer's Handbook by Murray Stokely.
+
+
+ Synopsis
+
+ This document is an introduction to using some of the
+ programming tools supplied with FreeBSD, although much of it
+ will be applicable to many other versions of Unix. It does
+ not attempt to describe coding in any
+ detail. Most of the document assumes little or no previous
+ programming knowledge, although it is hoped that most
+ programmers will find something of value in it
+
+
+
+ Introduction
+
+ FreeBSD offers an excellent development environment.
+ Compilers for C, C++, and Fortran and an assembler come with the
+ basic system, not to mention a Perl interpreter and classic Unix
+ tools such as sed and awk.
+ If that is not enough, there are many more compilers and
+ interpreters in the Ports collection. FreeBSD is very
+ compatible with standards such as POSIX and
+ ANSI C, as well with its own BSD heritage, so
+ it is possible to write applications that will compile and run
+ with little or no modification on a wide range of
+ platforms.
+
+ However, all this power can be rather overwhelming at
+ first if you've never written programs on a Unix platform
+ before. This document aims to help you get up and running,
+ without getting too deeply into more advanced topics. The
+ intention is that this document should give you enough of the
+ basics to be able to make some sense of the
+ documentation.
+
+ Most of the document requires little or no knowledge of
+ programming, although it does assume a basic competence with
+ using Unix and a willingness to learn!
+
+
+
+
+ Introduction to Programming
+
+ A program is a set of instructions that tell the computer
+ to do various things; sometimes the instruction it has to
+ perform depends on what happened when it performed a previous
+ instruction. This section gives an overview of the two main
+ ways in which you can give these instructions, or
+ commands as they are usually called. One way
+ uses an interpreter, the other a
+ compiler. As human languages are too
+ difficult for a computer to understand in an unambiguous way,
+ commands are usually written in one or other languages specially
+ designed for the purpose.
+
+
+ Interpreters
+
+ With an interpreter, the language comes as an environment,
+ where you type in commands at a prompt and the environment
+ executes them for you. For more complicated programs, you can
+ type the commands into a file and get the interpreter to load
+ the file and execute the commands in it. If anything goes
+ wrong, many interpreters will drop you into a debugger to help
+ you track down the problem.
+
+ The advantage of this is that you can see the results of
+ your commands immediately, and mistakes can be corrected
+ readily. The biggest disadvantage comes when you want to
+ share your programs with someone. They must have the same
+ interpreter, or you must have some way of giving it to them,
+ and they need to understand how to use it. Also users may not
+ appreciate being thrown into a debugger if they press the
+ wrong key! From a performance point of view, interpreters can
+ use up a lot of memory, and generally do not generate code as
+ efficiently as compilers.
+
+ In my opinion, interpreted languages are the best way to
+ start if you have not done any programming before. This kind
+ of environment is typically found with languages like Lisp,
+ Smalltalk, Perl and Basic. It could also be argued that the
+ Unix shell (sh, csh) is itself an
+ interpreter, and many people do in fact write shell
+ scripts to help with various
+ housekeeping tasks on their machine. Indeed, part
+ of the original Unix philosophy was to provide lots of small
+ utility programs that could be linked together in shell
+ scripts to perform useful tasks.
+
+
+
+ Interpreters available with FreeBSD
+
+ Here is a list of interpreters that are available as
+ FreeBSD
+ packages, with a brief discussion of some of the
+ more popular interpreted languages.
+
+ To get one of these packages, all you need to do is to
+ click on the hotlink for the package, then run
+
+ &prompt.root; pkg_add package name
+
+
+ as root. Obviously, you will need to have a fully
+ functional FreeBSD 2.1.0 or later system for the package to
+ work!
+
+
+
+ BASIC
+
+
+ Short for Beginner's All-purpose Symbolic
+ Instruction Code. Developed in the 1950s for teaching
+ University students to program and provided with every
+ self-respecting personal computer in the 1980s,
+ BASIC has been the first programming
+ language for many programmers. It's also the foundation
+ for Visual Basic.
+
+ The Bywater
+ Basic Interpreter and the Phil
+ Cockroft's Basic Interpreter (formerly Rabbit
+ Basic) are available as FreeBSD FreeBSD
+ packages
+
+
+
+
+ Lisp
+
+
+ A language that was developed in the late 1950s as
+ an alternative to the number-crunching
+ languages that were popular at the time. Instead of
+ being based on numbers, Lisp is based on lists; in fact
+ the name is short for List Processing.
+ Very popular in AI (Artificial Intelligence)
+ circles.
+
+ Lisp is an extremely powerful and sophisticated
+ language, but can be rather large and unwieldy.
+
+ FreeBSD has GNU
+ Common Lisp available as a package.
+
+
+
+
+ Perl
+
+
+ Very popular with system administrators for writing
+ scripts; also often used on World Wide Web servers for
+ writing CGI scripts.
+
+ The latest version (version 5) comes with FreeBSD.
+
+
+
+
+ Scheme
+
+
+ A dialect of Lisp that is rather more compact and
+ cleaner than Common Lisp. Popular in Universities as it
+ is simple enough to teach to undergraduates as a first
+ language, while it has a high enough level of
+ abstraction to be used in research work.
+
+ FreeBSD has packages of the Elk
+ Scheme Interpreter, the MIT
+ Scheme Interpreter and the SCM
+ Scheme Interpreter.
+
+
+
+
+ Icon
+
+
+ The
+ Icon Programming Language.
+
+
+
+
+ Logo
+
+
+ Brian
+ Harvey's LOGO Interpreter.
+
+
+
+
+ Python
+
+
+ The
+ Python Object-Oriented Programming
+ Language
+
+
+
+
+
+
+ Compilers
+
+ Compilers are rather different. First of all, you write
+ your code in a file (or files) using an editor. You then run
+ the compiler and see if it accepts your program. If it did
+ not compile, grit your teeth and go back to the editor; if it
+ did compile and gave you a program, you can run it either at a
+ shell command prompt or in a debugger to see if it works
+ properly.
+
+
+ If you run it in the shell, you may get a core
+ dump.
+
+
+ Obviously, this is not quite as direct as using an
+ interpreter. However it allows you to do a lot of things
+ which are very difficult or even impossible with an
+ interpreter, such as writing code which interacts closely with
+ the operating system—or even writing your own operating
+ system! It's also useful if you need to write very efficient
+ code, as the compiler can take its time and optimise the code,
+ which would not be acceptable in an interpreter. And
+ distributing a program written for a compiler is usually more
+ straightforward than one written for an interpreter—you
+ can just give them a copy of the executable, assuming they
+ have the same operating system as you.
+
+ Compiled languages include Pascal, C and C++. C and C++
+ are rather unforgiving languages, and best suited to more
+ experienced programmers; Pascal, on the other hand, was
+ designed as an educational language, and is quite a good
+ language to start with. Unfortunately, FreeBSD doesn't have
+ any Pascal support, except for a Pascal-to-C converter in the
+ ports.
+
+ As the edit-compile-run-debug cycle is rather tedious when
+ using separate programs, many commercial compiler makers have
+ produced Integrated Development Environments
+
+ (IDEs for short). FreeBSD does not have an
+ IDE as such; however it is possible to use Emacs
+ for this purpose. This is discussed in .
+
+
+
+
+
+
+
+ Compiling with <command>cc</command>
+
+ This section deals only with the GNU compiler for C and C++,
+ since that comes with the base FreeBSD system. It can be
+ invoked by either cc or gcc. The
+ details of producing a program with an interpreter vary
+ considerably between interpreters, and are usually well covered
+ in the documentation and on-line help for the
+ interpreter.
+
+ Once you've written your masterpiece, the next step is to
+ convert it into something that will (hopefully!) run on FreeBSD.
+ This usually involves several steps, each of which is done by a
+ separate program.
+
+
+
+ Pre-process your source code to remove comments and do
+ other tricks like expanding macros in C.
+
+
+
+ Check the syntax of your code to see if you have obeyed
+ the rules of the language. If you have not, it will
+ complain!
+
+
+
+ Convert the source code into assembly
+ language—this is very close to machine code, but still
+ understandable by humans. Allegedly.
+
+
+ To be strictly accurate, cc converts the
+ source code into its own, machine-independent
+ p-code instead of assembly language at
+ this stage.
+
+
+
+
+ Convert the assembly language into machine
+ code—yep, we are talking bits and bytes, ones and
+ zeros here.
+
+
+
+ Check that you have used things like functions and
+ global variables in a consistent way. For example, if you
+ have called a non-existent function, it will
+ complain.
+
+
+
+ If you are trying to produce an executable from several
+ source code files, work out how to fit them all
+ together.
+
+
+
+ Work out how to produce something that the system's
+ run-time loader will be able to load into memory and
+ run.
+
+
+
+ Finally, write the executable on the file system.
+
+
+
+ The word compiling is often used to refer to
+ just steps 1 to 4—the others are referred to as
+ linking. Sometimes step 1 is referred to as
+ pre-processing and steps 3-4 as
+ assembling.
+
+ Fortunately, almost all this detail is hidden from you, as
+ cc is a front end that manages calling all these
+ programs with the right arguments for you; simply typing
+
+ &prompt.user; cc foobar.c
+
+
+ will cause foobar.c to be compiled by all the
+ steps above. If you have more than one file to compile, just do
+ something like
+
+ &prompt.user; cc foo.c bar.c
+
+
+ Note that the syntax checking is just that—checking
+ the syntax. It will not check for any logical mistakes you may
+ have made, like putting the program into an infinite loop, or
+ using a bubble sort when you meant to use a binary
+ sort.
+
+
+ In case you didn't know, a binary sort is an efficient
+ way of sorting things into order and a bubble sort
+ isn't.
+
+
+ There are lots and lots of options for cc, which
+ are all in the man page. Here are a few of the most important
+ ones, with examples of how to use them.
+
+
+
+
+
+
+ The output name of the file. If you do not use this
+ option, cc will produce an executable called
+ a.out.
+
+
+ The reasons for this are buried in the mists of
+ history.
+
+
+
+ &prompt.user; cc foobar.c executable is a.out
+&prompt.user; cc -o foobar foobar.c executable is foobar
+
+
+
+
+
+
+
+
+
+ Just compile the file, do not link it. Useful for toy
+ programs where you just want to check the syntax, or if
+ you are using a Makefile.
+
+
+ &prompt.user; cc -c foobar.c
+
+
+
+ This will produce an object file (not an
+ executable) called foobar.o. This
+ can be linked together with other object files into an
+ executable.
+
+
+
+
+
+
+
+ Create a debug version of the executable. This makes
+ the compiler put information into the executable about
+ which line of which source file corresponds to which
+ function call. A debugger can use this information to show
+ the source code as you step through the program, which is
+ very useful; the disadvantage is that
+ all this extra information makes the program much bigger.
+ Normally, you compile with while you
+ are developing a program and then compile a release
+ version without when you're
+ satisfied it works properly.
+
+
+ &prompt.user; cc -g foobar.c
+
+
+
+ This will produce a debug version of the
+ program.
+
+
+ Note, we didn't use the flag
+ to specify the executable name, so we will get an
+ executable called a.out.
+ Producing a debug version called
+ foobar is left as an exercise for
+ the reader!
+
+
+
+
+
+
+
+
+ Create an optimised version of the executable. The
+ compiler performs various clever tricks to try and produce
+ an executable that runs faster than normal. You can add a
+ number after the to specify a higher
+ level of optimisation, but this often exposes bugs in the
+ compiler's optimiser. For instance, the version of
+ cc that comes with the 2.1.0 release of
+ FreeBSD is known to produce bad code with the
+ option in some circumstances.
+
+ Optimisation is usually only turned on when compiling
+ a release version.
+
+
+ &prompt.user; cc -O -o foobar foobar.c
+
+
+
+ This will produce an optimised version of
+ foobar.
+
+
+
+
+ The following three flags will force cc
+ to check that your code complies to the relevant international
+ standard, often referred to as the ANSI
+ standard, though strictly speaking it is an
+ ISO standard.
+
+
+
+
+
+
+ Enable all the warnings which the authors of
+ cc believe are worthwhile. Despite the
+ name, it will not enable all the warnings
+ cc is capable of.
+
+
+
+
+
+
+
+ Turn off most, but not all, of the
+ non-ANSI C features provided by
+ cc. Despite the name, it does not
+ guarantee strictly that your code will comply to the
+ standard.
+
+
+
+
+
+
+
+ Turn off all
+ cc's non-ANSI C
+ features.
+
+
+
+
+ Without these flags, cc will allow you to
+ use some of its non-standard extensions to the standard. Some
+ of these are very useful, but will not work with other
+ compilers—in fact, one of the main aims of the standard is
+ to allow people to write code that will work with any compiler
+ on any system. This is known as portable
+ code.
+
+ Generally, you should try to make your code as portable as
+ possible, as otherwise you may have to completely re-write the
+ program later to get it to work somewhere else—and who
+ knows what you may be using in a few years time?
+
+
+ &prompt.user; cc -Wall -ansi -pedantic -o foobar foobar.c
+
+
+
+ This will produce an executable foobar
+ after checking foobar.c for standard
+ compliance.
+
+
+
+
+
+
+ Specify a function library to be used during when
+ linking.
+
+ The most common example of this is when compiling a
+ program that uses some of the mathematical functions in C.
+ Unlike most other platforms, these are in a separate
+ library from the standard C one and you have to tell the
+ compiler to add it.
+
+ The rule is that if the library is called
+ libsomething.a,
+ you give cc the argument
+ .
+ For example, the math library is
+ libm.a, so you give
+ cc the argument .
+ A common gotcha with the math library is
+ that it has to be the last library on the command
+ line.
+
+
+ &prompt.user; cc -o foobar foobar.c -lm
+
+
+
+ This will link the math library functions into
+ foobar.
+
+ If you are compiling C++ code, you need to add
+ , or if
+ you are using FreeBSD 2.2 or later, to the command line
+ argument to link the C++ library functions.
+ Alternatively, you can run c++ instead
+ of cc, which does this for you.
+ c++ can also be invoked as
+ g++ on FreeBSD.
+
+
+ &prompt.user; cc -o foobar foobar.cc -lg++For FreeBSD 2.1.6 and earlier
+&prompt.user; cc -o foobar foobar.cc -lstdc++For FreeBSD 2.2 and later
+&prompt.user; c++ -o foobar foobar.cc
+
+
+
+ Each of these will both produce an executable
+ foobar from the C++ source file
+ foobar.cc. Note that, on Unix
+ systems, C++ source files traditionally end in
+ .C, .cxx or
+ .cc, rather than the
+ MS-DOS style
+ .cpp (which was already used for
+ something else). gcc used to rely on
+ this to work out what kind of compiler to use on the
+ source file; however, this restriction no longer applies,
+ so you may now call your C++ files
+ .cpp with impunity!
+
+
+
+
+
+ Common <command>cc</command> Queries and Problems
+
+
+
+
+ I am trying to write a program which uses the
+ sin() function and I get an error
+ like this. What does it mean?
+
+
+ /var/tmp/cc0143941.o: Undefined symbol `_sin' referenced from text segment
+
+
+
+
+
+ When using mathematical functions like
+ sin(), you have to tell
+ cc to link in the math library, like
+ so:
+
+
+ &prompt.user; cc -o foobar foobar.c -lm
+
+
+
+
+
+
+
+ All right, I wrote this simple program to practice
+ using . All it does is raise 2.1 to
+ the power of 6.
+
+
+ #include <stdio.h>
+
+int main() {
+ float f;
+
+ f = pow(2.1, 6);
+ printf("2.1 ^ 6 = %f\n", f);
+ return 0;
+}
+
+
+
+ and I compiled it as:
+
+
+ &prompt.user; cc temp.c -lm
+
+
+
+ like you said I should, but I get this when I run
+ it:
+
+
+ &prompt.user; ./a.out
+2.1 ^ 6 = 1023.000000
+
+
+
+ This is not the right answer!
+ What is going on?
+
+
+
+ When the compiler sees you call a function, it
+ checks if it has already seen a prototype for it. If it
+ has not, it assumes the function returns an
+ int, which is definitely not what you want
+ here.
+
+
+
+
+
+ So how do I fix this?
+
+
+
+ The prototypes for the mathematical functions are in
+ math.h. If you include this file,
+ the compiler will be able to find the prototype and it
+ will stop doing strange things to your
+ calculation!
+
+
+ #include <math.h>
+#include <stdio.h>
+
+int main() {
+...
+
+
+
+ After recompiling it as you did before, run
+ it:
+
+
+ &prompt.user; ./a.out
+2.1 ^ 6 = 85.766121
+
+
+
+ If you are using any of the mathematical functions,
+ always include
+ math.h and remember to link in the
+ math library.
+
+
+
+
+
+ I compiled a file called
+ foobar.c and I cannot find an
+ executable called foobar. Where's
+ it gone?
+
+
+
+ Remember, cc will call the
+ executable a.out unless you tell it
+ differently. Use the
+
+ option:
+
+
+ &prompt.user; cc -o foobar foobar.c
+
+
+
+
+
+
+
+ OK, I have an executable called
+ foobar, I can see it when I run
+ ls, but when I type in
+ foobar at the command prompt it tells
+ me there is no such file. Why can it not find
+ it?
+
+
+
+ Unlike MS-DOS, Unix does not
+ look in the current directory when it is trying to find
+ out which executable you want it to run, unless you tell
+ it to. Either type ./foobar, which
+ means run the file called
+ foobar in the current
+ directory, or change your PATH environment
+ variable so that it looks something like
+
+
+ bin:/usr/bin:/usr/local/bin:.
+
+
+
+ The dot at the end means look in the current
+ directory if it is not in any of the
+ others.
+
+
+
+
+
+ I called my executable test,
+ but nothing happens when I run it. What is going
+ on?
+
+
+
+ Most Unix systems have a program called
+ test in /usr/bin
+ and the shell is picking that one up before it gets to
+ checking the current directory. Either type:
+
+
+ &prompt.user; ./test
+
+
+
+ or choose a better name for your program!
+
+
+
+
+
+ I compiled my program and it seemed to run all right
+ at first, then there was an error and it said something
+ about core dumped. What does that
+ mean?
+
+
+
+ The name core dump dates back
+ to the very early days of Unix, when the machines used
+ core memory for storing data. Basically, if the program
+ failed under certain conditions, the system would write
+ the contents of core memory to disk in a file called
+ core, which the programmer could
+ then pore over to find out what went wrong.
+
+
+
+
+
+ Fascinating stuff, but what I am supposed to do
+ now?
+
+
+
+ Use gdb to analyse the core (see
+ ).
+
+
+
+
+
+ When my program dumped core, it said something about
+ a segmentation fault. What's
+ that?
+
+
+
+ This basically means that your program tried to
+ perform some sort of illegal operation on memory; Unix
+ is designed to protect the operating system and other
+ programs from rogue programs.
+
+ Common causes for this are:
+
+
+
+ Trying to write to a NULL
+ pointer, eg
+
+ char *foo = NULL;
+strcpy(foo, "bang!");
+
+
+
+
+ Using a pointer that hasn't been initialised,
+ eg
+
+ char *foo;
+strcpy(foo, "bang!");
+
+
+ The pointer will have some random value that,
+ with luck, will point into an area of memory that
+ isn't available to your program and the kernel will
+ kill your program before it can do any damage. If
+ you're unlucky, it'll point somewhere inside your
+ own program and corrupt one of your data structures,
+ causing the program to fail mysteriously.
+
+
+
+ Trying to access past the end of an array,
+ eg
+
+ int bar[20];
+bar[27] = 6;
+
+
+
+
+ Trying to store something in read-only memory,
+ eg
+
+ char *foo = "My string";
+strcpy(foo, "bang!");
+
+
+ Unix compilers often put string literals like
+ "My string" into read-only areas
+ of memory.
+
+
+
+ Doing naughty things with
+ malloc() and
+ free(), eg
+
+ char bar[80];
+free(bar);
+
+
+ or
+
+ char *foo = malloc(27);
+free(foo);
+free(foo);
+
+
+
+
+ Making one of these mistakes will not always lead to
+ an error, but they are always bad practice. Some
+ systems and compilers are more tolerant than others,
+ which is why programs that ran well on one system can
+ crash when you try them on an another.
+
+
+
+
+
+ Sometimes when I get a core dump it says
+ bus error. It says in my Unix
+ book that this means a hardware problem, but the
+ computer still seems to be working. Is this
+ true?
+
+
+
+ No, fortunately not (unless of course you really do
+ have a hardware problem…). This is usually
+ another way of saying that you accessed memory in a way
+ you shouldn't have.
+
+
+
+
+
+ This dumping core business sounds as though it could
+ be quite useful, if I can make it happen when I want to.
+ Can I do this, or do I have to wait until there's an
+ error?
+
+
+
+ Yes, just go to another console or xterm, do
+
+ &prompt.user; ps
+
+
+ to find out the process ID of your program, and
+ do
+
+ &prompt.user; kill -ABRT pid
+
+
+ where
+ pid is
+ the process ID you looked up.
+
+ This is useful if your program has got stuck in an
+ infinite loop, for instance. If your program happens to
+ trap SIGABRT, there are several other
+ signals which have a similar effect.
+
+
+
+
+
+
+
+ Make
+
+
+ What is <command>make</command>?
+
+ When you're working on a simple program with only one or
+ two source files, typing in
+
+ &prompt.user; cc file1.c file2.c
+
+
+ is not too bad, but it quickly becomes very tedious when
+ there are several files—and it can take a while to
+ compile, too.
+
+ One way to get around this is to use object files and only
+ recompile the source file if the source code has changed. So
+ we could have something like:
+
+ &prompt.user; cc file1.o file2.o … file37.c &hellip
+
+
+ if we'd changed file37.c, but not any
+ of the others, since the last time we compiled. This may
+ speed up the compilation quite a bit, but doesn't solve the
+ typing problem.
+
+ Or we could write a shell script to solve the typing
+ problem, but it would have to re-compile everything, making it
+ very inefficient on a large project.
+
+ What happens if we have hundreds of source files lying
+ about? What if we're working in a team with other people who
+ forget to tell us when they've changed one of their source
+ files that we use?
+
+ Perhaps we could put the two solutions together and write
+ something like a shell script that would contain some kind of
+ magic rule saying when a source file needs compiling. Now all
+ we need now is a program that can understand these rules, as
+ it's a bit too complicated for the shell.
+
+ This program is called make. It reads
+ in a file, called a makefile, that
+ tells it how different files depend on each other, and works
+ out which files need to be re-compiled and which ones don't.
+ For example, a rule could say something like if
+ fromboz.o is older than
+ fromboz.c, that means someone must have
+ changed fromboz.c, so it needs to be
+ re-compiled. The makefile also has rules telling
+ make how to re-compile the source file,
+ making it a much more powerful tool.
+
+ Makefiles are typically kept in the same directory as the
+ source they apply to, and can be called
+ makefile, Makefile
+ or MAKEFILE. Most programmers use the
+ name Makefile, as this puts it near the
+ top of a directory listing, where it can easily be
+ seen.
+
+
+ They don't use the MAKEFILE form
+ as block capitals are often used for documentation files
+ like README.
+
+
+
+
+ Example of using <command>make</command>
+
+ Here's a very simple make file:
+
+ foo: foo.c
+ cc -o foo foo.c
+
+
+ It consists of two lines, a dependency line and a creation
+ line.
+
+ The dependency line here consists of the name of the
+ program (known as the target), followed
+ by a colon, then whitespace, then the name of the source file.
+ When make reads this line, it looks to see
+ if foo exists; if it exists, it compares
+ the time foo was last modified to the
+ time foo.c was last modified. If
+ foo does not exist, or is older than
+ foo.c, it then looks at the creation line
+ to find out what to do. In other words, this is the rule for
+ working out when foo.c needs to be
+ re-compiled.
+
+ The creation line starts with a tab (press
+ the tab key) and then the command you would
+ type to create foo if you were doing it
+ at a command prompt. If foo is out of
+ date, or does not exist, make then executes
+ this command to create it. In other words, this is the rule
+ which tells make how to re-compile
+ foo.c.
+
+ So, when you type make, it will
+ make sure that foo is up to date with
+ respect to your latest changes to foo.c.
+ This principle can be extended to
+ Makefiles with hundreds of
+ targets—in fact, on FreeBSD, it is possible to compile
+ the entire operating system just by typing make
+ world in the appropriate directory!
+
+ Another useful property of makefiles is that the targets
+ don't have to be programs. For instance, we could have a make
+ file that looks like this:
+
+ foo: foo.c
+ cc -o foo foo.c
+
+install:
+ cp foo /home/me
+
+
+ We can tell make which target we want to make by
+ typing:
+
+ &prompt.user; make target
+
+
+ make will then only look at that target
+ and ignore any others. For example, if we type
+ make foo with the makefile above, make
+ will ignore the install target.
+
+ If we just type make on its own,
+ make will always look at the first target and then stop
+ without looking at any others. So if we typed
+ make here, it will just go to the
+ foo target, re-compile
+ foo if necessary, and then stop without
+ going on to the install target.
+
+ Notice that the install target doesn't
+ actually depend on anything! This means that the command on
+ the following line is always executed when we try to make that
+ target by typing make install. In this
+ case, it will copy foo into the user's
+ home directory. This is often used by application makefiles,
+ so that the application can be installed in the correct
+ directory when it has been correctly compiled.
+
+ This is a slightly confusing subject to try and explain.
+ If you don't quite understand how make
+ works, the best thing to do is to write a simple program like
+ hello world and a make file like the one above
+ and experiment. Then progress to using more than one source
+ file, or having the source file include a header file. The
+ touch command is very useful here—it
+ changes the date on a file without you having to edit
+ it.
+
+
+
+ FreeBSD Makefiles
+
+ Makefiles can be rather complicated to write. Fortunately,
+ BSD-based systems like FreeBSD come with some very powerful
+ ones as part of the system. One very good example of this is
+ the FreeBSD ports system. Here's the essential part of a
+ typical ports Makefile:
+
+ MASTER_SITES= ftp://freefall.cdrom.com/pub/FreeBSD/LOCAL_PORTS/
+DISTFILES= scheme-microcode+dist-7.3-freebsd.tgz
+
+.include <bsd.port.mk>
+
+
+ Now, if we go to the directory for this port and type
+ make, the following happens:
+
+
+
+ A check is made to see if the source code for this
+ port is already on the system.
+
+
+
+ If it isn't, an FTP connection to the URL in
+ MASTER_SITES is set up to download the
+ source.
+
+
+
+ The checksum for the source is calculated and compared
+ it with one for a known, good, copy of the source. This
+ is to make sure that the source was not corrupted while in
+ transit.
+
+
+
+ Any changes required to make the source work on
+ FreeBSD are applied—this is known as
+ patching.
+
+
+
+ Any special configuration needed for the source is
+ done. (Many Unix program distributions try to work out
+ which version of Unix they are being compiled on and which
+ optional Unix features are present—this is where
+ they are given the information in the FreeBSD ports
+ scenario).
+
+
+
+ The source code for the program is compiled. In
+ effect, we change to the directory where the source was
+ unpacked and do make—the
+ program's own make file has the necessary information to
+ build the program.
+
+
+
+ We now have a compiled version of the program. If we
+ wish, we can test it now; when we feel confident about the
+ program, we can type make install.
+ This will cause the program and any supporting files it
+ needs to be copied into the correct location; an entry is
+ also made into a package database, so
+ that the port can easily be uninstalled later if we change
+ our mind about it.
+
+
+
+ Now I think you'll agree that's rather impressive for a
+ four line script!
+
+ The secret lies in the last line, which tells
+ make to look in the system makefile called
+ bsd.port.mk. It's easy to overlook this
+ line, but this is where all the clever stuff comes
+ from—someone has written a makefile that tells
+ make to do all the things above (plus a
+ couple of other things I didn't mention, including handling
+ any errors that may occur) and anyone can get access to that
+ just by putting a single line in their own make file!
+
+ If you want to have a look at these system makefiles,
+ they're in /usr/share/mk, but it's
+ probably best to wait until you've had a bit of practice with
+ makefiles, as they are very complicated (and if you do look at
+ them, make sure you have a flask of strong coffee
+ handy!)
+
+
+
+ More advanced uses of <command>make</command>
+
+ Make is a very powerful tool, and can
+ do much more than the simple example above shows.
+ Unfortunately, there are several different versions of
+ make, and they all differ considerably.
+ The best way to learn what they can do is probably to read the
+ documentation—hopefully this introduction will have
+ given you a base from which you can do this.
+
+ The version of make that comes with FreeBSD is the
+ Berkeley make; there is a tutorial
+ for it in /usr/share/doc/psd/12.make. To
+ view it, do
+
+ &prompt.user; zmore paper.ascii.gz
+
+
+ in that directory.
+
+ Many applications in the ports use GNU
+ make, which has a very good set of
+ info pages. If you have installed any of these
+ ports, GNU make will automatically
+ have been installed as gmake. It's also
+ available as a port and package in its own right.
+
+ To view the info pages for GNU
+ make, you will have to edit the
+ dir file in the
+ /usr/local/info directory to add an entry
+ for it. This involves adding a line like
+
+ * Make: (make). The GNU Make utility.
+
+
+ to the file. Once you have done this, you can type
+ info and then select
+ make from the menu (or in
+ Emacs, do C-h
+ i).
+
+
+
+
+ Debugging
+
+
+ The Debugger
+
+ The debugger that comes with FreeBSD is called
+ gdb (GNU
+ debugger). You start it up by typing
+
+ &prompt.user; gdb progname
+
+
+ although most people prefer to run it inside
+ Emacs. You can do this by:
+
+ M-x gdb RET progname RET
+
+
+ Using a debugger allows you to run the program under more
+ controlled circumstances. Typically, you can step through the
+ program a line at a time, inspect the value of variables,
+ change them, tell the debugger to run up to a certain point
+ and then stop, and so on. You can even attach to a program
+ that's already running, or load a core file to investigate why
+ the program crashed. It's even possible to debug the kernel,
+ though that's a little trickier than the user applications
+ we'll be discussing in this section.
+
+ gdb has quite good on-line help, as
+ well as a set of info pages, so this section will concentrate
+ on a few of the basic commands.
+
+ Finally, if you find its text-based command-prompt style
+ off-putting, there's a graphical front-end for it xxgdb in the ports
+ collection.
+
+ This section is intended to be an introduction to using
+ gdb and does not cover specialised topics
+ such as debugging the kernel.
+
+
+
+ Running a program in the debugger
+
+ You'll need to have compiled the program with the
+ option to get the most out of using
+ gdb. It will work without, but you'll only
+ see the name of the function you're in, instead of the source
+ code. If you see a line like:
+
+ … (no debugging symbols found) …
+
+
+ when gdb starts up, you'll know that
+ the program wasn't compiled with the
+ option.
+
+ At the gdb prompt, type
+ break main. This will tell the
+ debugger to skip over the preliminary set-up code in the
+ program and start at the beginning of your code. Now type
+ run to start the program—it will
+ start at the beginning of the set-up code and then get stopped
+ by the debugger when it calls main().
+ (If you've ever wondered where main()
+ gets called from, now you know!).
+
+ You can now step through the program, a line at a time, by
+ pressing n. If you get to a function call,
+ you can step into it by pressing s. Once
+ you're in a function call, you can return from stepping into a
+ function call by pressing f. You can also
+ use up and down to take
+ a quick look at the caller.
+
+ Here's a simple example of how to spot a mistake in a
+ program with gdb. This is our program
+ (with a deliberate mistake):
+
+ #include <stdio.h>
+
+int bazz(int anint);
+
+main() {
+ int i;
+
+ printf("This is my program\n");
+ bazz(i);
+ return 0;
+}
+
+int bazz(int anint) {
+ printf("You gave me %d\n", anint);
+ return anint;
+}
+
+
+ This program sets i to be
+ 5 and passes it to a function
+ bazz() which prints out the number we
+ gave it.
+
+ When we compile and run the program we get
+
+ &prompt.user; cc -g -o temp temp.c
+&prompt.user; ./temp
+This is my program
+anint = 4231
+
+
+ That wasn't what we expected! Time to see what's going
+ on!
+
+ &prompt.user; gdb temp
+GDB is free software and you are welcome to distribute copies of it
+ under certain conditions; type "show copying" to see the conditions.
+There is absolutely no warranty for GDB; type "show warranty" for details.
+GDB 4.13 (i386-unknown-freebsd), Copyright 1994 Free Software Foundation, Inc.
+(gdb) break main Skip the set-up code
+Breakpoint 1 at 0x160f: file temp.c, line 9. gdb puts breakpoint at main()
+(gdb) run Run as far as main()
+Starting program: /home/james/tmp/temp Program starts running
+
+Breakpoint 1, main () at temp.c:9 gdb stops at main()
+(gdb) n Go to next line
+This is my program Program prints out
+(gdb) s step into bazz()
+bazz (anint=4231) at temp.c:17 gdb displays stack frame
+(gdb)
+
+
+ Hang on a minute! How did anint get to be
+ 4231? Didn't we set it to be
+ 5 in main()? Let's
+ move up to main() and have a look.
+
+ (gdb) up Move up call stack
+#1 0x1625 in main () at temp.c:11 gdb displays stack frame
+(gdb) p i Show us the value of i
+$1 = 4231 gdb displays 4231
+
+
+ Oh dear! Looking at the code, we forgot to initialise
+ i. We meant to put
+
+ …
+main() {
+ int i;
+
+ i = 5;
+ printf("This is my program\n");
+&hellip
+
+
+ but we left the i=5; line out. As we
+ didn't initialise i, it had whatever number
+ happened to be in that area of memory when the program ran,
+ which in this case happened to be
+ 4231.
+
+
+ gdb displays the stack frame every
+ time we go into or out of a function, even if we're using
+ up and down to move
+ around the call stack. This shows the name of the function
+ and the values of its arguments, which helps us keep track
+ of where we are and what's going on. (The stack is a
+ storage area where the program stores information about the
+ arguments passed to functions and where to go when it
+ returns from a function call).
+
+
+
+
+ Examining a core file
+
+ A core file is basically a file which contains the
+ complete state of the process when it crashed. In the
+ good old days, programmers had to print out hex
+ listings of core files and sweat over machine code manuals,
+ but now life is a bit easier. Incidentally, under FreeBSD and
+ other 4.4BSD systems, a core file is called
+ progname.core instead of just
+ core, to make it clearer which program a
+ core file belongs to.
+
+ To examine a core file, start up gdb in
+ the usual way. Instead of typing break or
+ run, type
+
+ (gdb) core progname.core
+
+
+ If you're not in the same directory as the core file,
+ you'll have to do dir
+ /path/to/core/file first.
+
+ You should see something like this:
+
+ &prompt.user; gdb a.out
+GDB is free software and you are welcome to distribute copies of it
+ under certain conditions; type "show copying" to see the conditions.
+There is absolutely no warranty for GDB; type "show warranty" for details.
+GDB 4.13 (i386-unknown-freebsd), Copyright 1994 Free Software Foundation, Inc.
+(gdb) core a.out.core
+Core was generated by `a.out'.
+Program terminated with signal 11, Segmentation fault.
+Cannot access memory at address 0x7020796d.
+#0 0x164a in bazz (anint=0x5) at temp.c:17
+(gdb)
+
+
+ In this case, the program was called
+ a.out, so the core file is called
+ a.out.core. We can see that the program
+ crashed due to trying to access an area in memory that was not
+ available to it in a function called
+ bazz.
+
+ Sometimes it's useful to be able to see how a function was
+ called, as the problem could have occurred a long way up the
+ call stack in a complex program. The bt
+ command causes gdb to print out a
+ back-trace of the call stack:
+
+ (gdb) bt
+#0 0x164a in bazz (anint=0x5) at temp.c:17
+#1 0xefbfd888 in end ()
+#2 0x162c in main () at temp.c:11
+(gdb)
+
+
+ The end() function is called when a
+ program crashes; in this case, the bazz()
+ function was called from main().
+
+
+
+ Attaching to a running program
+
+ One of the neatest features about gdb
+ is that it can attach to a program that's already running. Of
+ course, that assumes you have sufficient permissions to do so.
+ A common problem is when you are stepping through a program
+ that forks, and you want to trace the child, but the debugger
+ will only let you trace the parent.
+
+ What you do is start up another gdb,
+ use ps to find the process ID for the
+ child, and do
+
+ (gdb) attach pid
+
+
+ in gdb, and then debug as usual.
+
+ That's all very well, you're probably
+ thinking, but by the time I've done that, the child
+ process will be over the hill and far away. Fear
+ not, gentle reader, here's how to do it (courtesy of the
+ gdb info pages):
+
+ &hellip
+if ((pid = fork()) < 0) /* _Always_ check this */
+ error();
+else if (pid == 0) { /* child */
+ int PauseMode = 1;
+
+ while (PauseMode)
+ sleep(10); /* Wait until someone attaches to us */
+ &hellip
+} else { /* parent */
+ &hellip
+
+
+ Now all you have to do is attach to the child, set
+ PauseMode to 0, and wait
+ for the sleep() call to return!
+
+
+
+
+ Using Emacs as a Development Environment
+
+
+ Emacs
+
+ Unfortunately, Unix systems don't come with the kind of
+ everything-you-ever-wanted-and-lots-more-you-didn't-in-one-gigantic-package
+ integrated development environments that other systems
+ have.
+
+
+ At least, not unless you pay out very large sums of
+ money.
+
+
+ However, it is possible to set up your own environment. It
+ may not be as pretty, and it may not be quite as integrated,
+ but you can set it up the way you want it. And it's free.
+ And you have the source to it.
+
+ The key to it all is Emacs. Now there are some people who
+ loathe it, but many who love it. If you're one of the former,
+ I'm afraid this section will hold little of interest to you.
+ Also, you'll need a fair amount of memory to run it—I'd
+ recommend 8MB in text mode and 16MB in X as the bare minimum
+ to get reasonable performance.
+
+ Emacs is basically a highly customisable
+ editor—indeed, it has been customised to the point where
+ it's more like an operating system than an editor! Many
+ developers and sysadmins do in fact spend practically all
+ their time working inside Emacs, leaving it only to log
+ out.
+
+ It's impossible even to summarise everything Emacs can do
+ here, but here are some of the features of interest to
+ developers:
+
+
+
+ Very powerful editor, allowing search-and-replace on
+ both strings and regular expressions (patterns), jumping
+ to start/end of block expression, etc, etc.
+
+
+
+ Pull-down menus and online help.
+
+
+
+ Language-dependent syntax highlighting and
+ indentation.
+
+
+
+ Completely customisable.
+
+
+
+ You can compile and debug programs within
+ Emacs.
+
+
+
+ On a compilation error, you can jump to the offending
+ line of source code.
+
+
+
+ Friendly-ish front-end to the info
+ program used for reading GNU hypertext documentation,
+ including the documentation on Emacs itself.
+
+
+
+ Friendly front-end to gdb, allowing
+ you to look at the source code as you step through your
+ program.
+
+
+
+ You can read Usenet news and mail while your program
+ is compiling.
+
+
+
+ And doubtless many more that I've overlooked.
+
+ Emacs can be installed on FreeBSD using the Emacs
+ port.
+
+ Once it's installed, start it up and do C-h
+ t to read an Emacs tutorial—that means
+ hold down the control key, press
+ h, let go of the control
+ key, and then press t. (Alternatively, you
+ can you use the mouse to select Emacs
+ Tutorial from the Help
+ menu).
+
+ Although Emacs does have menus, it's well worth learning
+ the key bindings, as it's much quicker when you're editing
+ something to press a couple of keys than to try and find the
+ mouse and then click on the right place. And, when you're
+ talking to seasoned Emacs users, you'll find they often
+ casually throw around expressions like M-x
+ replace-s RET foo RET bar RET so it's
+ useful to know what they mean. And in any case, Emacs has far
+ too many useful functions for them to all fit on the menu
+ bars.
+
+ Fortunately, it's quite easy to pick up the key-bindings,
+ as they're displayed next to the menu item. My advice is to
+ use the menu item for, say, opening a file until you
+ understand how it works and feel confident with it, then try
+ doing C-x C-f. When you're happy with that, move on to
+ another menu command.
+
+ If you can't remember what a particular combination of
+ keys does, select Describe Key from
+ the Help menu and type it in—Emacs
+ will tell you what it does. You can also use the
+ Command Apropos menu item to find
+ out all the commands which contain a particular word in them,
+ with the key binding next to it.
+
+ By the way, the expression above means hold down the
+ Meta key, press x, release
+ the Meta key, type
+ replace-s (short for
+ replace-string—another feature of
+ Emacs is that you can abbreviate commands), press the
+ return key, type foo
+ (the string you want replaced), press the
+ return key, type bar (the string you want to
+ replace foo with) and press
+ return again. Emacs will then do the
+ search-and-replace operation you've just requested.
+
+ If you're wondering what on earth the
+ Meta key is, it's a special key that many
+ Unix workstations have. Unfortunately, PC's don't have one,
+ so it's usually the alt key (or if you're
+ unlucky, the escape key).
+
+ Oh, and to get out of Emacs, do C-x C-c
+ (that means hold down the control key, press
+ x, press c and release the
+ control key). If you have any unsaved files
+ open, Emacs will ask you if you want to save them. (Ignore
+ the bit in the documentation where it says
+ C-z is the usual way to leave
+ Emacs—that leaves Emacs hanging around in the
+ background, and is only really useful if you're on a system
+ which doesn't have virtual terminals).
+
+
+
+ Configuring Emacs
+
+ Emacs does many wonderful things; some of them are built
+ in, some of them need to be configured.
+
+ Instead of using a proprietary macro language for
+ configuration, Emacs uses a version of Lisp specially adapted
+ for editors, known as Emacs Lisp. This can be quite useful if
+ you want to go on and learn something like Common Lisp, as
+ it's considerably smaller than Common Lisp (although still
+ quite big!).
+
+ The best way to learn Emacs Lisp is to download the Emacs
+ Tutorial
+
+ However, there's no need to actually know any Lisp to get
+ started with configuring Emacs, as I've included a sample
+ .emacs file, which should be enough to
+ get you started. Just copy it into your home directory and
+ restart Emacs if it's already running; it will read the
+ commands from the file and (hopefully) give you a useful basic
+ setup.
+
+
+
+ A sample <filename>.emacs</filename> file
+
+ Unfortunately, there's far too much here to explain it in
+ detail; however there are one or two points worth
+ mentioning.
+
+
+
+ Everything beginning with a ; is a comment
+ and is ignored by Emacs.
+
+
+
+ In the first line, the
+ -*- Emacs-Lisp -*- is so that
+ we can edit the .emacs file itself
+ within Emacs and get all the fancy features for editing
+ Emacs Lisp. Emacs usually tries to guess this based on
+ the filename, and may not get it right for
+ .emacs.
+
+
+
+ The tab key is bound to an
+ indentation function in some modes, so when you press the
+ tab key, it will indent the current line of code. If you
+ want to put a tab character in whatever
+ you're writing, hold the control key down
+ while you're pressing the tab key.
+
+
+
+ This file supports syntax highlighting for C, C++,
+ Perl, Lisp and Scheme, by guessing the language from the
+ filename.
+
+
+
+ Emacs already has a pre-defined function called
+ next-error. In a compilation output
+ window, this allows you to move from one compilation error
+ to the next by doing M-n; we define a
+ complementary function,
+ previous-error, that allows you to go
+ to a previous error by doing M-p. The
+ nicest feature of all is that C-c C-c
+ will open up the source file in which the error occurred
+ and jump to the appropriate line.
+
+
+
+ We enable Emacs's ability to act as a server, so that
+ if you're doing something outside Emacs and you want to
+ edit a file, you can just type in
+
+ &prompt.user; emacsclient filename
+
+
+ and then you can edit the file in your
+ Emacs!
+
+
+ Many Emacs users set their EDITOR environment to
+ emacsclient so this happens every
+ time they need to edit a file.
+
+
+
+
+
+ A sample <filename>.emacs</filename> file
+
+ ;; -*-Emacs-Lisp-*-
+
+;; This file is designed to be re-evaled; use the variable first-time
+;; to avoid any problems with this.
+(defvar first-time t
+ "Flag signifying this is the first time that .emacs has been evaled")
+
+;; Meta
+(global-set-key "\M- " 'set-mark-command)
+(global-set-key "\M-\C-h" 'backward-kill-word)
+(global-set-key "\M-\C-r" 'query-replace)
+(global-set-key "\M-r" 'replace-string)
+(global-set-key "\M-g" 'goto-line)
+(global-set-key "\M-h" 'help-command)
+
+;; Function keys
+(global-set-key [f1] 'manual-entry)
+(global-set-key [f2] 'info)
+(global-set-key [f3] 'repeat-complex-command)
+(global-set-key [f4] 'advertised-undo)
+(global-set-key [f5] 'eval-current-buffer)
+(global-set-key [f6] 'buffer-menu)
+(global-set-key [f7] 'other-window)
+(global-set-key [f8] 'find-file)
+(global-set-key [f9] 'save-buffer)
+(global-set-key [f10] 'next-error)
+(global-set-key [f11] 'compile)
+(global-set-key [f12] 'grep)
+(global-set-key [C-f1] 'compile)
+(global-set-key [C-f2] 'grep)
+(global-set-key [C-f3] 'next-error)
+(global-set-key [C-f4] 'previous-error)
+(global-set-key [C-f5] 'display-faces)
+(global-set-key [C-f8] 'dired)
+(global-set-key [C-f10] 'kill-compilation)
+
+;; Keypad bindings
+(global-set-key [up] "\C-p")
+(global-set-key [down] "\C-n")
+(global-set-key [left] "\C-b")
+(global-set-key [right] "\C-f")
+(global-set-key [home] "\C-a")
+(global-set-key [end] "\C-e")
+(global-set-key [prior] "\M-v")
+(global-set-key [next] "\C-v")
+(global-set-key [C-up] "\M-\C-b")
+(global-set-key [C-down] "\M-\C-f")
+(global-set-key [C-left] "\M-b")
+(global-set-key [C-right] "\M-f")
+(global-set-key [C-home] "\M-<")
+(global-set-key [C-end] "\M->")
+(global-set-key [C-prior] "\M-<")
+(global-set-key [C-next] "\M->")
+
+;; Mouse
+(global-set-key [mouse-3] 'imenu)
+
+;; Misc
+(global-set-key [C-tab] "\C-q\t") ; Control tab quotes a tab.
+(setq backup-by-copying-when-mismatch t)
+
+;; Treat 'y' or <CR> as yes, 'n' as no.
+(fset 'yes-or-no-p 'y-or-n-p)
+ (define-key query-replace-map [return] 'act)
+ (define-key query-replace-map [?\C-m] 'act)
+
+;; Load packages
+(require 'desktop)
+(require 'tar-mode)
+
+;; Pretty diff mode
+(autoload 'ediff-buffers "ediff" "Intelligent Emacs interface to diff" t)
+(autoload 'ediff-files "ediff" "Intelligent Emacs interface to diff" t)
+(autoload 'ediff-files-remote "ediff"
+ "Intelligent Emacs interface to diff")
+
+(if first-time
+ (setq auto-mode-alist
+ (append '(("\\.cpp$" . c++-mode)
+ ("\\.hpp$" . c++-mode)
+ ("\\.lsp$" . lisp-mode)
+ ("\\.scm$" . scheme-mode)
+ ("\\.pl$" . perl-mode)
+ ) auto-mode-alist)))
+
+;; Auto font lock mode
+(defvar font-lock-auto-mode-list
+ (list 'c-mode 'c++-mode 'c++-c-mode 'emacs-lisp-mode 'lisp-mode 'perl-mode 'scheme-mode)
+ "List of modes to always start in font-lock-mode")
+
+(defvar font-lock-mode-keyword-alist
+ '((c++-c-mode . c-font-lock-keywords)
+ (perl-mode . perl-font-lock-keywords))
+ "Associations between modes and keywords")
+
+(defun font-lock-auto-mode-select ()
+ "Automatically select font-lock-mode if the current major mode is
+in font-lock-auto-mode-list"
+ (if (memq major-mode font-lock-auto-mode-list)
+ (progn
+ (font-lock-mode t))
+ )
+ )
+
+(global-set-key [M-f1] 'font-lock-fontify-buffer)
+
+;; New dabbrev stuff
+;(require 'new-dabbrev)
+(setq dabbrev-always-check-other-buffers t)
+(setq dabbrev-abbrev-char-regexp "\\sw\\|\\s_")
+(add-hook 'emacs-lisp-mode-hook
+ '(lambda ()
+ (set (make-local-variable 'dabbrev-case-fold-search) nil)
+ (set (make-local-variable 'dabbrev-case-replace) nil)))
+(add-hook 'c-mode-hook
+ '(lambda ()
+ (set (make-local-variable 'dabbrev-case-fold-search) nil)
+ (set (make-local-variable 'dabbrev-case-replace) nil)))
+(add-hook 'text-mode-hook
+ '(lambda ()
+ (set (make-local-variable 'dabbrev-case-fold-search) t)
+ (set (make-local-variable 'dabbrev-case-replace) t)))
+
+;; C++ and C mode...
+(defun my-c++-mode-hook ()
+ (setq tab-width 4)
+ (define-key c++-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (define-key c++-mode-map "\C-ce" 'c-comment-edit)
+ (setq c++-auto-hungry-initial-state 'none)
+ (setq c++-delete-function 'backward-delete-char)
+ (setq c++-tab-always-indent t)
+ (setq c-indent-level 4)
+ (setq c-continued-statement-offset 4)
+ (setq c++-empty-arglist-indent 4))
+
+(defun my-c-mode-hook ()
+ (setq tab-width 4)
+ (define-key c-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (define-key c-mode-map "\C-ce" 'c-comment-edit)
+ (setq c-auto-hungry-initial-state 'none)
+ (setq c-delete-function 'backward-delete-char)
+ (setq c-tab-always-indent t)
+;; BSD-ish indentation style
+ (setq c-indent-level 4)
+ (setq c-continued-statement-offset 4)
+ (setq c-brace-offset -4)
+ (setq c-argdecl-indent 0)
+ (setq c-label-offset -4))
+
+;; Perl mode
+(defun my-perl-mode-hook ()
+ (setq tab-width 4)
+ (define-key c++-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (setq perl-indent-level 4)
+ (setq perl-continued-statement-offset 4))
+
+;; Scheme mode...
+(defun my-scheme-mode-hook ()
+ (define-key scheme-mode-map "\C-m" 'reindent-then-newline-and-indent))
+
+;; Emacs-Lisp mode...
+(defun my-lisp-mode-hook ()
+ (define-key lisp-mode-map "\C-m" 'reindent-then-newline-and-indent)
+ (define-key lisp-mode-map "\C-i" 'lisp-indent-line)
+ (define-key lisp-mode-map "\C-j" 'eval-print-last-sexp))
+
+;; Add all of the hooks...
+(add-hook 'c++-mode-hook 'my-c++-mode-hook)
+(add-hook 'c-mode-hook 'my-c-mode-hook)
+(add-hook 'scheme-mode-hook 'my-scheme-mode-hook)
+(add-hook 'emacs-lisp-mode-hook 'my-lisp-mode-hook)
+(add-hook 'lisp-mode-hook 'my-lisp-mode-hook)
+(add-hook 'perl-mode-hook 'my-perl-mode-hook)
+
+;; Complement to next-error
+(defun previous-error (n)
+ "Visit previous compilation error message and corresponding source code."
+ (interactive "p")
+ (next-error (- n)))
+
+;; Misc...
+(transient-mark-mode 1)
+(setq mark-even-if-inactive t)
+(setq visible-bell nil)
+(setq next-line-add-newlines nil)
+(setq compile-command "make")
+(setq suggest-key-bindings nil)
+(put 'eval-expression 'disabled nil)
+(put 'narrow-to-region 'disabled nil)
+(put 'set-goal-column 'disabled nil)
+
+;; Elisp archive searching
+(autoload 'format-lisp-code-directory "lispdir" nil t)
+(autoload 'lisp-dir-apropos "lispdir" nil t)
+(autoload 'lisp-dir-retrieve "lispdir" nil t)
+(autoload 'lisp-dir-verify "lispdir" nil t)
+
+;; Font lock mode
+(defun my-make-face (face colour &optional bold)
+ "Create a face from a colour and optionally make it bold"
+ (make-face face)
+ (copy-face 'default face)
+ (set-face-foreground face colour)
+ (if bold (make-face-bold face))
+ )
+
+(if (eq window-system 'x)
+ (progn
+ (my-make-face 'blue "blue")
+ (my-make-face 'red "red")
+ (my-make-face 'green "dark green")
+ (setq font-lock-comment-face 'blue)
+ (setq font-lock-string-face 'bold)
+ (setq font-lock-type-face 'bold)
+ (setq font-lock-keyword-face 'bold)
+ (setq font-lock-function-name-face 'red)
+ (setq font-lock-doc-string-face 'green)
+ (add-hook 'find-file-hooks 'font-lock-auto-mode-select)
+
+ (setq baud-rate 1000000)
+ (global-set-key "\C-cmm" 'menu-bar-mode)
+ (global-set-key "\C-cms" 'scroll-bar-mode)
+ (global-set-key [backspace] 'backward-delete-char)
+ ; (global-set-key [delete] 'delete-char)
+ (standard-display-european t)
+ (load-library "iso-transl")))
+
+;; X11 or PC using direct screen writes
+(if window-system
+ (progn
+ ;; (global-set-key [M-f1] 'hilit-repaint-command)
+ ;; (global-set-key [M-f2] [?\C-u M-f1])
+ (setq hilit-mode-enable-list
+ '(not text-mode c-mode c++-mode emacs-lisp-mode lisp-mode
+ scheme-mode)
+ hilit-auto-highlight nil
+ hilit-auto-rehighlight 'visible
+ hilit-inhibit-hooks nil
+ hilit-inhibit-rebinding t)
+ (require 'hilit19)
+ (require 'paren))
+ (setq baud-rate 2400) ; For slow serial connections
+ )
+
+;; TTY type terminal
+(if (and (not window-system)
+ (not (equal system-type 'ms-dos)))
+ (progn
+ (if first-time
+ (progn
+ (keyboard-translate ?\C-h ?\C-?)
+ (keyboard-translate ?\C-? ?\C-h)))))
+
+;; Under UNIX
+(if (not (equal system-type 'ms-dos))
+ (progn
+ (if first-time
+ (server-start))))
+
+;; Add any face changes here
+(add-hook 'term-setup-hook 'my-term-setup-hook)
+(defun my-term-setup-hook ()
+ (if (eq window-system 'pc)
+ (progn
+;; (set-face-background 'default "red")
+ )))
+
+;; Restore the "desktop" - do this as late as possible
+(if first-time
+ (progn
+ (desktop-load-default)
+ (desktop-read)))
+
+;; Indicate that this file has been read at least once
+(setq first-time nil)
+
+;; No need to debug anything now
+(setq debug-on-error nil)
+
+;; All done
+(message "All done, %s%s" (user-login-name) ".")
+
+
+
+
+
+ Extending the Range of Languages Emacs Understands
+
+ Now, this is all very well if you only want to program in
+ the languages already catered for in the
+ .emacs file (C, C++, Perl, Lisp and
+ Scheme), but what happens if a new language called
+ whizbang comes out, full of exciting
+ features?
+
+ The first thing to do is find out if whizbang comes with
+ any files that tell Emacs about the language. These usually
+ end in .el, short for Emacs
+ Lisp. For example, if whizbang is a FreeBSD port, we
+ can locate these files by doing
+
+ &prompt.user; find /usr/ports/lang/whizbang -name "*.el" -print
+
+
+ and install them by copying them into the Emacs site Lisp
+ directory. On FreeBSD 2.1.0-RELEASE, this is
+ /usr/local/share/emacs/site-lisp.
+
+ So for example, if the output from the find command
+ was
+
+ /usr/ports/lang/whizbang/work/misc/whizbang.el
+
+
+ we would do
+
+ &prompt.root; cp /usr/ports/lang/whizbang/work/misc/whizbang.el /usr/local/share/emacs/site-lisp
+
+
+ Next, we need to decide what extension whizbang source
+ files have. Let's say for the sake of argument that they all
+ end in .wiz. We need to add an entry to
+ our .emacs file to make sure Emacs will
+ be able to use the information in
+ whizbang.el.
+
+ Find the auto-mode-alist entry in
+ .emacs and add a line for whizbang, such
+ as:
+
+ …
+("\\.lsp$" . lisp-mode)
+("\\.wiz$" . whizbang-mode)
+("\\.scm$" . scheme-mode)
+…
+
+
+ This means that Emacs will automatically go into
+ whizbang-mode when you edit a file ending
+ in .wiz.
+
+ Just below this, you'll find the
+ font-lock-auto-mode-list entry. Add
+ whizbang-mode to it like so:
+
+ ;; Auto font lock mode
+(defvar font-lock-auto-mode-list
+ (list 'c-mode 'c++-mode 'c++-c-mode 'emacs-lisp-mode 'whizbang-mode 'lisp-mode 'perl-mode 'scheme-mode)
+ "List of modes to always start in font-lock-mode")
+
+
+ This means that Emacs will always enable
+ font-lock-mode (ie syntax highlighting)
+ when editing a .wiz file.
+
+ And that's all that's needed. If there's anything else
+ you want done automatically when you open up a
+ .wiz file, you can add a
+ whizbang-mode hook (see
+ my-scheme-mode-hook for a simple example
+ that adds auto-indent).
+
+
+
+
+ Further Reading
+
+
+
+ Brian Harvey and Matthew Wright
+ Simply Scheme
+ MIT 1994.
+ ISBN 0-262-08226-8
+
+
+
+ Randall Schwartz
+ Learning Perl
+ O'Reilly 1993
+ ISBN 1-56592-042-2
+
+
+
+ Patrick Henry Winston and Berthold Klaus Paul Horn
+ Lisp (3rd Edition)
+ Addison-Wesley 1989
+ ISBN 0-201-08319-1
+
+
+
+ Brian W. Kernighan and Rob Pike
+ The Unix Programming Environment
+ Prentice-Hall 1984
+ ISBN 0-13-937681-X
+
+
+
+ Brian W. Kernighan and Dennis M. Ritchie
+ The C Programming Language (2nd Edition)
+ Prentice-Hall 1988
+ ISBN 0-13-110362-8
+
+
+
+ Bjarne Stroustrup
+ The C++ Programming Language
+ Addison-Wesley 1991
+ ISBN 0-201-53992-6
+
+
+
+ W. Richard Stevens
+ Advanced Programming in the Unix Environment
+ Addison-Wesley 1992
+ ISBN 0-201-56317-7
+
+
+
+ W. Richard Stevens
+ Unix Network Programming
+ Prentice-Hall 1990
+ ISBN 0-13-949876-1
+
+
+
- Secure ProgrammingThis chapter was written by Murray Stokely.SynopsisThis chapter describes some of the security issues that
have plagued Unix programmers for decades and some of the new
tools available to help programmers avoid writing exploitable
code.Secure Design
MethodologyWriting secure applications takes a very scrutinous and
pessimistic outlook on life. Applications should be run with
the principle of least privilege so that no
process is ever running than more with the bare minimum access
that it needs to accomplish its function. Previously tested
code should be reused whenever possible to avoid common
mistakes that others may have already fixed.One of the pitfalls of the Unix environment is how easy it
is to make assumptions about the sanity of the environment.
Applications should never trust user input (in all its forms),
system resources, inter-process communication, or the timing of
events. Unix processes do not execute synchronously so logical
operations are rarely atomic.Buffer OverflowsBuffer Overflows have been around since the very
beginnings of the Von-Neuman architecture.
They first gained widespread notoriety in 1988 with the Moorse
Internet worm. Unfortunately, the same basic attack remains
effective today. Of the 17 CERT security advisories of 1999, 10
of them were directly caused by buffer-overflow software bugs.
By far the most common type of buffer overflow attack is based
on corrupting the stack.Most modern computer systems use a stack to pass arguments
to procedures and to store local variables. A stack is a last
in first out (LIFO) buffer in the high memory area of a process
image. When a program invokes a function a new "stack frame" is
created. This stack frame consists of the arguments passed to
the function as well as a dynamic amount of local variable
space. The "stack pointer" is a register that holds the current
location of the top of the stack. Since this value is
constantly changing as new values are pushed onto the top of the
stack, many implementations also provide a "frame pointer" that
is located near the beginning of a stack frame so that local
variables can more easily be addressed relative to this
value. The return address for function
calls is also stored on the stack, and this is the cause of
stack-overflow exploits since overflowing a local variable in a
function can overwrite the return address of that function,
potentially allowing a malicious user to execute any code he or
she wants.Although stack-based attacks are by far the most common,
it would also be possible to overrun the stack with a heap-based
(malloc/free) attack.The C programming language does not perform automatic
bounds checking on arrays or pointers as many other languages
do. In addition, the standard C library is filled with a
handful of very dangerous functions.strcpy(char *dest, const char
*src)May overflow the dest bufferstrcat(char *dest, const char
*src)May overflow the dest buffergetwd(char *buf)May overflow the buf buffergets(char *s)May overflow the s buffer[vf]scanf(const char *format,
...)May overflow its arguments.realpath(char *path, char
resolved_path[])May overflow the path buffer[v]sprintf(char *str, const char
*format, ...)May overflow the str buffer.Example Buffer OverflowThe following example code contains a buffer overflow
designed to overwrite the return address and skip the
instruction immediately following the function call. (Inspired
by )
#include stdio.h
void manipulate(char *buffer) {
char newbuffer[80];
strcpy(newbuffer,buffer);
}
int main() {
char ch,buffer[4096];
int i=0;
while ((buffer[i++] = getchar()) != '\n') {};
i=1;
manipulate(buffer);
i=2;
printf("The value of i is : %d\n",i);
return 0;
}
Let us examine what the memory image of this process would
look like if we were to input 160 spaces into our little program
before hitting return.[XXX figure here!]Obviously more malicious input can be devised to execute
actual compiled instructions (such as exec(/bin/sh)).Avoiding Buffer OverflowsThe most straightforward solution to the problem of
stack-overflows is to always use length restricted memory and
string copy functions. strncpy and
strncat are part of the standard C library.
These functions accept a length value as a parameter which
should be no larger than the size of the destination buffer.
These functions will then copy up to `length' bytes from the
source to the destination. However there are a number of
problems with these functions. Neither function guarantees NUL
termination if the size of the input buffer is as large as the
destination. The length parameter is also used inconsistently
between strncpy and strncat so it is easy for programmers to get
confused as to their proper usage. There is also a significant
performance loss compared to strcpy when
copying a short string into a large buffer since
strncpy NUL fills up the the size
specified.In OpenBSD, another memory copy implementation has been
created to get around these problem. The
strlcpy and strlcat
functions guarantee that they will always null terminate the
destination string when given a non-zero length argument. For
more information about these functions see . The OpenBSD strlcpy and
strlcat instructions have been in FreeBSD
since 3.5.Compiler based run-time bounds checkingUnfortunately there is still a very large assortment of
code in public use which blindly copies memory around without
using any of the bounded copy routines we just discussed.
Fortunately, there is another solution. Several compiler
add-ons and libraries exist to do Run-time bounds checking in
C/C++.StackGuard is one such add-on that is implemented as a
small patch to the gcc code generator. From the StackGuard
website, http://immunix.org/stackguard.html :
"StackGuard detects and defeats stack
smashing attacks by protecting the return address on the stack
from being altered. StackGuard places a "canary" word next to
the return address when a function is called. If the canary
word has been altered when the function returns, then a stack
smashing attack has been attempted, and the program responds
by emitting an intruder alert into syslog, and then
halts."
"StackGuard is implemented as a small patch
to the gcc code generator, specifically the function_prolog()
and function_epilog() routines. function_prolog() has been
enhanced to lay down canaries on the stack when functions
start, and function_epilog() checks canary integrity when the
function exits. Any attempt at corrupting the return address
is thus detected before the function
returns."
Recompiling your application with StackGuard is an
effective means of stopping most buffer-overflow attacks, but
it can still be compromised.Library based run-time bounds checkingCompiler-based mechanisms are completely useless for
binary-only software for which you cannot recompile. For
these situations there are a number of libraries which
re-implement the unsafe functions of the C-library
(strcpy, fscanf,
getwd, etc..) and ensure that these
functions can never write past the stack pointer.libsafelibverifylibparnoiaUnfortunately these library-based defenses have a number
of shortcomings. These libraries only protect against a very
small set of security related issues and they neglect to fix
the actual problem. These defenses may fail if the
application was compiled with -fomit-frame-pointer. Also, the
LD_PRELOAD and LD_LIBRARY_PATH environment variables can be
overwritten/unset by the user.SetUID issuesThere are at least 6 different IDs associated with any
given process. Because of this you have to be very careful with
the access that your process has at any given time. In
particular, all seteuid applications should give up their
privileges as soon as it is no longer required.The real user ID can only be changed by a superuser
process. The login program sets this
when a user initially logs in and it is seldom changed.The effective user ID is set by the
exec() functions if a program has its
seteuid bit set. An application can call
seteuid() at any time to set the effective
user ID to either the real user ID or the saved set-user-ID.
When the effective user ID is set by exec()
functions, the previous value is saved in the saved set-user-ID.Limiting your program's environmentThe traditional method of restricting access to a process
is with the chroot() system call. This
system call changes the root directory from which all other
paths are referenced for a process and any child processes. For
this call to succeed the process must have execute (search)
permission on the directory being referenced. The new
environment does not actually take affect until you
chdir() into your new environment. It
should also be noted that a process can easily break out of a
chroot environment if it has root privilege. This could be
accomplished by creating device nodes to read kernel memory,
attaching a debugger to a process outside of the jail, or in
many other creative ways.The behavior of the chroot() system
call can be controlled somewhat with the
kern.chroot_allow_open_directories sysctl
variable. When this value is set to 0,
chroot() will fail with EPERM if there are
any directories open. If set to the default value of 1, then
chroot() will fail with EPERM if there are
any directories open and the process is already subject to a
chroot() call. For any other value, the
check for open directories will be bypassed completely.FreeBSD's jail functionalityThe concept of a Jail extends upon the
chroot() by limiting the powers of the
superuser to create a true `virtual server'. Once a prison is
setup all network communication must take place through the
specified IP address, and the power of "root privilege" in this
jail is severely constrained.While in a prison, any tests of superuser power within the
kernel using the suser() call will fail.
However, some calls to suser() have been
changed to a new interface suser_xxx().
This function is responsible for recognizing or denying access
to superuser power for imprisoned processes.A superuser process within a jailed environment has the
power to : Manipulate credential with
setuid, seteuid,
setgid, setegid,
setgroups, setreuid,
setregid, setloginSet resource limits with setrlimitModify some sysctl nodes
(kern.hostname)chroot()Set flags on a vnode:
chflags,
fchflagsSet attributes of a vnode such as file
permission, owner, group, size, access time, and modification
time.Bind to privileged ports in the Internet
domain (ports < 1024)Jail is a very useful tool for
running applications in a secure environment but it does have
some shortcomings. Currently, the IPC mechanisms have not been
converted to the suser_xxx so applications
such as MySQL can not be run within a jail. Superuser access
may have a very limited meaning within a jail, but there is
no way to specify exactly what "very limited" means.POSIX.1e Process CapabilitiesPosix has released a working draft that adds event
auditing, access control lists, fine grained privileges,
information labeling, and mandatory access control.This is a work in progress and is the focus of the TrustedBSD project. Some
of the initial work has been committed to FreeBSD-current
(cap_set_proc(3)).TrustAn application should never assume that anything about the
users environment is sane. This includes (but is certainly not
limited to) : user input, signals, environment variables,
resources, IPC, mmaps, the file system working directory, file
descriptors, the # of open files, etc.You should never assume that you can catch all forms of
invalid input that a user might supply. Instead, your
application should use positive filtering to only allow a
specific subset of inputs that you deem safe. Improper data
validation has been the cause of many exploits, especially with
CGI scripts on the world wide web. For filenames you need to be
extra careful about paths ("../", "/"), symbolic links, and
shell escape characters.Perl has a really cool feature called "Taint" mode which
can be used to prevent scripts for using data derived outside
the program in an unsafe way. This mode will check command line
arguments, environment variables, locale information, the
results of certain syscalls (readdir(),
readlink(),
getpwxxx(), and all file input.Race ConditionsA race condition is anomalous behavior caused by the
unexpected dependence on the relative timing of events. In
other words, a programmer incorrectly assumed that a particular
event would always happen before another.Some of the common causes of race conditions are signals,
access checks, and file opens. Signals are asynchronous events
by nature so special care must be taken in dealing with them.
Checking access with access(2) then
open(2) is clearly non-atomic. Users can
move files in between the two calls. Instead, privileged
applications should seteuid() and then call
open() directly. Along the same lines, an
application should always set a proper umask before
open() to obviate the need for spurious
chmod() calls.KernelHistory of the Unix KernelSome history of the Unix/BSD kernel, system calls, how do
processes work, blocking, scheduling, threads (kernel),
context switching, signals, interrupts, modules, etc.Memory and Virtual MemoryVirtual MemoryVM, paging, swapping, allocating memory, testing for
memory leaks, mmap, vnodes, etc.I/O SystemUFSUFS, FFS, Ext2FS, JFS, inodes, buffer cache, labeling,
locking, metadata, soft-updates, LFS, portalfs, procfs,
vnodes, memory sharing, memory objects, TLBs, cachingInterprocess CommunicationSignalsSignals, pipes, semaphores, message queues, shared memory,
ports, sockets, doorsNetworkingSocketsSockets, bpf, IP, TCP, UDP, ICMP, OSI, bridging,
firewalling, NAT, switching, etcNetwork FilesystemsAFSAFS, NFS, SANs etc]Terminal HandlingSysconsSyscons, tty, PCVT, serial console, screen savers,
etcSoundOSSOSS, waveforms, etcDevice DriversWriting FreeBSD Device DriversThis chapter was written by Murray Stokely with selections from
a variety of sources including the intro(4) man page by Joerg
Wunsch.Introduction
This chapter provides a brief introduction to writing device
drivers for FreeBSD. A device in this context is a term used
mostly for hardware-related stuff that belongs to the system,
like disks, printers, or a graphics display with its keyboard.
A device driver is the software component of the operating
system that controls a specific device. There are also
so-called pseudo-devices where a device driver emulates the
behaviour of a device in software without any particular
underlying hardware. Device drivers can be compiled into the
system statically or loaded on demand through the dynamic
kernel linker facility `kld'.Most devices in a Unix-like operating system are
accessed through device-nodes, sometimes also called special
files. These files are usually located under the directory
/dev in the file system hierarchy. Until
devfs is fully integrated into FreeBSD, each device node must
be created statically and independent of the existence of the
associated device driver. Most device nodes on the system are
created by running MAKEDEV.Device drivers can roughly be broken down into three
categories; character (unbuffered), block (buffered), and
network drivers.Dynamic Kernel Linker Facility - KLDThe kld interface allows system administrators to
dynamically add and remove functionality from a running
system. This allows device driver writers to load their new
changes into a running kernel without constantly rebooting to
test changes.The kld interface is used through the following
administrator commands :
kldload - loads a new kernel
modulekldunload - unloads a kernel
modulekldstat - lists the currently loadded
modulesSkeleton Layout of a kernel module
/*
* KLD Skeleton
* Inspired by Andrew Reiter's Daemonnews article
*/
#include <sys/types.h>
#include <sys/module.h>
#include <sys/systm.h> /* uprintf */
#include <sys/errno.h>
#include <sys/param.h> /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
/*
* Load handler that deals with the loading and unloading of a KLD.
*/
static int
skel_loader(struct module *m, int what, void *arg)
{
int err = 0;
switch (what) {
case MOD_LOAD: /* kldload */
uprintf("Skeleton KLD loaded.\n");
break;
case MOD_UNLOAD:
uprintf("Skeleton KLD unloaded.\n");
break;
default:
err = EINVAL;
break;
}
return(err);
}
/* Declare this module to the rest of the kernel */
DECLARE_MODULE(skeleton, skel_loader, SI_SUB_KLD, SI_ORDER_ANY);
MakefileFreeBSD provides a makefile include that you can use
to quickly compile your kernel addition.
SRCS=skeleton.c
KMOD=skeleton
.include <bsd.kmod.mk>
Simply running make with
this makefile will create a file
skeleton.ko that can be loaded into
your system by typing :
&prompt.root kldload -v ./skeleton.ko
Accessing a device driverUnix provides a common set of system calls for user
applications to use. The upper layers of the kernel dispatch
these calls to the corresponding device driver when a user
accesses a device node. The /dev/MAKEDEV
script makes most of the device nodes for your system but if
you are doing your own driver development it may be necessary
to create your own device nodes with mknodCreating static device nodesThe mknod command requires four
arguments to create a device node. You must specify the
name of this device node, the type of device, the major number
of the device, and the minor number of the device.Dynamic device nodesThe device filesystem, or devfs, provides access to the
kernel's device namespace in the global filesystem namespace.
This eliminates the problems of potentially having a device
driver without a static device node, or a device node without
an installed device driver. Unfortunately, devfs is still a
work in progress.Character DevicesA character device driver is one that transfers data
directly to and from a user process. This is the most common
type of device driver and there are plenty of simple examples
in the source tree.This simple example pseudo-device remembers whatever values you write
to it and can then supply them back to you when you read from
it.
/*
* Simple `echo' pseudo-device KLD
*
* Murray Stokely
*/
#define MIN(a,b) (((a) < (b)) ? (a) : (b))
#include <sys/types.h>
#include <sys/module.h>
#include <sys/systm.h> /* uprintf */
#include <sys/errno.h>
#include <sys/param.h> /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
#include <sys/conf.h> /* cdevsw struct */
#include <sys/uio.h> /* uio struct */
#include <sys/malloc.h>
#define BUFFERSIZE 256
/* Function prototypes */
d_open_t echo_open;
d_close_t echo_close;
d_read_t echo_read;
d_write_t echo_write;
/* Character device entry points */
static struct cdevsw echo_cdevsw = {
echo_open,
echo_close,
echo_read,
echo_write,
noioctl,
nopoll,
nommap,
nostrategy,
"echo",
33, /* reserved for lkms - /usr/src/sys/conf/majors */
nodump,
nopsize,
D_TTY,
-1
};
typedef struct s_echo {
char msg[BUFFERSIZE];
int len;
} t_echo;
/* vars */
static dev_t sdev;
static int len;
static int count;
static t_echo *echomsg;
MALLOC_DECLARE(M_ECHOBUF);
MALLOC_DEFINE(M_ECHOBUF, "echobuffer", "buffer for echo module");
/*
* This function acts is called by the kld[un]load(2) system calls to
* determine what actions to take when a module is loaded or unloaded.
*/
static int
echo_loader(struct module *m, int what, void *arg)
{
int err = 0;
switch (what) {
case MOD_LOAD: /* kldload */
sdev = make_dev(&echo_cdevsw,
0,
UID_ROOT,
GID_WHEEL,
0600,
"echo");
/* kmalloc memory for use by this driver */
/* malloc(256,M_ECHOBUF,M_WAITOK); */
MALLOC(echomsg, t_echo *, sizeof(t_echo), M_ECHOBUF, M_WAITOK);
printf("Echo device loaded.\n");
break;
case MOD_UNLOAD:
destroy_dev(sdev);
FREE(echomsg,M_ECHOBUF);
printf("Echo device unloaded.\n");
break;
default:
err = EINVAL;
break;
}
return(err);
}
int
echo_open(dev_t dev, int oflags, int devtype, struct proc *p)
{
int err = 0;
uprintf("Opened device \"echo\" successfully.\n");
return(err);
}
int
echo_close(dev_t dev, int fflag, int devtype, struct proc *p)
{
uprintf("Closing device \"echo.\"\n");
return(0);
}
/*
* The read function just takes the buf that was saved via
* echo_write() and returns it to userland for accessing.
* uio(9)
*/
int
echo_read(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
int amt;
/* How big is this read operation? Either as big as the user wants,
or as big as the remaining data */
amt = MIN(uio->uio_resid, (echomsg->len - uio->uio_offset > 0) ? echomsg->len - uio->uio_offset : 0);
if ((err = uiomove(echomsg->msg + uio->uio_offset,amt,uio)) != 0) {
uprintf("uiomove failed!\n");
}
return err;
}
/*
* echo_write takes in a character string and saves it
* to buf for later accessing.
*/
int
echo_write(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
/* Copy the string in from user memory to kernel memory */
err = copyin(uio->uio_iov->iov_base, echomsg->msg, MIN(uio->uio_iov->iov_len,BUFFERSIZE));
/* Now we need to null terminate */
*(echomsg->msg + MIN(uio->uio_iov->iov_len,BUFFERSIZE)) = 0;
/* Record the length */
echomsg->len = MIN(uio->uio_iov->iov_len,BUFFERSIZE);
if (err != 0) {
uprintf("Write failed: bad address!\n");
}
count++;
return(err);
}
DEV_MODULE(echo,echo_loader,NULL);
To install this driver you will first need to make a node on
your filesystem with a command such as :
&prompt.root mknod /dev/echo c 33 0
With this driver loaded you should now be able to type something
like :
&prompt.root echo -n "Test Data" > /dev/echo
&prompt.root cat /dev/echo
Test Data
Real hardware devices in the next chapter..Additional Resources
Dynamic
Kernel Linker (KLD) Facility Programming Tutorial -
Daemonnews October 2000How
to Write Kernel Drivers with NEWBUS - Daemonnews July
2000Block DevicesA block device driver transfers data to and from the
operating system's buffer cache. They are solely intended to
layer a file system on top of them. For this reason they are
normally implemented for disks and disk-like devices only.Example test data generator ... Example ramdisk device ... Real hardware devices in the next chapter..Network DriversDrivers for network devices do not use device nodes in
ord to be accessed. Their selection is based on other
decisions made inside the kernel and instead of calling
open(), use of a network device is generally introduced by
using the system call socket(2).man ifnet(), loopback device, Bill Pauls drivers, etc..PCI DevicesThis chapter will talk about the FreeBSD mechanisms for
writing a device driver for a device on a PCI bus.Probe and AttachInformation here about how the PCI bus code iterates
through the unattached devices and see if a newly loaded kld
will attach to any of them.
/*
* Simple KLD to play with the PCI functions.
*
* Murray Stokely
*/
#define MIN(a,b) (((a) < (b)) ? (a) : (b))
#include <sys/types.h>
#include <sys/module.h>
#include <sys/systm.h> /* uprintf */
#include <sys/errno.h>
#include <sys/param.h> /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
#include <sys/conf.h> /* cdevsw struct */
#include <sys/uio.h> /* uio struct */
#include <sys/malloc.h>
#include <sys/bus.h> /* structs, prototypes for pci bus stuff */
#include <pci/pcivar.h> /* For get_pci macros! */
/* Function prototypes */
d_open_t mypci_open;
d_close_t mypci_close;
d_read_t mypci_read;
d_write_t mypci_write;
/* Character device entry points */
static struct cdevsw mypci_cdevsw = {
mypci_open,
mypci_close,
mypci_read,
mypci_write,
noioctl,
nopoll,
nommap,
nostrategy,
"mypci",
36, /* reserved for lkms - /usr/src/sys/conf/majors */
nodump,
nopsize,
D_TTY,
-1
};
/* vars */
static dev_t sdev;
/* We're more interested in probe/attach than with
open/close/read/write at this point */
int
mypci_open(dev_t dev, int oflags, int devtype, struct proc *p)
{
int err = 0;
uprintf("Opened device \"mypci\" successfully.\n");
return(err);
}
int
mypci_close(dev_t dev, int fflag, int devtype, struct proc *p)
{
int err=0;
uprintf("Closing device \"mypci.\"\n");
return(err);
}
int
mypci_read(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
uprintf("mypci read!\n");
return err;
}
int
mypci_write(dev_t dev, struct uio *uio, int ioflag)
{
int err = 0;
uprintf("mypci write!\n");
return(err);
}
/* PCI Support Functions */
/*
* Return identification string if this is device is ours.
*/
static int
mypci_probe(device_t dev)
{
uprintf("MyPCI Probe\n"
"Vendor ID : 0x%x\n"
"Device ID : 0x%x\n",pci_get_vendor(dev),pci_get_device(dev));
if (pci_get_vendor(dev) == 0x11c1) {
uprintf("We've got the Winmodem, probe successful!\n");
return 0;
}
return ENXIO;
}
/* Attach function is only called if the probe is successful */
static int
mypci_attach(device_t dev)
{
uprintf("MyPCI Attach for : deviceID : 0x%x\n",pci_get_vendor(dev));
sdev = make_dev(&mypci_cdevsw,
0,
UID_ROOT,
GID_WHEEL,
0600,
"mypci");
uprintf("Mypci device loaded.\n");
return ENXIO;
}
/* Detach device. */
static int
mypci_detach(device_t dev)
{
uprintf("Mypci detach!\n");
return 0;
}
/* Called during system shutdown after sync. */
static int
mypci_shutdown(device_t dev)
{
uprintf("Mypci shutdown!\n");
return 0;
}
/*
* Device suspend routine.
*/
static int
mypci_suspend(device_t dev)
{
uprintf("Mypci suspend!\n");
return 0;
}
/*
* Device resume routine.
*/
static int
mypci_resume(device_t dev)
{
uprintf("Mypci resume!\n");
return 0;
}
static device_method_t mypci_methods[] = {
/* Device interface */
DEVMETHOD(device_probe, mypci_probe),
DEVMETHOD(device_attach, mypci_attach),
DEVMETHOD(device_detach, mypci_detach),
DEVMETHOD(device_shutdown, mypci_shutdown),
DEVMETHOD(device_suspend, mypci_suspend),
DEVMETHOD(device_resume, mypci_resume),
{ 0, 0 }
};
static driver_t mypci_driver = {
"mypci",
mypci_methods,
0,
/* sizeof(struct mypci_softc), */
};
static devclass_t mypci_devclass;
DRIVER_MODULE(mypci, pci, mypci_driver, mypci_devclass, 0, 0);
Additional Resources
PCI Special Interest
GroupPCI System Architecture, Fourth Edition by
Tom Shanley, et al.USB DevicesThis chapter will talk about the FreeBSD mechanisms for
writing a device driver for a device on a USB bus.NewBusThis chapter will talk about the FreeBSD NewBus
architecture.ArchitecturesIA-32Talk about the architectural specifics of FreeBSD/x86.AlphaTalk about the architectural specifics of
FreeBSD/alpha.Explanation of allignment errors, how to fix, how to
ignore.Example assembly language code for FreeBSD/alpha.IA-64Talk about the architectural specifics of
FreeBSD/ia64.
-
+ DebuggingTrussvarious descriptions on how to debug certain aspects of
the system using truss, ktrace, gdb, kgdb, etcCompatibility LayersLinuxLinux, SVR4, etcAppendicesDaveAPattersonJohnLHennessy1998Morgan Kaufmann Publishers,
Inc.1-55860-428-6Morgan Kaufmann Publishers, Inc.Computer Organization and DesignThe Hardware / Software Interface1-2W.RichardStevens1993Addison Wesley Longman,
Inc.0-201-56317-7Addison Wesley Longman, Inc.Advanced Programming in the Unix Environment1-2MarshallKirkMcKusickKeithBosticMichaelJKarelsJohnSQuarterman1996Addison-Wesley Publishing Company,
Inc.0-201-54979-4Addison-Wesley Publishing Company, Inc.The Design and Implementation of the 4.4 BSD Operating System1-2AlephOnePhrack 49; "Smashing the Stack for Fun and Profit"ChrispinCowanCaltonPuDaveMaierStackGuard; Automatic Adaptive Detection and Prevention of
Buffer-Overflow AttacksToddMillerTheode Raadtstrlcpy and strlcat -- consistent, safe string copy and
concatenation.