Stop using lorder and ranlib when building libraries


Stop using lorder and ranlib when building libraries

Use of ranlib or lorder is no longer necessary with current linkers
(probably anything newer than ~1990) and ar's ability to create an object
index and symbol table in the archive.
Currently the build system uses lorder+tsort to sort the .o files in
dependency order so that a single-pass linker can use them. However,
we can use the -s flag to ar to add an index to the .a file which makes
lorder unnecessary.
Running ar -s is equivalent to running ranlib afterwards, so we can also
skip the ranlib invocation.

Similarly, we don't have to pass the .o files for shared libraries in
dependency order since both ld.bfd and ld.lld will correctly resolve
references between the .o files.

This removes many fork()+execve calls for each library so should speed up
builds a bit. Additionally lorder.sh uses a regular expression that is not
supported by the macOS libc or glibc and results in many warnings when
cross-building (see D25989).

There is one functional change: lorder.sh removed duplicated .o files
from the linker command line which now no longer happens. I fixed the duplicates
in the base system in r364649. I also checked the ports tree for uses of
bsd.lib.mk and found one duplicate source file which I fixed in r548168.
Most ports use CMake/autotools rather than bsd.lib.mk but if this breaks any
ports that I missed in my search please let me know.

Avoiding the shell script actually speeds up the linking step noticeably: I
measured how long it takes to rebuild the .a and .so files for lib/libc using a
basic benchmark: rm $LIBC_OBJDIR/*.so* $LIBC_OBJDIR/*.a* && /usr/bin/time make -DWITHOUT_TESTS -s > /dev/null
Without this change ~4.5 seconds and afterwards ~3.1 seconds.
Looking at truss -cf output we can see that the number fork() system
calls goes down from 27 to 12 (and the speedup while tracing is more
noticeable: 81 seconds -> 65 seconds).

See also https://www.gnu.org/software/coreutils/manual/html_node/tsort-background.html
for some more background:
This whole procedure has been obsolete since about 1980, because Unix
archives now contain a symbol table (traditionally built by ranlib, now
generally built by ar itself), and the Unix linker uses the symbol table
to effectively make multiple passes over an archive file.

Or alternatively https://www.unix.com/man-page/osf1/1/lorder/:
The lorder command is essentially obsolete. Use the following command in
its place: % ar -ts file.a

Reviewed By: emaste, imp, dim
Differential Revision: https://reviews.freebsd.org/D26044


arichardsonAuthored on
Differential Revision
D26044: Stop using lorder and ranlib when building libraries
rS365835: Add dtb/sifive module