Use relative object directories where possible.

[bdrewery]

Summary

Make generally runs from the .OBJDIR, so using relative paths improves
namecache lookups.

This can be disabled in /etc/src-env.conf with:

RELOBJTOP= ${OBJTOP}
RELSRCTOP= ${SRCTOP}

Sponsored by: Dell EMC Isilon

This uses RELOBJTOP added in rS325190

Test Plan

Ran buildworld, installworld, buildkernel, installkernel, DIRDEPS_BUILD

[ngie]

I'm fine with this change. It's pretty straightforward.

gnu/usr.bin/cc/Makefile.inc

78–79

This part of the change seems incorrect (or partial, at the very least) given the conditional on line 78.

[bdrewery]

gnu/usr.bin/cc/Makefile.inc

78–79

exists does funny things. If not given ${.OBJDIR} it goes searching in ${.CURDIR} too... really all of .PATH:

exists   Takes a file name as an argument and evaluates to true if the file exists.  The file is searched for on the system search path (see .PATH).

I tried exists(../cc_tools) and exists(./../cc_tools) without having the directory really there (but the .OBJDIR existed for cc/cpp) and got this output:

~/git/freebsd/gnu/usr.bin/cc/cpp # make -V '${CFLAGS:M*cc_tools*}'
-I../cc_tools -I/root/git/freebsd/gnu/usr.bin/cc/cpp/../cc_tools

Only if I used exists(${.OBJDIR}/../cc_tools) did it do the right thing.
Without dir present:

~/git/freebsd/gnu/usr.bin/cc/cpp # make -V '${CFLAGS:M*cc_tools*}'
-I/root/git/freebsd/gnu/usr.bin/cc/cpp/../cc_tools

With dir present:

~/git/freebsd/gnu/usr.bin/cc/cpp # make -V '${CFLAGS:M*cc_tools*}'
-I../cc_tools -I/root/git/freebsd/gnu/usr.bin/cc/cpp/../cc_tools

[dim]

Hmm, I rather liked the absolute paths that ${.OBJDIR} and ${OBJTOP} introduced. I find relative path output during builds a bit obfuscating. How much performance gain does this change deliver, in exchange for more obscurity?

[bdrewery]

In D12839#266680, @dim wrote:

Hmm, I rather liked the absolute paths that ${.OBJDIR} and ${OBJTOP} introduced. I find relative path output during builds a bit obfuscating. How much performance gain does this change deliver, in exchange for more obscurity?

I can do some measurements. I could compromise and only enable this for META_MODE since it records all files that are touched and the CWD in the meta file. That makes debugging feasible.