Emit an error when we seen absolute paths to .o files

[arichardson]

Summary

This is usually an error caused by using an absolute path in SRCS. This
happened to me in 83c20b8a2da0 due to changing LDADD to SRCS.
I did not notice that this had created a .o file inside the source tree
since .gitignore contains "*.o" and therefore git did not report any
changes.

Adding this warning message to bsd.lib.mk/bsd.prog.mk should prevent
issues like this in the future.

There is one case of an absolute OBJS path in the current source tree
which I have tagged as such using _ABSOLUTE_PATH_OBJS.

[arichardson]

Example warning message:

+ make -C tests/sys/kern all -j36
make[3]: "/local/scratch/alr48/cheri/freebsd/share/mk/bsd.prog.mk" line 147: warning: "Found absolute path to .o file, this will almost certainly break the build with a read-only source directory: /local/scratch/alr48/cheri/freebsd/sys/libkern/arm64/crc32c_armv8.o"

[emaste]

IMO we don't need the extra commentary - e.g. maybe just "\$OBJS absolute path not allowed: ${OBJS:M/*}"

[arichardson]

• shorten message
• make it an error below ${SRCTOP}

[emaste]

I think this is fine, we can adjust later if necessary (in case of unexpected consequences)

[arichardson]

Turns out this is triggered by loader:

===> stand/i386/loader_4th (includes)
make[5]: "/home/alr48/devel/freebsd/src/share/mk/bsd.prog.mk" line 151: warning: "$OBJS absolute path not allowed: /home/alr48/obj/freebsd/home/alr48/devel/freebsd/src/amd64.amd64/stand/i386/btx/lib/crt0.o"
===> stand/i386/loader_lua (includes)
make[5]: "/home/alr48/devel/freebsd/src/share/mk/bsd.prog.mk" line 151: warning: "$OBJS absolute path not allowed: /home/alr48/obj/freebsd/home/alr48/devel/freebsd/src/amd64.amd64/stand/i386/btx/lib/crt0.o"
===> stand/i386/loader_simp (includes)
make[5]: "/home/alr48/devel/freebsd/src/share/mk/bsd.prog.mk" line 151: warning: "$OBJS absolute path not allowed: /home/alr48/obj/freebsd/home/alr48/devel/freebsd/src/amd64.amd64/stand/i386/btx/lib/crt0.o"

This is fine since it's inside the OBJDIR, so we probably need a way to silence it? Ignore it if it starts with OBJTOP/.OBJDIR?

# XXX crt0.o needs to be first for pxeboot(8) to work
OBJS=	${BTXCRT}

[arichardson]

fix error message

[sjg]

share/mk/bsd.lib.mk

262

What about folk who insist on dribbling .o's in src tree?
I may have little sympathy for them, but ...

share/mk/bsd.prog.mk

145

There are several .includes shared by bsd.lib.mk and bsd.prog.mk - why not put this in one place rather. than duplictae?

[arichardson]

share/mk/bsd.prog.mk

145

That would indeed be much better. However, I'm not sure which file would be suitable for this. Could you suggest one?

[arichardson]

share/mk/bsd.lib.mk

262

I could add a hidden variable such as _ALLOW_OBJS_IN_SRC to avoid this .error/.warning?

[arichardson]

• Move to shared file
• add opt-out mechanism
• Use it to fix loader build

[arichardson]

With the latest version I get the following error :

bmake[5]: "/Users/alex/cheri/freebsd/share/mk/bsd.dep.mk" line 203: "$OBJS absolute path not allowed: /Users/alex/cheri/build/freebsd-amd64-build/Users/alex/cheri/freebsd/amd64.amd64/stand/i386/btx/lib/crt0.o.  If this is intended, add them to _ABSOLUTE_PATH_OBJS to silence this error or define _ALLOW_ABSOLUTE_OBJ_PATH to disable this diagnostic."
bmake[5]: stopped in /Users/alex/cheri/freebsd/stand/i386/loader_4th

To avoid this I changed loader/Makefile.

[imp]

In D28467#637141, @arichardson wrote:

Turns out this is triggered by loader:

===> stand/i386/loader_4th (includes)
make[5]: "/home/alr48/devel/freebsd/src/share/mk/bsd.prog.mk" line 151: warning: "$OBJS absolute path not allowed: /home/alr48/obj/freebsd/home/alr48/devel/freebsd/src/amd64.amd64/stand/i386/btx/lib/crt0.o"
===> stand/i386/loader_lua (includes)
make[5]: "/home/alr48/devel/freebsd/src/share/mk/bsd.prog.mk" line 151: warning: "$OBJS absolute path not allowed: /home/alr48/obj/freebsd/home/alr48/devel/freebsd/src/amd64.amd64/stand/i386/btx/lib/crt0.o"
===> stand/i386/loader_simp (includes)
make[5]: "/home/alr48/devel/freebsd/src/share/mk/bsd.prog.mk" line 151: warning: "$OBJS absolute path not allowed: /home/alr48/obj/freebsd/home/alr48/devel/freebsd/src/amd64.amd64/stand/i386/btx/lib/crt0.o"

This is fine since it's inside the OBJDIR, so we probably need a way to silence it? Ignore it if it starts with OBJTOP/.OBJDIR?

# XXX crt0.o needs to be first for pxeboot(8) to work
OBJS=	${BTXCRT}

I'm surprised this isn't more pervasive... I'd prefer if we suppressed the warning if it starts with OBJTOP.

[arichardson]

Rebased. The only time this was triggered in-tree has been fixed by e713d3a013882893fceb84dd14569052271497a9

[imp]

Given the additional testing reported, I think this is good...