Differential D2039

Add LIB_CXX so that c++ libraries will use CXX to link.
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Authored by bdrewery on Mar 10 2015, 7:18 PM.

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bapt
imp

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rS280179: Add LIB_CXX so that C++ libraries will use CXX to link.

Summary

This fixes c++ libraries not implicitly linking in libc++. This is
generally not an issue because the final linking with the compiled binary
will involve CXX via PROG_CXX or other means. It is however
inconsistent with libraries implicitly linking in libc and problematic
for trying to build libraries with '-z defs' to ensure all direct
dependencies are linked in.

libatf-c++ is currently the only consumer of this new feature. Its
before and after direct-linkage is shown below:

Before:
/usr/lib/private/libatf-c++.so.2:

libatf-c.so.1 => /usr/lib/private/libatf-c.so.1 (0x80161e000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x801835000)
libc.so.7 => /lib/libc.so.7 (0x800822000)

After:
/usr/lib/private/libatf-c++.so.2:

libatf-c.so.1 => /usr/lib/private/libatf-c.so.1 (0x80161e000)
libc++.so.1 => /usr/lib/libc++.so.1 (0x801835000)
libcxxrt.so.1 => /lib/libcxxrt.so.1 (0x801af5000)
libm.so.5 => /lib/libm.so.5 (0x801d13000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x801f3d000)
libc.so.7 => /lib/libc.so.7 (0x800822000)

While here, unduplicate the linker line for handling of NM and unhide
the linker execution line.

Sponsored by: EMC / Isilon Storage Division

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rS FreeBSD src repository - subversion

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bdrewery updated this revision to Diff 4169.Mar 10 2015, 7:18 PM

bdrewery retitled this revision from to Add LIB_CXX so that c++ libraries will use CXX to link..

bdrewery updated this object.

bdrewery edited the test plan for this revision. (Show Details)

bdrewery added reviewers: imp, bapt.

Herald added subscribers: imp, bdrewery. · View Herald TranscriptMar 10 2015, 7:18 PM

I used ldd -a for that example.

I find it strange libm is linked in there. I don't see any obvious reason for it to be. readelf -a libatf-c++.so.2|grep UND doesn't show any libm symbols that I can tell of, and the libatf consumers don't have -lm either.

In D2039#5, @bdrewery wrote:

I find it strange libm is linked in there. I don't see any obvious reason for it to be. readelf -a libatf-c++.so.2|grep UND doesn't show any libm symbols that I can tell of, and the libatf consumers don't have -lm either.

Found it. freebsd::Link::ConstructJob in contrib/llvm/tools/clang/lib/Driver/Tools.cpp forces -lm with c++(1).

imp added inline comments.Mar 12 2015, 1:31 PM

share/mk/bsd.lib.mk
225 ↗	(On Diff #4169)	This is an interesting construct. NM should always be defined, which makes this unnecessary. It is unrelated to the change at hand in any event. I'm not sure why the current code has this construct other than historical reasons. share/mk/sys.mk sets this unconditionally.

In D2039#7, @imp wrote:

This is an interesting construct. NM should always be defined, which makes this unnecessary. It is unrelated to the change at hand in any event. I'm not sure why the current code has this construct other than historical reasons. share/mk/sys.mk sets this unconditionally.

I made 2 unrelated changes. I normally make individual commits. I figured it would be simpler to bunch into 1 review for discussion.

Note I also made the linker line non-quiet to be consistent with compilation lines. I constantly wonder what the linker line is doing.

bdrewery added inline comments.Mar 12 2015, 1:35 PM

share/mk/bsd.lib.mk
225 ↗	(On Diff #4169)	Ok, I'll remove this piece.

imp added inline comments.Mar 12 2015, 1:39 PM

share/mk/bsd.lib.mk
225 ↗	(On Diff #4169)	It isn't so much the unrelated part as the 'NM is always defined so we don't need to play games like this at all' bit I was hoping would be the take a way message :)