Various issues with Clang and libc++ while playing with OpenCL (FYI)

[Jean-Sébastien Pédron]

Hello!

[Note: I'm not subscribed to this list]

I'm trying to make OpenCL work on FreeBSD, using Mesa 10.1 release
candidate.

The implementation of libOpenCL.so in Mesa, called Clover, is in C++. In
the configure.ac script, they require GCC 4.7+, but I think it's mainly
for C++11 support. When building Mesa with Clang 3.4 and 11-CURRENT's
libc++, I had the following issues:

1. Clang 3.4 fails to build Clover, see this PR:
   https://bugs.freedesktop.org/show_bug.cgi?id=74098

   In the last comment, there's a patch to Clover, working around the
   problem. Its author opened a ticket on LLVM bug tracker:
   http://llvm.org/bugs/show_bug.cgi?id=18645

2. Mesa's configure script is looking for stddef.h here:
   /usr/local/llvm34/lib/clang/3.4/include

   LLVM/Clang ports don't install this file. I just added a symlink to
   /usr/include/stddef.h and Mesa was happy. I still need to check how
   it goes if I remove the check and the symlink. But perhaps Mesa is
   right to expect this header (and maybe other) in this directory, I
   don't know.

3. Our base libc++ has a bug in the <functional> header. I posted a PR
   on Mesa bug tracker here, before I found out it was a problem with
   libc++:
   https://bugs.freedesktop.org/show_bug.cgi?id=75505

   Apparently, it's fixed in libc++ upstream, in r199848.

4. At runtime, any OpenCL program segfaults in libc++ (I don't have the
   stack trace at hand and can't remember what it was... Something with
   basic_string).

When using libc++ from ports (devel/libc++, r200683) and the work around
for problem #1, Clover builds and OpenCL programs run fine.

This is mostly a "FYI" report, I think we can live with libc++ from
ports for Mesa.

-- 
Jean-Sébastien Pédron

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