On Tue, 13 Oct 2015, Hendrik Leppkes wrote:
On Tue, Oct 13, 2015 at 11:56 AM, Christophe Gisquet
<[email protected]> wrote:
Hi
2015-10-06 12:41 GMT+02:00 Hendrik Leppkes <[email protected]>:
+static av_unused int pthread_once(pthread_once_t *once_control, void
(*init_routine)(void))
[...]
+ MemoryBarrier();
This resolves to _mm_mfence() which results (see configuration below)
in an undefined symbol (paths redacted):
ffmpeg/compat/w32pthreads.h:202: undefined reference to `_mm_mfence'
libavformat/libavformat.a(async.o): In function `w32thread_once_fallback':
ffmpeg/compat/w32pthreads.h:202: undefined reference to `_mm_mfence'
libavcodec/libavcodec.a(pthread_frame.o): In function `w32thread_once_fallback':
ffmpeg/compat/w32pthreads.h:202: undefined reference to `_mm_mfence'
libavcodec/libavcodec.a(pthread_slice.o): In function `w32thread_once_fallback':
ffmpeg/compat/w32pthreads.h:202: undefined reference to `_mm_mfence'
ffmpeg/compat/w32pthreads.h:202: undefined reference to `_mm_mfence'
libavcodec/libavcodec.a(vp8.o):ffmpeg/compat/w32pthreads.h:202: more
undefined references to `_mm_mfence' follow
Configuration:
In a MSYS2 Mingw32 shell
gcc version 5.2.0 (Rev4, Built by MSYS2 project), target: x86_64-w64-mingw32
Exact configure line:
../configure --disable-ffplay --disable-ffprobe --disable-ffserver \
--disable-hwaccels --disable-dxva2 \
--extra-cflags="-msse4.2" --cc="ccache gcc"
The above command-line is fine for the equivalent Win64 configuration.
Removing --extra-cflags fixes the issue. Adding -msse2 to it causes
the same compilation error.
MSVC has platform-specific implementations of MemoryBarrier() which
may resolve to the SSE2 mfence instruction. I'm not sure if
--extra-cflags="-msse4.2" cannot be expected to always work, or if
there's another issue here.
Why would adding -msse4.2 hide the symbol? Sounds like you should
complain to mingw.
In the meantime we could add an ugly ifdef for mingw/gcc and use
__sync_synchronize there instead (the gcc built-in)
This would probably be useful in general as well. There's a bunch of mingw
setups on fate which lack MemoryBarrier altogether.
// Martin
_______________________________________________
libav-devel mailing list
[email protected]
https://lists.libav.org/mailman/listinfo/libav-devel
