On 09/01/2014 04:59 PM, wm4 wrote:
On Mon, 01 Sep 2014 16:14:52 +0200
Jörg Krause <jkra...@posteo.de> wrote:
When building against musl instead of glibc, compilation fails at
libavutil/error.c
CC libavutil/error.o
libavutil/error.c: In function 'av_strerror':
libavutil/error.c:68:9: error: implicit declaration of function
'strerror_r' [-Werror=implicit-function-declaration]
cc1: some warnings being treated as errors
make: *** [libavutil/error.o] Error 1
I tried to find a fix and I am very unsure about the solution.
I am cross compiling for a linux target. I took a look at
ffmpeg/configure and added the following line:
# OS specific
case $target_os in
[..]
linux)
add_cppflags -D_POSIX_SOURCE
enable dv1394
;;
[..]
With this I can compile ffmpeg successfully.
What do you think about this solution?
Why is #undef _GNU_SOURCE in libavutil/error.c defined?
Because there are two strerror_r variants: standard and GNU. They have
different semantics (but same signature). I guess this undef is supposed
to select the POSIX one?
In general, I suspect it might be best to never define _GNU_SOURCE, but
_POSIX_C_SOURCE instead.
Instead of breaking everything, maybe this would be best to put into
error.c:
#undef _GNU_SOURCE
#define _POSIX_C_SOURCE 200809L
I see! I found this on the linux man page
(http://linux.die.net/man/3/strerror_r) for strerror_r:
The XSI-compliant version of *strerror_r*() is provided if:
(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600) && ! _GNU_SOURCE
Otherwise, the GNU-specific version is provided.
And here
(http://man7.org/linux/man-pages/man7/feature_test_macros.7.html) I
found this:
*_POSIX_C_SOURCE *is defined, according to the value of *_XOPEN_SOURCE*:
600 <= *_XOPEN_SOURCE *< 700: *_POSIX_C_SOURCE *is defined with the
value 200112L.
So I will propose a patch with:
#undef _GNU_SOURCE
#define _XOPEN_SOURCE 600
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