Re: why is there no __MUSL__ macro?

[Natanael Copa <ncopa@alpinelinux.org>]

On Thu, 11 Sep 2014 13:00:09 +0200
Jörg Krause <jkrause@posteo.de> wrote:

> Hi,
> 
> I am trying to add support for the musl toolchain to FFmpeg.
> 
> FFmpeg needs support for library features defined in POSIX.1-2001 with 
> XSI extension and the standards below. Currently configure probes the 
> host and target libc by checking for defined macros like __GLIBC__ and 
> __UCLIBC__. In case of glibc and uclibc it sets -D_XOPEN_SOURCE=600 
> properly.
> 
> After this it checks for some combinations of hardware and the probed 
> libc to set some more compile options, if necessary.
> 
> I know that musl does not have a macro __MUSL__ and I have read the 
> explanation. However, I don't understand what's meant by "[..] it's a 
> bug to assume a certain implementation has particular properties rather 
> than testing." and how does it affect the way FFmpeg probes for the libc.
> 
> What could be a solution which supports musl?
> 
> Many thanks!
> Jörg

This is what we do on alpine linux:
http://git.alpinelinux.org/cgit/aports/tree/main/ffmpeg/fix-defines.patch

--- ffmpeg-1.2.2.orig/libavutil/error.c
+++ ffmpeg-1.2.2/libavutil/error.c
@@ -17,6 +17,7 @@
  */
 
 #undef _GNU_SOURCE
+#define _XOPEN_SOURCE 600
 #include "avutil.h"
 #include "avstring.h"
 #include "common.h"