[FFmpeg-devel] [PATCH v2 1/1] configure: Refactor setting of feature test macro _XOPEN_SOURCE

[Reimar Döffinger]

On 18.09.2014, at 17:26, Michael Niedermayer <michaelni at gmx.at> wrote:
> On Thu, Sep 18, 2014 at 04:22:27PM +0200, Jörg Krause wrote:
>> glibc, uclibc, and musl uses feature test macros to expose definitions 
>> conforming to the standards ISO C, POSIX and extensions. According to
>> which feature test macros are defined by the user or the compiler, 
>> the header file <features.h> used by these libraries internally defines
>> various other macros.
>> 
>> glibc and uclibc also defines release test macros, eg __GLIBC__ and
>> __UCLIBC__ in <features.h>. musl does not have (and do not want) such 
>> a macro like __MUSL__. 
>> 
>> Building ffmpeg with the musl toolchain needs the feature test macro
>> _XOPEN_SOURCE=600 to be defined. As it is not possible to detect musl  
>> check for the <features.h> header file, which is assumed to be specific 
>> to glibc, uclibc, and musl. 
>> 
>> Signed-off-by: Jörg Krause <jkrause at posteo.de>
>> ---
>> Changes  v1 -> v2:
>>  - do not set _XOPEN_SOURCE twice for glibc and uclibc
> 
> why do you not add the musl check at the end of the if/elif chain as
> suggested ?
> does that have some issue or problem ?
> 
> now your patch removes POSIX_C_SOURCE=200112 for glibc & uclibc
> maybe thats ok, maybe its not but it certainly doesnt belong in a
> patch that adds musl support
> If you think this change is desireable, please submit a seperate
> patch

May I suggest to change configure to always add these (POSIX_C_SOURCE and _XOPEN_SOURCE) and we just remove them specifically for cases that cause issues?
And this time _document_ why we even have these hacks.
Because as it it's impossible to know if all those special case are there for a reason or if they only exist because it's fun and nicely obfuscates configure.