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

Jörg Krause jkrause at posteo.de
Sat Sep 20 21:41:49 CEST 2014

On 09/18/2014 07:10 PM, Reimar Döffinger wrote:
> 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.

I would suggest two possibilities:

a) Define POSIX_C_SOURCE and _XOPEN_SOURCE at the beginning of 
probe_libc as default setting for all the libs:

         add_${pfx}cppflags -D_POSIX_C_SOURCE=200112L -D_XOPEN_SOURCE=600
         if uclibc ...
         elif glibc ...

b) Define it at the end after all the specific lib handlers:

    elif solaris
         add_${pfx}cppflags -D_POSIX_C_SOURCE=200112L -D_XOPEN_SOURCE=600

What's your opinion?

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