Proper Conditionals for POSIX CX and XSI

[Yaakov (Cygwin/X)]

On 2013-07-17 19:56, Sebastian Huber wrote:
> On 2013-07-18 06:15, Yaakov (Cygwin/X) wrote:
>> On 2013-07-17 15:34, Joel Sherrill wrote:
>>> While this was still fresh, I wanted to ask what was the
>>> proper conditional for methods marked as CX or XSI
>>> in the POSIX standard.
>>
>> This is what is done in glibc:
>>
>> http://man7.org/linux/man-pages/man7/feature_test_macros.7.html
>>
>> In short, <features.h> recognizes _*_SOURCE macros, which it uses to set
>> various __USE_* private macros which are used throughout the headers as
>> conditionals to control which APIs are made available.
>>
>> Having this done *properly* in the Newlib/Cygwin headers would be a
>> big step to
>> fixing a lot of compiling incompatibilities with glibc.  It is also a
>> very
>> tedious task, although it may not have to be done all at once
>
> Unfortunately the GNU and BSD people don't talk much with each other.
> In FreeBSD we have this _*_SOURCE evaluation in <sys/cdefs.h>.  Since I
> updated Newlibs "newlib/libc/include/sys/cdefs.h" a couple of weeks ago
> we should consider to use the infrastructure already available (see line
> 535 and below).  Due to license issues it is more likely that Newlib
> will use code from BSD sources.

AFAIK it doesn't really matter which header provides this functionality, 
as long as all affected headers include that one.  However, IMO we need 
to support all the _*_SOURCE options, particularly _GNU_SOURCE.  It is 
also necessary to #undef all the __*_VISIBLE macros at the beginning of 
that section, otherwise you can get redefinition warnings in certain 
situations.

Let's try to make that more compatible with feature_test_macros(7), then 
we can start working on conditionalizing the standard headers.


Yaakov
Cygwin/X