[cfe-dev] Clang++ always defines _GNU_SOURCE

[Lei Zhang via cfe-dev]

2016-06-14 20:12 GMT+08:00 Joerg Sonnenberger via cfe-dev
<cfe-dev at lists.llvm.org>:
> On Tue, Jun 14, 2016 at 06:04:56PM +0800, Lei Zhang via cfe-dev wrote:
>> 2016-06-14 17:59 GMT+08:00 Ismail Donmez <ismail at i10z.com>:
>> > Hi,
>> >
>> > On Tue, Jun 14, 2016 at 12:54 PM, Lei Zhang via cfe-dev
>> > <cfe-dev at lists.llvm.org> wrote:
>> >> 2016-06-14 16:54 GMT+08:00 Eric Fiselier <eric at efcs.ca>:
>> >>>>  Does libc++ also rely on this macro to work on Linux?
>> >>>
>> >>> Yes. Adding -U_GNU_SOURCE during the libc++ build results in a litany of
>> >>> errors.
>> >>> The libc++ headers depend on a number of C library symbols that only get
>> >>> defined when -D_GNU_SOURCE=1 is present.
>> >>
>> >> Is it feasible to use some finer-grain control like _ISOC99_SOURCE,
>> >> instead of resorting to the too versatile _GNU_SOURCE?
>> >>
>> >> I'd be willing to work out such a patch to libc++, if it makes sense.
>> >
>> > Note that _GNU_SOURCE is more extensive:
>>
>> Yes, it requires the use of multiple different finer-grain macros to
>> replace _GNU_SOURCE, but it's worth the effort IMHO. Simply defining
>> _GNU_SOURCE may pollute users' code with many unwanted symbols.
>
> Compared to breaking lots of applications that expect the GNU symbols by
> default?

That's a valid point. OTOH, should we encourage applications to use
GNU symbols with out explicitly defining _GNU_SOURCE? Then what's the
point of such a macro?


Lei