[cfe-dev] Clang++ always defines _GNU_SOURCE

[Joerg Sonnenberger via cfe-dev]

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?

Joerg