Re: [PATCH] libstdc++: Fix up FAIL in 17_intro/names.cc on glibc < 2.19 [PR108568]

[Jonathan Wakely <jwakely@redhat.com>]

On Fri, 27 Jan 2023 at 09:29, Jakub Jelinek <jakub@redhat.com> wrote:
>
> Hi!
>
> On gcc112 which has glibc 2.17 I've noticed
> FAIL: 17_intro/names.cc (test for excess errors)
> FAIL: experimental/names.cc (test for excess errors)
> These are because glibc < 2.19 used __unused as field member of various structs,
> including mcontext_t in sys/ucontext.h on ppc64le.
> This was changed in glibc with
> https://gcc.gnu.org/pipermail/libc-alpha/2013-November/045766.html
> names.cc even has
> #ifdef __GLIBC_PREREQ
> #if ! __GLIBC_PREREQ(2, 19)
> // Glibc defines this prior to 2.19
> #undef __unused
> #endif
> #endif
> for it, but it doesn't work.  The reason is that __GLIBC_PREREQ is defined in
> <features.h> but nothing included that header before this spot (it is included later
> from bits/stdc++.h).
>
> The following patch on Linux/Hurd conditionally includes features.h to get
> the needed macros before deciding if __unused should be undefined or not.
> If needed, I could use __GLIBC_PREREQ then but would need to check if it is
> defined and between 1996 and 1999 it wasn't.
>
> Tested on powerpc64le-linux with glibc 2.17 (where it fixes the
> regressions), on x86_64-linux with glibc 2.35 (where it still PASSes),
> plus on the latter with -E -dD on the test to verify __unused is just
> defined and not undefined later on, ok for trunk?

OK, thanks.