[Bug libc/23993] New: glibc 2.29 doesn't build with gcc 4.9

["romain.naour at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=23993

            Bug ID: 23993
           Summary: glibc 2.29 doesn't build with gcc 4.9
           Product: glibc
           Version: 2.29
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: romain.naour at gmail dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Hi,

There is a regression when the toolchain is built with glibc 2.29 and
gcc 4.9 (when USE_ATOMIC_COMPILER_BUILTINS is not defined) for all platform I
tested [1] :

In file included from ../sysdeps/nptl/internaltypes.h:23:0,
                 from ./pthreadP.h:30,
                 from pthread_mutex_getprioceiling.c:21:
pthread_mutex_getprioceiling.c: In function 'pthread_mutex_getprioceiling':
../include/atomic.h:672:4: error: read-only variable '__atg100_val' used as
'asm' output
    __asm ("" : "=r" (__atg100_val) : "0" (*(mem)));         \
    ^
pthread_mutex_getprioceiling.c:29:26: note: in expansion of macro
'atomic_load_relaxed'
   if (__builtin_expect ((atomic_load_relaxed (&(mutex->__data.__kind))
                          ^
The issue has been introduced by [2].

Joseph Myers suggested to remove the support for building glibc with GCC 4.9
[3].

Best regards,
Romain

[1] https://gitlab.com/kubu93/toolchains-builder/pipelines/40259702
[2]
https://github.com/bminor/glibc/commit/403b4feb22dcbc85ace72a361d2a951380372471
[3] https://sourceware.org/ml/libc-alpha/2018-12/msg00510.html

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