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[Bug malloc/22052] malloc failed to compile with GCC 7 and -O3

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- Log -----------------------------------------------------------------;h=8e57c9432a2b68c8a1e7f4df28f0e8c7acc04753

commit 8e57c9432a2b68c8a1e7f4df28f0e8c7acc04753
Author: H.J. Lu <>
Date:   Sun Oct 15 08:16:26 2017 -0700

    Silence -O3 -Wall warning in malloc/hooks.c with GCC 7 [BZ #22052]

    realloc_check has

      unsigned char *magic_p;
      __libc_lock_lock (main_arena.mutex);
      const mchunkptr oldp = mem2chunk_check (oldmem, &magic_p);
      __libc_lock_unlock (main_arena.mutex);
      if (!oldp)
        malloc_printerr ("realloc(): invalid pointer");
      if (newmem == NULL)
        *magic_p ^= 0xFF;


    static void malloc_printerr(const char *str) __attribute__ ((noreturn));

    GCC 7 -O3 warns

    hooks.c: In function ‘realloc_check’:
    hooks.c:352:14: error: ‘magic_p’ may be used uninitialized in this function
         *magic_p ^= 0xFF;

    due to the GCC bug:

    This patch silences GCC 7 by using DIAG_IGNORE_NEEDS_COMMENT.

        [BZ #22052]
        * malloc/hooks.c (realloc_check): Use DIAG_IGNORE_NEEDS_COMMENT
        to silence -O3 -Wall warning with GCC 7.


Summary of changes:
 ChangeLog      |    6 ++++++
 malloc/hooks.c |    7 +++++++
 2 files changed, 13 insertions(+), 0 deletions(-)

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