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

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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;

with

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 [-Werror=maybe-uninitialized]
     *magic_p ^= 0xFF;

due to the GCC bug:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82090

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.
This commit is contained in:
H.J. Lu
2017-10-15 08:16:26 -07:00
parent a4777c46af
commit 8e57c9432a
2 changed files with 13 additions and 0 deletions
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6
ChangeLog
View File

@ -1,3 +1,9 @@
2017-10-15 H.J. Lu <hongjiu.lu@intel.com>
[BZ #22052]
* malloc/hooks.c (realloc_check): Use DIAG_IGNORE_NEEDS_COMMENT
to silence -O3 -Wall warning with GCC 7.
2017-10-14 H.J. Lu <hongjiu.lu@intel.com> 2017-10-14 H.J. Lu <hongjiu.lu@intel.com>
* Makeconfig (+link-static-before-libc): Use the first of * Makeconfig (+link-static-before-libc): Use the first of

7
malloc/hooks.c
View File

@ -345,11 +345,18 @@ realloc_check (void *oldmem, size_t bytes, const void *caller)
newmem = _int_realloc (&main_arena, oldp, oldsize, nb); newmem = _int_realloc (&main_arena, oldp, oldsize, nb);
} }
DIAG_PUSH_NEEDS_COMMENT;
#if __GNUC_PREREQ (7, 0)
/* GCC 7 warns about magic_p may be used uninitialized. But we never
reach here if magic_p is uninitialized. */
DIAG_IGNORE_NEEDS_COMMENT (7, "-Wmaybe-uninitialized");
#endif
/* mem2chunk_check changed the magic byte in the old chunk. /* mem2chunk_check changed the magic byte in the old chunk.
If newmem is NULL, then the old chunk will still be used though, If newmem is NULL, then the old chunk will still be used though,
so we need to invert that change here. */ so we need to invert that change here. */
if (newmem == NULL) if (newmem == NULL)
*magic_p ^= 0xFF; *magic_p ^= 0xFF;
DIAG_POP_NEEDS_COMMENT;
__libc_lock_unlock (main_arena.mutex); __libc_lock_unlock (main_arena.mutex);