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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>
* 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);
}
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.
If newmem is NULL, then the old chunk will still be used though,
so we need to invert that change here. */
if (newmem == NULL)
*magic_p ^= 0xFF;
DIAG_POP_NEEDS_COMMENT;
__libc_lock_unlock (main_arena.mutex);