From 8e57c9432a2b68c8a1e7f4df28f0e8c7acc04753 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Sun, 15 Oct 2017 08:16:26 -0700 Subject: [PATCH] Silence -O3 -Wall warning in malloc/hooks.c with GCC 7 [BZ #22052] MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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. --- ChangeLog | 6 ++++++ malloc/hooks.c | 7 +++++++ 2 files changed, 13 insertions(+) diff --git a/ChangeLog b/ChangeLog index eed74500f7..17fbe55b5d 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,9 @@ +2017-10-15 H.J. Lu + + [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 * Makeconfig (+link-static-before-libc): Use the first of diff --git a/malloc/hooks.c b/malloc/hooks.c index 01be076f5e..17d8907727 100644 --- a/malloc/hooks.c +++ b/malloc/hooks.c @@ -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); -- 2.43.5