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GNU C Library master sources branch release/2.26/master updated. glibc-2.26-107-g73a9236

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      from  df8c219cb987cfe85c550efa693a1383a11e38aa (commit)

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- Log -----------------------------------------------------------------;a=commitdiff;h=73a92363619e52c458146e903dfb9b1ba823aa40

commit 73a92363619e52c458146e903dfb9b1ba823aa40
Author: H.J. Lu <>
Date:   Wed Dec 6 16:15:47 2017 +0100

    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 â??realloc_checkâ??:
    hooks.c:352:14: error: â??magic_pâ?? may be used uninitialized in this function [-Werror=maybe-uninitialized]
         *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.
    (cherry picked from commit 8e57c9432a2b68c8a1e7f4df28f0e8c7acc04753)

diff --git a/ChangeLog b/ChangeLog
index 29bd704..42224c0 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.
 2017-11-30  Arjun Shankar  <>
 	[BZ #22375]
diff --git a/NEWS b/NEWS
index 895e2bc..8810b57 100644
--- a/NEWS
+++ b/NEWS
@@ -63,6 +63,7 @@ The following bugs are resolved with this release:
     occur with -O3
   [21987] Fix sparc32 bits/long-double.h
   [22051] libc: zero terminator in the middle of glibc's .eh_frame
+  [22052] malloc failed to compile with GCC 7 and -O3
   [22078] nss_files performance issue in hosts multi mode
   [22093] x86: Add x86_64 to x86-64 HWCAP
   [22095] resolv: Fix memory leak with OOM during resolv.conf parsing
diff --git a/malloc/hooks.c b/malloc/hooks.c
index 4398c0a..2c6cebc 100644
--- a/malloc/hooks.c
+++ b/malloc/hooks.c
@@ -347,11 +347,18 @@ realloc_check (void *oldmem, size_t bytes, const void *caller)
       newmem = _int_realloc (&main_arena, oldp, oldsize, nb);
+#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");
   /* 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;
   __libc_lock_unlock (main_arena.mutex);


Summary of changes:
 ChangeLog      |    6 ++++++
 NEWS           |    1 +
 malloc/hooks.c |    7 +++++++
 3 files changed, 14 insertions(+), 0 deletions(-)

GNU C Library master sources

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