GNU C Library master sources branch, master, updated. glibc-2.15-729-gf0c1ded

[aj at sourceware dot org]

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- Log -----------------------------------------------------------------
http://sources.redhat.com/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=f0c1dedf0df71b4029d9b0ce8ba19d8af2a60af5

commit f0c1dedf0df71b4029d9b0ce8ba19d8af2a60af5
Author: Andreas Jaeger <aj@suse.de>
Date:   Thu May 3 22:12:59 2012 +0200

    Fix tst-obprintf - and mcheck in general
    
    tst-obprintf failed with GCC 4.7.
    
    It turned out that this is the fault of GCC optimizing away the
    following from malloc/mcheck.c:
          /* We call malloc() once here to ensure it is initialized.  */
          void *p = malloc (0);
          free (p);
    
    gcc sees the malloc(0);free pair and removes it completely.
    
    And now malloc is not properly initialized and we screw up if both
    mcheck is used (via tst-obprintf) and MALLOC_CHECK_ is set (as it is in my
    environment).

diff --git a/ChangeLog b/ChangeLog
index 1427a45..0bffdf9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,10 @@
 2012-05-03  Andreas Jaeger  <aj@suse.de>
+
+	* malloc/mcheck.c (mcheck): Add barrier so that malloc/free pair
+	does not get optimized out.
+	(malloc_opt_barrier): New.
+
+2012-05-03  Andreas Jaeger  <aj@suse.de>
 	    Roland McGrath <roland@hack.frob.com>
 
         * Makerules (.PRECIOUS): Add %.symlist pattern to prevent
diff --git a/malloc/mcheck.c b/malloc/mcheck.c
index 9213740..9d8a414 100644
--- a/malloc/mcheck.c
+++ b/malloc/mcheck.c
@@ -370,6 +370,10 @@ mabort (enum mcheck_status status)
 #endif
 }
 
+/* Memory barrier so that GCC does not optimize out the argument.  */
+#define malloc_opt_barrier(x) \
+({ __typeof (x) __x = x; __asm ("" : "+m" (__x)); __x; })
+
 int
 mcheck (func)
      void (*func) (enum mcheck_status);
@@ -381,6 +385,8 @@ mcheck (func)
     {
       /* We call malloc() once here to ensure it is initialized.  */
       void *p = malloc (0);
+      /* GCC might optimize out the malloc/free pair without a barrier.  */
+      p = malloc_opt_barrier (p);
       free (p);
 
       old_free_hook = __free_hook;

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog       |    6 ++++++
 malloc/mcheck.c |    6 ++++++
 2 files changed, 12 insertions(+), 0 deletions(-)


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