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Re: Fix tst-obprintf - and mcheck in general

Here's an updated patch.

Tested on Linux/x86-64 and x86. Ok to commit?


2012-05-03 Andreas Jaeger <>

	* malloc/mcheck.c (mcheck): Add barrier so that malloc/free pair
	does not get optimized out.
	(malloc_opt_barrier): New.

diff --git a/malloc/mcheck.c b/malloc/mcheck.c
index 9213740..d9e1bf9 100644
--- a/malloc/mcheck.c
+++ b/malloc/mcheck.c
@@ -370,6 +370,9 @@ mabort (enum mcheck_status status)

+#define malloc_opt_barrier(x) \
+({ __typeof (x) __x = x; __asm ("" : "+m" (__x)); __x; })
 mcheck (func)
      void (*func) (enum mcheck_status);
@@ -381,6 +384,8 @@ 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;

 Andreas Jaeger aj@{,} Twitter/Identica: jaegerandi
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   GF: Jeff Hawn,Jennifer Guild,Felix Imendörffer,HRB16746 (AG Nürnberg)
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