Fix tst-obprintf - and mcheck in general

[Richard Guenther]

On Thu, 26 Apr 2012, Marek Polacek wrote:

> On Thu, Apr 26, 2012 at 02:53:07PM +0200, Andreas Jaeger wrote:
> > Richard and myself analyzed the tst-obprintf failure 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).
> > 
> > One option is to compile with -fno-builtin-malloc, the alternative would be 
> > to use some otherways to initialize the malloc implementation.
> 
> Perhaps we could call e.g. malloc_get_state ();.  That shouldn't be optimized
> away and calls ptmalloc_init.  Not sure what's better though.

Consider people LD_PRELOADing tcmalloc or so.  Not sure if it makes sense
to use mcheck.c then, of course ..

Richard.

-- 
Richard Guenther <rguenther@suse.de>
SUSE / SUSE Labs
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