[FFmpeg-devel] [PATCH] [RFC] libavutil/mem.c: Check return value of posix_memalign

[Michael Niedermayer]

On Fri, Feb 13, 2009 at 07:37:16PM +0000, M?ns Rullg?rd wrote:
> Patrik Kullman <patrik at yes.nu> writes:
> 
> > On Fri, 2009-02-13 at 18:11 +0000, M?ns Rullg?rd wrote:
> >> Patrik Kullman <patrik at yes.nu> writes:
> >> 
> >> > On Fri, 2009-02-13 at 16:26 +0000, M?ns Rullg?rd wrote:
> >> >> Reimar D?ffinger <Reimar.Doeffinger at stud.uni-karlsruhe.de> writes:
> >> >> 
> >> >> > On Fri, Feb 13, 2009 at 03:47:23PM +0000, M?ns Rullg?rd wrote:
> >> >> >> > libavutil/mem.c: In function ?av_malloc?:
> >> >> >> > libavutil/mem.c:66: warning: ignoring return value of ?posix_memalign?,
> >> >> >> > declared with attribute warn_unused_result
> >> >> >> 
> >> >> >> That warning is bogus.  If posix_memalign() fails, memalign() will too
> >> >> >> since they are likely to be the same function.  We set the pointer to
> >> >> >> NULL before the call, so if it fails, we return NULL as we're supposed
> >> >> >> to.
> >> >> >
> >> >> > Well, if you are pedantic you here assume that posix_memalign will not
> >> >> > modify ptr if it fails (or at least not set it != NULL), but that
> >> >> > actually does not seem to be guaranteed by POSIX (it doesn't say
> >> >> > anything about the value of ptr when an error is returned...).
> >> >> 
> >> >> That is indeed the case, and thus your suggestion of explicitly
> >> >> setting it to NULL makes sense.
> >> >
> >> > So, this is OK?
> >> >
> >> > Index: libavutil/mem.c
> >> > ===================================================================
> >> > --- libavutil/mem.c	(revision 17211)
> >> > +++ libavutil/mem.c	(working copy)
> >> > @@ -63,7 +63,8 @@
> >> >      ptr = (char*)ptr + diff;
> >> >      ((char*)ptr)[-1]= diff;
> >> >  #elif HAVE_POSIX_MEMALIGN
> >> > -    posix_memalign(&ptr,16,size);
> >> > +    if (posix_memalign(&ptr,16,size) != 0)
> >> 
> >> Drop the != 0.
> >> 
> >> > +        ptr = NULL;
> >> >  #elif HAVE_MEMALIGN
> >> >      ptr = memalign(16,size);
> >> >      /* Why 64?
> >> 
> >> Otherwise no objections from me.  Maybe we should drop the initial
> >> NULL assignment since with this change, it is not necessary.
> >
> > Ok, dropped the != 0.
> >
> >
> > Index: libavutil/mem.c
> > ===================================================================
> > --- libavutil/mem.c	(revision 17211)
> > +++ libavutil/mem.c	(working copy)
> > @@ -63,7 +63,8 @@
> >      ptr = (char*)ptr + diff;
> >      ((char*)ptr)[-1]= diff;
> >  #elif HAVE_POSIX_MEMALIGN
> > -    posix_memalign(&ptr,16,size);
> > +    if (posix_memalign(&ptr,16,size))
> > +        ptr = NULL;
> >  #elif HAVE_MEMALIGN
> >      ptr = memalign(16,size);
> >      /* Why 64?
> 
> Now we're just waiting for the maintainer to give his approval (or not).

iam fine with it though i must say ive never been a friend of posix_memalign()
memalign() itself works fine and doesnt need such obscure checks

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato
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