[FFmpeg-devel] [PATCH] make sure initialization happens even after goto fires

[Reimar Döffinger]

On Thu, Jul 17, 2008 at 11:12:04AM -0700, Erik Hovland wrote:
> On Thu, Jul 17, 2008 at 07:03:43PM +0200, Michael Niedermayer wrote:
> > On Thu, Jul 17, 2008 at 09:08:40AM -0700, Erik Hovland wrote:
> > > The goto in ff_h264_find_frame_end() is inside an else clause. The
> > > initialization for v happens in the if clause elsewhere. That means that
> > > it is possible for the goto to fire without the initialization of v
> > > happening. Normally this isn't a problem. But gcc recognizes this and
> > > throws an internal parse warning. It then has to go through a special
> > > code branch to take care of this. If the initialization of v always
> > > happens before either clause this does not happen. The attached patch
> > > does just that.
> > 
> > Is there any bug in our code?
> 
> Well, that is an interesting question. It would be a bug if the goto
> fired without v being initialized. Which is possible, but highly
> unlikely.

Why, v is not used so why should it be wrong if it is not initialized?
Still, I do think the code would look nicer if it was done like in
attached patch, though the remaining code is sufficient to make the
average programmer's head explode on first sight anyway ;-)

Greetings,
Reimar D?ffinger
-------------- next part --------------
Index: libavcodec/h264_parser.c
===================================================================
--- libavcodec/h264_parser.c	(revision 14263)
+++ libavcodec/h264_parser.c	(working copy)
@@ -59,10 +59,7 @@
             if(v==7 || v==8 || v==9){
                 if(pc->frame_start_found){
                     i++;
-found:
-                    pc->state=7;
-                    pc->frame_start_found= 0;
-                    return i-(state&5);
+                    goto found;
                 }
             }else if(v==1 || v==2 || v==5){
                 if(pc->frame_start_found){
@@ -80,6 +77,11 @@
     }
     pc->state= state;
     return END_NOT_FOUND;
+
+found:
+    pc->state=7;
+    pc->frame_start_found= 0;
+    return i-(state&5);
 }
 
 static int h264_parse(AVCodecParserContext *s,