Re: Is there any word about this bug in gcc ?

[H. Peter Anvin]

WANG Cong wrote:
> On Tue, Nov 20, 2007 at 10:13:42AM +0800, zhengyi wrote:
> > Is there any relevance to the kernel ?
> >
> > I found the folowing code here:
> > http://linux.solidot.org/article.pl?sid=07/11/19/0512218&from=rss
> >
> > -------------------------------------------------------------------
> > int main( void )
> > {
> >  int i=2;
> >  if( -10*abs (i-1) == 10*abs(i-1) )
> >    printf ("OMG,-10==10 in linux!\n");
> >  else
> >    printf ("nothing special here\n") ;
> >
> >  return 0 ;
> > }
>
> I think no. It is considered a bug in abs(), kernel, of course,
> doesn't use glibc's abs().

Wrong.

abs() is internal to gcc, and the above is optimized out at compile 
time, so any user of abs() as a function at all is vulnerable.

However, the Linux kernel defines abs() as a macro:

#define abs(x) ({                               \
                int __x = (x);                  \
                (__x < 0) ? -__x : __x;         \
        })

... which means gcc never sees it.  So the kernel isn't affected, 
because it doesn't use *gcc's* abs().

	-hpa

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