Messages in this thread | | | Date | Mon, 19 Nov 2007 21:10:44 -0800 | From | "H. Peter Anvin" <> | Subject | Re: Is there any word about this bug in gcc ? |
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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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