Messages in this thread | | | Date | Tue, 20 Nov 2007 13:39:05 +0800 | From | WANG Cong <> | Subject | Re: Is there any word about this bug in gcc ? |
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On Mon, Nov 19, 2007 at 09:10:44PM -0800, H. Peter Anvin wrote: >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.
This is an urgent bug, I think.
And you mean abs() is not in glibc, then where is it? Built in gcc? And what's more, why not put it in glibc?
Thanks.
> >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().
Thanks for clarifying this!
Regards.
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