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    SubjectRe: Is there any word about this bug in gcc ?
    On Tue, Nov 20, 2007 at 02:03:12PM +0800, Li Zefan wrote:
    >WANG Cong wrote:
    >> 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?
    >>
    >
    >Gcc optimises abs() to use gcc builtin-in abs(). So if we use -fno-builin,
    >we'll get the correct result. That is to say the bug has nothing to do with
    >glibc.
    >
    >And this bug has been fixed just several days ago.
    >
    >http://www.nabble.com/-PATCH--Fix-PR34130,-extract_muldiv-broken-t4826688.html
    >

    Good explanation! Thank you!


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