Bug#635885: libc6: strchr() behavior changed

[Jonathan Nieder <jrnieder@gmail.com>]

Hi Michal,

Michal Kiedrowicz wrote:

> 	        static const char s[] = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 0};
[...]
> When running this application on Debian with libc6 2.7-18lenny2 and on my
> Gentoo machine I get:
>
> 	$ ./test_strchr
> 	strchr(228 [-28]) = [0]
[...]
> When running it on Debian with libc6 2.11.2-10:
>
> 	strchr(228 [-28]) = [255]

This sounded to me like PR12159, which was fixed by glibc-2.13~64 (Fix
x86-64 strchr propagation of search byte into all bytes of SSE
register, 2010-10-25), but I am not able to reproduce it.  I get all
[0] values (pointers to the end of string), the correct behavior.

I tried to reproduce first using strchr.S directly on Debian sid, then
using plain libc6 in a squeeze Debian live system running through kvm.
I compiled with -O0 so I don't think gcc optimized out the strchr
calls.  Any idea what I'm doing wrong?  What machine architecture do
you use?