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SubjectRe: Freeze on FPU exception with Athlon
Linus Torvalds wrote:
>
> In article <20001118014019.18006.qmail@web3404.mail.yahoo.com>,
> =?iso-8859-1?q?Markus=20Schoder?= <markus_schoder@yahoo.de> wrote:
> >The following small program (linked against glibc 2.1.3) reliably
> >freezes my system (Athlon Thunderbird CPU) with at least kernels
> >2.4.0-test10 and 2.4.0-test11-pre5. Even the SysRq keys do not work
> >after the freeze.
> >
> >Older kernels (e.g. 2.3.40) seem to work. Any Ideas?
>
> It certainly doesn't happen for me on any of the machines I work with,
> but it wouldn't compile as-is for me, so I exchanged the FPU setting
> with a simpler
>
> asm("fldcw %0": :"m" (0));
>
> which should do the equivalent (ie unmask divide by zero errors). Does
> that make a difference for you?
>
> Can you try to figure out where it started happening? Ie try test9 and
> back too, to figure out what might be bringing it on...
>
> I sure as hell hope this isn't an Athlon issue. Can other people try
> the test-program and see if we have a pattern (ie "it happens only on
> Athlons", or "Linus is on drugs and it happens for everybody else").
>
> Thanks,
>
> Linus

I get Floating Point Exception (core dumped), but I needed to use the
modified program below to keep GCC from optimizing the division away as
a constant. This is on test11-pre5.

--------------
#define _GNU_SOURCE

#include <fenv.h>
#include <unistd.h>

double a =1.0, b = 0.0;
int
main(void)
{
double c;
asm("fldcw %0": :"m" (0));
// fesetenv(FE_NOMASK_ENV);
c = a / b;
sleep(10);
return a;
}
--------------
processor : 0
vendor_id : AuthenticAMD
cpu family : 6
model : 2
model name : AMD Athlon(tm) Processor
stepping : 2
cpu MHz : 748.000573
cache size : 512 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 1
wp : yes
features : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pat
pse36 mmx fxsr syscall mmxext 3dnowext 3dnow
bogomips : 1494.22

--

Brian Gerst
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