Re: [Qemu-devel] fpu problems with qemu-system-sparc

[Joerg Platte]

Am Donnerstag, 18. Mai 2006 19:53 schrieb Blue Swirl:
> >I've checked a lot of the executed instructions in qemu and cannot find
> > any problems up to now. Does somebody else has an idea what to check? The
> > test program simply adds two float variables (fadds-instruction) in a
> > loop and this crashes the program reproducible.
>
> Some instructions trap when FPU is disabled, and they shouldn't, like
> stfsr?

I don't think so. I analyzed the core-file after the crash. Sometimes the user 
stack was corrupt or a register value invalid and the crashing instruction 
was not a FPU instruction. Hence, I think one simulated instruction somehow 
overwrites parts of the userstack or maybe the kernel itself does it because 
of a wrong behavior of the simulated hardware. 

I'm not sure where to add more debugging output, because in qemu a segfault is 
hard to detect and in the kernel I have no idea, if all executed instructions 
are correctly translated... And unfortunately this crash is reproducible, but 
timing dependent. It does not always happen at exact the same position and 
therefore, I can't check, for example, for an invalid register value to see, 
when it is loaded...

regards,
Jörg