On Wed, Oct 22, 2003 at 11:04:36PM +0200, Mark Kettenis wrote:
> (gdb) signal 5
> Continuing with signal SIGTRAP.
> 
> At this point the machine crashes.  Sometimes I get a message on the
> console that starts with:
> 
> fatal protection fault in supervisor mode
> rip ffffffff80100594
> 
> which corresponds to the 
> 
>    movq    %rcx,%cr0
> 
> instruction in locore.S:switch_exited.
> 
> The system call that crashes the machine is:
> 
>   ptrace (PT_CONTINUE, PID, 1, SIGTRAP);

Ah, thanks, that's very helpful. I'll look into this. Apparently the
ptrace call(s) somehow create an illegal process state (in this case
the saved CR0), which then generates a fault when it's restored
at process switch.

- Frank