On Wed, Feb 21, 2007 at 09:57:50PM -0800, H. Peter Anvin wrote:
> Russell King wrote:
>
> >Plainly, %ebx changed across the call to serial_in() at c01c0f7b.
> >First thing to notice is this violates the C code - "up" can not
> >change.
> >Now let's look at serial_in:
> >c01bfa70: 55 push %ebp
> >c01bfa71: 89 e5 mov %esp,%ebp
> >c01bfa73: 53 push %ebx
> >...
> >c01bfab7: 5b pop %ebx
> >c01bfab8: 5d pop %ebp
> >c01bfab9: c3 ret
> >This code tells the CPU to preserves %ebx and %ebp. But we know %ebx
> >_wasn't_ preserved. Ergo, your CPU is plainly not doing what the code
> >told it to do.
>
> ... assuming nothing else clobbered the stack slot (which would be a compiler
> error, or a wild pointer.)
>
> Got a disassembly of the whole function?
>
Jose posted it higher in the thread:
http://lkml.org/lkml/2007/2/21/139
Regards,
Frederik
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