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SubjectRe: Serial related oops
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?

-hpa
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