Re: Serial related oops

From: H. Peter Anvin
Date: Thu Feb 22 2007 - 00:58:46 EST


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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