Re: Serial related oops

["H. Peter Anvin" <hpa@zytor.com>]

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