linux-kernel - Re: Serial related oops

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Message-ID: <45DD30DE.20503@zytor.com>
Date:	Wed, 21 Feb 2007 21:57:50 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jose Goncalves <jose.goncalves@...v.pt>,
	Frederik Deweerdt <deweerdt@...e.fr>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: 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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