linux-kernel - Re: Serial related oops

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Message-ID: <20070222085213.GA15841@flint.arm.linux.org.uk>
Date:	Thu, 22 Feb 2007 08:52:13 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	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

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?

See Jose's subsequent message to the one I replied to.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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