linux-kernel - Re: RELEASE BLOCKER: Linux doesn't follow x86/x86-64 ABI wrt direction flag

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Date:	Thu, 06 Mar 2008 01:49:11 +0100
From:	Aurelien Jarno <aurelien@...el32.net>
To:	Chris Lattner <clattner@...le.com>
CC:	Michael Matz <matz@...e.de>, "H.Peter Anvin" <hpa@...or.com>,
	Richard Guenther <richard.guenther@...il.com>,
	Joe Buck <Joe.Buck@...opsys.com>, Jan Hubicka <hubicka@....cz>,
	linux-kernel@...r.kernel.org, gcc@....gnu.org
Subject: Re: RELEASE BLOCKER: Linux doesn't follow x86/x86-64 ABI wrt direction
 flag

Chris Lattner a écrit :
>>>> Richard Guenther wrote:
>>>>> We didn't yet run into this issue and build openSUSE with 4.3 since
>>>>> more
>>>>> than
>>>>> three month.
>>>>
>>>> Well, how often do you take a trap inside an overlapping memmove()?
>>>
>>> How hard is it to change the kernel signal entry path from "pushf" to
>>> "pushf;cld"?  Problem solved, no?
>>
>> The problem is with old kernels, which by definition stay unfixed.
> 
> My impression was that the problem occurs in GCC compiled code in the
> kernel itself, not in user space:
> 
> 1. User space has direction flag set.
> 2. signal occurs
> 3. kernel code is entered
> 4. kernel code does string operation <boom>

Wrong. Except maybe for the Hurd kernel. For other kernels:

  4. signal handler is called
  5. signal handler does string operation <boom>

The GCC used to compile the kernel doesn't matter. Using gcc 4.3 to
compile the user code triggers the bug.

-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   aurel32@...ian.org         | aurelien@...el32.net
   `-    people.debian.org/~aurel32 | www.aurel32.net
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