linux-kernel - Re: [PATCH 2/3] x86: Pass in pt_regs pointer for syscalls that need it

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Message-ID: <73c1f2160902110659i776e1d89qc23d89363881572e@mail.gmail.com>
Date:	Wed, 11 Feb 2009 09:59:23 -0500
From:	Brian Gerst <brgerst@...il.com>
To:	Tejun Heo <htejun@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] x86: Pass in pt_regs pointer for syscalls that need 
	it

On Wed, Feb 11, 2009 at 9:48 AM, Tejun Heo <htejun@...il.com> wrote:
> Tejun Heo wrote:
>>> I checked the disassembly of these functions and didn't see this
>>> happen on gcc 4.3.0.
>>
>> Well, tracking down why run_init_process() is returning 0 with
>> -fstack-protector wasn't much of fun.  These breakages are very subtle
>> and if we're gonna pass in pointer to pt_regs anyway and thus can
>> guarantee such breakage can't happen at no additional cost, I think we
>> should do that even if it means slightly more argument fetching in a
>> few places.
>
> In addition, if we do that, we can remove the horrible
> asmlinkage_protect() thing altogether.

Like I said before, the tail-call optimization problem isn't limited
to just this set of syscalls.  There are only two real ways to fix it.
 1) Set up a real stack frame for the syscalls instead of overalying
pt_regs, or 2) patch gcc to tell it not to touch the args area of the
stack.

--
Brian Gerst
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