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

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Message-ID: <4992E92C.5000000@gmail.com>
Date:	Thu, 12 Feb 2009 00:05:16 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Brian Gerst <brgerst@...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

Brian Gerst wrote:
> 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.

Right, I forgot about the generic ones.  We can pass pointer to
pt_regs to all of them like x86_64 does but yeah we're likely to lose
more than we gain by doing that.  :-(

-- 
tejun
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