linux-kernel - Re: stack overflow on Sparc64

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Message-ID: <Pine.LNX.4.64.0806190845300.6330@engineering.redhat.com>
Date:	Thu, 19 Jun 2008 09:01:58 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	David Miller <davem@...emloft.net>
cc:	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
	agk@...hat.com
Subject: Re: stack overflow on Sparc64

On Wed, 18 Jun 2008, David Miller wrote:

> From: Mikulas Patocka <mpatocka@...hat.com>
> Date: Thu, 19 Jun 2008 01:17:39 -0400 (EDT)
>
>> I see ... the callee writes arguments into caller's stack frame, if it has
>> variable number of arguments. That it misdesign, the callee should write
>> registers arguments into it's own frame like on AMD64 (then this space
>> would be allocated only if needed).
>
> The callee can do this even for non-variable argument lists.
>
> It's like a set of pre-allocated stack slots for those incoming
> argument registers when reloading under register pressure.
>
> In my opinion it is better to put this onus on the callee because only
> the callee knows if it needs to pop these values onto the stack to
> alleviate register pressure.
>
> I think it might be possible for the compiler to only use 176 bytes.
> I'll take a look at the gcc sparc backend and the ABI specification
> to see if this is the case.

Yes, it could be shrunk to 176 bytes. Maybe there could be some 
performance problems if the spills are cacheline-unaligned. Or better --- 
make special -mkernel-abi function to gcc that will drop this area at all 
and make 128-byte frames. In kernel it wouldn't matter that ABI is 
incompatible.

Mikulas
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