linux-kernel - Re: [RFC/PATCH] RLIMIT_ARG

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Message-ID: <47C84C6C.2000201@gmail.com>
Date:	Fri, 29 Feb 2008 19:18:20 +0100
From:	Michael Kerrisk <michael.kerrisk@...glemail.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michael Kerrisk <michael.kerrisk@...glemail.com>,
	aaw <aaw@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>,
	carlos@...esourcery.com, Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.org>, drepper@...hat.com,
	mtk.manpages@...il.com, Geoff Clare <gwc@...ngroup.org>
Subject: Re: [RFC/PATCH] RLIMIT_ARG_MAX

Peter Zijlstra wrote:
> On Fri, 2008-02-29 at 09:35 -0800, Linus Torvalds wrote:
>> On Fri, 29 Feb 2008, Peter Zijlstra wrote:
>>> You fail to mention that <23 will still fault the first time it tries to
>>> grow the stack when you set rlimit_stack to 128k and actually supply
>>> 128k of env+arg.
>> So? That's what rlimit_stack has always meant (and not just on Linux 
>> either, afaik). That's not a bug, it's a feature. If the system has a 
>> limited stack, it has a limited stack. That's what RLIMIT_STACK means.
> 
> Well, I agree with that point. It just that apparently POSIX does not.
> According to Michael POSIX does not consider the arg+env array part of
> the stack proper.

AFAIK, POSIX.1 makes no requirement here.  Most (all?) Unix systems have 
traditionally placed argv+environ just above the stack, but that isn't 
required.

My reading of POSIX.1 (and POSIX doesn't seem very explicit on this 
point), is that the limits on argv+environ and on stack are decoupled, 
since POSIX specifies RLIMIT_STACK and sysconf(_SC_ARG_MAX) and doesn't 
specify any relationship between the two.
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