linux-kernel - Re: Detailed Stack Information Patch [0/3]

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Message-ID: <20090331190214.GB25879@logfs.org>
Date:	Tue, 31 Mar 2009 21:02:14 +0200
From:	Jörn Engel <joern@...fs.org>
To:	Stefani Seibold <stefani@...bold.net>
Cc:	Andi Kleen <andi@...stfloor.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: Detailed Stack Information Patch [0/3]

On Tue, 31 March 2009 20:22:15 +0200, Stefani Seibold wrote:
> Am Dienstag, den 31.03.2009, 17:49 +0200 schrieb Andi Kleen:
> > Stefani Seibold <stefani@...bold.net> writes:
> 
> > > - Misuse the thread stack for big temporary data buffers
> > 
> > That would be better checked for at compile time
> > (except for alloca, but that is quite rare)
> 
> Fine but it did not work for functions like:
> 
> void foo(int n)
> {
> 	char buf[n*1024];
> 
> }
> 
> This is valid with gcc.

Good call.  checkstack should look for those as well.  It is certainly
possible to detect statically and warn about:

  10:   29 c4                   sub    %eax,%esp

Runaway recursions are a different matter, though.  The code I once had
to detect them depends on an old version of smatch, which in turn
depends on gcc 3.1.  And even assuming this was in a reasonable shape, I
still don't know what to do about it.  The kernel has thousands of
recursions and trying to work out how deep each one may stack is a
never-ending project.

Jörn

-- 
A quarrel is quickly settled when deserted by one party; there is
no battle unless there be two.
-- Seneca
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