linux-kernel - Re: "elf core dump: fix get_user use" breaks mips compilation

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Message-ID: <20090216233216.GA19484@linux-mips.org>
Date:	Mon, 16 Feb 2009 23:32:16 +0000
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Martin Michlmayr <tbm@...ius.com>
Cc:	Roland McGrath <roland@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: "elf core dump: fix get_user use" breaks mips compilation

On Mon, Feb 16, 2009 at 01:01:36PM +0100, Martin Michlmayr wrote:

> Hi Roland,
> 
> Your change "elf core dump: fix get_user use"  (which made it into
> 2.6.28.5) breaks the compilation on MIPS (which sets -Werror):
> 
>   CC      arch/mips/kernel/binfmt_elfn32.o
> cc1: warnings being treated as errors
> arch/mips/kernel/../../../fs/binfmt_elf.c: In function ‘vma_dump_size’:
> arch/mips/kernel/../../../fs/binfmt_elf.c:1202: warning: ‘word’ may be used uninitialized in this function
> make[1]: *** [arch/mips/kernel/binfmt_elfn32.o] Error 1

Partially expanding get_user() the code basically does this:

	int word;

	if (access_ok(...))
		__get_user(word, header);
	else
		word = 0;

And gcc is unable to figure out that word will always be assigned to by
both paths of the if statement.  Older gcc versions used to have that
problem.  I can't reproduce your problem with gcc 4.3.2 and I assume
you're using something older than that?

  Ralf
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