linux-kernel - Re: [PATCH] FDPIC: Ignore the loader's PT_GNU

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Message-ID: <20090709101930.GJ10937@elf.ucw.cz>
Date:	Thu, 9 Jul 2009 12:19:30 +0200
From:	Pavel Machek <pavel@....cz>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	David Howells <dhowells@...hat.com>, rgetz@...ckfin.uclinux.org,
	lethal@...ux-sh.org, gerg@...inux.org,
	uclinux-dist-devel@...ckfin.uclinux.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] FDPIC: Ignore the loader's PT_GNU_STACK when
	calculating the stack size

On Wed 2009-07-08 14:48:51, Mike Frysinger wrote:
> On Fri, Jul 3, 2009 at 23:34, Pavel Machek wrote:
> > On Wed 2009-07-08 12:01:40, David Howells wrote:
> >> Pavel Machek <pavel@....cz> wrote:
> >>
> >> > The patch seems wrong to me; loader needs the stack, too, right?
> >> >
> >> > What about making sure that the loader specifies reasonable stack
> >> > size, instead?
> >>
> >> The loader doesn't need its own stack, unless it _is_ the executable.  It uses
> >> the executable's stack.  The problem is that the executable and the loader can
> >> both specify the stack size for NOMMU, but which one do we pick, or do we
> >> consider both.
> >
> > Imageine loader needs 64K, while executable only needs 4K. You surely
> > want to execute it with 64K stack, because it will not fit into 4K?
> 
> i really dont think this is realistic.  there is exactly one ldso that
> everyone uses under FDPIC ELF, and it needs a very minuscule stack.

Not very realistic; but that argues that the patch is NOP.

And if it _is_ realistic, the patch adds a bug.

=> patch is bad idea.
									Pavel

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