linux-kernel - Re: [PATCH] binfmt_elf_fdpic: Magical stack pointer index, for NEW_AUX

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Message-ID: <20080519044141.GA10077@linux-sh.org>
Date:	Mon, 19 May 2008 13:41:41 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	David Howells <dhowells@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] binfmt_elf_fdpic: Magical stack pointer index, for NEW_AUX_ENT compat.

On Fri, May 16, 2008 at 12:22:33PM +0100, David Howells wrote:
> Paul Mundt <lethal@...ux-sh.org> wrote:
> 
> > While implementing binfmt_elf_fdpic on SH it quickly became apparent
> > that SH was the first platform to support both binfmt_elf_fdpic and
> > binfmt_elf, as well as the only of the FDPIC platforms to make use of the
> > auxvt.
> > 
> > Currently binfmt_elf_fdpic uses a special version of NEW_AUX_ENT() where
> > the first argument is the entry displacement after csp has been adjusted,
> > being reset after each adjustment. As we have no ability to sort this out
> > through the platform's ARCH_DLINFO, this index needs to be managed
> > entirely in create_elf_fdpic_tables(). Presently none of the platforms
> > that set their own auxvt entries are able to do so through their
> > respective ARCH_DLINFOs when using binfmt_elf_fdpic.
> > 
> > In addition to this, binfmt_elf_fdpic has been looking at
> > DLINFO_ARCH_ITEMS for the number of architecture-specific entries in the
> > auxvt. This is legacy cruft, and is not defined by any platforms in-tree,
> > even those that make heavy use of the auxvt. AT_VECTOR_SIZE_ARCH is
> > always available, and contains the number that is of interest here, so we
> > switch to using that unconditionally as well.
> > 
> > As this has direct bearing on how much stack is used, platforms that have
> > configurable (or dynamically adjustable) NEW_AUX_ENT calls need to either
> > make AT_VECTOR_SIZE_ARCH more fine-grained, or leave it as a worst-case
> > and live with some lost stack space if those entries aren't pushed (some
> > platforms may also need to purposely sacrifice some space here for
> > alignment considerations, as noted in the code -- although not an issue
> > for any FDPIC-capable platform today).
> > 
> > Signed-off-by: Paul Mundt <lethal@...ux-sh.org>
> 
> Acked-by: David Howells <dhowells@...hat.com>

As the SH FDPIC stuff depends on this, I'll fold this in to my 2.6.27
tree with the above Acked-by, which will trickle in to -mm and linux-next
directly.
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