linux-kernel - Re: [patch -v2] flat: fix data sections alignment

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Date:	Thu, 5 Mar 2009 11:53:46 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	Johannes Weiner <jw@...ix.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	Russell King <rmk@....linux.org.uk>,
	Bryan Wu <cooloney@...nel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	Greg Ungerer <gerg@...inux.org>, linux-kernel@...r.kernel.org
Subject: Re: [patch -v2] flat: fix data sections alignment

On Wed, Mar 04, 2009 at 04:48:04PM -0500, Mike Frysinger wrote:
> On Wed, Mar 4, 2009 at 08:51, Johannes Weiner wrote:
> > --- a/fs/binfmt_flat.c
> > +++ b/fs/binfmt_flat.c
> > +#ifdef ARCH_SLAB_MINALIGN
> > +#define FLAT_DATA_ALIGN        (ARCH_SLAB_MINALIGN)
> > +#else
> > +#define FLAT_DATA_ALIGN        (sizeof(void *))
> > +#endif
> > ...
> > +       sp = (unsigned long *) ((unsigned long)sp & -FLAT_DATA_ALIGN);
> > ...
> > -               datapos = realdatastart + MAX_SHARED_LIBS * sizeof(unsigned long);
> > +               datapos = ALIGN(realdatastart + MAX_SHARED_LIBS * sizeof(unsigned long),
> > +                               FLAT_DATA_ALIGN);
> > ...
> > -               datapos = realdatastart + MAX_SHARED_LIBS * sizeof(unsigned long);
> > +               datapos = ALIGN(realdatastart + MAX_SHARED_LIBS * sizeof(unsigned long),
> > +                               FLAT_DATA_ALIGN);
> 
> why not make FLAT_DATA_ALIGN into a macro ?  then it'd naturally
> follow the existing ALIGN() behavior.

datapos is aligned to the next higher bound while the stack pointer
grows down and is therefor aligned to the next lower bound.  A
FLAT_DATA_ALIGN() doesn't make sense.

> > -       sp = (unsigned long *) ((-(unsigned long)sizeof(char *))&(unsigned long) p);
> > -
> > -       sp -= envc+1;
> > -       envp = sp;
> > -       sp -= argc+1;
> > -       argv = sp;
> > +       sp = (unsigned long *)p;
> > +       sp -= (envc + argc + 2) + 1 + (flat_argvp_envp_on_stack() ? 2 : 0);
> > +       sp = (unsigned long *) ((unsigned long)sp & -FLAT_DATA_ALIGN);
> > +       argv = sp + 1 + (flat_argvp_envp_on_stack() ? 2 : 0);
> > +       envp = argv + (argc + 1);

	Hannes
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