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

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Message-ID: <8bd0f97a0903041348i2c88343fvbc7a1b6d428c7e7a@mail.gmail.com>
Date:	Wed, 4 Mar 2009 16:48:04 -0500
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Johannes Weiner <jw@...ix.com>
Cc:	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 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.

> -       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);

can this be cleaned up a bit so that the argv/envp assignment happens
by using sp before aligning sp ?  that would be defensive coding wrt
preventing sp adjustment falling out of line with argv initialization,
and cut down on duplicated code.

> -       put_user(argc,--sp);
> +       put_user(argc,sp);

might as well fix the style issues here while you're changing code ...
stick a space after the comma

> @@ -854,7 +861,7 @@ static int load_flat_binary(struct linux
>        stack_len = TOP_OF_ARGS - bprm->p;             /* the strings */
>        stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */
>        stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */
> -
> +       stack_len += FLAT_DATA_ALIGN;

this seems weird.  alignment is for aligning data, not padding it out
some value ...
-mike
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