linux-kernel - Re: [PATCH] FLAT: allow arches to declare a larger alignment than the slab

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Date:	Wed, 26 May 2010 08:59:26 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Jie Zhang <jie@...esourcery.com>
Cc:	Mike Frysinger <vapier.adi@...il.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Mike Frysinger <vapier@...too.org>, uclinux-dev@...inux.org,
	David Howells <dhowells@...hat.com>,
	David McCullough <davidm@...pgear.com>,
	Greg Ungerer <gerg@...inux.org>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	microblaze-uclinux@...e.uq.edu.au, Michal Simek <monstr@...str.eu>,
	linux-m32r@...linux-m32r.org,
	Hirokazu Takata <takata@...ux-m32r.org>,
	linux-kernel@...r.kernel.org,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [PATCH] FLAT: allow arches to declare a larger alignment than the 
	slab

On Wed, May 26, 2010 at 04:23, Jie Zhang <jie@...esourcery.com> wrote:
> On 05/26/2010 07:17 AM, Mike Frysinger wrote:
>>
>> i do not believe that is the reason for this, but unfortunately Jie is
>> about the only one atm who knows the inner details as for why shared
>> FLAT libraries requires 0x20 rather than just 0x4 alignment.  i do
>> know that there are some gcc fortran tests that fail otherwise.
>> hopefully he can remember details ;).
>>
> I encountered this issue when investigating some GCC test failures when
> using FLAT. I don't remember if they were in GCC Fortran testsuite. Some
> variables in those test cases were required to be aligned at a large
> boundary, for example 16-byte. I found 0x20 was a reasonably large alignment
> to fix all such failures in GCC testsuite.

I'm no FLAT expert (except for the AmigaOS HUNK loader :-), but isn't
the core of the
issue that alignment requirements in the object file are no longer
fulfilled after loading,
as a FLAT segment in memory is just allocated using kmalloc(), which may now
return 4-byte aligned blocks?

>From looking at <linux/flat.h>, it looks like the FLAT binary format
doesn't contain any
alignment information? So if I put __attribute__((aligned(4096))) in a
file, there's still
no guarantee it will actually be in memory at a 4Ki-aligned address?

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
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