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

Geert Uytterhoeven geert at linux-m68k.org
Wed May 26 02:59:26 EDT 2010


On Wed, May 26, 2010 at 04:23, Jie Zhang <jie at codesourcery.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 at linux-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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