Re: [sodaville] [PATCH 3/4] of/dtc: force dtb size to modulo 32 bytes

[Dirk Brandewie <dirk.brandewie-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 11/11/2010 04:47 PM, H. Peter Anvin wrote:
> On 11/11/2010 04:03 PM, dirk.brandewie-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:
>> From: Dirk Brandewie<dirk.brandewie-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>>
>> This patch forces the size of the DTB to be modulo 32 bytes. This is
>> needed to support linking multiple DTB's into a single section in the
>> image. GCC wants structures to be 32 byte aligned without this change
>> DTB's after the first in the section may not be properly aligned so
>> the flat tree parsing code will fall over.
>>
>> Signed-off-by: Dirk Brandewie<dirk.brandewie-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>
> I don't think 32 is a universal number; it should depend on the ABI.  On
> x86, for one thing, I'm pretty sure that there is no particular
> alignment requirements beyond the natural alignment of the data items,
> for example.
>
> Although 32 is probably conservative on any platform, please flag the
> origin of this with a comment, or make it a constant defined in a header
> file... otherwise, if this breaks for whatever reason it'll be near
> impossible to find.
>

I will change . = ALIGN(32); to STRUCT_ALIGN();

from vmlinux.lds.h:
/*
  * Align to a 32 byte boundary equal to the
  * alignment gcc 4.5 uses for a struct
  */
#define STRUCT_ALIGN() . = ALIGN(32)

--Dirk