Date: Mon, 14 Aug 2000 12:09:35 +0200 From: Pascal Bouchareine <pb@grolier.fr> To: "MATTHEW JOHN,LUCKIE" <mjl12@waikato.ac.nz> Cc: alpha@FreeBSD.ORG, jdp@polstra.com Subject: Re: kernel modules/unaligned access fault Message-ID: <20000814120935.A21561@kalou.in.grolier.fr> In-Reply-To: <45E87454FFC2D211AD9800508B65009420F8E4@stu-ex1.waikato.ac.nz>; from mjl12@waikato.ac.nz on Mon, Aug 14, 2000 at 12:57:54PM %2B1200 References: <45E87454FFC2D211AD9800508B65009420F8E4@stu-ex1.waikato.ac.nz>
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On Mon, Aug 14, 2000 at 12:57:54PM +1200, MATTHEW JOHN,LUCKIE wrote:
> would you mind explaining to me the rules of programming for the alpha in
> terms of unaligned accesses.
Well i'm not sure i'm aware enough to explain. Let's try it.
IMHO, aligned access means, you may write memory using a (type) pointer,
but you need to write at an address that is on a (type-size) boundary.
Ie, if ((ptr % sizeof(ptr) != 0)), (miss casts), you're wrong.
If you have a struct :
s {
short int a;
long b;
}
Then a is aligned on a 2 bytes boundary, but (if compiler doesn't help),
b may not be.
With struct issues, usually when accessing userspace from kernel space,
i guess the best way is to prepare locally your structure, and then
bcopy() it to user space.
I have the same problem with the vfs_aio code, where suword() is used
to access int in user space structures. I was wondering how to fix it
when you wrote your mail..
Hope this helps,
kalou
--
Kalou.
ldiq t0, 0xbeeffedadeadbabe
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