kdump on ARM

[Rafal Jaworowski]

On 2010-02-17, at 18:00, M. Warner Losh wrote:

> In message: <20100217152900.GX43625 at cicely7.cicely.de>
>            Bernd Walter <ticso at cicely7.cicely.de> writes:
> : On Wed, Feb 17, 2010 at 04:19:41PM +0100, Bernd Walter wrote:
> : > On Wed, Feb 17, 2010 at 04:16:07PM +0100, Bernd Walter wrote:
> : > > On Wed, Feb 17, 2010 at 02:54:05PM +0000, Rui Paulo wrote:
> : > > > On 17 Feb 2010, at 14:18, Grzegorz Bernacki wrote:
> : > > > I wonder if this can't be made non arm conditional?
> : > 
> : > Ups - I'd just recovered from Mr. Sandman's work.
> : > So we all agree about.
> : > Nevertheless it should be verified if this is just a faulty struct
> : > definition.
> : > On the other hand I think it is not because someone else wrote it is
> : > a brokem on mips as well.
> : 
> : I'm really still sleeping - noone mentioned mips at all.
> : > > Either this struct is properly aligned or not.
> : > > So why should this be made conditional?
> : > > Non strict alignment architecturs also have problems with this, but
> : > > it is usualy just speed penalties.
> : > > There is one ARM sepcific struct missalignment problem.
> : > > In this case we usually add __packed macro to structure definition.
> : > > For most structures this usually means no change on other
> : > > archtitectures and we only declare the struct to forcibly be what the
> : > > programmer already expected.
> : > > Only a few programmers are aware that they expect something from
> : > > structures, which is not garantied.
> 
> This code is clearly nutso when it comes to alignment.  I've come up
> with a slightly better patch.  I'd though about doing the structure
> assignment that I suggested in a prior note, but the compiler is free
> to assume alignment when copying the structures, which may end badly.
> There's no way we can add __packed or __aligned easily to this code
> (although the ktrstat and ktrsockaddr routines should be able to have
> that annotation, a quick test suggests that the annotations I tried
> didn't take right).
> 
> I don't have a good ARM setup at the moment to actually test these
> changes.  Can others test them?  They seem to work for me on x86, but
> that isn't saying much.

Thanks, this looks better. We'll test this in our set-up and verify, but only tomorrow I guess...

Rafal