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Re: [Qemu-arm] [PATCH v3 0/3] hmp: fix "dump-quest-memory" segfault


From: David Gibson
Subject: Re: [Qemu-arm] [PATCH v3 0/3] hmp: fix "dump-quest-memory" segfault
Date: Wed, 13 Sep 2017 15:34:36 +1000
User-agent: Mutt/1.8.3 (2017-05-23)

On Tue, Sep 12, 2017 at 04:36:30PM +0100, Dr. David Alan Gilbert wrote:
> * Thomas Huth (address@hidden) wrote:
> > On 12.09.2017 16:46, Greg Kurz wrote:
> > > On Tue, 12 Sep 2017 16:01:46 +0200
> > > Laurent Vivier <address@hidden> wrote:
> > > 
> > >> Fix aarch64 and ppc when dump-guest-memory is
> > >> used with none machine type and no CPU.
> > >>
> > >> The other machine types don't have the problem.
> > >>
> > >> Update test-hmp, to test none machine type
> > >> with (2 MB) and without memory, and add a test
> > >> to test dump-quest-memory without filter parameters
> > >> (it needs the fix from Cornelia Huck to work)
> > >>
> > >> v3:
> > >>   - remove blank line after a comment
> > >>   - forbid memory dump when there is no CPU
> > >>
> > > 
> > > So in the end, we would forbid dump on aarch64 and
> > > ppc, while it is allowed on i386... I don't really
> > > care about which behavior is more appropriate but
> > > I guess they should be consistent at least.
> > 
> > It's kind of consistent: Allow it on architectures with fixed endianess,
> > but disallow it on architectures without fixed endianess ;-)
> 
> Another way to put it is that you can dump unless you need
> information about the CPU.
> 
> It also makes me wonder what happens on those CPUs that can
> change their endianness dynamically.

We already have code for that on ppc, we actually look in on the CPU's
mode register at dump time to decide which.  Theoretically that could
still be tricked, but in the almost-always case of boot an OS which
sets the endianness then leaves it there, it should be fine.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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