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From: Segher Boessenkool <segher@kernel.crashing.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Christophe LEROY <christophe.leroy@c-s.fr>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>
Subject: Re: How is this possible - Register r30 contains 0xc2236400 instead of 0xc6236400
Date: Wed, 4 Jul 2018 08:45:15 -0500	[thread overview]
Message-ID: <20180704134515.GI16221@gate.crashing.org> (raw)
In-Reply-To: <87k1qbkuw0.fsf@concordia.ellerman.id.au>

On Wed, Jul 04, 2018 at 11:11:59PM +1000, Michael Ellerman wrote:
> Christophe LEROY <christophe.leroy@c-s.fr> writes:
> 
> > Kernel Oops at 0xc0334d5c for reading at address 0xc2236450 which 
> > corresponds to r30 + 80
> >
> > But r30 should contain what's at r3 + 16 that is at 0xc619ec10 so r30 
> > should be c6236400 as shown below (print_hex_dump(regs->gpr[3]) added at 
> > end of __die() )
> >
> > So how can r30 contain 0xc2236400 instead ?
> 
> The simplest answer is that memory was modified between the time we
> loaded it into r30 and when you print it.
> 
> So it did contain 0xc2236400 but has since been modified to now contain
> 0xc6236400.
> 
> The thing that makes me less certain, is that c6 would be the correct
> value (I think?), so it's been modified back to the correct value, which
> seems lucky.
> 
> Mysterious.

That depends.  Is this reproducible at all?  It is a single bit flip.


Segher

  reply	other threads:[~2018-07-04 13:46 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-03 13:20 How is this possible - Register r30 contains 0xc2236400 instead of 0xc6236400 Christophe LEROY
2018-07-04 13:11 ` Michael Ellerman
2018-07-04 13:45   ` Segher Boessenkool [this message]
2018-07-04 13:59     ` Christophe LEROY

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