From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 41LMhX113HzF1NW for ; Wed, 4 Jul 2018 23:46:03 +1000 (AEST) Date: Wed, 4 Jul 2018 08:45:15 -0500 From: Segher Boessenkool To: Michael Ellerman Cc: Christophe LEROY , "linuxppc-dev@lists.ozlabs.org" , Benjamin Herrenschmidt , Paul Mackerras Subject: Re: How is this possible - Register r30 contains 0xc2236400 instead of 0xc6236400 Message-ID: <20180704134515.GI16221@gate.crashing.org> References: <09ae0460-11e7-c893-5a5f-55e55a3ef372@c-s.fr> <87k1qbkuw0.fsf@concordia.ellerman.id.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <87k1qbkuw0.fsf@concordia.ellerman.id.au> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Jul 04, 2018 at 11:11:59PM +1000, Michael Ellerman wrote: > Christophe LEROY 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