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Re: [Qemu-ppc] How to debug crash in TCG code?

From: Mark Cave-Ayland
Subject: Re: [Qemu-ppc] How to debug crash in TCG code?
Date: Mon, 21 Aug 2017 06:39:24 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

On 20/08/17 21:51, BALATON Zoltan wrote:

> On Sat, 19 Aug 2017, BALATON Zoltan wrote:
>> On Thu, 27 Jul 2017, BALATON Zoltan wrote:
>>> Hello,
>>> I'm getting a segfault in generated code that I don't know how to
>>> debug further. The back trace shows:
>> This can be reproduced trying to boot this iso:
>> http://www.xenosoft.de/Sam460ex_Debian_Jessie-3.iso
> With the latest version of the series I've posted today no iso is even
> needed, it happens when the firmware is accessing the SATA controller
> even without any disks (but depends on which firmware version I use).
> This problem also seems to be timing dependent: it disappears if I add
> -d in_asm but happens with --accel tcg,thread=single so it does not seem
> to be a threading issue but I don't know what to do now. Any advice on
> what to try?

Are you running QEMU with -icount? That should at least give you more
deterministic behaviour if the fault is related to IO.

>> with the Sam460ex emulation posted here:
>> http://lists.nongnu.org/archive/html/qemu-ppc/2017-08/msg00112.html
>> This leads to a QEMU crash while reading from the SATA controller (the
>> addr below belongs to that controller) but not always, it depends on
>> the amount of code run in the guest and the problem may go away or
>> happen elsewhere when I add debug logs to firmware code. Does anyone
>> have an idea how to debug this?
>> Could it be somehow related to my other problem described here:
>> http://lists.nongnu.org/archive/html/qemu-ppc/2017-08/msg00220.html
>> Any help is greatly appreciated.

It looks like you're faulting at the same address both times 3623882752
(0xd8001000). What does that look like with respect to your memory
layout, i.e. compare with the output of "info mtree" from the QEMU monitor?



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