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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Wed, 30 Nov 2016 18:12:07 +0000
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Subject: Re: [Qemu-devel] Confusion regarding temporaries with branch
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To: Richard Henderson <rth@twiddle.net>
Cc: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>, qemu-devel@nongnu.org


Richard Henderson <rth@twiddle.net> writes:

> On 11/30/2016 08:55 AM, Alex Bennée wrote:
>>
>> Nikunj A Dadhania <nikunj@linux.vnet.ibm.com> writes:
>>
>>> Hi,
>>>
>>> I was writing one instruction and hit following issue:
>>>
>>> [snip]/qemu/tcg/tcg.c:2039: tcg fatal error
>>> qemu-ppc64le: [snip]/qemu/translate-all.c:175: tb_lock: Assertion `!have_tb_lock' failed.
>>> Segmentation fault (core dumped)
>>
>> This is confusing because something is trying to take the tb_lock while
>> you are in code generation. tb_lock is held for code generation to
>> ensure serialisation of generation.
>
> Yes, I've seen this myself.  I never got around to reporting the "problem"
> properly.  It's a confusing side effect of a SIGSEGV arriving during tcg code
> generation.  The signal handler longjmps back with unexpected locks
> held.

So this is a SEGV which belongs to the translation code rather than the
guest?

There are places in the cpu loop where we exit that should reset the
locks on a restart - see tb_lock_reset() so I'm not quite sure what has
happened here.

>
> Probably we should simply crash earlier and less confusingly.
>
>
> r~


--
Alex Bennée