Re: [Qemu-devel] Confusion regarding temporaries with branch conditional

["Alex Bennée" <alex.bennee@linaro.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