From: "Alex Bennée" <alex.bennee@linaro.org>
To: qemu-devel@nongnu.org
Subject: Re: SIGSEGV question (Hexagon)
Date: Tue, 05 Nov 2019 10:13:22 +0000 [thread overview]
Message-ID: <87a79ak4vx.fsf@linaro.org> (raw)
In-Reply-To: <BYAPR02MB4886C25E683DEAFB1B8121FCDE7F0@BYAPR02MB4886.namprd02.prod.outlook.com>
Taylor Simpson <tsimpson@quicinc.com> writes:
> Philippe suggested that I run the TCG tests for Hexagon. Thanks Philippe!!
>
>
>
> I discovered that I’m not handling SIGSEGV properly. We pass other signal tests, but not this one. I’m hoping someone can help.
> The first thing that I realized is that I hadn’t provided a tlb_fill function for CPUClass. What is this function supposed to
> do?
It's does two subtly different things depending on system emulation vs
user-mode:
* @tlb_fill: Callback for handling a softmmu tlb miss or user-only
* address fault. For system mode, if the access is valid, call
* tlb_set_page and return true; if the access is invalid, and
* probe is true, return false; otherwise raise an exception and
* do not return. For user-only mode, always raise an exception
* and do not return.
>I looked at other targets and found they are setting
>cs->exception_index to something and then call cpu_loop_exit_restore.
cpu_loop_exit_* brings you back to the sigsetjmp of cpu_exec short
circuiting any more TCG code. For linux-user the exception code should
get kicked back to cpu_loop. As we are jumping out of the TCG all your
CPUState should be coherent by this point. For pure TCG code this should
be the case. If you have faulted in a helper this could be problematic.
> I tried various values for exception_index, but the best I seem to get
> is re-executing the offending instruction forever.
For linux-user you need to then catch that exception in your cpu_loop
code and do the requisite setting up (probably a queue_signal in this
case). This should get picked up by the process_pending_signal at the
end of your cpu_loop which will then set the PC as appropriate to your
signal handler.
This is where we find out if your CPUState is now consistent ;-)
>
>
>
> Any insight would be greatly appreciated.
>
>
>
> Thanks,
>
> Taylor
>
>
>
>
>
> PS The only other bug that these tests uncovered was that truncate isn’t implemented properly. This was straightforward to fix.
--
Alex Bennée
next prev parent reply other threads:[~2019-11-05 10:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-04 22:59 SIGSEGV question (Hexagon) Taylor Simpson
2019-11-05 10:13 ` Alex Bennée [this message]
2019-11-05 19:30 ` Taylor Simpson
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