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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Mon, 10 Jul 2017 13:54:58 +0100
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Subject: Re: [Qemu-devel] [RFC PATCH] target/arm: ensure eret exits the
 run-loop
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Richard Henderson <rth@twiddle.net>, QEMU Developers <qemu-devel@nongnu.org>, qemu-arm <qemu-arm@nongnu.org>, Etienne Carriere <etienne.carriere@linaro.org>, Joakim Bech <joakim.bech@linaro.org>, "Emilio G . Cota" <cota@braap.org>


Peter Maydell <peter.maydell@linaro.org> writes:

> On 10 July 2017 at 13:15, Alex Bennée <alex.bennee@linaro.org> wrote:
>> Looking at translate.c (32 bit arm), we have:
>>
>>   gen_srs
>>   gen_mrs_banked
>>   gen_msr_banked
>>
>> These all manually set:
>>
>>   gen_set_pc_im(s, s->pc - 4);
>>
>> before their respective helpers. I think setting the PC after the helper
>> is superfluous given we are will at that point be exiting the block.
>
> No, you need both. We do
>   gen_set_pc_im(s, s->pc - 4);
> before calling the helper because the helper might throw an
> exception, in which case the PC needs to point to that insn.
> We then call
>  gen_set_pc_im(dc, dc->pc);
> before exiting the block because if we leave execution by
> falling off the end of the block then the PC should point to
> the insn that comes next (ie just after the last one in the block)

OK I see now. I think I have a plan going forward.

>
> thanks
> -- PMM


--
Alex Bennée