Re: [Qemu-devel] [PATCH v6 01/22] instrument: Add documentation

From: Peter Maydell <peter.maydell@linaro.org>
To: Peter Maydell <peter.maydell@linaro.org>,
	"Emilio G. Cota" <cota@braap.org>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Markus Armbruster <armbru@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v6 01/22] instrument: Add documentation
Date: Tue, 19 Sep 2017 14:09:07 +0100	[thread overview]
Message-ID: <CAFEAcA9pc8Q4THRK8P3y_5OFPsJt9qYg9zNG5Wh6m_LYhTAyag@mail.gmail.com> (raw)
In-Reply-To: <87d16o53xr.fsf@frigg.lan>

On 18 September 2017 at 18:09, Lluís Vilanova <vilanova@ac.upc.edu> wrote:
> TCI still has a separation of translation-time (translate.c) and execution-time
> (interpreting the TCG opcodes), and I don't think that's gonna go away anytime
> soon.
>
> Even if it did, I think there still will be a translation/execution separation
> easy enough to hook into (even if it's a "fake" one for the cold-path
> interpreted instructions).

As a slightly more immediate and practical example, I'm currently
implementing the v8M "SG" instruction. This is a somewhat weird
corner-case of an instruction (it's the only instruction you can
execute in non-secure state from a code region that's secure).
I'm implementing it in the exception-handling code path: if we
detect "NS execute from S memory" we throw a QEMU internal exception,
and in the cpu_do_interrupt code we either (a) identify that this
is the SG instruction and execute it or (b) generate the right guest
CPU exception.

That's definitely executing an instruction, and there's no translation
time for it...

thanks
-- PMM