linux-kernel - Re: [PATCH v12 7/7] ARM: kprobes: enable OPTPROBES for ARM 32

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Date:	Fri, 5 Dec 2014 19:57:43 +0000
From:	Peter Maydell <peter.maydell@...aro.org>
To:	"Jon Medhurst (Tixy)" <tixy@...aro.org>
Cc:	Wang Nan <wangnan0@...wei.com>, masami.hiramatsu.pt@...achi.com,
	lizefan@...wei.com, Russell King <linux@....linux.org.uk>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	arm-mail-list <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v12 7/7] ARM: kprobes: enable OPTPROBES for ARM 32

On 5 December 2014 at 10:10, Jon Medhurst (Tixy) <tixy@...aro.org> wrote:
> I don't know much about QEMU and have never used it, but I'm assuming
> QEMU doesn't make any attempt to simulate caches like the data cache,
> instruction cache, TLBs, branch predictor? Does it even emulate multiple
> CPUs with multiple host CPU threads? Basically, I very much doubt QEMU
> is a very good test of kernel code in general, and especially code that
> modifies code and has multiple cpus running in parallel.

You're generally correct here, yes. QEMU doesn't emulate caches
or TLBs or branch predictors, and we currently emulate SMP by
doing round-robin execution on a single host thread (though
we're working on that for performance reasons). There are also
a range of buggy-guest-code conditions (alignment faults, for
instance) which we don't emulate. I tend to think of QEMU's
overall philosophy as "run known-good code quickly" rather
than "diagnose problems in buggy code". So it's definitely wise
to test complicated kernel code like this on real hardware
(though of course QEMU may be very helpful in speeding up the
development cycle compared to h/w).

thanks
-- PMM
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