linux-kernel - Re: [Qemu-devel] arm64 qemu tests failing in linux-next since 'arm64: kernel: enforce pmuserenr

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Date:	Thu, 7 Jan 2016 17:19:59 +0000
From:	Peter Maydell <peter.maydell@...aro.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mark Rutland <mark.rutland@....com>,
	Will Deacon <will.deacon@....com>,
	QEMU Developers <qemu-devel@...gnu.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Qemu-devel] arm64 qemu tests failing in linux-next since 'arm64:
 kernel: enforce pmuserenr_el0 initialization and restore'

On 7 January 2016 at 17:10, Guenter Roeck <linux@...ck-us.net> wrote:
> Strictly speaking you may be right (regression is a bit strong, though),
> but for my part I tend to be pragmatic.
>
> A warning message such as "Access to unimplemented register X" may be
> useful

You can get these from QEMU if you pass it "-d unimp", which logs
various kinds of things-not-yet-implemented, with a couple of caveats:
 * the warning is when we translate the code, not when we execute it
 * it won't warn for registers which we implement but not completely
   (eg only partial functionality or dummy reads-as-written)

In this case it printed
"write access to unsupported AArch64 system register op0:3 op1:3 crn:9
crm:14 op2:0"

The 'guest_errors' suboption to -d warns about things which appear
to be errors in the guest OS, for instance some kinds of UNPREDICTABLE,
and may also be of interest.

Neither guest_errors nor unimp are comprehensive (there are many
more situations where we don't warn than where we do) but they can
be helpful sometimes.

thanks
-- PMM
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