From: Michael Ellerman <michael@ellerman•id.au>
To: Matt Evans <matt@ozlabs•org>
Cc: linuxppc-dev@ozlabs•org, Paul Mackerras <paulus@samba•org>,
"K.Prasad" <prasad@linux•vnet.ibm.com>
Subject: Re: [PATCH] powerpc: Emulate most Book I instructions in emulate_step()
Date: Thu, 03 Jun 2010 11:43:55 +1000 [thread overview]
Message-ID: <1275529435.22020.1.camel@concordia> (raw)
In-Reply-To: <4C0700FD.6060303@ozlabs.org>
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On Thu, 2010-06-03 at 11:10 +1000, Matt Evans wrote:
> Paul Mackerras wrote:
> > [snip]
> > The second alternative -- emulating the lwarx/stwcx and all the
> > instructions in between -- sounds complicated but turns out to be
> > pretty straightforward in fact, since the code for each instruction is
> > pretty small, easy to verify that it's correct, and has little
> > interaction with other code.
>
> Easy to verify -- visually or logically?
>
> Having had a little experience with interpreters 'invisibly' operating
> behind the scenes I am all for very rigorous testing of these things.
> I have lost at least four of my nine lives to incorrect flag values,
> odd data problems and hideous heisenbugs etc. of such interpreters.
> Looked at another way, you'd be surprised how much one can break in an
> interpreter and still successfully run various programs.
>
> Presumably your first pass is completely correct already, but I'm
> thinking that if any future changes are made to it
> it would be good to include test code/modes alongside the interpreter
> so others can check alterations. E.g. include the "run user program
> interpreted" test switch patch, or even better compare the interpreted
> state to real hardware execution. There are other more directed test
> strategies (e.g. handwritten tests, random code) but these would be a
> good start.
Emphatic nod. We all trust Paulus to get this right, but I for one would
not be game to touch it without a test suite.
It's ripe territory for a boot time selftest IMHO.
cheers
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next prev parent reply other threads:[~2010-06-03 1:43 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-02 11:29 [PATCH] powerpc: Emulate most Book I instructions in emulate_step() Paul Mackerras
2010-06-02 12:45 ` Kumar Gala
2010-06-03 0:47 ` Paul Mackerras
2010-06-03 1:10 ` Matt Evans
2010-06-03 1:43 ` Michael Ellerman [this message]
2010-06-03 6:25 ` Kumar Gala
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