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From: Andreas Schwab <schwab@linux-m68k.org>
To: Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: [PATCH] powerpc: 32 bit getcpu VDSO function uses 64 bit
 instructions
References: <1417036288-22079-1-git-send-email-anton@samba.org>
 <1417041497.12952.2.camel@concordia> <1417045827.16862.32.camel@otta>
 <20141127160829.GA26139@gate.crashing.org>
Date: Thu, 27 Nov 2014 19:20:53 +0100
In-Reply-To: <20141127160829.GA26139@gate.crashing.org> (Segher Boessenkool's
 message of "Thu, 27 Nov 2014 10:08:29 -0600")
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Cc: linuxppc-dev@lists.ozlabs.org, Anton Blanchard <anton@samba.org>,
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Segher Boessenkool <segher@kernel.crashing.org> writes:

> On Wed, Nov 26, 2014 at 05:50:27PM -0600, Peter Bergner wrote:
>> On Thu, 2014-11-27 at 09:38 +1100, Michael Ellerman wrote:
>> > On Thu, 2014-11-27 at 08:11 +1100, Anton Blanchard wrote:
>> > > I used some 64 bit instructions when adding the 32 bit getcpu VDSO
>> > > function. Fix it.
>> > 
>> > Ouch. The symptom is a SIGILL I presume?
>> 
>> Nope, you don't get a SIGILL when executing 64-bit instructions in
>> 32-bit mode, so it'll happily just execute the instruction, doing
>> a full 64-bit compare.  I'm guessing that the upper 32-bits of both
>> r3 and r4 contain zeros, so we're probably just getting lucky.
>
> You will get a SIGILL if you run on 32-bit hardware.

Not on the 7447A, fwiw.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
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