From: Peter Bergner <bergner@vnet.ibm.com>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: linuxppc-dev@lists.ozlabs.org, Anton Blanchard <anton@samba.org>,
paulus@samba.org
Subject: Re: [PATCH] powerpc: 32 bit getcpu VDSO function uses 64 bit instructions
Date: Thu, 27 Nov 2014 11:41:40 -0600 [thread overview]
Message-ID: <1417110100.16862.36.camel@otta> (raw)
In-Reply-To: <20141127160829.GA26139@gate.crashing.org>
On Thu, 2014-11-27 at 10:08 -0600, Segher Boessenkool wrote:
> On Wed, Nov 26, 2014 at 05:50:27PM -0600, Peter Bergner wrote:
> > 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.
Ha, I completely forgot about 32-bit hardware. Anyway, I looked
at the ISA, and cmpdi and cmpwi are just extended mnemonics for
cmpi, with cmpdi setting the L field to 1. Probably on 32-bit
hardware, the hardware is just ignoring the L bit being set and
doing a cmpwi for us???
Peter
next prev parent reply other threads:[~2014-11-27 17:41 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-26 21:11 [PATCH] powerpc: 32 bit getcpu VDSO function uses 64 bit instructions Anton Blanchard
2014-11-26 22:38 ` Michael Ellerman
2014-11-26 23:23 ` Segher Boessenkool
2014-11-26 23:28 ` Segher Boessenkool
2014-11-26 23:50 ` Peter Bergner
2014-11-27 16:08 ` Segher Boessenkool
2014-11-27 17:41 ` Peter Bergner [this message]
2014-11-27 20:50 ` Segher Boessenkool
2014-11-28 2:00 ` Benjamin Herrenschmidt
2014-11-27 18:20 ` Andreas Schwab
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