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Subject: Re: [PATCH] powerpc: 32 bit getcpu VDSO function uses 64 bit
 instructions
From: Peter Bergner <bergner@vnet.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>
In-Reply-To: <1417041497.12952.2.camel@concordia>
References: <1417036288-22079-1-git-send-email-anton@samba.org>
 <1417041497.12952.2.camel@concordia>
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Date: Wed, 26 Nov 2014 17:50:27 -0600
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Cc: linuxppc-dev@lists.ozlabs.org, paulus@samba.org,
 Anton Blanchard <anton@samba.org>
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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.


> Could we catch this by forcing -m32 in the CFLAGS for vdso32 ?

As Segher mentioned, GCC passing -many down to the assembler means
-m32 won't help.  It was due to Anton disabling that gcc "feature",
that this was caught.

Peter