linux-kernel - Re: Missing operand for tlbie instruction on Power7

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Message-ID: <20151004000009.GA10997@gate.crashing.org>
Date:	Sat, 3 Oct 2015 19:00:09 -0500
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Peter Bergner <bergner@...t.ibm.com>
Cc:	Denis Kirjanov <kda@...ux-powerpc.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Laura Abbott <labbott@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Missing operand for tlbie instruction on Power7

On Fri, Oct 02, 2015 at 09:24:46PM -0500, Peter Bergner wrote:
> > > Ok, than we can just zero out r5 for example and use it in tlbie as RS,
> > > right?
> > 
> > That won't assemble _unless_ your assembler is in POWER7 mode.  It also
> > won't do the right thing at run time on older machines.
> 
> Correct, getting this to work on both pre-power7 and power7 and later
> is tricky.  One really horrible hack would be to do:
> 
>   li r0,0
>   tlbie r4,0
> 
> On pre-power7, the "0" will be taken as a zero L operand and on
> power7 and later, it'll be r0, but with a zero value we loaded in
> the insn before.  I know, really ugly. :-)

Hide the "li 0,0" somewhere earlier, and write it as "tlbie 4,0", and
don't write a comment -- we *like* tricky!

It should really be a separate macro define for power7 and 4xx etc.;
and the macro should not be called "tlbia", but something that makes
it obvious at the usage sites that it is in fact a macro; and why a
macro anyway, a function call might be better here?


Segher
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