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

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Date:	Fri, 2 Oct 2015 17:00:51 -0500
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Denis Kirjanov <kda@...ux-powerpc.org>
Cc:	Peter Bergner <bergner@...t.ibm.com>,
	"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 Sat, Oct 03, 2015 at 12:37:35AM +0300, Denis Kirjanov wrote:
> >> -0:     tlbie   r4;                             \
> >> +0:     tlbie   r4, 0;                          \
> >
> > This isn't correct.  With POWER7 and later (which this compile
> > is, since it's on LE), the tlbie instruction takes two register
> > operands:
> >
> >     tlbie RB, RS
> >
> > The tlbie instruction on pre POWER7 cpus had one required register
> > operand (RB) and an optional second L operand, where if you omitted
> > it, it was the same as using "0":
> >
> >     tlbie RB, L
> >
> > This is a POWER7 and later build, so your change which adds the "0"
> > above is really adding r0 for RS.  The new tlbie instruction doesn't
> > treat r0 specially, so you'll be using whatever random bits which
> > happen to be in r0 which I don't think that is what you want.
> 
> 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.

Where is this tlbia macro used at all, for 64-bit machines?


Segher
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