linux-kernel - Re: [PATCH 05/12] powerpc/ftrace: ftrace_graph

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Date:	Thu, 25 Feb 2016 21:39:50 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Balbir Singh <bsingharora@...il.com>, linuxppc-dev@...abs.org
Cc:	duwe@....de, linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	kamalesh@...ux.vnet.ibm.com, pmladek@...e.com, jeyu@...hat.com,
	jkosina@...e.cz, live-patching@...r.kernel.org, mbenes@...e.cz
Subject: Re: [PATCH 05/12] powerpc/ftrace: ftrace_graph_caller() needs to
 save/restore toc

On Thu, 2016-02-25 at 11:30 +1100, Balbir Singh wrote:
> 
> On 25/02/16 01:28, Michael Ellerman wrote:
> > Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
> > 
> > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> > index 2a7313cfbc7d..9e77a2c8f218 100644
> > --- a/arch/powerpc/kernel/entry_64.S
> > +++ b/arch/powerpc/kernel/entry_64.S
> > @@ -1237,6 +1237,11 @@ _GLOBAL(ftrace_graph_caller)
> >  	std	r5, 64(r1)
> >  	std	r4, 56(r1)
> >  	std	r3, 48(r1)
> > +
> > +	/* Save callee's TOC in the ABI compliant location */
> > +	std	r2, 24(r1)

> R2_STACK_OFFSET for readability?

Hmm, maybe. Personally when I see "24(r1)" what my brain reads is "stack TOC
save slot", but maybe I've been spending too much time with powerpc assembly.

R2_STACK_OFFSET is actually new, pulled out from the module code by Torsten.
Other code uses STK_GOT to mean the same thing. I don't really like either
name, so I'll probably leave do a clean up once this is in.

cheers