linux-kernel - Re: [RFC][PATCH] ppc: Implement save_stack_trace

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Date:	Wed, 09 Dec 2015 12:03:05 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, linuxppc-dev@...ts.ozlabs.org,
	chuhu@...hat.com
Subject: Re: [RFC][PATCH] ppc: Implement save_stack_trace_regs()

On Tue, 2015-12-08 at 19:28 -0500, Steven Rostedt wrote:
> On Wed, 09 Dec 2015 11:20:22 +1100
> Michael Ellerman <mpe@...erman.id.au> wrote:
> > On Tue, 2015-12-08 at 13:50 -0500, Steven Rostedt wrote:
> > > It has come to my attention that kprobe event stack tracing does not
> > > work on powerpc.  

> > > diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
> > > index ea43a347a104..0142c86801ba 100644
> > > --- a/arch/powerpc/kernel/stacktrace.c
> > > +++ b/arch/powerpc/kernel/stacktrace.c
> > > @@ -61,3 +61,10 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
> > >  	save_context_stack(trace, tsk->thread.ksp, tsk, 0);
> > >  }
> > >  EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
> > > +
> > > +void
> > > +save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
> > > +{
> > > +	save_context_stack(trace, regs->gpr[PT_R1], current, 0);  
> > 
> > In the kernel we would normally use just '1' here rather than 'PT_R1', but it's
> > not a huge deal.
> > 
> > Should I take this via powerpc or do you want it to go in via tracing?
> 
> You can take it. And you can replace the PT_R1 if you want. I just
> noticed that it was defined, and I try to use macro names instead of
> hard coded numbers. I was actually looking for a "PT_SP" :-)

OK thanks.

Looks like we actually have:

  #define kernel_stack_pointer(regs) ((regs)->gpr[1])

So that would be the most self documenting way to do it I guess, though I've
never actually seen that macro used anywhere before :)

cheers

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