linux-kernel - Re: [RFC PATCH v1.9 07/14] x86/stacktrace: add function for detecting reliable stack traces

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Date:	Mon, 4 Apr 2016 12:54:37 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Miroslav Benes <mbenes@...e.cz>
Cc:	Jiri Kosina <jikos@...nel.org>, Jessica Yu <jeyu@...hat.com>,
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	Vojtech Pavlik <vojtech@...e.com>
Subject: Re: [RFC PATCH v1.9 07/14] x86/stacktrace: add function for
 detecting reliable stack traces

On Thu, Mar 31, 2016 at 03:03:16PM +0200, Miroslav Benes wrote:
> On Fri, 25 Mar 2016, Josh Poimboeuf wrote:
> 
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 2dc18605..76274b8 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -138,6 +138,7 @@ config X86
> >  	select HAVE_PERF_REGS
> >  	select HAVE_PERF_USER_STACK_DUMP
> >  	select HAVE_REGS_AND_STACK_ACCESS_API
> > +	select HAVE_RELIABLE_STACKTRACE		if X86_64 && FRAME_POINTER
> 
> I understand we have to rely on frame pointer for now. Do you plan to 
> switch to dwarf unwinder one day in the future? IOW is there a plan to 
> implement dwarf stuff generation in objtool and then to have a dwarf-based 
> stack unwinder upstream and to use it for live patching? 

Yes, adding DWARF validation and generation to objtool and creating a
DWARF unwinder upstream are all planned, hopefully soon.

> We have FRAME_POINTER unset in SLES for performance reasons (there was 
> some 5 percent slowdown measured in the past. However we should redo the 
> experiments.) and one day we'd really like to switch to upstream from 
> kgraft :). So I'm just asking.

If you redo the experiments and have some useful data to share, please
do share :-)

-- 
Josh