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

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Message-ID: <alpine.LNX.2.00.1603311456150.23131@pobox.suse.cz>
Date:	Thu, 31 Mar 2016 15:03:16 +0200 (CEST)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
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 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? 

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.

Miroslav