linux-kernel - Re: [RFC] systemtap: begin the process of using proper kernel APIs (part1: use kprobe symbol

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Message-ID: <20080718132840.GN18295@redhat.com>
Date:	Fri, 18 Jul 2008 09:28:40 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	systemtap@...rceware.org, jbeulich@...ell.com,
	arjan <arjan@...radead.org>, sandmann@...mi.au.dk,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC] systemtap: begin the process of using proper kernel APIs (part1: use kprobe symbol_name/offset instead of address)

Hi -

On Fri, Jul 18, 2008 at 03:10:27PM +0200, Peter Zijlstra wrote:
> [...]
> > For example, we're about to do unwinding/stack-traces of userspace
> > programs.  To what extent do you think the kernel unwinder (should one
> > reappear in git) would welcome patches that provide zero benefit to
> > the kernel, but only enable a peculiar (nonintrusive) sort of
> > unwinding we would need for complex userspace stacks?
> 
> I think sysprof (kernel/trace/trace_sysprof.c) already does user-space
> stack unwinding. So pushing that capability further up the chain when a
> second user (stap) comes along makes perfect sense.

trace_sysprof relies on dump_stack, which is x86-only and does not do
elf/dwarf unwinding proper.  (Likewise oprofile, etc.)  They can't
even start, because they don't have unwind data available - something
we plan to make available to the systemtap runtime.


- FChE
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