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

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Date:	Fri, 18 Jul 2008 11:11:07 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	systemtap@...rceware.org, jbeulich@...ell.com
Subject: Re: [RFC] systemtap: begin the process of using proper kernel APIs (part1: use kprobe symbol_name/offset instead of address)

James Bottomley <James.Bottomley@...senPartnership.com> writes:

> One of the big nasties of systemtap is the way it tries to embed
> virtually the entirety of the kernel symbol table in the probe modules
> it constructs.  This is highly undesirable because it represents a
> subversion of the kernel API to gain access to unexported symbols.  At
> least for kprobes, the correct way to do this is to specify the probe
> point by symbol and offset.
>
> This patch converts systemtap to use the correct kprobe
> symbol_name/offset pair to identify the probe location.
>
> This only represents a baby step:  after this is done, there are at
> least three other consumers of the systemtap module relocation
> machinery:
>
>      1. unwind information.  I think the consumers of this can be
>         converted to use the arch specific unwinders that already exist
>         within the kernel


Right now x86 doesn't really have a good reliable unwinder that
works without frame pointer. I think systemtap
recently switched to Jan Beulich's dwarf2 unwinder. Before
switching to the in kernel unwinder that one would need to be 
re-merged again.

-Andi

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