linux-kernel - Re: [PATCH v20] tracing: Fix kconfig warning due to a typo

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Message-ID: <1336483073.16236.37.camel@twins>
Date:	Tue, 08 May 2012 15:17:53 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Anton Arapov <anton@...hat.com>,
	Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH v20] tracing: Fix kconfig warning due to a typo

On Tue, 2012-05-08 at 08:48 -0400, Steven Rostedt wrote:
> On Tue, 2012-05-08 at 13:29 +0200, Peter Zijlstra wrote:
> > On Tue, 2012-05-08 at 16:41 +0530, Srikar Dronamraju wrote:
> > > +    p:uprobes/p_zsh_0x46420 /bin/zsh:0x00046420 arg1=%ip arg2=%ax
> > 
> > can you also do things like:
> > 
> >  p:uprobes/ponies /bin/zsh:foo arg1=bar
> > 
> > when bar is either a function argument of foo (or an otherwise live
> > variable at the probe point)?
> > 
> > Only sampling register content is somewhat limiting, you might want to
> > have %ax[5] + 24 for example, or a pure memory deref -- and the dwarves
> > know where it all lives.
> 
> But this is for the raw entry into the kernel. The kernel wont know the
> variable name. Although perf could do that parsing for you.

Ah, ok. Yes I meant for perf to do this, I overlooked it was the kernel
input.

> That said, the %ax[5] + 24 could be done in kernel, and that would be
> useful. Does kprobes handle that?

In general something like: %mr + %c * %cr + %cr would be most useful I
think (%m - memory address, %r - register, %c - constant). Although
maybe it needs segment registers too, dunno. Also no idea if this covers
the addressing scope of all archs.
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