linux-kernel - Re: [PATCHv10 2.6.35-rc6-tip 8/14] trace: Extract out common code for kprobes/uprobes traceevents.

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Date:	Wed, 28 Jul 2010 16:56:09 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Mark Wielaard <mjw@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Naren A Devaiah <naren.devaiah@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	2nddept-manager@....hitachi.co.jp
Subject: Re: [PATCHv10 2.6.35-rc6-tip 8/14]  trace: Extract out common code
 for kprobes/uprobes traceevents.

Srikar Dronamraju wrote:
>>> ---
>> [...]
>>> +/* Recursive argument parser */
>>> +static int parse_probe_arg(char *arg, const struct fetch_type *t,
>>> +		     struct fetch_param *f, int is_return, bool is_kprobe)
>> If you use "bool" for "is_kprobe", change "is_return" type too.
> 
> Okay. 
> 
> 
>> And, maybe you missed that the fetch function supports "string" type now,
>> which needs a bit different manner for storing fetched value. You can find
>> store_trace_args() function in trace_kprobe.c.
> 
> Yes, I have seen your changes for supporting string type.  Though all
> the fetch functions are in common code, uprobe based probes for now
> supports register fetching only. We have to add support for other
> types gradually. Please let me know if you see a reason to change the
> way we fetch even when we only support register type access.

Ah, OK. So uprobe-tracer restricts specifying string type on register :)

>> BTW, current fetch functions doesn't support fetching "paged-out" user-variables
>> because kprobe can't sleep inside its handler.
>> However, user-space memory can be paged out, and I assume that uprobes allows
>> its handler to I/O (and yield). If so, it can wait for accessing paged-out
>> variable, can't it?
> 
> Yes, the uprobes handler might sleep and hence we would have to
> handle accessing the paged-out user variables. When perf-uprobes
> starts supporting dwarf based probing, we should look into these
> issues.  Currently its a todo.

Great!

Thank you,

-- 
Masami HIRAMATSU
2nd Research Dept.
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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