linux-kernel - Re: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch methods (v6)

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Date:	Wed, 6 Nov 2013 19:24:08 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch
	methods (v6)

Forgot to mention,

On 11/06, Oleg Nesterov wrote:
>
> I meant,
>
> 		saved_ip = instruction_pointer(regs);
>
> 		// pass the "ip" which was used to calculate
> 		// the @addr argument to fetch_*() methods
>
> 		temp_ip = is_ret_probe(tu) ? func : saved_ip;
> 		temp_ip -= tu->offset;
> 		instruction_pointer_set(temp_ip);
>
> 		store_trace_args(...);

Note that instruction_pointer_set() is not really nice in any case,
this can obviously confuse FETCH_MTD_reg("ip").

But lets ignore this. The solution is simple, we can pass/use this
info via current->utask. We can either add the new member, or add
a union. Or simply reuse xol_vaddr. Doesn't matter.

So the only question is should we rely on instruction_pointer/func
to translate the address or we should do something else (say, vma).

So far I like this approach.

Oleg.

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