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

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Message-ID: <87vc05x5zf.fsf@sejong.aot.lge.com>
Date:	Wed, 06 Nov 2013 17:57:24 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
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)

On Tue, 5 Nov 2013 20:24:01 +0100, Oleg Nesterov wrote:
> On 11/05, Oleg Nesterov wrote:
>>
>> As for "-= tu->offset"... Can't we avoid it? User-space needs to calculate
>> the "@" argument anyway, why it can't also substruct this offset?
>>
>> Or perhaps we can change parse_probe_arg("@") to update "param" ? Yes,
>> in this case it needs another argument, not sure...
>
> Or,
>
>> 	+	if (is_ret_probe(tu)) {
>> 	+		saved_ip = instruction_pointer(regs);
>> 	+		instruction_pointer_set(func);
>> 	+	}
>> 		store_trace_args(...);
>> 	+	if (is_ret_probe(tu))
>> 	+		instruction_pointer_set(saved_ip);
>
> we can put "-= tu->offset" here.

I don't think I get the point.

>
> Or. Perhaps we can leave "case '@'" in parse_probe_arg() and
> FETCH_MTD_memory alone. You seem to agree that "absolute address"
> can be useful anyway.

Yes, but it's only meaningful to process-wide tracing sessions IMHO.

>
> Instead, perhaps we can add FETCH_MTD_memory_do_fancy_addr_translation,
> and, say, the new "case '*'" in parse_probe_arg() should add all the
> neccessary info as f->data (like, say, FETCH_MTD_symbol).

Could you elaborate this more?

>
> But, just in case, I do not have a strong opinion. Just I think it
> is better to discuss every choice we have.

Okay.  I really appreciate your reviews.


Thanks,
Namhyung
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