linux-kernel - Re: [PATCH 2/2] perf probe: Support probing at absolute address

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Message-ID: <20150826133235.GA18596@kernel.org>
Date:	Wed, 26 Aug 2015 10:32:35 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	平松雅巳 / HIRAMATU，MASAMI 
	<masami.hiramatsu.pt@...achi.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"pi3orama@....com" <pi3orama@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] perf probe: Support probing at absolute address

Em Wed, Aug 26, 2015 at 09:19:27PM +0800, Wangnan (F) escreveu:
> On 2015/8/26 21:02, acme@...nel.org wrote:
> >Em Wed, Aug 26, 2015 at 10:38:18AM +0800, Wangnan (F) escreveu:
> >>On 2015/8/26 8:02, 平松雅巳 / HIRAMATU，MASAMI wrote:
> >>>>From: Wang Nan [mailto:wangnan0@...wei.com]
> >>>>  # perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860
> >>>Why do we need "+" for the absolute address?
> >>>It seems that we can do it if we find that the given probe point
> >>>starts with "0x".

> >>I will change 2/2 as you suggestion.

> >>However, we can only ensure that in kernel side symbol never leading
> >>with '0x'. Although I don't think symbol leading with 0x is useful,
> >>it is still possible for a userspace program compiled and linked by
> >>a language other than C produces such symbol. '+' helps us separate
> >>address and function name semantically, make us don't rely on assumption
> >>on function names. If in future we do meet '0x' symbols, I think we still
> >>need the '+' syntax back. But we can do it at that time.

> >Agreed, I also think that using '+' is better, but will not dwell on
> >this so as to make progress :-)
 
> Maybe we should support both of them, making '+0x1234' the core
> syntax, and '0x1234' style as a syntax sugar. However I have worked
> on this problem for nearly a full day but my main work should be BPF
> related things...
 
> Since Masami has acked all of the 6 v3 patches, if we still need '+' I can
> bring it back with a new patch when I have time. However, same to you,
> I don't think this should be a blocking problem.

Agreed, we don't have to agree on everything all the time, lets keep
Masami happy this time :-)

- Arnaldo
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