linux-kernel - Re: [PATCH 27/31] perf record: Support custom vmlinux path

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Date:	Tue, 1 Sep 2015 18:33:28 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	pi3orama <pi3orama@....com>
Cc:	Wang Nan <wangnan0@...wei.com>, He Kuang <hekuang@...wei.com>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"ast@...mgrid.com" <ast@...mgrid.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lizefan@...wei.com" <lizefan@...wei.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...nel.org>,
	Kaixu Xia <xiakaixu@...wei.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 27/31] perf record: Support custom vmlinux path

Em Wed, Sep 02, 2015 at 05:00:39AM +0800, pi3orama escreveu:
> 发自我的 iPhone
> > 在 2015年9月2日，上午4:21，Arnaldo Carvalho de Melo <acme@...hat.com> 写道：
> > Em Tue, Sep 01, 2015 at 05:19:17PM -0300, Arnaldo Carvalho de Melo escreveu:
> >> Em Sat, Aug 29, 2015 at 04:22:01AM +0000, Wang Nan escreveu:
> >>> From: He Kuang <hekuang@...wei.com>

> >>> Make perf-record command support --vmlinux option if BPF_PROLOGUE is on.

> >> Ok, this should be supported, i.e. letting the user specify a vmlinux
> >> path to use.

> >> But it shouldn't be _required_, i.e. we have things like vmlinux_path to
> >> try to find it in well known places.

> >> Right now it will search for it in the process of trying to load its
> >> symtab, but I think we should have a function that tries to find a
> >> vmlinux that matches the build-id of the running kernel, for things that
> >> want to have access directly to the ELF file with debuginfo without
> >> having to load the symtab in a struct dso, etc.

> >> I'll look at the next patches to check how you make use of this info...
> > 
> > So, the do it all from 'perf record' is in not yet in this patchkit,
> > right? At least not in [ N/31 ] with N > 27, can you point me to it?
 
> It is for patch 8/31, which create kprobe points using add_perf_probe_events().
> 
> Before this patch it won't search debug info, prevent us use argument like this:
> 
> SEC("lock_page=lock_page page->flags")
> 
> or probe at line number, expect it finds a valid vmlinux from the default path.

Argh, that is because init_symbol_maps() uses symbol__init() that is
also being used in 'perf record' by now... I.e. it was designed to be
called just once, at tool start :-\

Will have to get my head around how this is being used to try to
untangle this mess...

- Arnaldo
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