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

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Date:	Wed, 2 Sep 2015 05:00:39 +0800
From:	pi3orama <pi3orama@....com>
To:	Arnaldo Carvalho de Melo <acme@...hat.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



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.

Thank you.

> - Arnaldo
> 
>> - Arnaldo
>> 
>>> 'perf record' needs vmlinux as the source of DWARF info to generate
>>> prologue for BPF programs, so path of vmlinux should be specified.
>>> 
>>> Short name 'k' has been taken by 'clockid'. This patch skips the short
>>> option name and use '--vmlinux' for vmlinux path.
>>> 
>>> Signed-off-by: He Kuang <hekuang@...wei.com>
>>> Signed-off-by: Wang Nan <wangnan0@...wei.com>
>>> Cc: Alexei Starovoitov <ast@...mgrid.com>
>>> Cc: Brendan Gregg <brendan.d.gregg@...il.com>
>>> Cc: Daniel Borkmann <daniel@...earbox.net>
>>> Cc: David Ahern <dsahern@...il.com>
>>> Cc: He Kuang <hekuang@...wei.com>
>>> Cc: Jiri Olsa <jolsa@...nel.org>
>>> Cc: Kaixu Xia <xiakaixu@...wei.com>
>>> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
>>> Cc: Namhyung Kim <namhyung@...nel.org>
>>> Cc: Paul Mackerras <paulus@...ba.org>
>>> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>>> Cc: Zefan Li <lizefan@...wei.com>
>>> Cc: pi3orama@....com
>>> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
>>> Link: http://lkml.kernel.org/n/1436445342-1402-38-git-send-email-wangnan0@huawei.com
>>> ---
>>> tools/perf/builtin-record.c | 4 ++++
>>> 1 file changed, 4 insertions(+)
>>> 
>>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>>> index 212718c..8eb39d5 100644
>>> --- a/tools/perf/builtin-record.c
>>> +++ b/tools/perf/builtin-record.c
>>> @@ -1100,6 +1100,10 @@ struct option __record_options[] = {
>>>           "clang binary to use for compiling BPF scriptlets"),
>>>    OPT_STRING(0, "clang-opt", &llvm_param.clang_opt, "clang options",
>>>           "options passed to clang when compiling BPF scriptlets"),
>>> +#ifdef HAVE_BPF_PROLOGUE
>>> +    OPT_STRING(0, "vmlinux", &symbol_conf.vmlinux_name,
>>> +           "file", "vmlinux pathname"),
>>> +#endif
>>> #endif
>>>    OPT_END()
>>> };
>>> -- 
>>> 2.1.0

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