linux-kernel - Re: [PATCH 1/3] perf tools: Allow vmlinux to fallback to kallsyms on NO

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Message-ID: <87mw7zva3c.fsf@sejong.aot.lge.com>
Date:	Mon, 10 Nov 2014 15:33:11 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 1/3] perf tools: Allow vmlinux to fallback to kallsyms on NO_LIBELF=1

Hi Peter,

On Fri, 7 Nov 2014 18:37:18 +0100, Peter Zijlstra wrote:
> On Fri, Nov 07, 2014 at 11:57:39PM +0900, Namhyung Kim wrote:
>
>> > Why does this live in the minimal implementation; should we not always
>> > discard ELF files with 0 symbols?
>> > 
>> > Suppose I have a vmlinux but removed all symbols from it; I want it to
>> > fall back to kallsyms too.
>> 
>> I'm not sure I understood what you said correctly.  With this change,
>> dso__load_kernel_sym() always ends up calling dso__load_kallsyms() since
>> dso__load_vmlinux() will always return 0;
>> 
>> So I think you'll fall back to kallsyms even though you have a vmlinux
>> with symbol.  This makes dso__load_sym() in the patch 2/3 simpler IMHO.
>
> But why have it specific to the minimal elf thing? Why not discard any
> DSO with 0 symbols and try the next option to acquire symbols?

Hmm.. I don't think it's specific to the minimal elf parser.  The return
value of dso__load_sym() is a number of symbols found so when it sees a
dso with 0 symbols it'll fall back to the next option IMHO (not
tested).  Did you see a problem with the current code?

Thanks,
Namhyung
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