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

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Message-ID: <20141107173718.GD29390@twins.programming.kicks-ass.net>
Date:	Fri, 7 Nov 2014 18:37:18 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Namhyung Kim <namhyung@...nel.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

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?
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