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

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Date:	Tue, 11 Nov 2014 13:24:38 +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 Mon, Nov 10, 2014 at 9:11 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Nov 10, 2014 at 03:33:11PM +0900, Namhyung Kim wrote:
>> 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?
>
> So your patch:
>
> +++ b/tools/perf/util/symbol-minimal.c
> @@ -335,6 +335,9 @@ int dso__load_sym(struct dso *dso, struct map *map __maybe_unused,
>         unsigned char *build_id[BUILD_ID_SIZE];
>         int ret;
>
> +       if (dso->kernel)
> +               return 0;  /* always use kallsyms */
> +
>
> changes the symbol-minimal.c file to add this exception. That is very
> much specific to the minimal elf parser, or am I just seeing things?

What minimal parser does here is just skip kernel dsos (vmlinux) since
it didn't deal with all the details of parsing vmlinux currently.


>
> What I was saying, why not have a util/symbol.c change that disregards
> all DSOs with 0 symbols in.

The util/symbol.c doesn't need this because it can handle vmlinux
reliably.  So after reading symbol table, it'll use the dso if it
actually contains symbols or fallback to next dso if it has 0 symbols.
IOW it already disregards all dsos with 0 symbols in.

-- 
Thanks,
Namhyung
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