linux-kernel - Re: [PATCH 1/6] perf top: teach it to autolocate vmlinux

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Message-ID: <20100113133952.GD2934@ghostprotocols.net>
Date:	Wed, 13 Jan 2010 11:39:52 -0200
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Kirill Smelkov <kirr@...dau.phys.spbu.ru>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Mike Galbraith <efault@....de>,
	Masami Hiramatsu <mhiramat@...hat.com>
Subject: Re: [PATCH 1/6] perf top: teach it to autolocate vmlinux

Em Fri, Jan 08, 2010 at 03:23:04PM +0300, Kirill Smelkov escreveu:
> By relying on logic in dso__load_kernel_sym(), we can automatically load
> vmlinux.
> 
> The only thing which needs to be adjusted, is how --sym-annotate option
> is handled - now we can't rely on vmlinux been loaded until full
> successful pass of dso__load_vmlinux(), but that's not the case if we'll
> do sym_filter_entry setup in symbol_filter().
> 
> So move this step right after event__process_sample() where we know the
> whole dso__load_kernel_sym() pass is done.
> 
> By the way, though conceptually similar `perf top` still can't annotate
> userspace - see next patches with fixes.
> 
> Signed-off-by: Kirill Smelkov <kirr@...dau.phys.spbu.ru>
> Cc: Mike Galbraith <efault@....de>
> ---

<SNIP>

> @@ -951,6 +953,13 @@ static void event__process_sample(const event_t *self,
>  	    al.sym == NULL || al.filtered)
>  		return;
>  
> +	/* let's see, whether we need to install initial sym_filter_entry */
> +	if (sym_filter_entry_sched) {
> +		sym_filter_entry = sym_filter_entry_sched;
> +		sym_filter_entry_sched = NULL;
> +		parse_source(sym_filter_entry);
> +	}
> +

You're assuming that the first sample is for the kernel, right? It may
be not and then the vmlinux won't be loaded at this point.

I think that the right way is to force it to be loaded by calling:

	map__load(session->vmlinux_maps[MAP__FUNCTION], session, filter);

after perf_session__create_kernel_maps and before parse_source(), ok?

	You can even create a helper:

int perf_session__load_vmlinux(struct perf_session *self,
                               symbol_filter_t filter)
{
	return map__load(session->vmlinux_maps[MAP__FUNCTION],
			 session, filter);
}

	As this probably will be of interest for tools such as 'perf
probe', etc.

- Arnaldo
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