linux-kernel - Re: [PATCH] perf probe: Fix failure to probe events on arm

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Message-ID: <20150615144911.GA5845@kernel.org>
Date:	Mon, 15 Jun 2015 11:49:11 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	He Kuang <hekuang@...wei.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	a.p.zijlstra@...llo.nl, mingo@...hat.com, namhyung@...nel.org,
	wangnan0@...wei.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf probe: Fix failure to probe events on arm

Em Mon, Jun 15, 2015 at 08:06:53AM +0000, He Kuang escreveu:
> Fix failure to probe events on arm, problem is introduced by commit
> 5a51fcd1f30c ("perf probe: Skip kernel symbols which is out of
> .text"). For some architectures, label '_etext' is not in the .text
> section(in .notes section for arm/arm64). Label out of .text section is
> not loaded as symbols and we got a zero value when look up its address,
> which causes all events be wrongly skiped.
> 
> This patch uses kernel map->end when failed to get the address of
> '_etext' and fixes the problem.

Masami, can't we always use map->end then? Can you please take a look at
this patch and ack/nack it?

- Arnaldo

 
> Problem can be reproduced on arm as following:
> 
>   # perf probe --add='generic_perform_write'
>   generic_perform_write+0 is out of .text, skip it.
>   Probe point 'generic_perform_write' not found.
>     Error: Failed to add events. Reason: No such file or directory (Code: -2)
> 
> After this patch:
> 
>   # perf probe --add='generic_perform_write'
>   Added new event:
>     probe:generic_perform_write (on generic_perform_write)
> 
>   You can now use it in all perf tools, such as:
> 
>     perf record -e probe:generic_perform_write -aR sleep 1
> 
> Signed-off-by: He Kuang <hekuang@...wei.com>
> ---
>  tools/perf/util/probe-event.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index daa24a2..ee26961 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -575,8 +575,22 @@ static int post_process_probe_trace_events(struct probe_trace_event *tevs,
>  		pr_warning("Relocated base symbol is not found!\n");
>  		return -EINVAL;
>  	}
> -	/* Get the address of _etext for checking non-probable text symbol */
> +	/* Get the address of _etext for checking non-probable text symbol,
> +	   for some architectures (e.g. arm, arm64), _etext is out of .text
> +	   section and not loaded as symbols, use kernel map->end instead.
> +	 */
>  	etext_addr = kernel_get_symbol_address_by_name("_etext", false);
> +	if (etext_addr == 0) {
> +		struct map *map;
> +
> +		map = kernel_get_module_map(NULL);
> +		if (!map) {
> +			pr_err("Failed to get a map for kernel\n");
> +			return -EINVAL;
> +		}
> +
> +		etext_addr = map->end;
> +	}
>  
>  	for (i = 0; i < ntevs; i++) {
>  		if (tevs[i].point.address && !tevs[i].point.retprobe) {
> -- 
> 1.8.5.2
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