Re: [PATCH v2] perf probe: Fix failure to probe events on arm

From: Masami Hiramatsu
Date: Mon Jun 22 2015 - 23:07:45 EST


On 2015/06/18 11:49, He Kuang wrote:
> 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 skip checking text address range when failed to get the
> address of '_etext' and fixes the problem.
>
> 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.
>
> 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

Looks good to me :)

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>

Thanks!

>
> Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
> ---
> tools/perf/util/probe-event.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 076527b..381f23a 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -249,8 +249,12 @@ static void clear_probe_trace_events(struct probe_trace_event *tevs, int ntevs)
> static bool kprobe_blacklist__listed(unsigned long address);
> static bool kprobe_warn_out_range(const char *symbol, unsigned long address)
> {
> + u64 etext_addr;
> +
> /* Get the address of _etext for checking non-probable text symbol */
> - if (kernel_get_symbol_address_by_name("_etext", false) < address)
> + etext_addr = kernel_get_symbol_address_by_name("_etext", false);
> +
> + if (etext_addr != 0 && etext_addr < address)
> pr_warning("%s is out of .text, skip it.\n", symbol);
> else if (kprobe_blacklist__listed(address))
> pr_warning("%s is blacklisted function, skip it.\n", symbol);
>


--
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
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