linux-kernel - Re: [PATCH v5 0/2] perf probe: add sdt probes arguments into the uprobe cmd string

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Date:   Wed, 14 Dec 2016 08:36:56 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Alexis Berlemont <alexis.berlemont@...il.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH v5 0/2] perf probe: add sdt probes arguments into the
 uprobe cmd string

* Alexis Berlemont <alexis.berlemont@...il.com> wrote:

> Hi Masami,
> 
> Many thanks for your mail.
> 
> Here is another patch set which tries to fix the points you mentioned:
> 
> * Skip the arguments containing a constant ($123); 
> * Review the code in charge of the register renaming (search for '%'
>   and parse it);
> * Minor changes (print the argument in case of error, skipping, check
>   the sdt arg type index);
> 
> Many thanks,
> 
> Alexis.
> 
> Alexis Berlemont (2):
>   perf sdt: add scanning of sdt probles arguments
>   perf probe: add sdt probes arguments into the uprobe cmd string

I'd like to hijack this thread to report an SDT oddity - one of my boxen reports 
lots of SDT tracepoints in 'perf list':

  mem:<addr>[/len][:access]                          [Hardware breakpoint]

  sdt_libc:lll_lock_wait_private                     [SDT event]
  sdt_libc:longjmp                                   [SDT event]
  sdt_libc:longjmp_target                            [SDT event]
  sdt_libc:memory_arena_new                          [SDT event]
  sdt_libc:memory_arena_retry                        [SDT event]
  sdt_libc:memory_arena_reuse                        [SDT event]
  sdt_libc:memory_arena_reuse_free_list              [SDT event]
  sdt_libc:memory_arena_reuse_wait                   [SDT event]
  sdt_libc:memory_calloc_retry                       [SDT event]
  sdt_libc:memory_heap_free                          [SDT event]
  ...

But none of them work:

  Error:  No permissions to read /sys/kernel/debug/tracing/events/sdt_libc/longjmp
  Hint:   Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing'

  ...

  Error:  File /sys/kernel/debug/tracing/events/sdt_libc/longjmp not found.
  Hint:   Perhaps this kernel misses some CONFIG_ setting to enable this feature?.

What kind of patches are required for SDT probes to work?

Thanks,

	Ingo