perf probe: Trying to read a 'ctx' named local variable

perf probe: Trying to read a 'ctx' named local variable

[Arnaldo Carvalho de Melo]

Hi Masami,

	Trying to use perf to debug perf I stumbled on this:

[root@quaco ~]# perf probe -x ~/bin/perf -L sigtrap_handler
<sigtrap_handler@/home/acme/git/perf-tools/tools/perf/tests/sigtrap.c:0>
      0  sigtrap_handler(int signum __maybe_unused, siginfo_t *info, void *ucontext __maybe_unused)
         {
                if (!__atomic_fetch_add(&ctx.signal_count, 1, __ATOMIC_RELAXED))
      3                 ctx.first_siginfo = *info;
      4         __atomic_fetch_sub(&ctx.tids_want_signal, syscall(SYS_gettid), __ATOMIC_RELAXED);
         }

         static void *test_thread(void *arg)

[root@quaco ~]# perf probe -x ~/bin/perf sigtrap_handler:4 "ctx.signal_count"
Failed to write event: Invalid argument
Please upgrade your kernel to at least 3.14 to have access to feature @ctx
  Error: Failed to add events.
[root@quaco ~]#

[root@quaco ~]# uname -a
Linux quaco 6.3.8-100.fc37.x86_64 #1 SMP PREEMPT_DYNAMIC Thu Jun 15 01:51:54 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
[root@quaco ~]# rpm -qa | grep kernel-debuginfo
kernel-debuginfo-common-x86_64-6.3.8-100.fc37.x86_64
kernel-debuginfo-6.3.8-100.fc37.x86_64
[root@quaco ~]#

-- 

- Arnaldo

Re: perf probe: Trying to read a 'ctx' named local variable

[Masami Hiramatsu]

On Mon, 17 Jul 2023 15:06:10 -0300
Arnaldo Carvalho de Melo <acme@kernel.org> wrote:

> Hi Masami,
> 
> 	Trying to use perf to debug perf I stumbled on this:
> 
> [root@quaco ~]# perf probe -x ~/bin/perf -L sigtrap_handler
> <sigtrap_handler@/home/acme/git/perf-tools/tools/perf/tests/sigtrap.c:0>
>       0  sigtrap_handler(int signum __maybe_unused, siginfo_t *info, void *ucontext __maybe_unused)
>          {
>                 if (!__atomic_fetch_add(&ctx.signal_count, 1, __ATOMIC_RELAXED))
>       3                 ctx.first_siginfo = *info;
>       4         __atomic_fetch_sub(&ctx.tids_want_signal, syscall(SYS_gettid), __ATOMIC_RELAXED);
>          }
> 
>          static void *test_thread(void *arg)
> 
> [root@quaco ~]# perf probe -x ~/bin/perf sigtrap_handler:4 "ctx.signal_count"
> Failed to write event: Invalid argument
> Please upgrade your kernel to at least 3.14 to have access to feature @ctx
>   Error: Failed to add events.
> [root@quaco ~]#

Ah, this is a wrong usage (I'm also trapped the same thing). Correctly, it should
pass it as a single parameter.

perf probe -x ~/bin/perf "sigtrap_handler:4 ctx.signal_count"

This is for adding several events at the same time. But now it becomes just a trap.
Can I change the syntax from

perf probe [OPTIONS] <PROBE-DEFINITION> [PROBE-DEFINITION...]

To,

perf probe [OPTIONS] <PROBE-POINT> [ARGS...]

?

We can keep --add having optional parameter as below.

perf probe [OPTIONS] --add <PROBE-DEFINITION>

Thank you,

> 
> [root@quaco ~]# uname -a
> Linux quaco 6.3.8-100.fc37.x86_64 #1 SMP PREEMPT_DYNAMIC Thu Jun 15 01:51:54 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
> [root@quaco ~]# rpm -qa | grep kernel-debuginfo
> kernel-debuginfo-common-x86_64-6.3.8-100.fc37.x86_64
> kernel-debuginfo-6.3.8-100.fc37.x86_64
> [root@quaco ~]#
> 
> -- 
> 
> - Arnaldo


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

Re: perf probe: Trying to read a 'ctx' named local variable

[Arnaldo Carvalho de Melo]

Em Tue, Jul 18, 2023 at 08:54:51AM +0900, Masami Hiramatsu escreveu:
> On Mon, 17 Jul 2023 15:06:10 -0300
> Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> 
> > Hi Masami,
> > 
> > 	Trying to use perf to debug perf I stumbled on this:
> > 
> > [root@quaco ~]# perf probe -x ~/bin/perf -L sigtrap_handler
> > <sigtrap_handler@/home/acme/git/perf-tools/tools/perf/tests/sigtrap.c:0>
> >       0  sigtrap_handler(int signum __maybe_unused, siginfo_t *info, void *ucontext __maybe_unused)
> >          {
> >                 if (!__atomic_fetch_add(&ctx.signal_count, 1, __ATOMIC_RELAXED))
> >       3                 ctx.first_siginfo = *info;
> >       4         __atomic_fetch_sub(&ctx.tids_want_signal, syscall(SYS_gettid), __ATOMIC_RELAXED);
> >          }
> > 
> >          static void *test_thread(void *arg)
> > 
> > [root@quaco ~]# perf probe -x ~/bin/perf sigtrap_handler:4 "ctx.signal_count"
> > Failed to write event: Invalid argument
> > Please upgrade your kernel to at least 3.14 to have access to feature @ctx
> >   Error: Failed to add events.
> > [root@quaco ~]#
> 
> Ah, this is a wrong usage (I'm also trapped the same thing). Correctly, it should
> pass it as a single parameter.
> 
> perf probe -x ~/bin/perf "sigtrap_handler:4 ctx.signal_count"

[root@five ~]# perf probe -x ~/bin/perf "sigtrap_handler:4 ctx.signal_count"
Failed to write event: Invalid argument
Please upgrade your kernel to at least 3.14 to have access to feature @ctx
  Error: Failed to add events.
[root@five ~]#

Didn't work?

- Arnaldo
 
> This is for adding several events at the same time. But now it becomes just a trap.
> Can I change the syntax from
> 
> perf probe [OPTIONS] <PROBE-DEFINITION> [PROBE-DEFINITION...]
> 
> To,
> 
> perf probe [OPTIONS] <PROBE-POINT> [ARGS...]
> 
> ?
> 
> We can keep --add having optional parameter as below.
> 
> perf probe [OPTIONS] --add <PROBE-DEFINITION>
> 
> Thank you,
> 
> > 
> > [root@quaco ~]# uname -a
> > Linux quaco 6.3.8-100.fc37.x86_64 #1 SMP PREEMPT_DYNAMIC Thu Jun 15 01:51:54 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
> > [root@quaco ~]# rpm -qa | grep kernel-debuginfo
> > kernel-debuginfo-common-x86_64-6.3.8-100.fc37.x86_64
> > kernel-debuginfo-6.3.8-100.fc37.x86_64
> > [root@quaco ~]#
> > 
> > -- 
> > 
> > - Arnaldo
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@kernel.org>

-- 

- Arnaldo

Re: perf probe: Trying to read a 'ctx' named local variable

[Masami Hiramatsu]

On Thu, 20 Jul 2023 11:40:42 -0300
Arnaldo Carvalho de Melo <acme@kernel.org> wrote:

> Em Tue, Jul 18, 2023 at 08:54:51AM +0900, Masami Hiramatsu escreveu:
> > On Mon, 17 Jul 2023 15:06:10 -0300
> > Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> > 
> > > Hi Masami,
> > > 
> > > 	Trying to use perf to debug perf I stumbled on this:
> > > 
> > > [root@quaco ~]# perf probe -x ~/bin/perf -L sigtrap_handler
> > > <sigtrap_handler@/home/acme/git/perf-tools/tools/perf/tests/sigtrap.c:0>
> > >       0  sigtrap_handler(int signum __maybe_unused, siginfo_t *info, void *ucontext __maybe_unused)
> > >          {
> > >                 if (!__atomic_fetch_add(&ctx.signal_count, 1, __ATOMIC_RELAXED))
> > >       3                 ctx.first_siginfo = *info;
> > >       4         __atomic_fetch_sub(&ctx.tids_want_signal, syscall(SYS_gettid), __ATOMIC_RELAXED);
> > >          }
> > > 
> > >          static void *test_thread(void *arg)
> > > 
> > > [root@quaco ~]# perf probe -x ~/bin/perf sigtrap_handler:4 "ctx.signal_count"
> > > Failed to write event: Invalid argument
> > > Please upgrade your kernel to at least 3.14 to have access to feature @ctx
> > >   Error: Failed to add events.
> > > [root@quaco ~]#
> > 
> > Ah, this is a wrong usage (I'm also trapped the same thing). Correctly, it should
> > pass it as a single parameter.
> > 
> > perf probe -x ~/bin/perf "sigtrap_handler:4 ctx.signal_count"
> 
> [root@five ~]# perf probe -x ~/bin/perf "sigtrap_handler:4 ctx.signal_count"
> Failed to write event: Invalid argument
> Please upgrade your kernel to at least 3.14 to have access to feature @ctx
>   Error: Failed to add events.
> [root@five ~]#
> 
> Didn't work?

Ah, I got it. The error message is wrong.

/sys/kernel/debug/tracing# cat error_log 
[122869.758693] trace_uprobe: error: Symbol is not available with uprobe
  Command: p:probe_perf/sigtrap_handler_L4 /usr/local/bin/perf:0xfc8e9 signal_count=@ctx+4:s32
                                                                                                          ^
"ctx" is not a local variable in this context and @ctx (global variable) is not
accessible from uprobe events.
Hmm, it must be checked while parsing the debuginfo.

Thank you,

> 
> - Arnaldo
>  
> > This is for adding several events at the same time. But now it becomes just a trap.
> > Can I change the syntax from
> > 
> > perf probe [OPTIONS] <PROBE-DEFINITION> [PROBE-DEFINITION...]
> > 
> > To,
> > 
> > perf probe [OPTIONS] <PROBE-POINT> [ARGS...]
> > 
> > ?
> > 
> > We can keep --add having optional parameter as below.
> > 
> > perf probe [OPTIONS] --add <PROBE-DEFINITION>
> > 
> > Thank you,
> > 
> > > 
> > > [root@quaco ~]# uname -a
> > > Linux quaco 6.3.8-100.fc37.x86_64 #1 SMP PREEMPT_DYNAMIC Thu Jun 15 01:51:54 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
> > > [root@quaco ~]# rpm -qa | grep kernel-debuginfo
> > > kernel-debuginfo-common-x86_64-6.3.8-100.fc37.x86_64
> > > kernel-debuginfo-6.3.8-100.fc37.x86_64
> > > [root@quaco ~]#
> > > 
> > > -- 
> > > 
> > > - Arnaldo
> > 
> > 
> > -- 
> > Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> -- 
> 
> - Arnaldo


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>