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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

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