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Message-ID: <CAP-5=fWyFDR87ojYLwwsn9+6zNzBgGXu-hHqsjSHmah8-HM-Fw@mail.gmail.com>
Date: Mon, 23 Jun 2025 09:02:16 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>,
James Clark <james.clark@...aro.org>, Howard Chu <howardchu95@...il.com>,
Yicong Yang <yangyicong@...ilicon.com>, linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] perf debug: Add function symbols to dump_stack
On Fri, Jun 20, 2025 at 1:23 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Wed, Jun 11, 2025 at 03:15:21PM -0700, Ian Rogers wrote:
> > Symbolize stack traces by creating a live machine. Add this
> > functionality to dump_stack and switch dump_stack users to use
> > it. Switch TUI to use it. Add stack traces to the child test function
> > which can be useful to diagnose blocked code.
> >
> > Example output:
> > ```
> > 8: PERF_RECORD_* events & perf_sample fields : Running (1 active)
> > ^C
> > Signal (2) while running tests.
> > Terminating tests with the same signal
> > Internal test harness failure. Completing any started tests:
> > : 8: PERF_RECORD_* events & perf_sample fields:
> >
> > ---- unexpected signal (2) ----
> > #0 0x5590fb6209b6 in child_test_sig_handler builtin-test.c:243
> > #1 0x7f4a91e49e20 in __restore_rt libc_sigaction.c:0
> > #2 0x7f4a91ee4f33 in clock_nanosleep@...BC_2.2.5 clock_nanosleep.c:71
> > #3 0x7f4a91ef0333 in __nanosleep nanosleep.c:26
> > #4 0x7f4a91f01f68 in __sleep sleep.c:55
> > #5 0x5590fb638c63 in test__PERF_RECORD perf-record.c:295
> > #6 0x5590fb620b43 in run_test_child builtin-test.c:269
> > #7 0x5590fb5b83ab in start_command run-command.c:127
> > #8 0x5590fb621572 in start_test builtin-test.c:467
> > #9 0x5590fb621a47 in __cmd_test builtin-test.c:573
> > #10 0x5590fb6225ea in cmd_test builtin-test.c:775
> > #11 0x5590fb5a9099 in run_builtin perf.c:351
> > #12 0x5590fb5a9340 in handle_internal_command perf.c:404
> > #13 0x5590fb5a9499 in run_argv perf.c:451
> > #14 0x5590fb5a97e2 in main perf.c:558
> > #15 0x7f4a91e33d68 in __libc_start_call_main libc_start_call_main.h:74
> > #16 0x7f4a91e33e25 in __libc_start_main@@GLIBC_2.34 libc-start.c:128
> > #17 0x5590fb4fd6d1 in _start perf[436d1]
> > ```
> >
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > ---
> > tools/perf/tests/builtin-test.c | 15 +++++++-
> > tools/perf/ui/tui/setup.c | 2 +-
> > tools/perf/util/debug.c | 64 +++++++++++++++++++++++++++------
> > tools/perf/util/debug.h | 1 +
> > 4 files changed, 69 insertions(+), 13 deletions(-)
> >
> > diff --git a/tools/perf/tests/builtin-test.c b/tools/perf/tests/builtin-test.c
> > index 45d3d8b3317a..80375ca39a37 100644
> > --- a/tools/perf/tests/builtin-test.c
> > +++ b/tools/perf/tests/builtin-test.c
> > @@ -6,6 +6,9 @@
> > */
> > #include <fcntl.h>
> > #include <errno.h>
> > +#ifdef HAVE_BACKTRACE_SUPPORT
> > +#include <execinfo.h>
> > +#endif
> > #include <poll.h>
> > #include <unistd.h>
> > #include <setjmp.h>
> > @@ -231,6 +234,16 @@ static jmp_buf run_test_jmp_buf;
> >
> > static void child_test_sig_handler(int sig)
> > {
> > +#ifdef HAVE_BACKTRACE_SUPPORT
> > + void *stackdump[32];
> > + size_t stackdump_size;
> > +#endif
> > +
> > + fprintf(stderr, "\n---- unexpected signal (%d) ----\n", sig);
> > +#ifdef HAVE_BACKTRACE_SUPPORT
> > + stackdump_size = backtrace(stackdump, ARRAY_SIZE(stackdump));
> > + __dump_stack(stderr, stackdump, stackdump_size);
> > +#endif
> > siglongjmp(run_test_jmp_buf, sig);
> > }
> >
> > @@ -244,7 +257,7 @@ static int run_test_child(struct child_process *process)
> >
> > err = sigsetjmp(run_test_jmp_buf, 1);
> > if (err) {
> > - fprintf(stderr, "\n---- unexpected signal (%d) ----\n", err);
> > + /* Received signal. */
> > err = err > 0 ? -err : -1;
> > goto err_out;
> > }
> > diff --git a/tools/perf/ui/tui/setup.c b/tools/perf/ui/tui/setup.c
> > index 16c6eff4d241..022534eed68c 100644
> > --- a/tools/perf/ui/tui/setup.c
> > +++ b/tools/perf/ui/tui/setup.c
> > @@ -108,7 +108,7 @@ static void ui__signal_backtrace(int sig)
> >
> > printf("-------- backtrace --------\n");
> > size = backtrace(stackdump, ARRAY_SIZE(stackdump));
> > - backtrace_symbols_fd(stackdump, size, STDOUT_FILENO);
> > + __dump_stack(stdout, stackdump, size);
> >
> > exit(0);
> > }
> > diff --git a/tools/perf/util/debug.c b/tools/perf/util/debug.c
> > index f9ef7d045c92..8987ac250079 100644
> > --- a/tools/perf/util/debug.c
> > +++ b/tools/perf/util/debug.c
> > @@ -14,11 +14,18 @@
> > #ifdef HAVE_BACKTRACE_SUPPORT
> > #include <execinfo.h>
> > #endif
> > +#include "addr_location.h"
> > #include "color.h"
> > -#include "event.h"
> > #include "debug.h"
> > +#include "event.h"
> > +#include "machine.h"
> > +#include "map.h"
> > #include "print_binary.h"
> > +#include "srcline.h"
> > +#include "symbol.h"
> > +#include "synthetic-events.h"
> > #include "target.h"
> > +#include "thread.h"
> > #include "trace-event.h"
> > #include "ui/helpline.h"
> > #include "ui/ui.h"
> > @@ -298,21 +305,56 @@ void perf_debug_setup(void)
> > libapi_set_print(pr_warning_wrapper, pr_warning_wrapper, pr_debug_wrapper);
> > }
> >
> > +void __dump_stack(FILE *file, void **stackdump, size_t stackdump_size)
> > +{
> > + /* TODO: async safety. printf, malloc, etc. aren't safe inside a signal handler. */
> > + pid_t pid = getpid();
> > + struct machine *machine = machine__new_live(/*kernel_maps=*/false, pid);
> > + struct thread *thread = NULL;
> > +
> > + if (machine)
> > + thread = machine__find_thread(machine, pid, pid);
> > +
> > + if (!machine || !thread) {
> > + /*
> > + * Backtrace functions are async signal safe. Fall back on them
> > + * if machine/thread creation fails.
> > + */
> > + backtrace_symbols_fd(stackdump, stackdump_size, fileno(file));
> > + machine__delete(machine);
> > + return;
> > + }
> > +
> > + for (size_t i = 0; i < stackdump_size; i++) {
> > + struct addr_location al;
> > + u64 addr = (u64)stackdump[i];
> > +
> > + addr_location__init(&al);
> > + if (!thread__find_map(thread, PERF_RECORD_MISC_USER, addr, &al))
>
> It seems addr_location__exit(&al) is needed here.
Good catch. I don't think it changes the behavior of the code but is
cleaner. I'll fix in v4.
Thanks,
Ian
> Thanks,
> Namhyung
>
>
> > + continue;
> > +
> > + al.sym = map__find_symbol(al.map, al.addr);
> > + if (al.sym)
> > + fprintf(file, " #%zd %p in %s ", i, stackdump[i], al.sym->name);
> > + else
> > + fprintf(file, " #%zd %p ", i, stackdump[i]);
> > +
> > + map__fprintf_srcline(al.map, al.addr, "", file);
> > + fprintf(file, "\n");
> > + addr_location__exit(&al);
> > + }
> > + thread__put(thread);
> > + machine__delete(machine);
> > +}
> > +
> > /* Obtain a backtrace and print it to stdout. */
> > #ifdef HAVE_BACKTRACE_SUPPORT
> > void dump_stack(void)
> > {
> > - void *array[16];
> > - size_t size = backtrace(array, ARRAY_SIZE(array));
> > - char **strings = backtrace_symbols(array, size);
> > - size_t i;
> > -
> > - printf("Obtained %zd stack frames.\n", size);
> > -
> > - for (i = 0; i < size; i++)
> > - printf("%s\n", strings[i]);
> > + void *stackdump[32];
> > + size_t size = backtrace(stackdump, ARRAY_SIZE(stackdump));
> >
> > - free(strings);
> > + __dump_stack(stdout, stackdump, size);
> > }
> > #else
> > void dump_stack(void) {}
> > diff --git a/tools/perf/util/debug.h b/tools/perf/util/debug.h
> > index a4026d1fd6a3..6b737e195ce1 100644
> > --- a/tools/perf/util/debug.h
> > +++ b/tools/perf/util/debug.h
> > @@ -85,6 +85,7 @@ void debug_set_display_time(bool set);
> > void perf_debug_setup(void);
> > int perf_quiet_option(void);
> >
> > +void __dump_stack(FILE *file, void **stackdump, size_t stackdump_size);
> > void dump_stack(void);
> > void sighandler_dump_stack(int sig);
> >
> > --
> > 2.50.0.rc1.591.g9c95f17f64-goog
> >
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