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Message-ID: <aFrkQDcKpZilSOpj@google.com>
Date: Tue, 24 Jun 2025 10:45:36 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
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 v4 1/2] perf debug: Add function symbols to dump_stack
Hi Ian,
On Mon, Jun 23, 2025 at 09:19:28AM -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:
> ```
> $ perf test -vv PERF_RECORD_
> ...
> 7: PERF_RECORD_* events & perf_sample fields:
> 7: 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:
> : 7: PERF_RECORD_* events & perf_sample fields:
>
> ---- unexpected signal (2) ----
> #0 0x5628ad5570a3 in child_test_sig_handler builtin-test.c:0
> #1 0x7f561de49df0 in __restore_rt libc_sigaction.c:0
> #2 0x7f561de99687 in __internal_syscall_cancel cancellation.c:64
> #3 0x7f561dee5f7a in clock_nanosleep@...BC_2.2.5 clock_nanosleep.c:72
> #4 0x7f561def1393 in __nanosleep nanosleep.c:26
> #5 0x7f561df02d68 in __sleep sleep.c:55
> #6 0x5628ad5679ab in test__PERF_RECORD perf-record.c:0
> #7 0x5628ad556fb0 in run_test_child builtin-test.c:0
> #8 0x5628ad4f318d in start_command run-command.c:127
> #9 0x5628ad557ef3 in __cmd_test builtin-test.c:0
> #10 0x5628ad5585bf in cmd_test ??:0
> #11 0x5628ad4e5bb0 in run_builtin perf.c:0
> #12 0x5628ad4e5ecb in handle_internal_command perf.c:0
> #13 0x5628ad461383 in main ??:0
> #14 0x7f561de33ca8 in __libc_start_call_main libc_start_call_main.h:74
> #15 0x7f561de33d65 in __libc_start_main@@GLIBC_2.34 libc-start.c:128
> #16 0x5628ad4619d1 in _start ??:0
>
> ---- unexpected signal (2) ----
> #0 0x5628ad5570a3 in child_test_sig_handler builtin-test.c:0
> #1 0x7f561de49df0 in __restore_rt libc_sigaction.c:0
> #2 0x7f561dea3a14 in pthread_sigmask@...BC_2.2.5 pthread_sigmask.c:45
> #3 0x7f561de49fd9 in __GI___sigprocmask sigprocmask.c:26
> #4 0x7f561df2601b in __longjmp_chk longjmp.c:36
> #5 0x5628ad5570c0 in print_test_result.isra.0 builtin-test.c:0
> #6 0x7f561de49df0 in __restore_rt libc_sigaction.c:0
> #7 0x7f561de99687 in __internal_syscall_cancel cancellation.c:64
> #8 0x7f561dee5f7a in clock_nanosleep@...BC_2.2.5 clock_nanosleep.c:72
> #9 0x7f561def1393 in __nanosleep nanosleep.c:26
> #10 0x7f561df02d68 in __sleep sleep.c:55
> #11 0x5628ad5679ab in test__PERF_RECORD perf-record.c:0
> #12 0x5628ad556fb0 in run_test_child builtin-test.c:0
> #13 0x5628ad4f318d in start_command run-command.c:127
> #14 0x5628ad557ef3 in __cmd_test builtin-test.c:0
> #15 0x5628ad5585bf in cmd_test ??:0
> #16 0x5628ad4e5bb0 in run_builtin perf.c:0
> #17 0x5628ad4e5ecb in handle_internal_command perf.c:0
> #18 0x5628ad461383 in main ??:0
> #19 0x7f561de33ca8 in __libc_start_call_main libc_start_call_main.h:74
> #20 0x7f561de33d65 in __libc_start_main@@GLIBC_2.34 libc-start.c:128
> #21 0x5628ad4619d1 in _start ??:0
> 7: PERF_RECORD_* events & perf_sample fields : Skip (permissions)
> ```
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>
Unfortunately it has some build errors so I had to remove it from the
tree. I'll keep the patch 2/2 btw.
The NO_BACKTRACE=1 build caused a trouble like below.
CC /tmp/tmp.huqYLzBWIi/util/debug.o
util/debug.c: In function '__dump_stack':
util/debug.c:323:17: error: implicit declaration of function 'backtrace_symbols_fd' [-Wimplicit-function-declaration]
323 | backtrace_symbols_fd(stackdump, stackdump_size, fileno(file));
| ^~~~~~~~~~~~~~~~~~~~
make[6]: *** [/usr/local/google/home/namhyung/project/linux/tools/build/Makefile.build:86: /tmp/tmp.huqYLzBWIi/util/debug.o] Error 1
make[5]: *** [/usr/local/google/home/namhyung/project/linux/tools/build/Makefile.build:142: util] Error 2
make[4]: *** [Makefile.perf:798: /tmp/tmp.huqYLzBWIi/perf-util-in.o] Error 2
make[4]: *** Waiting for unfinished jobs....
make[3]: *** [Makefile.perf:290: sub-make] Error 2
make[2]: *** [Makefile:76: all] Error 2
make[1]: *** [tests/make:341: make_no_backtrace_O] Error 1
make: *** [Makefile:109: build-test] Error 2
And on 32-bit, it also shows:
CC /build/util/debug.o
util/debug.c: In function '__dump_stack':
util/debug.c:331:28: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
331 | u64 addr = (u64)stackdump[i];
| ^
cc1: all warnings being treated as errors
make[4]: *** [/linux/tools/build/Makefile.build:85: /build/util/debug.o] Error 1
make[4]: *** Waiting for unfinished jobs....
make[3]: *** [/linux/tools/build/Makefile.build:142: util] Error 2
make[2]: *** [Makefile.perf:798: /build/perf-util-in.o] Error 2
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [Makefile.perf:290: sub-make] Error 2
make: *** [Makefile:76: all] Error 2
Thanks,
Namhyung
> ---
> v4: Additional addr_location__exit (Namhyung)
> v3: Rebase
> v2: Fix NO_BACKTRACE=1 build (Arnaldo)
> ---
> tools/perf/tests/builtin-test.c | 15 +++++++-
> tools/perf/ui/tui/setup.c | 2 +-
> tools/perf/util/debug.c | 66 +++++++++++++++++++++++++++------
> tools/perf/util/debug.h | 1 +
> 4 files changed, 71 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..efc9d2c6448d 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 +305,58 @@ 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)) {
> + addr_location__exit(&al);
> + 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.rc2.761.g2dc52ea45b-goog
>
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