From 92ea788d2af4e65ad7a144ccfff50667e9a0d227 Mon Sep 17 00:00:00 2001 From: Namhyung Kim Date: Tue, 13 Jan 2026 15:29:02 -0800 Subject: [PATCH] perf inject: Add --convert-callchain option There are applications not built with frame pointers, so DWARF is needed to get the stack traces. `perf record --call-graph dwarf` saves the stack and register data for each sample to get the stacktrace offline. But sometimes this data may have sensitive information and we don't want to keep them in the file. This new 'perf inject --convert-callchain' option creates the callchains and discards the stack and register after that. This saves storage space and processing time for the new data file. Of course, users should remove the original data file to not keep sensitive data around. :) The down side is that it cannot handle inlined callchain entries as they all have the same IPs. Maybe we can add an option to 'perf report' to look up inlined functions using DWARF - IIUC it doesn't require stack and register data. This is an example. $ perf record --call-graph dwarf -- perf test -w noploop $ perf report --stdio --no-children --percent-limit=0 > output-prev $ perf inject -i perf.data --convert-callchain -o perf.data.out $ perf report --stdio --no-children --percent-limit=0 -i perf.data.out > output-next $ diff -u output-prev output-next ... 0.23% perf ld-linux-x86-64.so.2 [.] _dl_relocate_object_no_relro | - ---elf_dynamic_do_Rela (inlined) - _dl_relocate_object_no_relro + ---_dl_relocate_object_no_relro _dl_relocate_object dl_main _dl_sysdep_start - _dl_start_final (inlined) _dl_start _start Reviewed-by: Ian Rogers Signed-off-by: Namhyung Kim Cc: Adrian Hunter Cc: Ingo Molnar Cc: James Clark Cc: Jiri Olsa Cc: Peter Zijlstra Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/Documentation/perf-inject.txt | 5 + tools/perf/builtin-inject.c | 152 +++++++++++++++++++++++ 2 files changed, 157 insertions(+) diff --git a/tools/perf/Documentation/perf-inject.txt b/tools/perf/Documentation/perf-inject.txt index c972032f4ca0..95dfdf39666e 100644 --- a/tools/perf/Documentation/perf-inject.txt +++ b/tools/perf/Documentation/perf-inject.txt @@ -109,6 +109,11 @@ include::itrace.txt[] should be used, and also --buildid-all and --switch-events may be useful. +--convert-callchain:: + Parse DWARF callchains and convert them to usual callchains. This also + discards stack and register data from the samples. This will lose + inlined callchain entries. + :GMEXAMPLECMD: inject :GMEXAMPLESUBCMD: include::guestmount.txt[] diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c index 6080afec537d..e2a653280e1b 100644 --- a/tools/perf/builtin-inject.c +++ b/tools/perf/builtin-inject.c @@ -122,6 +122,7 @@ struct perf_inject { bool in_place_update; bool in_place_update_dry_run; bool copy_kcore_dir; + bool convert_callchain; const char *input_name; struct perf_data output; u64 bytes_written; @@ -133,6 +134,7 @@ struct perf_inject { struct guest_session guest_session; struct strlist *known_build_ids; const struct evsel *mmap_evsel; + struct ip_callchain *raw_callchain; }; struct event_entry { @@ -383,6 +385,90 @@ static int perf_event__repipe_sample(const struct perf_tool *tool, return perf_event__repipe_synth(tool, event); } +static int perf_event__convert_sample_callchain(const struct perf_tool *tool, + union perf_event *event, + struct perf_sample *sample, + struct evsel *evsel, + struct machine *machine) +{ + struct perf_inject *inject = container_of(tool, struct perf_inject, tool); + struct callchain_cursor *cursor = get_tls_callchain_cursor(); + union perf_event *event_copy = (void *)inject->event_copy; + struct callchain_cursor_node *node; + struct thread *thread; + u64 sample_type = evsel->core.attr.sample_type; + u32 sample_size = event->header.size; + u64 i, k; + int ret; + + if (event_copy == NULL) { + inject->event_copy = malloc(PERF_SAMPLE_MAX_SIZE); + if (!inject->event_copy) + return -ENOMEM; + + event_copy = (void *)inject->event_copy; + } + + if (cursor == NULL) + return -ENOMEM; + + callchain_cursor_reset(cursor); + + thread = machine__find_thread(machine, sample->tid, sample->pid); + if (thread == NULL) + goto out; + + /* this will parse DWARF using stack and register data */ + ret = thread__resolve_callchain(thread, cursor, evsel, sample, + /*parent=*/NULL, /*root_al=*/NULL, + PERF_MAX_STACK_DEPTH); + thread__put(thread); + if (ret != 0) + goto out; + + /* copy kernel callchain and context entries */ + for (i = 0; i < sample->callchain->nr; i++) { + inject->raw_callchain->ips[i] = sample->callchain->ips[i]; + if (sample->callchain->ips[i] == PERF_CONTEXT_USER) { + i++; + break; + } + } + if (i == 0 || inject->raw_callchain->ips[i - 1] != PERF_CONTEXT_USER) + inject->raw_callchain->ips[i++] = PERF_CONTEXT_USER; + + node = cursor->first; + for (k = 0; k < cursor->nr && i < PERF_MAX_STACK_DEPTH; k++) { + if (machine__kernel_ip(machine, node->ip)) + /* kernel IPs were added already */; + else if (node->ms.sym && node->ms.sym->inlined) + /* we can't handle inlined callchains */; + else + inject->raw_callchain->ips[i++] = node->ip; + + node = node->next; + } + + inject->raw_callchain->nr = i; + sample->callchain = inject->raw_callchain; + +out: + memcpy(event_copy, event, sizeof(event->header)); + + /* adjust sample size for stack and regs */ + sample_size -= sample->user_stack.size; + sample_size -= (hweight64(evsel->core.attr.sample_regs_user) + 1) * sizeof(u64); + sample_size += (sample->callchain->nr + 1) * sizeof(u64); + event_copy->header.size = sample_size; + + /* remove sample_type {STACK,REGS}_USER for synthesize */ + sample_type &= ~(PERF_SAMPLE_STACK_USER | PERF_SAMPLE_REGS_USER); + + perf_event__synthesize_sample(event_copy, sample_type, + evsel->core.attr.read_format, sample); + return perf_event__repipe_synth(tool, event_copy); +} + static struct dso *findnew_dso(int pid, int tid, const char *filename, const struct dso_id *id, struct machine *machine) { @@ -2270,6 +2356,15 @@ static int __cmd_inject(struct perf_inject *inject) /* Allow space in the header for guest attributes */ output_data_offset += gs->session->header.data_offset; output_data_offset = roundup(output_data_offset, 4096); + } else if (inject->convert_callchain) { + inject->tool.sample = perf_event__convert_sample_callchain; + inject->tool.fork = perf_event__repipe_fork; + inject->tool.comm = perf_event__repipe_comm; + inject->tool.exit = perf_event__repipe_exit; + inject->tool.mmap = perf_event__repipe_mmap; + inject->tool.mmap2 = perf_event__repipe_mmap2; + inject->tool.ordered_events = true; + inject->tool.ordering_requires_timestamps = true; } if (!inject->itrace_synth_opts.set) @@ -2322,6 +2417,23 @@ static int __cmd_inject(struct perf_inject *inject) perf_header__set_feat(&session->header, HEADER_BRANCH_STACK); } + + /* + * The converted data file won't have stack and registers. + * Update the perf_event_attr to remove them before writing. + */ + if (inject->convert_callchain) { + struct evsel *evsel; + + evlist__for_each_entry(session->evlist, evsel) { + evsel__reset_sample_bit(evsel, REGS_USER); + evsel__reset_sample_bit(evsel, STACK_USER); + evsel->core.attr.sample_regs_user = 0; + evsel->core.attr.sample_stack_user = 0; + evsel->core.attr.exclude_callchain_user = 0; + } + } + session->header.data_offset = output_data_offset; session->header.data_size = inject->bytes_written; perf_session__inject_header(session, session->evlist, fd, &inj_fc.fc, @@ -2346,6 +2458,18 @@ static int __cmd_inject(struct perf_inject *inject) return ret; } +static bool evsel__has_dwarf_callchain(struct evsel *evsel) +{ + struct perf_event_attr *attr = &evsel->core.attr; + const u64 dwarf_callchain_flags = + PERF_SAMPLE_STACK_USER | PERF_SAMPLE_REGS_USER | PERF_SAMPLE_CALLCHAIN; + + if (!attr->exclude_callchain_user) + return false; + + return (attr->sample_type & dwarf_callchain_flags) == dwarf_callchain_flags; +} + int cmd_inject(int argc, const char **argv) { struct perf_inject inject = { @@ -2414,6 +2538,8 @@ int cmd_inject(int argc, const char **argv) OPT_STRING(0, "guestmount", &symbol_conf.guestmount, "directory", "guest mount directory under which every guest os" " instance has a subdir"), + OPT_BOOLEAN(0, "convert-callchain", &inject.convert_callchain, + "Generate callchains using DWARF and drop register/stack data"), OPT_END() }; const char * const inject_usage[] = { @@ -2429,6 +2555,9 @@ int cmd_inject(int argc, const char **argv) #ifndef HAVE_JITDUMP set_option_nobuild(options, 'j', "jit", "NO_LIBELF=1", true); +#endif +#ifndef HAVE_LIBDW_SUPPORT + set_option_nobuild(options, 0, "convert-callchain", "NO_LIBDW=1", true); #endif argc = parse_options(argc, argv, options, inject_usage, 0); @@ -2588,6 +2717,28 @@ int cmd_inject(int argc, const char **argv) } } + if (inject.convert_callchain) { + struct evsel *evsel; + + if (inject.output.is_pipe || inject.session->data->is_pipe) { + pr_err("--convert-callchain cannot work with pipe\n"); + goto out_delete; + } + + evlist__for_each_entry(inject.session->evlist, evsel) { + if (!evsel__has_dwarf_callchain(evsel)) { + pr_err("--convert-callchain requires DWARF call graph.\n"); + goto out_delete; + } + } + + inject.raw_callchain = calloc(PERF_MAX_STACK_DEPTH, sizeof(u64)); + if (inject.raw_callchain == NULL) { + pr_err("callchain allocation failed\n"); + goto out_delete; + } + } + #ifdef HAVE_JITDUMP if (inject.jit_mode) { inject.tool.mmap2 = perf_event__repipe_mmap2; @@ -2618,5 +2769,6 @@ out_close_output: free(inject.itrace_synth_opts.vm_tm_corr_args); free(inject.event_copy); free(inject.guest_session.ev.event_buf); + free(inject.raw_callchain); return ret; } -- 2.47.3