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 <[e-mail]>
Signed-off-by: Namhyung Kim <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/perf-inject.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[]

tools/perf/builtin-inject.c

···
 	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;
···
 	struct guest_session	guest_session;
 	struct strlist		*known_build_ids;
 	const struct evsel	*mmap_evsel;
+	struct ip_callchain	*raw_callchain;
 };
 
 struct event_entry {
···
 	}
 
 	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,
···
 		/* 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)
···
 				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,
···
 	}
 
 	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)
···
 		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[] = {
···
 
 #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);
 
···
 		}
 	}
 
+	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;
···
 	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;
 }