[PATCH 2/2] Support to perf to probe on SDT markers:

[Hemant Kumar]

This patch enables perf to probe on the marker name specified on the command line.
---
 tools/perf/builtin-probe.c    |    7 +++
 tools/perf/util/probe-event.c |   11 ++++
 tools/perf/util/symbol-elf.c  |  112 +++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/symbol.h      |    5 ++
 4 files changed, 135 insertions(+)

diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
index 3d8dcdf..8382853 100644
--- a/tools/perf/builtin-probe.c
+++ b/tools/perf/builtin-probe.c
@@ -378,6 +378,13 @@ int cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
 				       " (%d)\n", ret);
 			return ret;
 		}
+		params.uprobes = true;
+		ret = probe_marker(params.target,
+				   params.events[0].point.function);
+		if (ret < 0)
+			pr_err("Could not probe at %s marker\n",
+			       params.events[0].point.function);
+		return ret;
 	}
 
 	if (params.list_events) {
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 7f846f9..014d642 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -2378,3 +2378,14 @@ int show_available_markers(const char *target)
 	setup_pager();
 	return list_markers(target);
 }
+
+int probe_marker(const char *name, char *mark)
+{
+	int fd;
+
+	fd = open_uprobe_events(true);
+	if (fd == -1)
+		return fd;
+	else
+		return probe__marker(name, mark, fd);
+}
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index f3630f2..60938a5 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1040,6 +1040,118 @@ out_ret:
 	return ret;
 }
 
+static void extract_first_name(const char *target, char *fname)
+{
+	int i, len;
+	char *file;
+
+	file = strrchr(target, DIR_SEP);
+	file++;
+	len = strlen(file);
+	for (i = 0; i <= len; i++) {
+		if (!isalpha(file[i]))
+			break;
+		fname[i] = file[i];
+	}
+	fname[i] = '\0';
+}
+
+static int probe_at_note(struct sdt_note *r_note, const char *target, bool exec,
+			 int fd)
+{
+	char buf[MAX_CMDLEN];
+	int len, err = -1;
+	Elf64_Addr offset;
+	char *fname = NULL;
+
+	if (exec)
+		offset = r_note->addr.a64[0] - TEXT_SCN;
+	else
+		offset = r_note->addr.a64[0];
+
+	fname = (char *)zalloc(sizeof(char) * strlen(target));
+	if (fname == NULL) {
+		pr_err("Error in allocating memory to fname\n");
+		goto out_ret;
+	}
+
+	extract_first_name(target, fname);
+	len = snprintf(buf, MAX_CMDLEN, "%c:%s%s/%s %s:0x%x", 'p', "probe_",
+		       fname, r_note->name, target, (unsigned)offset);
+
+	len = write(fd, buf, MAX_CMDLEN);
+	if (len < 0) {
+		pr_err("Couldn't write into uprobe_events!\n");
+		goto out_close;
+	} else {
+		printf("Added new event :\n");
+		printf("event = %s \t (on 0x%x)\n\n", r_note->name,
+		       (unsigned)offset);
+		printf("You can now use it on all perf tools such as :\n\n");
+		printf("\t perf record -e %s%s:%s -aR sleep 1\n\n", "probe_", fname, r_note->name);
+		err = 0;
+	}
+
+out_close:
+	close(fd);
+	free(fname);
+out_ret:
+	return err;
+}
+
+static int search_and_probe_at_note(char *key, struct sdt_note **start,
+				    const char *target, bool exec, int fd)
+{
+	int ret = -1;
+	struct sdt_note *req;
+
+	for (req = (*start); req != NULL; req = req->next) {
+		if (!strcmp(key, req->name))
+			break;
+	}
+	if (!req) {
+		pr_err("Could not find marker %s\n", key);
+		return ret;
+	}
+
+	ret = probe_at_note(req, target, exec, fd);
+	return ret;
+}
+
+int probe__marker(const char *name, char *mark, int evfd)
+{
+	int ret = -1, fd;
+	Elf *elf;
+	bool exec = false;
+	struct sdt_note *head = NULL;
+
+	fd = open(name, O_RDONLY);
+	if (fd < 0) {
+		pr_err("Failed to open the file\n");
+		goto out_ret;
+	}
+
+	symbol__elf_init();
+	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
+	if (elf == NULL) {
+		pr_debug("%s: cannot read %s ELF file.\n", __func__, name);
+		goto out_close;
+	}
+
+	head = get_elf_markers(elf, &exec, true);
+	if (head) {
+		ret = search_and_probe_at_note(mark, &head, name, exec, evfd);
+		cleanup_notes(head);
+	}
+
+	elf_end(elf);
+
+out_close:
+	close(fd);
+out_ret:
+	return ret;
+}
+
 void cleanup_notes(struct sdt_note *start)
 {
 	struct sdt_note *tmp;
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index f2d17b7..95289fd 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -262,8 +262,13 @@ void __map_groups__fixup_end(struct map_groups *mg, enum map_type type);
 int show_available_markers(const char *module);
 int list_markers(const char *name);
 void cleanup_notes(struct sdt_note *start);
+int probe_marker(const char *name, char *mark);
+int probe__marker(const char *name, char *mark, int fd);
 
 #define SDT_NOTE_TYPE 3
 #define NOTE_SCN ".note.stapsdt"
+#define TEXT_SCN 0x400000
+#define DIR_SEP '/'
+#define MAX_CMDLEN 256
 
 #endif /* __PERF_SYMBOL */

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