[PATCH v4 1/3] SDT markers listing by perf:

[Hemant Kumar]

This patch will enable perf to list all the sdt markers present
in an elf file. The markers are present in the .note.stapsdt section
of the elf. We can traverse through this section and collect the
required info about the markers.
We can use '-M/--markers' with perf to view the SDT notes.

Currently, the sdt notes which have their semaphores enabled, are being
ignored silently. But, they will be supported soon.

Wrapping this inside #ifdef LIBELF_SUPPORT pair is not required,
because, if NO_LIBELF = 1, then 'probe' command of perf is itself disabled.

Usage:
perf probe --markers -x /lib64/libc.so.6

Output :
%libc:setjmp
%libc:longjmp
%libc:longjmp_target
%libc:lll_futex_wake
%libc:lll_lock_wait_private
%libc:longjmp
%libc:longjmp_target
%libc:lll_futex_wake

Signed-off-by: Hemant Kumar Shaw <hkshaw@xxxxxxxxxxxxxxxxxx>
---
 tools/perf/builtin-probe.c    |   41 +++++++
 tools/perf/util/probe-event.c |   23 ++++
 tools/perf/util/probe-event.h |    1 
 tools/perf/util/symbol-elf.c  |  225 +++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/symbol.h      |   19 +++
 5 files changed, 307 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
index 89acc17..2450613 100644
--- a/tools/perf/builtin-probe.c
+++ b/tools/perf/builtin-probe.c
@@ -55,6 +55,8 @@ static struct {
 	bool show_funcs;
 	bool mod_events;
 	bool uprobes;
+	bool exec;
+	bool sdt;
 	int nevents;
 	struct perf_probe_event events[MAX_PROBES];
 	struct strlist *dellist;
@@ -171,8 +173,10 @@ static int opt_set_target(const struct option *opt, const char *str,
 	int ret = -ENOENT;
 
 	if  (str && !params.target) {
-		if (!strcmp(opt->long_name, "exec"))
+		if (!strcmp(opt->long_name, "exec")) {
 			params.uprobes = true;
+			params.exec = true;
+		}
 #ifdef HAVE_DWARF_SUPPORT
 		else if (!strcmp(opt->long_name, "module"))
 			params.uprobes = false;
@@ -325,6 +329,7 @@ int cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
 		     opt_set_filter),
 	OPT_CALLBACK('x', "exec", NULL, "executable|path",
 			"target executable name or path", opt_set_target),
+	OPT_BOOLEAN('M', "markers", &params.sdt, "Show proba-able sdt notes"),
 	OPT_END()
 	};
 	int ret;
@@ -347,7 +352,7 @@ int cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
 		params.max_probe_points = MAX_PROBES;
 
 	if ((!params.nevents && !params.dellist && !params.list_events &&
-	     !params.show_lines && !params.show_funcs))
+	     !params.show_lines && !params.show_funcs && !params.sdt))
 		usage_with_options(probe_usage, options);
 
 	/*
@@ -355,6 +360,38 @@ int cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
 	 */
 	symbol_conf.try_vmlinux_path = (symbol_conf.vmlinux_name == NULL);
 
+	if (params.sdt) {
+		if (params.show_lines) {
+			pr_err("Error: Don't use --markers with --lines.\n");
+			usage_with_options(probe_usage, options);
+		}
+		if (params.show_vars) {
+			pr_err("Error: Don't use --markers with --vars.\n");
+			usage_with_options(probe_usage, options);
+		}
+		if (params.show_funcs) {
+			pr_err("Error: Don't use --markers with --funcs.\n");
+			usage_with_options(probe_usage, options);
+		}
+		if (params.mod_events) {
+			pr_err("Error: Don't use --markers with --add/--del.\n");
+			usage_with_options(probe_usage, options);
+		}
+		if (!params.exec) {
+			pr_err("Error: Always use --exec with --markers.\n");
+			usage_with_options(probe_usage, options);
+		}
+		if (!params.target) {
+			pr_err("Error: Please specify a target binary!\n");
+			usage_with_options(probe_usage, options);
+		}
+		ret = show_sdt_notes(params.target);
+		if (ret < 0) {
+			pr_err("  Error : Failed to find SDT markers in %s !"
+			       " (%d)\n", params.target, ret);
+		}
+		return ret;
+	}
 	if (params.list_events) {
 		if (params.mod_events) {
 			pr_err("  Error: Don't use --list with --add/--del.\n");
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 779b2da..19182f7 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -2372,3 +2372,26 @@ out:
 		free(name);
 	return ret;
 }
+
+static void display_sdt_note_info(struct list_head *start)
+{
+	struct sdt_note *pos;
+
+	if (list_empty(start))
+		return;
+	list_for_each_entry(pos, start, note_list) {
+		printf("%%%s:%s\n", pos->provider, pos->name);
+	}
+}
+
+int show_sdt_notes(const char *target)
+{
+	int ret;
+	LIST_HEAD(sdt_notes);
+
+	ret = get_sdt_note_list(&sdt_notes, target);
+	if (!ret)
+		display_sdt_note_info(&sdt_notes);
+	cleanup_sdt_note_list(&sdt_notes);
+	return ret;
+}
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index f9f3de8..32de5a3 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -133,6 +133,7 @@ extern int show_available_vars(struct perf_probe_event *pevs, int npevs,
 			       struct strfilter *filter, bool externs);
 extern int show_available_funcs(const char *module, struct strfilter *filter,
 				bool user);
+int show_sdt_notes(const char *target);
 
 /* Maximum index number of event-name postfix */
 #define MAX_EVENT_INDEX	1024
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index eed0b96..a065b04 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1613,6 +1613,231 @@ void kcore_extract__delete(struct kcore_extract *kce)
 	unlink(kce->extract_filename);
 }
 
+/*
+ * Populate the name, type, offset in the SDT note structure and
+ * ignore the argument fields (for now)
+ */
+static int populate_sdt_note(Elf **elf, const char *data, size_t len, int type,
+			     struct sdt_note **note)
+{
+	const char *provider, *name;
+	struct sdt_note *tmp = NULL;
+	int ret = -1;
+
+	/*
+	 * Three addresses need to be obtained :
+	 * Marker location, address of base section and semaphore location
+	 */
+	union {
+		Elf64_Addr a64[3];
+		Elf32_Addr a32[3];
+	} buf;
+
+	/*
+	 * dst and src are required for translation from file to memory
+	 * representation
+	 */
+	Elf_Data dst = {
+		.d_buf = &buf, .d_type = ELF_T_ADDR, .d_version = EV_CURRENT,
+		.d_size = gelf_fsize((*elf), ELF_T_ADDR, 3, EV_CURRENT),
+		.d_off = 0, .d_align = 0
+	};
+
+	Elf_Data src = {
+		.d_buf = (void *) data, .d_type = ELF_T_ADDR,
+		.d_version = EV_CURRENT, .d_size = dst.d_size, .d_off = 0,
+		.d_align = 0
+	};
+
+	/* Check the type of each of the notes */
+	if (type != SDT_NOTE_TYPE)
+		goto out_err;
+
+	tmp = (struct sdt_note *)zalloc(sizeof(struct sdt_note));
+	if (tmp == NULL) {
+		ret = -ENOMEM;
+		goto out_err;
+	}
+	INIT_LIST_HEAD(&tmp->note_list);
+
+	if (len < dst.d_size + 3)
+		goto out_free_note;
+
+	/* Translation from file representation to memory representation */
+	if (gelf_xlatetom(*elf, &dst, &src,
+			  elf_getident(*elf, NULL)[EI_DATA]) == NULL)
+		pr_debug("gelf_xlatetom : %s", elf_errmsg(-1));
+
+	/* Populate the fields of sdt_note */
+	provider = data + dst.d_size;
+
+	name = (const char *)memchr(provider, '\0', data + len - provider);
+	if (name++ == NULL)
+		goto out_free_note;
+	tmp->provider = strdup(provider);
+	if (!tmp->provider) {
+		ret = -ENOMEM;
+		goto out_free_note;
+	}
+	tmp->name = strdup(name);
+	if (!tmp->name) {
+		ret = -ENOMEM;
+		goto out_free_prov;
+	}
+
+	/* Obtain the addresses and ignore notes with semaphores set*/
+	if (gelf_getclass(*elf) == ELFCLASS32) {
+		if (buf.a32[2] != 0)
+			goto out_free_name;
+		tmp->addr.a32[0] = buf.a32[0];
+		tmp->addr.a32[1] = buf.a32[1];
+		tmp->addr.a32[2] = buf.a32[2];
+		tmp->bit32 = true;
+	} else {
+		if (buf.a64[2] != 0)
+			goto out_free_name;
+		tmp->addr.a64[0] = buf.a64[0];
+		tmp->addr.a64[1] = buf.a64[1];
+		tmp->addr.a64[2] = buf.a64[2];
+		tmp->bit32 = false;
+	}
+	*note = tmp;
+	return 0;
+
+out_free_name:
+	free(tmp->name);
+out_free_prov:
+	free(tmp->provider);
+out_free_note:
+	free(tmp);
+out_err:
+	return ret;
+}
+
+static int construct_sdt_notes_list(Elf *elf, struct list_head *sdt_notes)
+{
+	GElf_Ehdr ehdr;
+	Elf_Scn *scn = NULL;
+	Elf_Data *data;
+	GElf_Shdr shdr;
+	size_t shstrndx;
+	size_t next;
+	GElf_Nhdr nhdr;
+	size_t name_off, desc_off, offset;
+	struct sdt_note *tmp = NULL;
+	int ret = 0, val = 0;
+
+	if (gelf_getehdr(elf, &ehdr) == NULL) {
+		ret = -EBADF;
+		pr_debug("Can't get elf header!");
+		goto out_ret;
+	}
+	if (elf_getshdrstrndx(elf, &shstrndx) != 0) {
+		ret = -EBADF;
+		pr_debug("getshdrstrndx failed\n");
+		goto out_ret;
+	}
+
+	/*
+	 * Look for section type = SHT_NOTE, flags = no SHF_ALLOC
+	 * and name = .note.stapsdt
+	 */
+	scn = elf_section_by_name(elf, &ehdr, &shdr, SDT_NOTE_SCN, NULL);
+	if (!scn) {
+		ret = -ENOENT;
+		pr_debug("Can't get section .note.stapsdt\n");
+		goto out_ret;
+	}
+	if (!(shdr.sh_type == SHT_NOTE) || (shdr.sh_flags & SHF_ALLOC)) {
+		ret = -ENOENT;
+		goto out_ret;
+	}
+
+	data = elf_getdata(scn, NULL);
+
+	/* Get the SDT notes */
+	for (offset = 0; (next = gelf_getnote(data, offset, &nhdr, &name_off,
+					      &desc_off)) > 0; offset = next) {
+		if (nhdr.n_namesz == sizeof(SDT_NOTE_NAME) &&
+		    !memcmp(data->d_buf + name_off, SDT_NOTE_NAME,
+			    sizeof(SDT_NOTE_NAME))) {
+			val = populate_sdt_note(&elf, ((data->d_buf) + desc_off),
+						nhdr.n_descsz, nhdr.n_type,
+						&tmp);
+			if (!val)
+				list_add_tail(&tmp->note_list, sdt_notes);
+			if (val == -ENOMEM) {
+				ret = -ENOMEM;
+				goto out_ret;
+			}
+		}
+	}
+	if (!sdt_notes)
+		ret = -ENOENT;
+
+out_ret:
+	return ret;
+}
+
+static int sdt_err(int val, const char *target)
+{
+	switch (-val) {
+	case 0:
+		break;
+	case ENOENT:
+		/* Absence of SDT markers isn't an error */
+		val = 0;
+		printf("%s : No SDT markers found!\n", target);
+		break;
+	case EBADF:
+		pr_err("%s : Bad file name\n", target);
+		break;
+	default:
+		pr_err("%s\n", strerror(val));
+	}
+	return val;
+}
+
+int get_sdt_note_list(struct list_head *head, const char *target)
+{
+	Elf *elf;
+	int fd, ret;
+
+	fd = open(target, O_RDONLY);
+	if (fd < 0) {
+		pr_err("%s : %s\n", target, strerror(errno));
+		return -errno;
+	}
+
+	symbol__elf_init();
+	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
+	if (!elf) {
+		ret = -EBADF;
+		pr_debug("%s : %s\n", target, elf_errmsg(elf_errno()));
+		goto out_close;
+	}
+	ret = construct_sdt_notes_list(elf, head);
+	elf_end(elf);
+
+out_close:
+	close(fd);
+	return sdt_err(ret, target);
+}
+
+void cleanup_sdt_note_list(struct list_head *sdt_notes)
+{
+	struct sdt_note *tmp, *pos;
+
+	if (list_empty(sdt_notes))
+		return;
+	list_for_each_entry_safe(pos, tmp, sdt_notes, note_list) {
+		list_del(&pos->note_list);
+		free(pos->name);
+		free(pos->provider);
+		free(pos);
+	}
+}
+
 void symbol__elf_init(void)
 {
 	elf_version(EV_CURRENT);
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index 07de8fe..1e50300 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -198,6 +198,17 @@ struct symsrc {
 #endif
 };
 
+struct sdt_note {
+	char *name;
+	char *provider;
+	bool bit32;                 /* 32 or 64 bit flag */
+	union {
+		Elf64_Addr a64[3];
+		Elf32_Addr a32[3];
+	} addr;
+	struct list_head note_list;
+};
+
 void symsrc__destroy(struct symsrc *ss);
 int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
 		 enum dso_binary_type type);
@@ -273,4 +284,12 @@ void kcore_extract__delete(struct kcore_extract *kce);
 int kcore_copy(const char *from_dir, const char *to_dir);
 int compare_proc_modules(const char *from, const char *to);
 
+/* Specific to SDT notes */
+int get_sdt_note_list(struct list_head *head, const char *target);
+void cleanup_sdt_note_list(struct list_head *sdt_notes);
+
+#define SDT_NOTE_TYPE 3
+#define SDT_NOTE_SCN ".note.stapsdt"
+#define SDT_NOTE_NAME "stapsdt"
+
 #endif /* __PERF_SYMBOL */

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