Re: [PATCH v2 1/3] SDT markers listing by perf:

From: Hemant
Date: Tue Oct 08 2013 - 09:26:18 EST

On 10/08/2013 05:09 PM, Masami Hiramatsu wrote:
(2013/10/07 15:47), Hemant Kumar wrote:
@@ -325,6 +326,7 @@ 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('S', "markers", &params.sdt, "Show probe-able sdt notes"),
BTW, "-S" for short of "--markers" option is a bit odd. Would we better use -M ? :)

I thought of -S as SDT. :) Anyways, on second thought, will change that to -M.


[...]
@@ -355,6 +357,26 @@ 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);
+ }
+ ret = show_sdt_notes(params.target);
You have to ensure params.target is set before use it.

Yes, will do that.

+ if (ret < 0) {
+ pr_err(" Error : Failed to find SDT markers!"
+ "(%d)\n", 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/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 4b12bf8..6b17260 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -846,6 +846,182 @@ out_elf_end:
return err;
}
+/*
+ * Populate the name, type, offset in the SDT note structure and
+ * ignore the argument fields (for now)
+ */
+static struct sdt_note *populate_sdt_note(Elf **elf, const char *data,
+ size_t len, int type)
+{
+ const char *provider, *name;
+ struct sdt_note *note;
+
+ /*
+ * 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_ret;
+
+ note = (struct sdt_note *)zalloc(sizeof(struct sdt_note));
+ if (note == NULL) {
+ pr_err("Memory allocation error\n");
No need to state out of memory for each place...
If you hit an out of memory for such small piece, you'd better
abort execution. For that purpose, I recommend you to return
errno from each function, and caller must check it.

Yeah this will be better... will return errno from each function.

+ goto out_ret;
+ }
+ INIT_LIST_HEAD(&note->note_list);
+
+ if (len < dst.d_size + 3)
+ goto out_free;
+
+ /* 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->provider = strdup(provider);
+ note->name = strdup(name);
+
+ /* Obtain the addresses and ignore notes with semaphores set*/
+ if (gelf_getclass(*elf) == ELFCLASS32) {
+ note->addr.a32[0] = buf.a32[0];
+ note->addr.a32[1] = buf.a32[1];
+ note->addr.a32[2] = buf.a32[2];
+ note->bit32 = true;
+ if (buf.a32[2] != 0)
+ goto out_free;
+ } else {
+ note->addr.a64[0] = buf.a64[0];
+ note->addr.a64[1] = buf.a64[1];
+ note->addr.a64[2] = buf.a64[2];
+ note->bit32 = false;
+ if (buf.a64[2] != 0)
+ goto out_free;
+ }
+ return note;
+
+out_free:
+ free(note);
+out_ret:
+ return NULL;
+}
+
+static struct list_head *construct_sdt_notes_list(Elf *elf)
This also would better return errno.

Ok.

+{
+ 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, *note = NULL;
+
+ if (gelf_getehdr(elf, &ehdr) == NULL) {
+ pr_debug("%s: Can't get elf header.\n", __func__);
+ goto out_err;
+ }
+ if (elf_getshdrstrndx(elf, &shstrndx) != 0) {
+ pr_debug("getshdrstrndx failed\n");
+ goto out_err;
+ }
+
+ /*
+ * Look for section type = SHT_NOTE, flags = no SHF_ALLOC
+ * and name = .note.stapsdt
+ */
+ scn = elf_section_by_name(elf, &ehdr, &shdr, NOTE_SCN, NULL);
+ if (!scn) {
+ printf("SDT markers not present!\n");
Why you don't use pr_err() here ? :)

Because, I thought it isn't an error that SDT markers are not present. It won't make much of a difference though. :)

And also, as I commented, I'd like to know which binary doesn't have SDT markers,
at least with -v (verbose) option.

Yes, I guess it would be better to show the binary name even without -v option. Will make the changes.

--
Thanks
Hemant

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