Message-ID: <87ioyht7e4.fsf@sejong.aot.lge.com>
Date:	Wed, 04 Sep 2013 15:42:27 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, srikar@...ux.vnet.ibm.com,
	peterz@...radead.org, oleg@...hat.com, mingo@...hat.com,
	anton@...hat.com, systemtap@...rceware.org,
	masami.hiramatsu.pt@...achi.com
Subject: Re: [PATCH 1/2] SDT markers listing by perf

On Tue, 03 Sep 2013 13:06:55 +0530, Hemant Kumar wrote:

[SNIP]

> diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
> index e8a66f9..3d8dcdf 100644
> --- a/tools/perf/builtin-probe.c
> +++ b/tools/perf/builtin-probe.c
> @@ -55,6 +55,7 @@ static struct {
>  	bool show_funcs;
>  	bool mod_events;
>  	bool uprobes;
> +	bool sdt;
>  	int nevents;
>  	struct perf_probe_event events[MAX_PROBES];
>  	struct strlist *dellist;
> @@ -325,6 +326,8 @@ 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', "sdt", &params.sdt,
> +		    "Show and probe on the SDT markers"),

You need to add it to Documentation/perf-probe.txt too.  In addition if
the --sdt option is only able to work with libelf, it should be wrapped
into the #ifdef LIBELF_SUPPORT pair.

And I'm not sure that it's a good idea to have two behavior on a single
option (S) - show and probe (add).  Maybe it can be separated into two
or the S option can be used as a flag with existing --list and --add
option?


>  	OPT_END()
>  	};
>  	int ret;
> @@ -355,6 +358,28 @@ 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 --sdt with --line.\n");
> +			usage_with_options(probe_usage, options);
> +		}
> +		if (params.show_vars) {
> +			pr_err(" Error: Don't use --sdt with --vars.\n");
> +			usage_with_options(probe_usage, options);
> +		}
> +		if (params.show_funcs) {
> +			pr_err("  Error: Don't use --sdt with --funcs.\n");
> +			usage_with_options(probe_usage, options);
> +		}
> +		if (params.list_events) {
> +			ret = show_available_markers(params.target);
> +			if (ret < 0)
> +				pr_err("  Error: Failed to show 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");
> @@ -382,6 +407,7 @@ int cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
>  			       ret);
>  		return ret;
>  	}
> +
>  	if (params.show_funcs) {
>  		if (params.nevents != 0 || params.dellist) {
>  			pr_err("  Error: Don't use --funcs with"
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index aa04bf9..7f846f9 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -2372,3 +2372,9 @@ out:
>  		free(name);
>  	return ret;
>  }
> +
> +int show_available_markers(const char *target)
> +{
> +	setup_pager();
> +	return list_markers(target);
> +}

Did you build it with NO_LIBELF=1 ?  I guess not.  At least you need a
dummy list_markers() function which just returns -1 for such case.


> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 4b12bf8..f3630f2 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -846,6 +846,211 @@ out_elf_end:
>  	return err;
>  }
>  
> +/* Populate the name, type, offset and argument fields in the note structure */
> +static struct sdt_note *populate_note(Elf **elf, const char *data, size_t len,
> +				      int type)

Hmm.. I think the name needs to be changed more specific like
populate_sdt_note() or something?


> +{
> +	const char *provider, *name, *args;
> +	struct sdt_note *note;
> +
> +	/*
> +	 * There are 3 address values to be obtained: marker offset, base address
> +	 * and semaphore
> +	 */
> +	union {
> +		Elf64_Addr a64[3];
> +		Elf32_Addr a32[3];
> +	} buf;
> +
> +	/*
> +	 * dst and src (of Elf_Data) 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
> +	};
> +
> +	if (type != SDT_NOTE_TYPE)
> +		goto out_ret;
> +
> +	note = zalloc(sizeof(struct sdt_note));
> +	if (note == NULL) {
> +		pr_err("memory allocation error\n");
> +		goto out_ret;
> +	}
> +	note->next = NULL;
> +
> +	if (len < dst.d_size + 3)
> +		goto out_free;
> +	/*
> +	 * Translating from file representation to memory representation
> +	 * Data now points to the address (offset)
> +	 */
> +	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_ret;
> +
> +	args = (const char *)memchr(name, '\0', data + len - name);
> +	if (args++ == NULL ||
> +	    memchr(args, '\0', data + len - name) != data + len - 1)
> +		goto out_ret;
> +	note->provider = provider;
> +	note->name = name;
> +
> +	/* Three addr's for location, base and semaphore addresses */
> +	note->addr.a64[0] = (buf.a64[0]);
> +	note->addr.a64[1] = (buf.a64[1]);
> +	note->addr.a64[2] = (buf.a64[2]);
> +	return note;
> +
> +out_free:
> +	free(note);
> +out_ret:
> +	return NULL;
> +}
> +
> +/*
> + * Traverse the elf of the object, find out the .note.stapsdt section
> + * and accordingly initialize the notes' list head
> + */
> +static struct sdt_note *get_elf_markers(Elf *elf, bool *exe, bool probe)

Ditto.  How about get_sdt_markers() or get_sdt_notes()?  I can see that
there are places those 'marker' and 'note' are used here and there.  If
they indicate same thing it'd better to unify the term.


> +{
> +	Elf_Scn *scn = NULL;
> +	Elf_Data *data;
> +	GElf_Shdr shdr;
> +	GElf_Ehdr ehdr;
> +	size_t  shstrndx;
> +	size_t next;
> +	GElf_Nhdr nhdr;
> +	size_t name_off, desc_off, offset;
> +	struct sdt_note *note = NULL, *tmp, *head = NULL;
> +
> +	if (gelf_getehdr(elf, &ehdr) == NULL) {
> +		pr_debug("%s: cannot get elf header.\n", __func__);
> +		goto out_end;
> +	}
> +
> +	if (elf_getshdrstrndx(elf, &shstrndx) != 0) {
> +		pr_debug("getshdrstrndx failed\n");
> +		goto out_end;
> +	}
> +
> +	/* library or exec */
> +	if (probe) {
> +		if (ehdr.e_type == ET_EXEC)
> +			*exe = true;
> +	}
> +
> +	/*
> +	 * 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 == NULL) {
> +		pr_err("%s section not found!\n", NOTE_SCN);
> +		goto out_end;
> +	}
> +
> +	if (!(shdr.sh_type == SHT_NOTE) || (shdr.sh_flags & SHF_ALLOC))
> +		goto out_end;
> +
> +	data = elf_getdata(scn, NULL);
> +
> +	/* Get the notes */
> +	for (offset = 0; (next = gelf_getnote(data, offset, &nhdr, &name_off,
> +					      &desc_off)) > 0; offset = next) {
> +		tmp = populate_note(&elf, (const char *)((long)(data->d_buf) +
> +							 (long)desc_off),
> +				    nhdr.n_descsz, nhdr.n_type);

Shouldn't we check the name of note being "stapsdt" as well as version
(type) 3?

Thanks,
Namhyung


> +		/* For first note */
> +		if (!head) {
> +			note = tmp;
> +			head = note;
> +			continue;
> +		}
> +		note->next = tmp;
> +		note = note->next;
> +	}
> +
> +	if (!head)
> +		pr_err("No markers found\n");
> +
> +out_end:
> +	return head;
> +}
> +
> +static void print_notes(struct sdt_note *start)
> +{
> +	struct sdt_note *temp;
> +	int c;
> +
> +	for (temp = start, c = 0; temp != NULL; temp = temp->next, c++)
> +		printf("%s:%s\n", temp->provider, temp->name);
> +
> +	printf("\nTotal markers = %d\n", c);
> +}
> +
> +int list_markers(const char *name)
> +{
> +	int fd, ret = -1;
> +	Elf *elf;
> +	struct sdt_note *head = NULL;
> +
> +	fd = open(name, O_RDONLY);
> +	if (fd < 0) {
> +		pr_err("Failed to open %s\n", name);
> +		goto out_ret;
> +	}
> +
> +	symbol__elf_init();
> +	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
> +	if (elf == NULL) {
> +		pr_err("%s: cannot read %s ELF file.\n", __func__, name);
> +		goto out_close;
> +	}
> +
> +	head = get_elf_markers(elf, NULL, false);
> +	if (head) {
> +		print_notes(head);
> +		cleanup_notes(head);
> +		ret = 0;
> +	} else {
> +		pr_err("No SDT markers found in %s\n", name);
> +	}
> +	elf_end(elf);
> +
> +out_close:
> +	close(fd);
> +out_ret:
> +	return ret;
> +}
> +
> +void cleanup_notes(struct sdt_note *start)
> +{
> +	struct sdt_note *tmp;
> +
> +	while (start) {
> +		tmp = start->next;
> +		free(start);
> +		start = tmp;
> +	}
> +}
> +
>  void symbol__elf_init(void)
>  {
>  	elf_version(EV_CURRENT);
> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> index 5f720dc..f2d17b7 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -197,6 +197,17 @@ struct symsrc {
>  #endif
>  };
>  
> +/* Note structure */
> +struct sdt_note {
> +	const char *name;
> +	const char *provider;
> +	union {
> +		Elf64_Addr a64[3];
> +		Elf32_Addr a32[3];
> +	} addr;
> +	struct sdt_note *next;
> +};
> +
>  void symsrc__destroy(struct symsrc *ss);
>  int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
>  		 enum dso_binary_type type);
> @@ -247,4 +258,12 @@ void symbols__fixup_duplicate(struct rb_root *symbols);
>  void symbols__fixup_end(struct rb_root *symbols);
>  void __map_groups__fixup_end(struct map_groups *mg, enum map_type type);
>  
> +/* For SDT markers */
> +int show_available_markers(const char *module);
> +int list_markers(const char *name);
> +void cleanup_notes(struct sdt_note *start);
> +
> +#define SDT_NOTE_TYPE 3
> +#define NOTE_SCN ".note.stapsdt"
> +
>  #endif /* __PERF_SYMBOL */
--
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