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

From: Namhyung Kim
Date: Tue Oct 08 2013 - 04:57:56 EST

Hi Hemant,

On Mon, 07 Oct 2013 12:17:57 +0530, Hemant Kumar wrote:
> 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 '-S/--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.
>
> I think 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 | 24 +++++-
> tools/perf/util/probe-event.c | 39 +++++++++
> tools/perf/util/probe-event.h | 2
> tools/perf/util/symbol-elf.c | 176 +++++++++++++++++++++++++++++++++++++++++
> tools/perf/util/symbol.h | 18 ++++
> 5 files changed, 257 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
> index e8a66f9..cbd2383 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 +326,7 @@ 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"),
> OPT_END()
> };
> int ret;
> @@ -347,7 +349,7 @@ 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 +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);
> + 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/probe-event.c b/tools/perf/util/probe-event.c
> index aa04bf9..4e94092 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -1909,6 +1909,20 @@ static int __add_probe_trace_events(struct perf_probe_event *pev,
> return ret;
> }
>
> +static void cleanup_sdt_note_list(struct list_head *sdt_notes)
> +{
> + struct sdt_note *tmp;
> + struct list_head *pos, *s;
> +
> + list_for_each_safe(pos, s, sdt_notes) {
> + tmp = list_entry(pos, struct sdt_note, note_list);

You might use list_for_each_entry_safe() instead.


> + list_del(pos);
> + free(tmp->name);
> + free(tmp->provider);
> + free(tmp);
> + }
> +}
> +
> static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> struct probe_trace_event **tevs,
> int max_tevs, const char *target)
> @@ -2372,3 +2386,28 @@ out:
> free(name);
> return ret;
> }
> +
> +static void display_sdt_note_info(struct list_head *start)
> +{
> + struct list_head *pos;
> + struct sdt_note *tmp;
> +
> + list_for_each(pos, start) {
> + tmp = list_entry(pos, struct sdt_note, note_list);

Ditto. list_for_each_entry().


> + printf("%%%s:%s\n", tmp->provider, tmp->name);
> + }
> +}
> +
> +int show_sdt_notes(const char *target)
> +{
> + struct list_head sdt_notes;
> + int ret = -1;
> +
> + INIT_LIST_HEAD(&sdt_notes);

You can use LIST_HEAD(sdt_notes) here.


> + 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..b8a9347 100644
> --- a/tools/perf/util/probe-event.h
> +++ b/tools/perf/util/probe-event.h
> @@ -133,7 +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 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");
> + 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));

I doubt this translation is really needed as we only deal with SDTs on a
local system only, right?

> +
> + /* 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);

You need to check the return value of strdup's and it should also be
freed when an error occurres after this.

> +
> + /* 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)
> +{
> + 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");
> + goto out_err;
> + }
> + if (!(shdr.sh_type == SHT_NOTE) || (shdr.sh_flags & SHF_ALLOC))
> + goto out_err;
> +
> + 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))) {
> + tmp = populate_sdt_note(&elf, (const char *)
> + ((long)(data->d_buf) +
> + (long)desc_off),

It seems that data->d_buf is type of void *, so these casts can go away,
I guess.

> + nhdr.n_descsz, nhdr.n_type);
> + if (!note && tmp)
> + note = tmp;
> + else if (tmp)
> + list_add_tail(&tmp->note_list,
> + &(note->note_list));
> + }
> + }
> + if (tmp)
> + return &tmp->note_list;

This list handling code looks very strange to me. Why not just passing
a list head and connect notes to it?


> +out_err:
> + return NULL;
> +}
> +
> +int get_sdt_note_list(struct list_head *head, const char *target)
> +{
> + Elf *elf;
> + int fd, ret = -1;
> + struct list_head *tmp = NULL;
> +
> + fd = open(target, O_RDONLY);
> + if (fd < 0) {
> + pr_err("Failed to open %s\n", target);
> + goto out_ret;
> + }
> +
> + symbol__elf_init();
> + elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
> + if (!elf) {
> + pr_err("%s: cannot read %s ELF file.\n", __func__, target);
> + goto out_close;
> + }
> + tmp = construct_sdt_notes_list(elf);
> + if (tmp) {
> + list_add(head, tmp);

Look like the params are exchanged?

/**
* list_add - add a new entry
* @new: new entry to be added
* @head: list head to add it after
*
* Insert a new entry after the specified head.
* This is good for implementing stacks.
*/
static inline void list_add(struct list_head *new, struct list_head *head)
{
__list_add(new, head, head->next);
}


> + ret = 0;
> + }
> + elf_end(elf);
> +
> +out_close:
> + close(fd);
> +out_ret:
> + return ret;
> +}
> +
> 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..037185c 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -197,6 +197,17 @@ 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);
> @@ -247,4 +258,11 @@ 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);
>
> +/* Specific to SDT notes */
> +int get_sdt_note_list(struct list_head *head, const char *target);
> +
> +#define SDT_NOTE_TYPE 3
> +#define NOTE_SCN ".note.stapsdt"

What about SDT_NOTE_SCN for consistency?

Thanks,
Namhyung


> +#define SDT_NOTE_NAME "stapsdt"
> +
> #endif /* __PERF_SYMBOL */
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