Re: [PATCH v2 1/3] perf/sdt : Listing of SDT markers by perf

Namhyung Kim
2014-07-21T03:01:39Z

Hi Hemant,

On Thu, 17 Jul 2014 11:25:12 +0530, Hemant Kumar wrote:
> This patch enables perf to list the SDT markers present in a system. It looks
> in dsos given by ldconfig --print-cache and for other binaries, it looks into
> the PATH environment variable. After preparing a list of the binaries, then
> it starts searching for SDT markers in them.
> To find the SDT markers, first an elf section named .note.stapsdt is searched
> for. And then the SDT notes are retreived one by one from that section.
> To counter the effect of prelinking, the section ".stapsdt.base" is searched.
> If its found, then the location of the SDT marker is adjusted.
>
> All these markers' info is written into a cache file
> "/var/cache/perf/perf-sdt.cache".
> Since, the presence of SDT markers is quite common these days, hence, its better
> to make them visible to a user easily. Also, creating a cache file will help a user
> to probe (to be implemented) these markers without much hussle. This cache file will
> hold most of the SDT markers.
>
> The format of each SDT cache entry is -
>
> %provider:marker:file_path:build_id:location:semaphore_loc
>
> % - marks the beginning of each entry.
> provider - The provider name of the SDT marker.
> marker - The marker name of the SDT marker.
> file_path - Full/absolute path of the file in which this marker is present.
> location : Adjusted location of the SDT marker inside the program.
> semaphore_loc : The semaphore address if present otherwise 0x0.
>
> This format should help when probing will be implemented. The adjusted address
> from the required entry can be directly used in probing if the build_id matches.
>
> To scan the system for SDT markers invoke :
> # perf list sdt --scan
>
> "--scan" should be used for the first time and whenever there is any change in
> the files containing the SDT markers. It looks into the common binaries available
> in a system.
>
> And then use :
> # perf list sdt
>
> This displays the list of SDT markers recorded in the SDT cache.
> This shows the SDT markers present in the common binaries stored in the system,
> present in PATH variable and the /lib/ and /lib64/ directories.
>
> Or use:
> # perf list
>
> It should display all events including the SDT events.
>
> Signed-off-by : hemant@linux.vnet.ibm.com

Missing your real name in the sob line. (other patchse too)

> ---
> tools/perf/Makefile.perf | 1
> tools/perf/builtin-list.c | 6
> tools/perf/util/parse-events.h | 3
> tools/perf/util/sdt.c | 503 ++++++++++++++++++++++++++++++++++++++++
> tools/perf/util/symbol-elf.c | 229 ++++++++++++++++++
> tools/perf/util/symbol.h | 19 ++
> 6 files changed, 760 insertions(+), 1 deletion(-)
> create mode 100644 tools/perf/util/sdt.c
>
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index 9670a16..e098dcd 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -373,6 +373,7 @@ LIB_OBJS += $(OUTPUT)util/stat.o
> LIB_OBJS += $(OUTPUT)util/record.o
> LIB_OBJS += $(OUTPUT)util/srcline.o
> LIB_OBJS += $(OUTPUT)util/data.o
> +LIB_OBJS += $(OUTPUT)util/sdt.o
>
> LIB_OBJS += $(OUTPUT)ui/setup.o
> LIB_OBJS += $(OUTPUT)ui/helpline.o
> diff --git a/tools/perf/builtin-list.c b/tools/perf/builtin-list.c
> index 011195e..e1e654b 100644
> --- a/tools/perf/builtin-list.c
> +++ b/tools/perf/builtin-list.c
> @@ -23,7 +23,7 @@ int cmd_list(int argc, const char **argv, const char *prefix __maybe_unused)
> OPT_END()
> };
> const char * const list_usage[] = {
> - "perf list [hw|sw|cache|tracepoint|pmu|event_glob]",
> + "perf list [hw|sw|cache|tracepoint|pmu|event_glob|sdt]",

Hmm.. I think it'd be better like below

"perf list [hw|sw|cache|tracepoint|pmu|sdt|<event_glob>]",

> NULL
> };
>
> @@ -34,6 +34,8 @@ int cmd_list(int argc, const char **argv, const char *prefix __maybe_unused)
>
> if (argc == 0) {
> print_events(NULL, false);
> + printf("\n\nSDT events :\n");
> + sdt_cache__display();

What about make print_events() to print SDT events also?

> return 0;
> }
>
> @@ -55,6 +57,8 @@ int cmd_list(int argc, const char **argv, const char *prefix __maybe_unused)
> print_pmu_events(NULL, false);
> else if (strcmp(argv[i], "--raw-dump") == 0)
> print_events(NULL, true);
> + else if (strcmp(argv[i], "sdt") == 0)
> + print_sdt_events(argv[++i]);

Please move this above the --raw-dump block, it's a special marker to
help shell completion for event names so I'd like to keep it last.

> else {
> char *sep = strchr(argv[i], ':'), *s;
> int sep_idx;

[SNIP]
> +/*
> + * Finds out the libraries present in a system as shown by the command
> + * "ldconfig --print-cache". Uses "=>" and '/' to find out the start of a
> + * dso path.
> + */

If we received the list of libraries from user directly, it can go
away IMHO.

> +static char *parse_lib_name(char *str)
> +{
> + char *ptr, *q, *r;
> +
> + while (str != NULL) {
> + /* look for "=>" and then '/' */
> + ptr = strstr(str, "=>");
> + if (ptr) {
> + ptr++;
> + q = strchr(ptr, '/');
> + if (!q)
> + return NULL;
> + r = strchr(ptr, '\n');
> + *r = '\0';
> + return q;
> + } else if (ptr == NULL) {
> + return NULL;
> + } else {
> + str = ptr + 1;
> + continue;
> + }
> + }
> +
> + return NULL;
> +}
> +
> +/*
> + * Checks if a path is already present in the list.
> + * Returns 'true' if present and 'false' otherwise.
> + */
> +static bool is_present_in_list(struct list_head *path_list, char *path)
> +{
> + struct path_list *tmp;
> +
> + list_for_each_entry(tmp, path_list, list) {
> + if (!strcmp(path, tmp->path))
> + return true;
> + }

As Andi pointed out, you can use a hashtable for this.

> +
> + return false;
> +}
> +
> +static inline void append_path(char *path, struct list_head *list)
> +{
> + char *res_path = NULL;
> + struct path_list *tmp = NULL;
> +
> + res_path = (char *)malloc(sizeof(char) * PATH_MAX);
> +
> + if (!res_path)
> + return;
> +
> + memset(res_path, '\0', PATH_MAX);
> +
> + if (realpath(path, res_path) && !is_present_in_list(list, res_path)) {
> + tmp = (struct path_list *) malloc(sizeof(struct path_list));

Hmm... why not reusing res_path and make struct path_list to just have a
pointer? Also you can use readpath(path, NULL) rather than allocating
a PATH_MAX buffer and zero'ing it (can use calloc for it anyway).

> + if (!tmp) {
> + free(res_path);
> + return;
> + }
> + strcpy(tmp->path, res_path);
> + list_add(&(tmp->list), list);
> + if (res_path)
> + free(res_path);
> + }
> +}

[SNIP]
> +/*
> + * Go through all the files inside "path".
> + * But don't go into sub-directories.
> + */
> +static void walk_through_dir(char *path)
> +{
> + struct dirent *entry;
> + DIR *dir;
> + struct stat sb;
> + int ret = 0;
> + char *swd;
> +
> + dir = opendir(path);
> + if (!dir)
> + return;
> +
> + /* save the current working directory */
> + swd = getcwd(NULL, 0);
> + if (!swd) {
> + pr_err("getcwd : error");
> + return;
> + }
> +
> + ret = chdir(path);
> + if (ret) {
> + pr_err("chdir : error in %s", path);
> + return;
> + }

Is this really needed? I guess opendir() already covers possible
failure cases, if not, we might use stat() anyway.

> + while ((entry = readdir(dir)) != NULL) {
> +
> + ret = stat(entry->d_name, &sb);
> + if (ret == -1) {
> + pr_debug("%s : error in stat!\n", entry->d_name);
> + continue;
> + }
> +
> + /* Not pursuing sub-directories */
> + if ((sb.st_mode & S_IFMT) != S_IFDIR)
> + if (sb.st_mode & S_IXUSR)
> + append_path(entry->d_name, &execs.list);
> + }
> +
> + closedir(dir);
> +
> + /* return to the saved working directory */
> + ret = chdir(swd);
> + if (ret) {
> + pr_err("chdir : error");
> + return;
> + }
> +}

[SNIP]
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -1619,6 +1619,235 @@ void kcore_extract__delete(struct kcore_extract *kce)
> unlink(kce->extract_filename);
> }
>

Like I said earlier in a different thread, the below code can be a
sepatate change.

Thanks,
Namhyung

> +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;
> + GElf_Ehdr ehdr;
> + GElf_Addr base_off = 0;
> + GElf_Shdr shdr;
> + int ret = -1;
> + int i;
> +
> + union {
> + Elf64_Addr a64[3];
> + Elf32_Addr a32[3];
> + } buf;
> +
> + 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 *)calloc(1, sizeof(struct sdt_note));
> + if (!tmp) {
> + 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)
> + printf("gelf_xlatetom : %s\n", 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 */
> + if (gelf_getclass(*elf) == ELFCLASS32) {
> + for (i = 0; i < 3; i++)
> + tmp->addr.a32[i] = buf.a32[i];
> + tmp->bit32 = true;
> + } else {
> + for (i = 0; i < 3; i++)
> + tmp->addr.a64[i] = buf.a64[i];
> + tmp->bit32 = false;
> + }
> +
> + /* Now Adjust the prelink effect */
> + if (!gelf_getehdr(*elf, &ehdr)) {
> + pr_debug("%s : cannot get elf header.\n", __func__);
> + ret = -EBADF;
> + goto out_free_name;
> + }
> +
> + /*
> + * Find out the .stapsdt.base section.
> + * This scn will help us to handle prelinking (if present).
> + * Compare the retrieved file offset of the base section with the
> + * base address in the description of the SDT note. If its different,
> + * then accordingly, adjust the note location.
> + */
> + if (elf_section_by_name(*elf, &ehdr, &shdr, SDT_BASE_SCN, NULL)) {
> + base_off = shdr.sh_offset;
> + if (base_off) {
> + if (tmp->bit32)
> + tmp->addr.a32[0] = tmp->addr.a32[0] + base_off -
> + tmp->addr.a32[1];
> + else
> + tmp->addr.a64[0] = tmp->addr.a64[0] + base_off -
> + tmp->addr.a64[1];
> + }
> + }
> +
> + *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, 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;
> + goto out_ret;
> + }
> + if (elf_getshdrstrndx(elf, &shstrndx) != 0) {
> + ret = -EBADF;
> + goto out_ret;
> + }
> +
> + /* Look for the required section */
> + scn = elf_section_by_name(elf, &ehdr, &shdr, SDT_NOTE_SCN, NULL);
> + if (!scn) {
> + ret = -ENOENT;
> + 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 = val;
> + goto out_ret;
> + }
> + }
> + }
> + if (list_empty(sdt_notes))
> + ret = -ENOENT;
> +
> +out_ret:
> + return ret;
> +}
> +
> +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)
> + return -errno;
> +
> + symbol__elf_init();
> + elf = elf_begin(fd, ELF_C_READ, NULL);
> + if (!elf) {
> + ret = -EBADF;
> + goto out_close;
> + }
> + ret = construct_sdt_notes_list(elf, head);
> + elf_end(elf);
> +
> +out_close:
> + close(fd);
> + return ret;
> +}
> +
> +/*
> + * Returns 'true' if the file is an elf and 'false' otherwise
> + */
> +bool is_an_elf(char *file)
> +{
> + int fd;
> + Elf *elf;
> + bool ret = true;
> +
> + fd = open(file, O_RDONLY);
> + if (fd < 0) {
> + ret = false;
> + goto out_ret;
> + }
> +
> + symbol__elf_init();
> + elf = elf_begin(fd, ELF_C_READ, NULL);
> + if (!elf) {
> + ret = false;
> + goto out_close;
> + }
> + if (elf_kind(elf) != ELF_K_ELF)
> + ret = false;
> +
> + 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 615c752..83be31a 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -294,4 +294,23 @@ int compare_proc_modules(const char *from, const char *to);
> int setup_list(struct strlist **list, const char *list_str,
> const char *list_name);
>
> +struct sdt_note {
> + char *name;
> + char *provider;
> + bool bit32;
> + union {
> + Elf64_Addr a64[3];
> + Elf32_Addr a32[3];
> + } addr;
> + struct list_head note_list;
> +};
> +
> +int get_sdt_note_list(struct list_head *head, const char *target);
> +bool is_an_elf(char *file);
> +
> +#define SDT_BASE_SCN ".stapsdt.base"
> +#define SDT_NOTE_SCN ".note.stapsdt"
> +#define SDT_NOTE_TYPE 3
> +#define SDT_NOTE_NAME "stapsdt"
> +
> #endif /* __PERF_SYMBOL */