Re: [PATCH v3 2/3] Support for perf to probe into SDT markers:

[Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>]

(2013/10/18 23:44), Hemant Kumar wrote:
> This allows perf to probe into the sdt markers/notes present in
> the libraries and executables. We try to find the associated location
> and handle prelinking (since, stapsdt notes section is not allocated
> during runtime). Prelinking is handled with the help of base
> section which is allocated during runtime. This address can be compared
> with the address retrieved from the notes' description. If its different,
> we can take this difference and then add to the note's location.
> 
> We can use existing '-a/--add' option to add events for sdt markers.
> Also, we can add multiple events at once using the same '-a' option.
> 
> Usage:
> perf probe -x /lib64/libc.so.6 -a 'my_event=%libc:setjmp'
> 
> Output:
> Added new event:
>   libc:my_event        (on 0x35981)
> 
> You can now use it in all perf tools, such as:
> 
>     perf record -e libc:my_event -aR sleep 1
> 
> 
> Signed-off-by: Hemant Kumar Shaw <hkshaw@linux.vnet.ibm.com>
> ---
>  tools/perf/builtin-probe.c    |    4 ++
>  tools/perf/util/probe-event.c |   99 +++++++++++++++++++++++++++++++++++++----
>  tools/perf/util/probe-event.h |    2 +
>  tools/perf/util/symbol-elf.c  |   80 +++++++++++++++++++++++++++++++++
>  tools/perf/util/symbol.h      |    3 +
>  5 files changed, 178 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
> index 2450613..8f0dd48 100644
> --- a/tools/perf/builtin-probe.c
> +++ b/tools/perf/builtin-probe.c
> @@ -494,6 +494,10 @@ int cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
>  	}
>  
>  	if (params.nevents) {
> +		if (params.events->sdt && !params.target && !params.exec) {
> +			pr_err("SDT markers can be probed only with --exec.\n");
> +			usage_with_options(probe_usage, options);
> +		}
>  		ret = add_perf_probe_events(params.events, params.nevents,
>  					    params.max_probe_points,
>  					    params.target,
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index c228fe6..06665a8 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -816,6 +816,40 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
>  		pev->group = NULL;
>  		arg = tmp;
>  	}
> +	/* Check for SDT marker */
> +	if (*arg == '%') {
> +		ptr = strchr(++arg, ':');
> +		if (!ptr) {
> +			semantic_error("Provider name must follow an event "
> +				       "name\n");
> +			return -EINVAL;
> +		}
> +		*ptr++ = '\0';
> +		tmp = strdup(arg);
> +		if (!tmp)
> +			return -ENOMEM;
> +
> +		pev->point.note = (struct sdt_note *)
> +			zalloc(sizeof(struct sdt_note));
> +		if (!pev->point.note) {
> +			free(tmp);
> +			return -ENOMEM;
> +		}
> +		pev->point.note->provider = tmp;
> +
> +		tmp = strdup(ptr);
> +		if (!tmp) {
> +			free(pev->point.note->provider);
> +			free(pev->point.note);
> +			return -ENOMEM;
> +		}
> +		pev->point.note->name = tmp;
> +		pev->group = pev->point.note->provider;
> +		if (!pev->event)
> +			pev->event = pev->point.note->name;
> +		pev->sdt = true;
> +		return 0;
> +	}
>  
>  	ptr = strpbrk(arg, ";:+@%");
>  	if (ptr) {
> @@ -1238,6 +1272,7 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
>  	char *buf, *tmp;
>  	char offs[32] = "", line[32] = "", file[32] = "";
>  	int ret, len;
> +	unsigned long long addr;
>  
>  	buf = zalloc(MAX_CMDLEN);
>  	if (buf == NULL) {
> @@ -1266,12 +1301,17 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
>  			goto error;
>  	}
>  
> -	if (pp->function)
> +	if (pp->function) {
>  		ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
>  				 offs, pp->retprobe ? "%return" : "", line,
>  				 file);
> -	else
> +	} else if (pp->note) {
> +		addr = pp->note->bit32 ? pp->note->addr.a32[0] :
> +			pp->note->addr.a64[0];
> +		ret = e_snprintf(buf, MAX_CMDLEN, "0x%llx", addr);
> +	} else {
>  		ret = e_snprintf(buf, MAX_CMDLEN, "%s%s", file, line);
> +	}
>  	if (ret <= 0)
>  		goto error;
>  
> @@ -1921,6 +1961,21 @@ static void cleanup_sdt_note_list(struct list_head *sdt_notes)
>  	}
>  }
>  
> +static int try_to_find_sdt_notes(struct perf_probe_event *pev,
> +				 const char *target)
> +{
> +	int ret;
> +	LIST_HEAD(sdt_notes);
> +
> +	ret = search_sdt_note(pev->point.note, &sdt_notes, target);
> +	if (!list_empty(&sdt_notes))
> +		cleanup_sdt_note_list(&sdt_notes);
> +	/* Abssence of SDT markers is an error in this case */
> +	else if (list_empty(&sdt_notes) && !ret)
> +		ret = -ENOENT;
> +	return ret;
> +}
> +
>  static int convert_to_probe_trace_events(struct perf_probe_event *pev,
>  					  struct probe_trace_event **tevs,
>  					  int max_tevs, const char *target)
> @@ -1928,11 +1983,23 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
>  	struct symbol *sym;
>  	int ret = 0, i;
>  	struct probe_trace_event *tev;
> +	char *buf;
> +	unsigned long long addr;
>  
> -	/* Convert perf_probe_event with debuginfo */
> -	ret = try_to_find_probe_trace_events(pev, tevs, max_tevs, target);
> -	if (ret != 0)
> -		return ret;	/* Found in debuginfo or got an error */
> +	if (pev->sdt) {
> +		ret = -EBADF;
> +		if (pev->uprobes)
> +			ret = try_to_find_sdt_notes(pev, target);
> +		if (ret)
> +			return ret;
> +	} else {
> +		/* Convert perf_probe_event with debuginfo */
> +		ret = try_to_find_probe_trace_events(pev, tevs, max_tevs,
> +						     target);
> +		/* Found in debuginfo or got an error */
> +		if (ret != 0)
> +			return ret;
> +	}
>  
>  	/* Allocate trace event buffer */
>  	tev = *tevs = zalloc(sizeof(struct probe_trace_event));
> @@ -1940,10 +2007,22 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
>  		return -ENOMEM;
>  
>  	/* Copy parameters */
> -	tev->point.symbol = strdup(pev->point.function);
> -	if (tev->point.symbol == NULL) {
> -		ret = -ENOMEM;
> -		goto error;
> +	if (pev->sdt) {
> +		buf = (char *)zalloc(sizeof(char) * MAX_CMDLEN);
> +		if (!buf) {
> +			ret = -ENOMEM;
> +			goto error;
> +		}
> +		addr = pev->point.note->bit32 ? pev->point.note->addr.a32[0] :
> +			pev->point.note->addr.a64[0];
> +		sprintf(buf, "0x%llx", addr);
> +		tev->point.symbol = buf;
> +	} else {
> +		tev->point.symbol = strdup(pev->point.function);
> +		if (tev->point.symbol == NULL) {
> +			ret = -ENOMEM;
> +			goto error;
> +		}
>  	}
>  
>  	if (target) {
> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> index 32de5a3..beb1b4a 100644
> --- a/tools/perf/util/probe-event.h
> +++ b/tools/perf/util/probe-event.h
> @@ -47,6 +47,7 @@ struct perf_probe_point {
>  	bool		retprobe;	/* Return probe flag */
>  	char		*lazy_line;	/* Lazy matching pattern */
>  	unsigned long	offset;		/* Offset from function entry */
> +	struct sdt_note *note;
>  };
>  
>  /* Perf probe probing argument field chain */
> @@ -72,6 +73,7 @@ struct perf_probe_event {
>  	struct perf_probe_point	point;	/* Probe point */
>  	int			nargs;	/* Number of arguments */
>  	bool			uprobes;
> +	bool                    sdt;
>  	struct perf_probe_arg	*args;	/* Arguments */
>  };
>  
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 828ecad..73b368c 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -1824,6 +1824,86 @@ out_close:
>  	return sdt_err(ret, target);
>  }
>  
> +static void adjust_note_addr(struct sdt_note *tmp, struct sdt_note *key,
> +			     Elf *elf)
> +{
> +	GElf_Ehdr ehdr;
> +	GElf_Addr base_off = 0;
> +	GElf_Shdr shdr;
> +
> +	if (!gelf_getehdr(elf, &ehdr)) {
> +		pr_debug("%s : cannot get elf header.\n", __func__);
> +		return;
> +	}
> +
> +	/*
> +	 * 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)
> +			key->addr.a32[0] = tmp->addr.a32[0] + base_off -
> +				tmp->addr.a32[1];
> +		else
> +			key->addr.a64[0] = tmp->addr.a64[0] + base_off -
> +				tmp->addr.a64[1];
> +	}
> +	key->bit32 = tmp->bit32;
> +}
> +
> +int search_sdt_note(struct sdt_note *key, struct list_head *sdt_notes,
> +		    const char *target)

Hmm, this interface looks very odd.
 - This just finds the first matched sdt_note entry instead of the list.
   In that case, we don't need to pass the list_head.
 - If the purpose is just counting the number of matched entries (or just
   checking existence), we also don't need the list. Just returning the
   number is enough.

I recommend you to remove the "sdt_notes", and make the caller check
key->addr is set.

Thank you,

> +{
> +	Elf *elf;
> +	int fd, ret;
> +	bool found = false;
> +	struct sdt_note *pos = NULL;
> +
> +	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("Can't read the elf of %s\n", target);
> +		goto out_close;
> +	}
> +
> +	ret = construct_sdt_notes_list(elf, sdt_notes);
> +	if (ret)
> +		goto out_end;
> +
> +	/* Iterate through the notes and retrieve the required note */
> +	list_for_each_entry(pos, sdt_notes, note_list) {
> +		if (!strcmp(key->name, pos->name) &&
> +		    !strcmp(key->provider, pos->provider)) {
> +			adjust_note_addr(pos, key, elf);
> +			found = true;
> +			break;
> +		}
> +	}
> +	if (!found) {
> +		printf("%%%s:%s not found in %s!\n", key->provider, key->name,
> +		       target);
> +		return -ENOENT;
> +	}
> +
> +out_end:
> +	elf_end(elf);
> +out_close:
> +	close(fd);
> +	return sdt_err(ret, target);
> +}
> +
>  void symbol__elf_init(void)
>  {
>  	elf_version(EV_CURRENT);
> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> index b78397b..52b04e2 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -286,9 +286,12 @@ 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);
> +int search_sdt_note(struct sdt_note *key, struct list_head *head,
> +		    const char *target);
>  
>  #define SDT_NOTE_TYPE 3
>  #define SDT_NOTE_SCN ".note.stapsdt"
>  #define SDT_NOTE_NAME "stapsdt"
> +#define SDT_BASE_SCN ".stapsdt.base"
>  
>  #endif /* __PERF_SYMBOL */
> 
> 


-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com