Re: [PATCH v2 2/3] Support for perf to probe into SDT markers:

[Namhyung Kim <namhyung at kernel dot org>]

On Mon, 07 Oct 2013 12:18:29 +0530, 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'
>
> or
>
> perf probe -x /lib64/libc.so.6 %libc:setjmp
>
> Output (corresponding to the first usage):
> 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    |   11 +++++
>  tools/perf/util/probe-event.c |   89 +++++++++++++++++++++++++++++++++++++----
>  tools/perf/util/probe-event.h |    2 +
>  tools/perf/util/symbol-elf.c  |   80 +++++++++++++++++++++++++++++++++++++
>  tools/perf/util/symbol.h      |    3 +
>  5 files changed, 177 insertions(+), 8 deletions(-)
>
> diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
> index cbd2383..6f09723 100644
> --- a/tools/perf/builtin-probe.c
> +++ b/tools/perf/builtin-probe.c
> @@ -370,6 +370,17 @@ int cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
>  			pr_err("Error: Don't use --markers with --funcs.\n");
>  			usage_with_options(probe_usage, options);
>  		}
> +		if (params.mod_events) {
> +			ret = add_perf_probe_events(params.events,
> +						    params.nevents,
> +						    params.max_probe_points,
> +						    params.target,
> +						    params.force_add);
> +			if (ret < 0) {
> +				pr_err(" Error: Failed to add events. "
> +				       " (%d)\n", ret);
> +			}
> +		}
>  		ret = show_sdt_notes(params.target);
>  		if (ret < 0) {
>  			pr_err("  Error : Failed to find SDT markers!"
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 4e94092..43f8a69 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -817,6 +817,35 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
>  		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)
> +			return -ENOMEM;
> +		pev->point.note->provider = tmp;
> +
> +		tmp = strdup(ptr);
> +		if (!tmp)
> +			return -ENOMEM;

These -ENOMEM returning should free all memory region allocated
previously.


> +		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) {
>  		nc = *ptr;
> @@ -1270,6 +1299,13 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
>  		ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
>  				 offs, pp->retprobe ? "%return" : "", line,
>  				 file);
> +	else if (pp->note)
> +		if (pp->note->bit32)
> +			ret = e_snprintf(buf, MAX_CMDLEN, "0x%x",
> +					 pp->note->addr.a32[0]);
> +		else
> +			ret = e_snprintf(buf, MAX_CMDLEN, "0x%lx",
> +					 pp->note->addr.a64[0]);

This kind of code tends to cause 32/64-bit build problem.  Did you test
it on a 32-bit system too?  Anyway, I think things like below should
work:

		unsigned long long addr;

		if (pp->note->bit32)
			addr = pp->note->addr.a32[0];
		else
			addr = 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)
> @@ -1923,6 +1959,19 @@ 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)
> +{
> +	struct list_head sdt_notes;
> +	int ret = -1;
> +
> +	INIT_LIST_HEAD(&sdt_notes);

You can use just LIST_HEAD(sdt_notes) here.


> +	ret = search_sdt_note(pev->point.note, &sdt_notes, target);
> +	if (!list_empty(&sdt_notes))
> +		cleanup_sdt_note_list(&sdt_notes);
> +	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)
> @@ -1930,11 +1979,20 @@ 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;
>  
> -	/* 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 = 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));
> @@ -1942,10 +2000,25 @@ 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;
> +		}
> +		if (pev->point.note->bit32)
> +			sprintf(buf, "0x%x",
> +				(unsigned)pev->point.note->addr.a32[0]);
> +		else
> +			sprintf(buf, "0x%lx",
> +				(unsigned long)pev->point.note->addr.a64[0]);

Please see my comment above.


> +		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 b8a9347..4bd50cc 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;

I guess what you need is a 'struct list_head'.


>  };
>  
>  /* 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 6b17260..d0e7a66 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -1022,6 +1022,86 @@ out_ret:
>  	return ret;
>  }
>  
> +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, 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)
> +{
> +	Elf *elf;
> +	int fd, ret = -1;
> +	struct list_head *pos = NULL, *head = NULL;
> +	struct sdt_note *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 : can't read %s ELF file.\n", __func__, target);
> +		goto out_close;
> +	}
> +
> +	head = construct_sdt_notes_list(elf);
> +	if (!head)
> +		goto out_end;
> +
> +	list_add(sdt_notes, head);

This list code looks strange.


> +
> +	/* Iterate through the notes and retrieve the required note */
> +	list_for_each(pos, sdt_notes) {
> +		tmp = list_entry(pos, struct sdt_note, note_list);
> +		if (!strcmp(key->name, tmp->name) &&
> +		    !strcmp(key->provider, tmp->provider)) {
> +			adjust_note_addr(tmp, key, elf);
> +			ret = 0;
> +			break;
> +		}
> +	}
> +	if (ret)
> +		printf("%%%s:%s not found!\n", key->provider, key->name);
> +
> +out_end:
> +	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 037185c..0b0545b 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -260,9 +260,12 @@ 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);
> +int search_sdt_note(struct sdt_note *key, struct list_head *head,
> +		    const char *target);
>  
>  #define SDT_NOTE_TYPE 3
>  #define NOTE_SCN ".note.stapsdt"
>  #define SDT_NOTE_NAME "stapsdt"
> +#define SDT_BASE ".stapsdt.base"

What about SDT_BASE_SCN ?

Thanks,
Namhyung


>  
>  #endif /* __PERF_SYMBOL */