Re: [PATCH 2/2] Support to perf to probe on SDT markers:

[Hemant <hkshaw@linux.vnet.ibm.com>]

On 09/04/2013 12:30 PM, Namhyung Kim wrote:
> On Tue, 03 Sep 2013 13:07:03 +0530, Hemant Kumar wrote:
>> This patch enables perf to probe on the marker name specified on the command line.
> It looks like you didn't consider prelinked libraries.  You need to check
> the address of .stapsdt.base section too.  And obviously this patch

Will make the required changes to handle prelinking as well in the next 
iteration.

> ignores any argument the SDT has which I think pretty important info.
> But we can add it later once the uprobes arg fetch patches are in.

Yes, will add the arguments' support too in the next iteration.
> Also please see my previous comment on mixed usage of 'note' and
> 'marker'.

Yeah, made a note of that and make the required modifications.

Thanks
Hemant
>
> Thanks,
> Namhyung
>
>
>> ---
>>   tools/perf/builtin-probe.c    |    7 +++
>>   tools/perf/util/probe-event.c |   11 ++++
>>   tools/perf/util/symbol-elf.c  |  112 +++++++++++++++++++++++++++++++++++++++++
>>   tools/perf/util/symbol.h      |    5 ++
>>   4 files changed, 135 insertions(+)
>>
>> diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
>> index 3d8dcdf..8382853 100644
>> --- a/tools/perf/builtin-probe.c
>> +++ b/tools/perf/builtin-probe.c
>> @@ -378,6 +378,13 @@ int cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
>>   				       " (%d)\n", ret);
>>   			return ret;
>>   		}
>> +		params.uprobes = true;
>> +		ret = probe_marker(params.target,
>> +				   params.events[0].point.function);
>> +		if (ret < 0)
>> +			pr_err("Could not probe at %s marker\n",
>> +			       params.events[0].point.function);
>> +		return ret;
>>   	}
>>   
>>   	if (params.list_events) {
>> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
>> index 7f846f9..014d642 100644
>> --- a/tools/perf/util/probe-event.c
>> +++ b/tools/perf/util/probe-event.c
>> @@ -2378,3 +2378,14 @@ int show_available_markers(const char *target)
>>   	setup_pager();
>>   	return list_markers(target);
>>   }
>> +
>> +int probe_marker(const char *name, char *mark)
>> +{
>> +	int fd;
>> +
>> +	fd = open_uprobe_events(true);
>> +	if (fd == -1)
>> +		return fd;
>> +	else
>> +		return probe__marker(name, mark, fd);
>> +}
>> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
>> index f3630f2..60938a5 100644
>> --- a/tools/perf/util/symbol-elf.c
>> +++ b/tools/perf/util/symbol-elf.c
>> @@ -1040,6 +1040,118 @@ out_ret:
>>   	return ret;
>>   }
>>   
>> +static void extract_first_name(const char *target, char *fname)
>> +{
>> +	int i, len;
>> +	char *file;
>> +
>> +	file = strrchr(target, DIR_SEP);
>> +	file++;
>> +	len = strlen(file);
>> +	for (i = 0; i <= len; i++) {
>> +		if (!isalpha(file[i]))
>> +			break;
>> +		fname[i] = file[i];
>> +	}
>> +	fname[i] = '\0';
>> +}
>> +
>> +static int probe_at_note(struct sdt_note *r_note, const char *target, bool exec,
>> +			 int fd)
>> +{
>> +	char buf[MAX_CMDLEN];
>> +	int len, err = -1;
>> +	Elf64_Addr offset;
>> +	char *fname = NULL;
>> +
>> +	if (exec)
>> +		offset = r_note->addr.a64[0] - TEXT_SCN;
>> +	else
>> +		offset = r_note->addr.a64[0];
>> +
>> +	fname = (char *)zalloc(sizeof(char) * strlen(target));
>> +	if (fname == NULL) {
>> +		pr_err("Error in allocating memory to fname\n");
>> +		goto out_ret;
>> +	}
>> +
>> +	extract_first_name(target, fname);
>> +	len = snprintf(buf, MAX_CMDLEN, "%c:%s%s/%s %s:0x%x", 'p', "probe_",
>> +		       fname, r_note->name, target, (unsigned)offset);
>> +
>> +	len = write(fd, buf, MAX_CMDLEN);
>> +	if (len < 0) {
>> +		pr_err("Couldn't write into uprobe_events!\n");
>> +		goto out_close;
>> +	} else {
>> +		printf("Added new event :\n");
>> +		printf("event = %s \t (on 0x%x)\n\n", r_note->name,
>> +		       (unsigned)offset);
>> +		printf("You can now use it on all perf tools such as :\n\n");
>> +		printf("\t perf record -e %s%s:%s -aR sleep 1\n\n", "probe_", fname, r_note->name);
>> +		err = 0;
>> +	}
>> +
>> +out_close:
>> +	close(fd);
>> +	free(fname);
>> +out_ret:
>> +	return err;
>> +}
>> +
>> +static int search_and_probe_at_note(char *key, struct sdt_note **start,
>> +				    const char *target, bool exec, int fd)
>> +{
>> +	int ret = -1;
>> +	struct sdt_note *req;
>> +
>> +	for (req = (*start); req != NULL; req = req->next) {
>> +		if (!strcmp(key, req->name))
>> +			break;
>> +	}
>> +	if (!req) {
>> +		pr_err("Could not find marker %s\n", key);
>> +		return ret;
>> +	}
>> +
>> +	ret = probe_at_note(req, target, exec, fd);
>> +	return ret;
>> +}
>> +
>> +int probe__marker(const char *name, char *mark, int evfd)
>> +{
>> +	int ret = -1, fd;
>> +	Elf *elf;
>> +	bool exec = false;
>> +	struct sdt_note *head = NULL;
>> +
>> +	fd = open(name, O_RDONLY);
>> +	if (fd < 0) {
>> +		pr_err("Failed to open the file\n");
>> +		goto out_ret;
>> +	}
>> +
>> +	symbol__elf_init();
>> +	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
>> +	if (elf == NULL) {
>> +		pr_debug("%s: cannot read %s ELF file.\n", __func__, name);
>> +		goto out_close;
>> +	}
>> +
>> +	head = get_elf_markers(elf, &exec, true);
>> +	if (head) {
>> +		ret = search_and_probe_at_note(mark, &head, name, exec, evfd);
>> +		cleanup_notes(head);
>> +	}
>> +
>> +	elf_end(elf);
>> +
>> +out_close:
>> +	close(fd);
>> +out_ret:
>> +	return ret;
>> +}
>> +
>>   void cleanup_notes(struct sdt_note *start)
>>   {
>>   	struct sdt_note *tmp;
>> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
>> index f2d17b7..95289fd 100644
>> --- a/tools/perf/util/symbol.h
>> +++ b/tools/perf/util/symbol.h
>> @@ -262,8 +262,13 @@ void __map_groups__fixup_end(struct map_groups *mg, enum map_type type);
>>   int show_available_markers(const char *module);
>>   int list_markers(const char *name);
>>   void cleanup_notes(struct sdt_note *start);
>> +int probe_marker(const char *name, char *mark);
>> +int probe__marker(const char *name, char *mark, int fd);
>>   
>>   #define SDT_NOTE_TYPE 3
>>   #define NOTE_SCN ".note.stapsdt"
>> +#define TEXT_SCN 0x400000
>> +#define DIR_SEP '/'
>> +#define MAX_CMDLEN 256
>>   
>>   #endif /* __PERF_SYMBOL */