Message-ID: <525407B2.9070401@linux.vnet.ibm.com>
Date: Tue, 08 Oct 2013 18:55:06 +0530
From: Hemant <hkshaw@linux.vnet.ibm.com>
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To: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
CC: linux-kernel@vger.kernel.org, srikar@linux.vnet.ibm.com,
        peterz@infradead.org, oleg@redhat.com, hegdevasant@linux.vnet.ibm.com,
        mingo@redhat.com, anton@redhat.com, systemtap@sourceware.org,
        namhyung@kernel.org, aravinda@linux.vnet.ibm.com
Subject: Re: [PATCH v2 1/3] SDT markers listing by perf:
References: <20131007063911.11693.33624.stgit@hemant-fedora> <20131007064707.11693.27056.stgit@hemant-fedora> <5253EF03.5090502@hitachi.com>
In-Reply-To: <5253EF03.5090502@hitachi.com>
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On 10/08/2013 05:09 PM, Masami Hiramatsu wrote:
> (2013/10/07 15:47), Hemant Kumar wrote:
>> @@ -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"),
> BTW, "-S" for short of "--markers" option is a bit odd. Would we better use -M ? :)

I thought of -S as SDT. :) Anyways, on second thought, will change that 
to -M.

>
> [...]
>> @@ -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);
> You have to ensure params.target is set before use it.

Yes, will do that.

>> +		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/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");
> No need to state out of memory for each place...
> If you hit an out of memory for such small piece, you'd better
> abort execution. For that purpose, I recommend you to return
> errno from each function, and caller must check it.

Yeah this will be better... will return errno from each function.

>> +		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));
>> +
>> +	/* 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);
>> +
>> +	/* 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)
> This also would better return errno.

Ok.

>> +{
>> +	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");
> Why you don't use pr_err() here ? :)

Because, I thought it isn't an error that SDT markers are not present. 
It won't make much of a difference though. :)

> And also, as I commented, I'd like to know which binary doesn't have SDT markers,
> at least with -v (verbose) option.

Yes, I guess it would be better to show the binary name even without -v 
option. Will make the changes.

-- 
Thanks
Hemant

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