linux-kernel - Re: Re: [PATCH -tip v2 2/2] perf-probe: Support basic dwarf-based operations on uprobe events

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Date:	Fri, 27 Dec 2013 15:52:30 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	David Ahern <dsahern@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"David A. Long" <dave.long@...aro.org>, systemtap@...rceware.org,
	yrl.pp-manager.tt@...achi.com, Namhyung Kim <namhyung@...nel.org>
Subject: Re: Re: [PATCH -tip v2 2/2] perf-probe: Support basic dwarf-based
 operations on uprobe events

(2013/12/26 23:38), David Ahern wrote:
> On 12/26/13, 12:41 AM, Masami Hiramatsu wrote:
>> And this shows the available variables at the given line of
>> the function.
>> ----
>> # ./perf probe -x perf --vars map__load:8
>> Available variables at map__load:8
>>          @<map__load+96>
>>                  char*   name
>>                  struct map*     map
>>                  symbol_filter_t filter
>>          @<map__find_symbol+112>
>>                  char*   name
>>                  symbol_filter_t filter
>>          @<map__find_symbol_by_name+136>
>>                  char*   name
>>                  symbol_filter_t filter
>>          @<map_groups__find_symbol_by_name+176>
>>                  char*   name
>>                  struct map*     map
>>                  symbol_filter_t filter
> 
> Still limitations. This is Fedora 18:
> 
> # rpm -qa | grep debug
> glibc-debuginfo-common-2.16-34.fc18.x86_64
> glibc-debuginfo-2.16-34.fc18.x86_64
> 
> # /tmp/perf/perf probe -V malloc -x /lib64/libc-2.16.so
> Failed to find variables at malloc (0)
> 
> So probing on system libraries does not benefit from this patch.

Yes, please see the todo list in 0/2

>  - Support distro style debuginfo path (/usr/lib/debug/...)

Not only the libraries but also all distro packaged binaries have
debuginfo as other binaries. We should locate it by using dso.
But since this is just the first step series, I'd like to start with
the "homebrew" debuginfo.


>> diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
>> index 5681266..20b3e15 100644
>> --- a/tools/perf/builtin-probe.c
>> +++ b/tools/perf/builtin-probe.c
>> @@ -425,7 +425,7 @@ int cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
>>   	}
>>
>>   #ifdef HAVE_DWARF_SUPPORT
>> -	if (params.show_lines && !params.uprobes) {
>> +	if (params.show_lines) {
>>   		if (params.mod_events) {
>>   			pr_err("  Error: Don't use --line with"
>>   			       " --add/--del.\n");
> 
> Unrelated change.

No, this is required for the --line dwarf support.


>> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
>> index 05be5de..2f82267 100644
>> --- a/tools/perf/util/probe-event.c
>> +++ b/tools/perf/util/probe-event.c
>> @@ -172,6 +172,52 @@ const char *kernel_get_module_path(const char *module)
>>   	return (dso) ? dso->long_name : NULL;
>>   }
>>
>> +/* Copied from unwind.c */
>> +static Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
>> +				    GElf_Shdr *shp, const char *name)
>> +{
>> +	Elf_Scn *sec = NULL;
>> +
>> +	while ((sec = elf_nextscn(elf, sec)) != NULL) {
>> +		char *str;
>> +
>> +		gelf_getshdr(sec, shp);
>> +		str = elf_strptr(elf, ep->e_shstrndx, shp->sh_name);
>> +		if (!strcmp(name, str))
>> +			break;
>> +	}
>> +
>> +	return sec;
>> +}
> 
> Why copy it? With unwind.c and util/symbol-elf.c we now have 2 copies. 
> How about exporting one of those?

Hm, OK, I missed the copy in symbol-elf.c. I'd like to use that, since
the unwind.c can be disabled by NO_LIBUNWIND.

>> @@ -261,6 +338,40 @@ static int kprobe_convert_to_perf_probe(struct probe_trace_point *tp,
>>   	return 0;
>>   }
>>
>> +static int add_exec_to_probe_trace_events(struct probe_trace_event *tevs,
>> +					  int ntevs, const char *exec)
>> +{
>> +	int i, ret = 0;
>> +	unsigned long offset, stext = 0;
>> +	char buf[32];
>> +
>> +	if (!exec)
>> +		return 0;
>> +
>> +	ret = get_text_start_address(exec, &stext);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	for (i = 0; i < ntevs && ret >= 0; i++) {
>> +		offset = tevs[i].point.address - stext;
>> +		offset += tevs[i].point.offset;
>> +		tevs[i].point.offset = 0;
>> +		free(tevs[i].point.symbol);
>> +		ret = e_snprintf(buf, 32, "0x%lx", offset);
>> +		if (ret < 0)
>> +			break;
>> +		tevs[i].point.module = strdup(exec);
>> +		tevs[i].point.symbol = strdup(buf);
>> +		if (!tevs[i].point.symbol || !tevs[i].point.module) {
>> +			ret = -ENOMEM;
>> +			break;
>> +		}
>> +		tevs[i].uprobes = true;
>> +	}
>> +
>> +	return ret;
>> +}
>> +
> 
> More strdup's. This is library code and we need methods to free that 
> memory as well.

Ah, yes. Still some error handling routine doesn't clean it at all.
And it should be a separated bugfix patch, since not only
add_exec_to_probe_trace_events but also add_module_to_probe_trace_events
does the similar strdups.

Thank you!

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


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