linux-kernel - Re: [PATCH v2 1/3] perf annotate: Get correct line numbers matched with addr

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Date:   Fri, 3 Mar 2017 12:25:28 +0900
From:   Taeung Song <treeze.taeung@...il.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Wang Nan <wangnan0@...wei.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Andi Kleen <andi@...stfloor.org>,
        kernel-team@....com
Subject: Re: [PATCH v2 1/3] perf annotate: Get correct line numbers matched
 with addr



On 03/03/2017 11:40 AM, Namhyung Kim wrote:
> + Andi Kleen who wrote the code.
>
> On Thu, Mar 02, 2017 at 03:05:14PM +0900, Taeung Song wrote:
>>
>>
>> On 03/01/2017 10:17 PM, Namhyung Kim wrote:
>>> Hi Taeung,
>>>
>>> On Wed, Mar 01, 2017 at 04:59:51AM +0900, Taeung Song wrote:
>>>> Currently perf-annotate show wrong line numbers.
>>>>
>>>> For example,
>>>> Actual source code is as below
>>>>
>>>> ...
>>>>   21 };
>>>>   22
>>>>   23 unsigned int limited_wgt;
>>>>   24
>>>>   25 unsigned int get_cond_maxprice(int wgt)
>>>>   26 {
>>>> ...
>>>>
>>>> However, the output of perf-annotate is as below.
>>>>
>>>>   4   Disassembly of section .text:
>>>>
>>>>   6   0000000000400966 <get_cond_maxprice>:
>>>>   7   get_cond_maxprice():
>>>>   26  };
>>>>
>>>>   28  unsigned int limited_wgt;
>>>>
>>>>   30  unsigned int get_cond_maxprice(int wgt)
>>>>   31  {
>>>>
>>>> The cause is the wrong way counting line numbers
>>>> in symbol__parse_objdump_line().
>>>> So remove wrong current code counting line number and
>>>> use other method for it using functions related to addr2line
>>>> instead of the output of '-l' of objdump.
>>>
>>> Hmm.. do you think it's a bug of objdump or it's perf failing to parse
>>> the line number correctly?  I'd like to see the output of `objdump -l`
>>>
>>
>> Both are ok.
>> 'objdump -l' hasn't a bug related to line number
>> and perf's method parsing the line number is ok.
>>
>> But symbol__parse_objdump_line() wrongly count line numbers
>> after parsing it as below.
>>
>> 1172         /* /filename:linenr ? Save line number and ignore. */
>> 1173         if (regexec(&file_lineno, line, 2, match, 0) == 0) {
>> 1174                 *line_nr = atoi(line + match[1].rm_so);
>> 1175                 return 0;
>> 1176         }
>> ...
>> 1208         dl = disasm_line__new(offset, parsed_line, privsize, *line_nr,
>> arch, map);
>> 1209         free(line);
>> 1210         (*line_nr)++;
>>
>> Increasing line_nr each asm line is wrong method.
>> Because 'line_nr' means actual source code line number.
>
> Hmm.. ok.  It looks like that it should reuse the old line_nr as is.
>
>>
>> Sure, I can fix only the wrong counting way.
>> But the above parsing method(1172~1176) is never used because of 'grep -v'
>> in command as below.
>> (the grep already remove lines containing filename:linenr of output)
>
> Right, but only if filename is same as binary name.
>
>>
>> 1435         snprintf(command, sizeof(command),
>> 1436                  "%s %s%s --start-address=0x%016" PRIx64
>> 1437                  " --stop-address=0x%016" PRIx64
>> 1438                  " -l -d %s %s -C %s 2>/dev/null|grep -v %s|expand",
>> 1439                  objdump_path ? objdump_path : "objdump",
>> 1440                  disassembler_style ? "-M " : "",
>> 1441                  disassembler_style ? disassembler_style : "",
>> 1442                  map__rip_2objdump(map, sym->start),
>> 1443                  map__rip_2objdump(map, sym->end),
>> 1444                  symbol_conf.annotate_asm_raw ? "" : "--no-show-raw",
>> 1445                  symbol_conf.annotate_src ? "-S" : "",
>> 1446                  symfs_filename, symfs_filename);
>>
>> Therefore, I think it is better to do three things
>>
>>   1) fix the wrong counting line number problem
>>   2) remove unused the line number parsing method
>>   3) In addtion, a bit reduce objdump dependency
>>      using functions related to addr2line of perf.
>>
>> What do you think about that ?
>> Is it bad idea ?
>
> I think we need to fix 1) definitely, but not sure about 2) and 3).
> If objdump could do all necessary works, why not use it? :)
>
> Thanks,
> Namhyung
>
>

Okey! I'll concentrate on fixing 1)
,not removing objdump -l :)

Thanks,
Taeung