linux-kernel - Re: [RFC] The -Og debugging experience

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Date:	Thu, 10 Dec 2015 14:07:35 +0100
From:	Martin Liška <mliska@...e.cz>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC] The -Og debugging experience

On 12/07/2015 03:16 PM, Jiri Olsa wrote:
> On Mon, Dec 07, 2015 at 03:04:27PM +0100, Martin Liška wrote:
> 
> SNIP
> 
>> Hi.
>>
>> Unfortunately, running 'perf report' for a medium-size report is very fast a
> 
> not if you use TUI ;-)
> 
>> killing the process from other terminal produces:
>>
>> [Current thread is 1 (Thread 0x7ffff7fc5740 (LWP 7429))]
>> (gdb) bt
>> #0  0x00007ffff632d230 in __write_nocancel () from /lib64/libc.so.6
>> #1  0x00007ffff62c4dff in _IO_new_file_write () from /lib64/libc.so.6
>> #2  0x00007ffff62c4403 in new_do_write () from /lib64/libc.so.6
>> #3  0x00007ffff62c5d09 in __GI__IO_do_write () from /lib64/libc.so.6
>> #4  0x00007ffff62c5417 in __GI__IO_file_xsputn () from /lib64/libc.so.6
>> #5  0x00007ffff6299cdb in vfprintf () from /lib64/libc.so.6
>> #6  0x00007ffff62a03f7 in fprintf () from /lib64/libc.so.6
>> #7  0x00000000004ef12c in hist_entry__fprintf (he=he@...ry=0x1c62b30, size=<optimized out>, size@...ry=0, hists=hists@...ry=0x1813818, 
>                                                                               ^^^^^^^^^^^^^^
>                                                                               
> 
>>     bf=bf@...ry=0x1d5cd40 "     0.08%  cc1plus   cc1plus", ' ' <repeats 11 times>, "[.] _Z25number_of_iterations_exitP4loopP8edge_defP15tree_niter_descbb", ' ' <repeats 91 times>..., bfsz=bfsz@...ry=479, fp=fp@...ry=0x7ffff65f0640 <_IO_2_1_stdout_>)
>>     at ui/stdio/hist.c:427
>> #8  0x00000000004ef549 in hists__fprintf (hists=hists@...ry=0x1813818, show_header=show_header@...ry=true, max_rows=max_rows@...ry=0, max_cols=max_cols@...ry=0, min_pcnt=0, fp=0x7ffff65f0640 <_IO_2_1_stdout_>) at ui/stdio/hist.c:534
>> #9  0x000000000042d6a3 in perf_evlist__tty_browse_hists (evlist=0x1812c90, rep=rep@...ry=0x7fffffffc6e0, help=help@...ry=0x515948 "For a higher level overview, try: perf report --sort comm,dso") at builtin-report.c:370
>> #10 0x000000000042d7d2 in report__browse_hists (rep=rep@...ry=0x7fffffffc6e0) at builtin-report.c:455
>> #11 0x000000000042d992 in __cmd_report (rep=rep@...ry=0x7fffffffc6e0) at builtin-report.c:571
>> #12 0x000000000042ec1f in cmd_report (argc=0, argv=0x7fffffffde00, prefix=<optimized out>) at builtin-report.c:957
>                                                                              ^^^^^^^^^^^^^^
> 
> 
>> #13 0x000000000046c496 in run_builtin (p=p@...ry=0x7771a0 <commands+192>, argc=argc@...ry=1, argv=argv@...ry=0x7fffffffde00) at perf.c:387
>> #14 0x000000000046c693 in handle_internal_command (argc=1, argv=0x7fffffffde00) at perf.c:448
>> #15 0x000000000046c6fe in run_argv (argcp=argcp@...ry=0x7fffffffdc6c, argv=argv@...ry=0x7fffffffdc60) at perf.c:492
>> #16 0x000000000046c94c in main (argc=1, argv=0x7fffffffde00) at perf.c:609
>>
>> Which is fine.
> 
> marked 2 instances of 'optimized out' cases above in your output
> 
>>
>> I've been using GCC 5.2. What version are you using?
> 
> 5.1.1
> 
>> I've also tried to run './perf test' and terminate the process at random places, but the back trace was OK.
>>
>> I would appreciate if you send me a patch that causes a segfault that is wrongly displayed.
> 
> if you run TUI, you dont need to be fast ;-) make sure you compile with slang devel pkg
> 
> thanks.
> jirka
> 

Hello.

I've just created PR for GCC:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68836

According to discussing with Jakub Jelinek, that's a semi-known issues that's going to be eventually fixed.

Martin
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