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

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Date:	Mon, 7 Dec 2015 11:48:07 +0100
From:	Martin Liška <mliska@...e.cz>
To:	Jiri Olsa <jolsa@...hat.com>, Jiri Olsa <jolsa@...nel.org>
Cc:	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 12/02/2015 05:48 PM, Jiri Olsa wrote:
> heya,
> using the -Og for DEBUG=1 builds gives me many 'optimized out' stuff
> 
> It was introduced in here:
>   e8b7ea4356fd perf tools: Improve setting of gcc debug option
> 
> - here's backtrace from segfault I was looking at, current code:

Hi.

Can you please provide a test-case which I can use for testing of the issue?
If -Og is problem, I would suggest to use -O0 as a default DEBUG configure option.

Thanks,
Martin

> 
> (gdb) bt
> #0  0x00000000004b490f in parse_events__scan_string (yystr=yystr@...ry=0x0, yyscanner=0x1916be0) at util/parse-events-flex.c:3353
> #1  0x000000000048fe6f in parse_events__scanner (str=0x0, data=data@...ry=0x7fffffffdac0, start_token=start_token@...ry=258)
>     at util/parse-events.c:1356
> #2  0x0000000000491775 in parse_events (evlist=evlist@...ry=0x1917c90, str=<optimized out>, err=err@...ry=0x0) at util/parse-events.c:1401
> #3  0x0000000000468bf6 in __perf_evsel__name_array_test (names=0x872c00 <perf_evsel.sw_names>, nr_names=nr_names@...ry=11)
>     at tests/evsel-roundtrip-name.c:74
> #4  0x0000000000468f13 in test__perf_evsel__roundtrip_name_test (subtest=<optimized out>) at tests/evsel-roundtrip-name.c:106
> #5  0x000000000045a2c8 in run_test (test=test@...ry=0x86fe50 <generic_tests+400>, subtest=subtest@...ry=-1) at tests/builtin-test.c:241
> #6  0x000000000045a3a1 in test_and_print (t=t@...ry=0x86fe50 <generic_tests+400>, force_skip=force_skip@...ry=false,
>     subtest=subtest@...ry=-1) at tests/builtin-test.c:268
> #7  0x000000000045a5cd in __cmd_test (argc=argc@...ry=1, argv=argv@...ry=0x7fffffffe200, skiplist=0x0) at tests/builtin-test.c:324
> #8  0x000000000045a8a9 in cmd_test (argc=1, argv=0x7fffffffe200, prefix=<optimized out>) at tests/builtin-test.c:416
> #9  0x00000000004784a9 in run_builtin (p=p@...ry=0x871e18 <commands+504>, argc=argc@...ry=2, argv=argv@...ry=0x7fffffffe200) at perf.c:387
> #10 0x00000000004786a4 in handle_internal_command (argc=2, argv=0x7fffffffe200) at perf.c:448
> #11 0x0000000000478710 in run_argv (argcp=argcp@...ry=0x7fffffffe06c, argv=argv@...ry=0x7fffffffe060) at perf.c:492
> #12 0x0000000000478981 in main (argc=2, argv=0x7fffffffe200) at perf.c:609
> 
> 
> - and same crash with above patch reverted:
> 
> (gdb) bt
> #0  0x00007ffff573f36a in strlen () from /lib64/libc.so.6
> #1  0x00000000004f458b in parse_events__scan_string (yystr=0x0, yyscanner=0x1985be0) at util/parse-events-flex.c:3353
> #2  0x00000000004bc752 in parse_events__scanner (str=0x0, data=0x7fffffffda50, start_token=258) at util/parse-events.c:1356
> #3  0x00000000004bc8e2 in parse_events (evlist=0x1986c90, str=0x0, err=0x0) at util/parse-events.c:1401
> #4  0x00000000004837c4 in __perf_evsel__name_array_test (names=0x8e1140 <perf_evsel.sw_names>, nr_names=11)
>     at tests/evsel-roundtrip-name.c:74
> #5  0x0000000000483969 in test__perf_evsel__roundtrip_name_test (subtest=-1) at tests/evsel-roundtrip-name.c:106
> #6  0x000000000047099b in run_test (test=0x8de030 <generic_tests+400>, subtest=-1) at tests/builtin-test.c:241
> #7  0x0000000000470ae3 in test_and_print (t=0x8de030 <generic_tests+400>, force_skip=false, subtest=-1) at tests/builtin-test.c:268
> #8  0x0000000000470d71 in __cmd_test (argc=1, argv=0x7fffffffe200, skiplist=0x0) at tests/builtin-test.c:324
> #9  0x00000000004711c4 in cmd_test (argc=1, argv=0x7fffffffe200, prefix=0x0) at tests/builtin-test.c:416
> #10 0x0000000000498070 in run_builtin (p=0x8dfe58 <commands+504>, argc=2, argv=0x7fffffffe200) at perf.c:387
> #11 0x00000000004982de in handle_internal_command (argc=2, argv=0x7fffffffe200) at perf.c:448
> #12 0x000000000049842a in run_argv (argcp=0x7fffffffe05c, argv=0x7fffffffe050) at perf.c:492
> #13 0x0000000000498786 in main (argc=2, argv=0x7fffffffe200) at perf.c:609
> 
> 
> I haven't tracked the history of -Og, maybe it gets better from some gcc version?
> 
> If there's no clue, I rather revert this one, because it does
> provide the proper debugging experience ;-)
> 
> thoughts?
> jirka
> 

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