linux-kernel - Re: [PATCH v2] tools/perf/inject: fix dwarf support detection

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Message-ID: <CABPqkBRj+77AR-6cMCHaNZ+ddgLMriO1zgrtWtqvU7NZ1wfkMA@mail.gmail.com>
Date:   Mon, 18 Dec 2017 00:19:01 -0800
From:   Stephane Eranian <eranian@...gle.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, mingo@...e.hu
Subject: Re: [PATCH v2] tools/perf/inject: fix dwarf support detection

On Sun, Dec 17, 2017 at 7:05 PM, Jiri Olsa <jolsa@...hat.com> wrote:
> On Fri, Dec 08, 2017 at 09:02:18AM -0800, Stephane Eranian wrote:
>> I ran into problems trying to use the JIT support and display
>> source-level information. Basically, there was no dwarf debug
>> info generated in the jitted-XX.so files, yet I had libdw-dev
>> installed.
>>
>> Turns out that the feature test build for test-dwarf.bin was broken
>> for me. It would die for the wrong reason:
>>
>> /usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/libdw.so: undefined reference to `elf_compress@...UTILS_1.7'
>>
>> In other words, the libdw has a dependency on libelf which the Makefile
>> was not accounting for. Thus perf was not compiled with HAVE_DWARF_SUPPORT
>> and the code in genelf.c was not compiled in.
>>
>> This patch fixes the issue by adding -lelf to the build rule for test-dwarf.c.
>>
>> I wasted quite some time trying to debug this, so I have added a warning
>> in builtin-inject.c so that the user is warned that in case dwarf support
>> is disabled, no source line information will be generated in the output
>> .so files from the jitted code.
>>
>> In v2, we removed the extraneaous echo in the make target.
>>
>> Signed-off-by: Stephane Eranian <eranian@...gle.com>
>> ---
>>  tools/build/feature/Makefile | 7 ++++++-
>>  tools/perf/builtin-inject.c  | 3 +++
>>  2 files changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
>> index cff38f342283..be5679707aa0 100644
>> --- a/tools/build/feature/Makefile
>> +++ b/tools/build/feature/Makefile
>> @@ -104,7 +104,12 @@ __BUILDXX = $(CXX) $(CXXFLAGS) -MD -Wall -Werror -o $@ $(patsubst %.bin,%.cpp,$(
>>  $(OUTPUT)test-setns.bin:
>>       $(BUILD)
>>
>> -DWARFLIBS := -ldw
>> +#
>> +# there may be a dependency between libdw and libelf such as
>> +# /usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/libdw.so: undefined reference to `elf_compress@...UTILS_1.7'
>> +# so force linking with libelf
>> +#
>> +DWARFLIBS := -ldw -lelf
>>  ifeq ($(findstring -static,${LDFLAGS}),-static)
>>  DWARFLIBS += -lelf -lebl -lz -llzma -lbz2
>
> you can remove '-lelf' from above line then (again)
>
Ok, I get it now. I thought you were talking about the line I added!
Let me resubmit.
Thanks.

> jirka
>
>>  endif
>> diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
>> index 16a28547ca86..524255ed9a39 100644
>> --- a/tools/perf/builtin-inject.c
>> +++ b/tools/perf/builtin-inject.c
>> @@ -856,6 +856,9 @@ int cmd_inject(int argc, const char **argv)
>>       }
>>  #ifdef HAVE_JITDUMP
>>       if (inject.jit_mode) {
>> +#ifndef HAVE_DWARF_SUPPORT
>> +             pr_warning("perf tool compiled without dwarf, no source line information will be generated\n");
>> +#endif
>>               inject.tool.mmap2          = perf_event__jit_repipe_mmap2;
>>               inject.tool.mmap           = perf_event__jit_repipe_mmap;
>>               inject.tool.ordered_events = true;
>> --
>> 2.7.4
>>