Date: Mon, 18 Dec 2017 04:05:10 +0100
From: Jiri Olsa <jolsa@redhat.com>
To: Stephane Eranian <eranian@google.com>
Cc: linux-kernel@vger.kernel.org, acme@redhat.com, peterz@infradead.org,
        mingo@elte.hu
Subject: Re: [PATCH v2] tools/perf/inject: fix dwarf support detection
Message-ID: <20171218030510.GA25654@krava.home>
References: <1512752538-10230-1-git-send-email-eranian@google.com>
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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@ELFUTILS_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@google.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:
>  	$(BUILD)
>  
> -DWARFLIBS := -ldw
> +#
> +# there may be a dependency between libdw and libelf such as
> +# /usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/libdw.so: undefined reference to `elf_compress@ELFUTILS_1.7'
> +# so force linking with libelf
> +#
> +DWARFLIBS := -ldw -lelf
>  ifeq ($(findstring -static,${LDFLAGS}),-static)
>  DWARFLIBS += -lelf -lebl -lz -llzma -lbz2

you can remove '-lelf' from above line then (again)

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
>