linux-kernel - Re: [PATCH v2 3/6] perf: build: Only link libebl.a for old libdw

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Date: Fri, 21 Jun 2024 16:40:42 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Leo Yan <leo.yan@....com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ian Rogers <irogers@...gle.com>, James Clark <james.clark@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	Nick Terrell <terrelln@...com>,
	Thomas Richter <tmricht@...ux.ibm.com>,
	Quentin Monnet <qmo@...nel.org>,
	Changbin Du <changbin.du@...wei.com>,
	Fangrui Song <maskray@...gle.com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	Guilherme Amadio <amadio@...too.org>
Subject: Re: [PATCH v2 3/6] perf: build: Only link libebl.a for old libdw

On Mon, Jun 10, 2024 at 10:54:30AM +0100, Leo Yan wrote:
> Since libdw version 0.177, elfutils has merged libebl.a into libdw (see
> the commit "libebl: Don't install libebl.a, libebl.h and remove backends
> from spec." in the elfutils repository).
> 
> As a result, libebl.a does not exist on Debian Bullseye and newer
> releases, causing static perf builds to fail on these distributions.

What about libebl.so?  I'm curious why it's ok with dynamic build and
causing a problem with static builds.

> 
> This commit checks the libdw version and only links libebl.a if it
> detects that the libdw version is older than 0.177.

Have you tested on the older versions too?

> 
> Signed-off-by: Leo Yan <leo.yan@....com>
> ---
>  tools/build/feature/Makefile | 12 +++++++++++-
>  tools/perf/Makefile.config   | 12 +++++++++++-
>  2 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
> index 084f803093c3..b23b3e8ad5e4 100644
> --- a/tools/build/feature/Makefile
> +++ b/tools/build/feature/Makefile
> @@ -171,7 +171,17 @@ $(OUTPUT)test-libopencsd.bin:
>  
>  DWARFLIBS := -ldw
>  ifeq ($(findstring -static,${LDFLAGS}),-static)
> -DWARFLIBS += -lelf -lebl -lz -llzma -lbz2
> +  DWARFLIBS += -lelf -lz -llzma -lbz2
> +
> +  LIBDW_VERSION := $(shell $(PKG_CONFIG) --modversion libdw)
> +  LIBDW_VERSION_1 := $(word 1, $(subst ., ,$(LIBDW_VERSION)))
> +  LIBDW_VERSION_2 := $(word 2, $(subst ., ,$(LIBDW_VERSION)))
> +
> +  # Elfutils merged libebl.a into libdw.a starting from version 0.177,
> +  # Link libebl.a only if libdw is older than this version.
> +  ifeq ($(shell test $(LIBDW_VERSION_2) -lt 177; echo $$?),0)
> +    DWARFLIBS += -lebl

I'm not sure if it's ok to change the order as libebl might depend on
later libraries like libz.

Thanks,
Namhyung


> +  endif
>  endif
>  
>  $(OUTPUT)test-dwarf.bin:
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index 755fb78be76a..db3bc460d4c2 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -152,7 +152,17 @@ ifdef LIBDW_DIR
>  endif
>  DWARFLIBS := -ldw
>  ifeq ($(findstring -static,${LDFLAGS}),-static)
> -  DWARFLIBS += -lelf -lebl -ldl -lz -llzma -lbz2
> +  DWARFLIBS += -lelf -ldl -lz -llzma -lbz2
> +
> +  LIBDW_VERSION := $(shell $(PKG_CONFIG) --modversion libdw)
> +  LIBDW_VERSION_1 := $(word 1, $(subst ., ,$(LIBDW_VERSION)))
> +  LIBDW_VERSION_2 := $(word 2, $(subst ., ,$(LIBDW_VERSION)))
> +
> +  # Elfutils merged libebl.a into libdw.a starting from version 0.177,
> +  # Link libebl.a only if libdw is older than this version.
> +  ifeq ($(shell test $(LIBDW_VERSION_2) -lt 177; echo $$?),0)
> +    DWARFLIBS += -lebl
> +  endif
>  endif
>  FEATURE_CHECK_CFLAGS-libdw-dwarf-unwind := $(LIBDW_CFLAGS)
>  FEATURE_CHECK_LDFLAGS-libdw-dwarf-unwind := $(LIBDW_LDFLAGS) $(DWARFLIBS)
> -- 
> 2.34.1
>