Re: [PATCH v1 4/6] perf: build: Only link libebl.a for old libdw

[Namhyung Kim]

On Tue, Jun 04, 2024 at 10:32:21AM +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.
> 
> This commit checks the libdw version and only links libebl.a if it
> detects that the libdw version is older than 0.177.
> 
> Signed-off-by: Leo Yan <leo.yan@xxxxxxx>
> ---
>  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 6f52f892f9a3..2f4cfb7b8c14 100644
> --- a/tools/build/feature/Makefile
> +++ b/tools/build/feature/Makefile
> @@ -159,7 +159,17 @@ $(OUTPUT)test-libopencsd.bin:
>  
>  DWARFLIBS := -ldw
>  ifeq ($(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
> +  endif
>  endif

Is there a better way to collect required libraries using pkg-config?
I guess that's what we want to with the pkg-config in the first place.
Maybe `pkg-config --print-requires-private libdw` ?

Thanks,
Namhyung

>  
>  $(OUTPUT)test-dwarf.bin:
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index 646e5af0ed51..e8d3713b081c 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -152,7 +152,17 @@ ifdef LIBDW_DIR
>  endif
>  DWARFLIBS := -ldw
>  ifeq ($(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
>