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

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Message-ID: <4a174cd7-7b52-40f8-b190-dc8fe90a7e39@arm.com>
Date: Fri, 7 Jun 2024 14:33:01 +0100
From: Leo Yan <leo.yan@....com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
 Mark Rutland <mark.rutland@....com>, James Clark <james.clark@....com>,
 Ian Rogers <irogers@...gle.com>, "Liang, Kan" <kan.liang@...ux.intel.com>,
 Nick Terrell <terrelln@...com>, Thomas Richter <tmricht@...ux.ibm.com>,
 Changbin Du <changbin.du@...wei.com>, Fangrui Song <maskray@...gle.com>,
 Mateusz Kowalczyk <fuuzetsu@...zetsu.co.uk>, linux-kernel@...r.kernel.org,
 linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v1 4/6] perf: build: Only link libebl.a for old libdw

On 6/6/24 18:40, Namhyung Kim wrote:

[...]

>> 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` ?

Unfortunately, `pkg-config --print-requires-private libdw` does not work 
for the libebl.a after checked on Debian:buster.

   # pkg-config --modversion libdw
   0.176

   # pkg-config --print-requires-private libdw
   zlib
   liblzma

   # pkg-config --libs-only-l libdw
   -ldw -lelf

   # ldd /usr/lib/x86_64-linux-gnu/libdw.so
	linux-vdso.so.1 (0x00007fff733e3000)
	libelf.so.1 => /usr/lib/x86_64-linux-gnu/libelf.so.1 (0x0000702e24ec6000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x0000702e24ec1000)
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x0000702e24ea3000)
	liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x0000702e24e7b000)
	libbz2.so.1.0 => /lib/x86_64-linux-gnu/libbz2.so.1.0 (0x0000702e24e68000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x0000702e24ca8000)
	/lib64/ld-linux-x86-64.so.2 (0x0000702e24f3e000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 
(0x0000702e24c85000)


I think libdw.pc cannot reflect the required dependencies, we still need 
to use a way liked in this patch (it is a bit ugly :) to link '-lebl'.

Thanks,
Leo