linux-kernel - Re: [PATCH] bpftool: Fix failure with static linkage

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Message-ID: <bf5da4d3-c317-4616-ac68-0d49bb5815c2@kernel.org>
Date: Wed, 4 Dec 2024 22:08:15 +0000
From: Quentin Monnet <qmo@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>, Leo Yan <leo.yan@....com>
Cc: Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman
 <eddyz87@...il.com>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Nick Terrell <terrelln@...com>,
 bpf@...r.kernel.org, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org, Mahe Tardy <mahe.tardy@...il.com>
Subject: Re: [PATCH] bpftool: Fix failure with static linkage

2024-12-04 13:36 UTC-0800 ~ Namhyung Kim <namhyung@...nel.org>
> Hi Leo,
> 
> On Wed, Dec 04, 2024 at 09:30:59PM +0000, Leo Yan wrote:
>> When building perf with static linkage:
>>
>>   make O=/build LDFLAGS="-static" -C tools/perf VF=1 DEBUG=1
>>   ...
>>   LINK    /build/util/bpf_skel/.tmp/bootstrap/bpftool
>>   /usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/13/../../../x86_64-linux-gnu/libelf.a(elf_compress.o): in function `__libelf_compress':
>>   (.text+0x113): undefined reference to `ZSTD_createCCtx'
>>   /usr/bin/ld: (.text+0x2a9): undefined reference to `ZSTD_compressStream2'
>>   /usr/bin/ld: (.text+0x2b4): undefined reference to `ZSTD_isError'
>>   /usr/bin/ld: (.text+0x2db): undefined reference to `ZSTD_freeCCtx'
>>   /usr/bin/ld: (.text+0x5a0): undefined reference to `ZSTD_compressStream2'
>>   /usr/bin/ld: (.text+0x5ab): undefined reference to `ZSTD_isError'
>>   /usr/bin/ld: (.text+0x6b9): undefined reference to `ZSTD_freeCCtx'
>>   /usr/bin/ld: (.text+0x835): undefined reference to `ZSTD_freeCCtx'
>>   /usr/bin/ld: (.text+0x86f): undefined reference to `ZSTD_freeCCtx'
>>   /usr/bin/ld: (.text+0x91b): undefined reference to `ZSTD_freeCCtx'
>>   /usr/bin/ld: (.text+0xa12): undefined reference to `ZSTD_freeCCtx'
>>   /usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/13/../../../x86_64-linux-gnu/libelf.a(elf_compress.o): in function `__libelf_decompress':
>>   (.text+0xbfc): undefined reference to `ZSTD_decompress'
>>   /usr/bin/ld: (.text+0xc04): undefined reference to `ZSTD_isError'
>>   /usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/13/../../../x86_64-linux-gnu/libelf.a(elf_compress.o): in function `__libelf_decompress_elf':
>>   (.text+0xd45): undefined reference to `ZSTD_decompress'
>>   /usr/bin/ld: (.text+0xd4d): undefined reference to `ZSTD_isError'
>>   collect2: error: ld returned 1 exit status
>>
>> Building bpftool with static linkage also fails with the same errors:
>>
>>   make O=/build -C tools/bpf/bpftool/ V=1
>>
>> To fix the issue, explicitly link libzstd.
> 
> I was about to report exactly the same. :)

Thank you both. This has been reported before [0] but I didn't find the
time to look into a proper fix.

The tricky part is that static linkage works well without libzstd for
older versions of elfutils [1], but newer versions now require this
library. Which means that we don't want to link against libzstd
unconditionally, or users trying to build bpftool may have to install
unnecessary dependencies. Instead we should add a new probe under
tools/build/feature (Note that we already have several combinations in
there, libbfd, libbfd-liberty, libbfd-liberty-z, and I'm not sure what's
the best approach in terms of new combinations).

Thanks,
Quentin


[0] https://github.com/libbpf/bpftool/issues/152
[1] https://github.com/libbpf/bpftool/issues/152#issuecomment-2343131810