Re: [PATCH] bpftool: Fix failure with static linkage

Quentin Monnet
2024-12-04T22:55:37Z

2024-12-04 14:25 UTC-0800 ~ Namhyung Kim <namhyung@kernel.org>
> Hello,
>
> On Wed, Dec 04, 2024 at 10:08:15PM +0000, Quentin Monnet wrote:
>> 2024-12-04 13:36 UTC-0800 ~ Namhyung Kim <namhyung@kernel.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).
>
> I think you can use pkg-config if available.
>
> $ pkg-config --static --libs libelf
> -lelf -lz -lzstd -pthread
>

That's another dependency that I'd like to avoid if I can :)

Quentin