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

[Namhyung Kim]

Hello,

On Wed, Dec 04, 2024 at 10:08:15PM +0000, Quentin Monnet wrote:
> 2024-12-04 13:36 UTC-0800 ~ Namhyung Kim <namhyung@xxxxxxxxxx>
> > 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 

Thanks,
Namhyung

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