Re: [PATCH v2 1/2] CMakeLists.txt: enable SHARED and STATIC lib creation

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Fri, Jun 11, 2021 at 12:34 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Thu, Jun 10, 2021 at 10:31 AM Arnaldo Carvalho de Melo
> <arnaldo.melo@gmail.com> wrote:
> >
> > Em Tue, Jun 08, 2021 at 12:50:13AM +0530, Deepak Kumar Mishra escreveu:
> > > CMakeLists.txt does not allow creation of static library and link applications
> > > accordingly.
> > >
> > > Creation of SHARED and STATIC should be allowed using -DBUILD_SHARED_LIBS
> > > If -DBUILD_SHARED_LIBS option is not supplied, CMakeLists.txt sets it to ON.
> > >
> > > Ex:
> > > cmake -D__LIB=lib -DBUILD_SHARED_LIBS=OFF ..
> > > cmake -D__LIB=lib -DBUILD_SHARED_LIBS=ON ..
> >
> > Had to do some fixups due to a previous patch touching CMakeLists.txt,
> > please check below.
> >
> > I tested it and added some performance notes.
>
> Hey Arnaldo, Deepak,

Should have added Luca as well, it might be his patch (ae2581647e84
("libbpf: Allow to use packaged version")) that might have introduced
this breakage in the first place.

>
> I think this commit actually breaks libbpf's CI (see [0]) and my local
> setup as well (see output below). It seems like now we are using
> system-wide libbpf headers, while still building local libbpf sources.
> This is pretty bad because system-wide headers might be too old or
> just missing.
>
> Is it possible to make sure that we always use local libbpf headers
> when building pahole with libbpf built from sources (the default case,
> right?). It's also important to use UAPI headers distributed with
> libbpf when building libbpf itself, I don't know if that's what is
> done right now or not.
>
> Note how libbpf CI case shows that system-wide bpf/btf.h is not
> available at all because we don't have system-wide libbpf installed.
> In my local case, you can see that my system-wide header is outdated
> and doesn't have BTF_LITTLE_ENDIAN/BTF_BIG_ENDIAN constants defined in
> libbpf.h.
>
> BTW, I tried -D__LIB=lib -DBUILD_SHARED_LIBS=OFF options and they
> didn't help. Maybe I'm doing something wrong.
>
>   [0] https://travis-ci.com/github/kernel-patches/bpf/builds/228673352
>
>
> $ make -j60
> -- Setting BUILD_SHARED_LIBS = ON
> -- Checking availability of DWARF and ELF development libraries
> -- Checking availability of DWARF and ELF development libraries - done
> -- Configuring done
> -- Generating done
> -- Build files have been written to: /home/andriin/local/pahole/build
>
> ....
>
> /home/andriin/local/pahole/btf_encoder.c:900:28: error:
> ‘BTF_LITTLE_ENDIAN’ undeclared (first use in this function)
>    btf__set_endianness(btf, BTF_LITTLE_ENDIAN);
>                             ^
> /home/andriin/local/pahole/btf_encoder.c:900:28: note: each undeclared
> identifier is reported only once for each function it appears in
> /home/andriin/local/pahole/btf_encoder.c:903:28: error:
> ‘BTF_BIG_ENDIAN’ undeclared (first use in this function)
>    btf__set_endianness(btf, BTF_BIG_ENDIAN);
>                             ^
> ...
>
>
> >
> > Thanks!
> >
> > - Arnaldo
> >
> > commit aa2027708659f172780f85698f14303c7de6a1d2
> > Author: Deepak Kumar Mishra <deepakkumar.mishra@arm.com>
> > Date:   Tue Jun 8 00:50:13 2021 +0530
> >
> >     CMakeLists.txt: Enable SHARED and STATIC lib creation
> >
> >     CMakeLists.txt does not allow creation of static library and link applications
> >     accordingly.
> >
> >     Creation of SHARED and STATIC should be allowed using -DBUILD_SHARED_LIBS
> >     If -DBUILD_SHARED_LIBS option is not supplied, CMakeLists.txt sets it to ON.
> >
> >     Ex:
> >
> >       $ cmake -D__LIB=lib -DBUILD_SHARED_LIBS=OFF ..
> >       $ cmake -D__LIB=lib -DBUILD_SHARED_LIBS=ON ..
> >
>
> [...]