netdev - Re: [PATCH bpf-next v1 4/6] bpf: selftests: Move test_ksyms

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Date:   Fri, 8 Oct 2021 02:16:09 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     Song Liu <song@...nel.org>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v1 4/6] bpf: selftests: Move test_ksyms_weak
 test to lskel, add libbpf test

On Fri, Oct 08, 2021 at 02:03:49AM IST, Song Liu wrote:
> On Tue, Oct 5, 2021 at 5:29 PM Kumar Kartikeya Dwivedi <memxor@...il.com> wrote:
> >
> > Also, avoid using CO-RE features, as lskel doesn't support CO-RE, yet.
> > Create a file for testing libbpf skeleton as well, so that both
> > gen_loader and libbpf get tested.
> >
> > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> [...]
> > diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms_weak_libbpf.c b/tools/testing/selftests/bpf/prog_tests/ksyms_weak_libbpf.c
> > new file mode 100644
> > index 000000000000..b75725e28647
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/ksyms_weak_libbpf.c
> > @@ -0,0 +1,31 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <test_progs.h>
> > +#include "test_ksyms_weak.skel.h"
> > +
> > +void test_ksyms_weak_libbpf(void)
>
> This is (almost?) the same as test_weak_syms(), right? Why do we need both?
>

One includes lskel.h (light skeleton), the other includes skel.h (libbpf
skeleton). Trying to include both in the same file, it ends up redefining the
same struct. I am not sure whether adding a prefix/suffix to light skeleton
struct names is possible now, maybe through another option to bpftool in
addition to name?

> > +{
> > +       struct test_ksyms_weak *skel;
> > +       struct test_ksyms_weak__data *data;
> > +       int err;
> > +
> > +       skel = test_ksyms_weak__open_and_load();
> > +       if (!ASSERT_OK_PTR(skel, "test_ksyms_weak__open_and_load"))
> > +               return;
>
> [...]
>
> > diff --git a/tools/testing/selftests/bpf/progs/test_ksyms_weak.c b/tools/testing/selftests/bpf/progs/test_ksyms_weak.c
> > index 5f8379aadb29..521e7b99db08 100644
> > --- a/tools/testing/selftests/bpf/progs/test_ksyms_weak.c
> > +++ b/tools/testing/selftests/bpf/progs/test_ksyms_weak.c
> > @@ -21,7 +21,6 @@ __u64 out__non_existent_typed = -1;
> >  extern const struct rq runqueues __ksym __weak; /* typed */
> >  extern const void bpf_prog_active __ksym __weak; /* typeless */
> >
> > -
> >  /* non-existent weak symbols. */
> >
> >  /* typeless symbols, default to zero. */
> > @@ -38,7 +37,7 @@ int pass_handler(const void *ctx)
> >         /* tests existing symbols. */
> >         rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, 0);
> >         if (rq)
> > -               out__existing_typed = rq->cpu;
> > +               out__existing_typed = 0;
>
> Why do we need this change?
>

Since they share the same BPF object for generating skeleton, it needs to remove
dependency on CO-RE which gen_loader does not support.

If it is kept, we get this:
...
libbpf: // TODO core_relo: prog 0 insn[5] rq kind 0
libbpf: prog 'pass_handler': relo #0: failed to relocate: -95
libbpf: failed to perform CO-RE relocations: -95
libbpf: failed to load object 'test_ksyms_weak'
...
> >         out__existing_typeless = (__u64)&bpf_prog_active;
> >
> >         /* tests non-existent symbols. */
> > --
> > 2.33.0
> >

--
Kartikeya