netdev - Re: [PATCH bpf-next v4 6/8] selftests/bpf: Add weak/typeless ksym test for light skeleton

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Date:   Wed, 20 Oct 2021 15:43:42 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
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 v4 6/8] selftests/bpf: Add weak/typeless ksym
 test for light skeleton

On Wed, Oct 20, 2021 at 3:37 PM Kumar Kartikeya Dwivedi
<memxor@...il.com> wrote:
>
> On Thu, Oct 21, 2021 at 03:47:19AM IST, Andrii Nakryiko wrote:
> > On Wed, Oct 20, 2021 at 12:15 PM Kumar Kartikeya Dwivedi
> > <memxor@...il.com> wrote:
> > >
> > > Also, avoid using CO-RE features, as lskel doesn't support CO-RE, yet.
> > > Include both light and libbpf skeleton in same file to test both of them
> > > together.
> > >
> > > In c48e51c8b07a ("bpf: selftests: Add selftests for module kfunc support"),
> > > I added support for generating both lskel and libbpf skel for a BPF
> > > object, however the name parameter for bpftool caused collisions when
> > > included in same file together. This meant that every test needed a
> > > separate file for a libbpf/light skeleton separation instead of
> > > subtests.
> > >
> > > Change that by appending a "_light" suffix to the name for files listed
> > > in LSKELS_EXTRA, such that both light and libbpf skeleton can be used in
> > > the same file for subtests, leading to better code sharing.
> > >
> > > While at it, improve the build output by saying GEN-LSKEL instead of
> > > GEN-SKEL for light skeleton generation recipe.
> > >
> > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> > > ---
> > >  tools/testing/selftests/bpf/Makefile          |  7 ++--
> > >  .../selftests/bpf/prog_tests/ksyms_btf.c      | 35 +++++++++++++++-
> > >  .../selftests/bpf/prog_tests/ksyms_module.c   | 40 +++++++++++++++++--
> > >  .../bpf/prog_tests/ksyms_module_libbpf.c      | 28 -------------
> > >  .../selftests/bpf/progs/test_ksyms_weak.c     |  3 +-
> > >  5 files changed, 74 insertions(+), 39 deletions(-)
> > >  delete mode 100644 tools/testing/selftests/bpf/prog_tests/ksyms_module_libbpf.c
> > >
> > > diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> > > index 498222543c37..1c3c8befc249 100644
> > > --- a/tools/testing/selftests/bpf/Makefile
> > > +++ b/tools/testing/selftests/bpf/Makefile
> > > @@ -325,7 +325,7 @@ LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h               \
> > >  LSKELS := kfunc_call_test.c fentry_test.c fexit_test.c fexit_sleep.c \
> > >         test_ringbuf.c atomics.c trace_printk.c trace_vprintk.c
> > >  # Generate both light skeleton and libbpf skeleton for these
> > > -LSKELS_EXTRA := test_ksyms_module.c
> > > +LSKELS_EXTRA := test_ksyms_module.c test_ksyms_weak.c
> > >  SKEL_BLACKLIST += $$(LSKELS)
> > >
> > >  test_static_linked.skel.h-deps := test_static_linked1.o test_static_linked2.o
> > > @@ -399,12 +399,13 @@ $(TRUNNER_BPF_SKELS): %.skel.h: %.o $(BPFTOOL) | $(TRUNNER_OUTPUT)
> > >         $(Q)$$(BPFTOOL) gen skeleton $$(<:.o=.linked3.o) name $$(notdir $$(<:.o=)) > $$@
> > >
> > >  $(TRUNNER_BPF_LSKELS): %.lskel.h: %.o $(BPFTOOL) | $(TRUNNER_OUTPUT)
> > > -       $$(call msg,GEN-SKEL,$(TRUNNER_BINARY),$$@)
> > > +       $$(call msg,GEN-LSKEL,$(TRUNNER_BINARY),$$@)
> >
> > This breaks nice output alignment:
> >
> >   GEN-SKEL [test_progs-no_alu32] bpf_iter_tcp4.skel.h
> >   GEN-LSKEL [test_progs-no_alu32] trace_vprintk.lskel.h
> >
>
> Ok, I'll drop it.
>
> > Isn't ".lskel.h" suffix enough to distinguish them?
> >
> > >         $(Q)$$(BPFTOOL) gen object $$(<:.o=.linked1.o) $$<
> > >         $(Q)$$(BPFTOOL) gen object $$(<:.o=.linked2.o) $$(<:.o=.linked1.o)
> > >         $(Q)$$(BPFTOOL) gen object $$(<:.o=.linked3.o) $$(<:.o=.linked2.o)
> > >         $(Q)diff $$(<:.o=.linked2.o) $$(<:.o=.linked3.o)
> > > -       $(Q)$$(BPFTOOL) gen skeleton -L $$(<:.o=.linked3.o) name $$(notdir $$(<:.o=)) > $$@
> > > +       $$(eval LSKEL_NAME := $$(notdir $$(<:.o=$$(if $$(filter $$(notdir $$(<:.o=.c)),$(LSKELS_EXTRA)),_light,))))
> >
> > eval inside eval?.. Wow, do we really need that? If you just want to
>
> I knew you'd like it ;-)

yeah, big fan, obviously :)

>
> > add _light (I suggest _lskel though, it will make for a more
> > meaningful and recognizable names in user-space code) suffix, do it
> > for all light skeletons unconditionally and keep it simple?
> >
>
> I avoided this because it would be a lot of unecessary changes, while we only
> need this for two files. Every struct/function name will get the suffix, but I
> can do it if the Makefile stuff looks too horrible.

There are 10 light skeleton-using selftests, it's not a problem to do
one-time renaming. Currently there are only two files that do both
skel and lskel, but that number will inevitably grow, so better to set
everything up now.

>
> > > +       $(Q)$$(BPFTOOL) gen skeleton -L $$(<:.o=.linked3.o) name $$(LSKEL_NAME) > $$@
> > >
> > >  $(TRUNNER_BPF_SKELS_LINKED): $(TRUNNER_BPF_OBJS) $(BPFTOOL) | $(TRUNNER_OUTPUT)
> > >         $$(call msg,LINK-BPF,$(TRUNNER_BINARY),$$(@:.skel.h=.o))
> >
> > [...]
>
> --
> Kartikeya