Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Tue, Feb 14, 2023 at 01:27:43PM +0100, Jiri Olsa escreveu:
> On Mon, Feb 13, 2023 at 07:12:33PM -0800, Alexei Starovoitov wrote:
> > On Thu, Feb 9, 2023 at 5:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
> > >
> > > v1.25 of pahole supports filtering out functions with multiple
> > > inconsistent function prototypes or optimized-out parameters
> > > from the BTF representation.  These present problems because
> > > there is no additional info in BTF saying which inconsistent
> > > prototype matches which function instance to help guide
> > > attachment, and functions with optimized-out parameters can
> > > lead to incorrect assumptions about register contents.
> > >
> > > So for now, filter out such functions while adding BTF
> > > representations for functions that have "."-suffixes
> > > (foo.isra.0) but not optimized-out parameters.
> > >
> > > This patch assumes changes in [1] land and pahole is bumped
> > > to v1.25.
> > >
> > > [1] https://lore.kernel.org/bpf/1675790102-23037-1-git-send-email-alan.maguire@oracle.com/
> > >
> > > Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> > > Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> > >
> > > ---
> > >  scripts/pahole-flags.sh | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> > > index 1f1f1d3..728d551 100755
> > > --- a/scripts/pahole-flags.sh
> > > +++ b/scripts/pahole-flags.sh
> > > @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
> > >         # see PAHOLE_HAS_LANG_EXCLUDE
> > >         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> > >  fi
> > > +if [ "${pahole_ver}" -ge "125" ]; then
> > > +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> > > +fi
> > 
> > We landed this too soon.
> > #229     tracing_struct:FAIL
> > is failing now.
> > since bpf_testmod.ko is missing a bunch of functions though they're global.
> > 
> 
> hum, didn't see this one failing.. I'll try that again

/me too, redoing tests her, with gcc and clang, running selftests on a
system booted with a kernel built with pahole 1.25, etc.

- Arnaldo
 
> jirka
> 
> > I've tried a bunch of different flags and attributes, but none of them
> > helped.
> > The only thing that works is:
> > diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > index 46500636d8cd..5fd0f75d5d20 100644
> > --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > @@ -28,6 +28,7 @@ struct bpf_testmod_struct_arg_2 {
> >         long b;
> >  };
> > 
> > +__attribute__((optimize("-O0")))
> >  noinline int
> >  bpf_testmod_test_struct_arg_1(struct bpf_testmod_struct_arg_2 a, int
> > b, int c) {
> > 
> > We cannot do:
> > --- a/tools/testing/selftests/bpf/bpf_testmod/Makefile
> > +++ b/tools/testing/selftests/bpf/bpf_testmod/Makefile
> > @@ -10,7 +10,7 @@ endif
> >  MODULES = bpf_testmod.ko
> > 
> >  obj-m += bpf_testmod.o
> > -CFLAGS_bpf_testmod.o = -I$(src)
> > +CFLAGS_bpf_testmod.o = -I$(src) -O0
> > 
> > The build fails due to asm stuff.
> > 
> > Maybe we should make scripts/pahole-flags.sh selective
> > and don't apply skip_encoding_btf_inconsiste to bpf_testmod ?
> > 
> > Thoughts?

-- 

- Arnaldo