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

[Jiri Olsa <olsajiri@gmail.com>]

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

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?