Re: [PATCH bpf-next v4 06/12] bpf: selftests: Fix bpf_session_cookie() kfunc prototype

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Jun 17, 2024 at 03:25:53PM -0700, Andrii Nakryiko wrote:
> On Mon, Jun 10, 2024 at 6:04 AM Jiri Olsa <olsajiri@gmail.com> wrote:
> >
> > On Sat, Jun 08, 2024 at 03:16:02PM -0600, Daniel Xu wrote:
> > > The prototype defined in bpf_kfuncs.h was not in line with how the
> > > actual kfunc was defined. This causes compilation errors when kfunc
> > > prototypes are generated from BTF.
> > >
> > > Fix by aligning with actual kfunc definition.
> > >
> > > Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
> > > ---
> > >  tools/testing/selftests/bpf/bpf_kfuncs.h                        | 2 +-
> > >  tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c | 2 +-
> > >  2 files changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/tools/testing/selftests/bpf/bpf_kfuncs.h b/tools/testing/selftests/bpf/bpf_kfuncs.h
> > > index be91a6919315..3b6675ab4086 100644
> > > --- a/tools/testing/selftests/bpf/bpf_kfuncs.h
> > > +++ b/tools/testing/selftests/bpf/bpf_kfuncs.h
> > > @@ -77,5 +77,5 @@ extern int bpf_verify_pkcs7_signature(struct bpf_dynptr *data_ptr,
> > >                                     struct bpf_key *trusted_keyring) __ksym;
> > >
> > >  extern bool bpf_session_is_return(void) __ksym __weak;
> > > -extern long *bpf_session_cookie(void) __ksym __weak;
> > > +extern __u64 *bpf_session_cookie(void) __ksym __weak;
> >
> > the original intent was to expose long instead of __u64 :-\
> >
> 
> Cookies internally are always u64 (8 byte values). Marking them
> internally in the kernel as long could lead to problems on 32-bit
> architectures, potentially (it still needs to be 64-bit value
> according to BPF contract, but we'll allocate only 4 bytes for them).
> 
> It seems better and safer to be explicit with __u64/u64 for cookies everywhere.

hum, I based that on what we did for kprobe session,
but I guess it makes sense just for bpf side:

  https://lore.kernel.org/bpf/CAEf4BzbyQpKvZS-mUECLRq3gyBJbsqQghOKyAbutoB76mJM8xw@mail.gmail.com/

jirka

> 
> What am I missing?
> 
> > could we rather change the bpf_session_cookie function to return long?
> > should be just return value type change
> >
> > thanks,
> > jirka
> >
> >
> > >  #endif
> > > diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c b/tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c
> > > index d49070803e22..0835b5edf685 100644
> > > --- a/tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c
> > > +++ b/tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c
> > > @@ -25,7 +25,7 @@ int BPF_PROG(trigger)
> > >
> > >  static int check_cookie(__u64 val, __u64 *result)
> > >  {
> > > -     long *cookie;
> > > +     __u64 *cookie;
> > >
> > >       if (bpf_get_current_pid_tgid() >> 32 != pid)
> > >               return 1;
> > > --
> > > 2.44.0
> > >