Subject: Re: [PATCHv3 bpf-next 7/7] selftests/bpf: Add test for bpf_get_func_ip in kprobe+offset probe

From: Jiri Olsa <[email-masked]>
Date: Sun, 11 Jul 2021 16:48:17 +0200

On Wed, Jul 07, 2021 at 05:18:49PM -0700, Andrii Nakryiko wrote:
> On Wed, Jul 7, 2021 at 2:54 PM Jiri Olsa <[email-masked]> wrote:
> >
> > Adding test for bpf_get_func_ip in kprobe+ofset probe.
> 
> typo: offset
> 
> > Because of the offset value it's arch specific, adding
> > it only for x86_64 architecture.
> 
> I'm not following, you specified +0x5 offset explicitly, why is this
> arch-specific?

I need some instruction offset != 0 in the traced function,
x86_64's fentry jump is 5 bytes, other archs will be different

> 
> >
> > Signed-off-by: Jiri Olsa <[email-masked]>
> > ---
> >  .../testing/selftests/bpf/progs/get_func_ip_test.c  | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/tools/testing/selftests/bpf/progs/get_func_ip_test.c b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > index 8ca54390d2b1..e8a9428a0ea3 100644
> > --- a/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > +++ b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > @@ -10,6 +10,7 @@ extern const void bpf_fentry_test2 __ksym;
> >  extern const void bpf_fentry_test3 __ksym;
> >  extern const void bpf_fentry_test4 __ksym;
> >  extern const void bpf_modify_return_test __ksym;
> > +extern const void bpf_fentry_test6 __ksym;
> >
> >  __u64 test1_result = 0;
> >  SEC("fentry/bpf_fentry_test1")
> > @@ -60,3 +61,15 @@ int BPF_PROG(fmod_ret_test, int a, int *b, int ret)
> >         test5_result = (const void *) addr == &bpf_modify_return_test;
> >         return ret;
> >  }
> > +
> > +#ifdef __x86_64__
> > +__u64 test6_result = 0;
> 
> see, and you just forgot to update the user-space part of the test to
> even check test6_result...
> 
> please group variables together and do explicit ASSERT_EQ

right.. will change

thanks,
jirka

> 
> > +SEC("kprobe/bpf_fentry_test6+0x5")
> > +int test6(struct pt_regs *ctx)
> > +{
> > +       __u64 addr = bpf_get_func_ip(ctx);
> > +
> > +       test6_result = (const void *) addr == &bpf_fentry_test6 + 5;
> > +       return 0;
> > +}
> > +#endif
> > --
> > 2.31.1
> >
>