Re: [PATCH bpf-next 7/8] selftests/bpf: Add kprobe_multi kmod link api tests

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Oct 13, 2022 at 12:06:06PM -0700, Andrii Nakryiko wrote:

SNIP

> > +static void test_testmod_link_api(struct bpf_link_create_opts *opts)
> > +{
> > +       int prog_fd, link1_fd = -1, link2_fd = -1;
> > +       struct kprobe_multi *skel = NULL;
> > +
> > +       skel = kprobe_multi__open_and_load();
> > +       if (!ASSERT_OK_PTR(skel, "fentry_raw_skel_load"))
> > +               goto cleanup;
> > +
> > +       skel->bss->pid = getpid();
> > +       prog_fd = bpf_program__fd(skel->progs.test_kprobe_testmod);
> > +       link1_fd = bpf_link_create(prog_fd, 0, BPF_TRACE_KPROBE_MULTI, opts);
> > +       if (!ASSERT_GE(link1_fd, 0, "link_fd1"))
> > +               goto cleanup;
> > +
> > +       opts->kprobe_multi.flags = BPF_F_KPROBE_MULTI_RETURN;
> > +       prog_fd = bpf_program__fd(skel->progs.test_kretprobe_testmod);
> > +       link2_fd = bpf_link_create(prog_fd, 0, BPF_TRACE_KPROBE_MULTI, opts);
> > +       if (!ASSERT_GE(link2_fd, 0, "link_fd2"))
> > +               goto cleanup;
> > +
> 
> any reason to not use bpf_program__attach_kprobe_multi_ops() and
> instead use low-level bpf_link_create?
> 
> > +       ASSERT_OK(trigger_module_test_read(1), "trigger_read");
> > +       kprobe_multi_testmod_check(skel);
> > +
> > +cleanup:
> > +       if (link1_fd != -1)
> > +               close(link1_fd);
> > +       if (link2_fd != -1)
> > +               close(link2_fd);
> 
> you don't need to even do this if you stick to high-level attach APIs

ok, I guess we can use bpf_program__attach_kprobe_multi_opts here

> 
> > +       kprobe_multi__destroy(skel);
> > +}
> > +
> > +#define GET_ADDR(__sym, __addr) ({                                     \
> > +       __addr = ksym_get_addr(__sym);                                  \
> > +       if (!ASSERT_NEQ(__addr, 0, "kallsyms load failed for " #__sym)) \
> > +               return;                                                 \
> > +})
> 
> macro for this? why? just make understanding the code and debugging
> it, if necessary, harder. You don't even need that return, just lookup
> and ASSERT_NEQ(). Go to symbol #2 and do the same. If something goes
> wrong you'll have three failed ASSERT_NEQs, which is totally fine.

sure

SNIP

> > diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi.c b/tools/testing/selftests/bpf/progs/kprobe_multi.c
> > index 98c3399e15c0..b3c54ec13a45 100644
> > --- a/tools/testing/selftests/bpf/progs/kprobe_multi.c
> > +++ b/tools/testing/selftests/bpf/progs/kprobe_multi.c
> > @@ -110,3 +110,54 @@ int test_kretprobe_manual(struct pt_regs *ctx)
> >         kprobe_multi_check(ctx, true);
> >         return 0;
> >  }
> > +
> > +extern const void bpf_testmod_fentry_test1 __ksym;
> > +extern const void bpf_testmod_fentry_test2 __ksym;
> > +extern const void bpf_testmod_fentry_test3 __ksym;
> > +
> > +__u64 kprobe_testmod_test1_result = 0;
> > +__u64 kprobe_testmod_test2_result = 0;
> > +__u64 kprobe_testmod_test3_result = 0;
> > +
> > +__u64 kretprobe_testmod_test1_result = 0;
> > +__u64 kretprobe_testmod_test2_result = 0;
> > +__u64 kretprobe_testmod_test3_result = 0;
> > +
> > +static void kprobe_multi_testmod_check(void *ctx, bool is_return)
> > +{
> > +       if (bpf_get_current_pid_tgid() >> 32 != pid)
> > +               return;
> > +
> > +       __u64 addr = bpf_get_func_ip(ctx);
> > +
> > +#define SET(__var, __addr) ({                          \
> > +       if ((const void *) addr == __addr)              \
> > +               __var = 1;                              \
> > +})
> > +
> 
> same feedback, why macro for this? There is nothing repetitive done in it at all

ok, will change

thanks,
jirka