Re: [PATCH bpf-next 2/2] selftests: bpf: Add a new test for bare tracepoints

[Andrii Nakryiko]

On Mon, Jan 11, 2021 at 10:20 AM Qais Yousef <qais.yousef@xxxxxxx> wrote:
>
> Reuse module_attach infrastructure to add a new bare tracepoint to check
> we can attach to it as a raw tracepoint.
>
> Signed-off-by: Qais Yousef <qais.yousef@xxxxxxx>
> ---
>
> Andrii
>
> I was getting the error below when I was trying to run the test.
> I had to comment out all related fentry* code to be able to test the raw_tp
> stuff. Not sure something I've done wrong or it's broken for some reason.
> I was on v5.11-rc2.

Check that you have all the required Kconfig options from
tools/testing/selftests/bpf/config. And also you will need to build
pahole from master, 1.19 doesn't have some fixes that add kernel
module support. I think pahole is the reasons why you have the failure
below.

>
>         $ sudo ./test_progs -v -t module_attach

use -vv when debugging stuff like that with test_progs, it will output
libbpf detailed logs, that often are very helpful

>         bpf_testmod.ko is already unloaded.
>         Loading bpf_testmod.ko...
>         Successfully loaded bpf_testmod.ko.
>         test_module_attach:PASS:skel_open 0 nsec
>         test_module_attach:PASS:set_attach_target 0 nsec
>         test_module_attach:PASS:skel_load 0 nsec
>         libbpf: prog 'handle_fentry': failed to attach: ERROR: strerror_r(-524)=22
>         libbpf: failed to auto-attach program 'handle_fentry': -524
>         test_module_attach:FAIL:skel_attach skeleton attach failed: -524
>         #58 module_attach:FAIL
>         Successfully unloaded bpf_testmod.ko.
>         Summary: 0/0 PASSED, 0 SKIPPED, 1 FAILED
>

But even apart from test failure, there seems to be kernel build
failure. See [0] for what fails in kernel-patches CI.

   [0] https://travis-ci.com/github/kernel-patches/bpf/builds/212730017


>
>  .../selftests/bpf/bpf_testmod/bpf_testmod-events.h     |  6 ++++++
>  tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c  |  2 ++
>  tools/testing/selftests/bpf/prog_tests/module_attach.c |  1 +
>  tools/testing/selftests/bpf/progs/test_module_attach.c | 10 ++++++++++
>  4 files changed, 19 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
> index b83ea448bc79..e1ada753f10c 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
> @@ -28,6 +28,12 @@ TRACE_EVENT(bpf_testmod_test_read,
>                   __entry->pid, __entry->comm, __entry->off, __entry->len)
>  );
>
> +/* A bare tracepoint with no event associated with it */
> +DECLARE_TRACE(bpf_testmod_test_read_bare,
> +       TP_PROTO(struct task_struct *task, struct bpf_testmod_test_read_ctx *ctx),
> +       TP_ARGS(task, ctx)
> +);
> +
>  #endif /* _BPF_TESTMOD_EVENTS_H */
>
>  #undef TRACE_INCLUDE_PATH
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> index 2df19d73ca49..d63cebdaca44 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> @@ -22,6 +22,8 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
>         };
>
>         trace_bpf_testmod_test_read(current, &ctx);
> +       ctx.len++;
> +       trace_bpf_testmod_test_read_bare(current, &ctx);

It's kind of boring to have two read tracepoints :) Do you mind adding
a write tracepoint and use bare tracepoint there? You won't need this
ctx.len++ hack as well. Feel free to add identical
bpf_testmod_test_write_ctx (renaming it is more of a pain).

>
>         return -EIO; /* always fail */
>  }
> diff --git a/tools/testing/selftests/bpf/prog_tests/module_attach.c b/tools/testing/selftests/bpf/prog_tests/module_attach.c
> index 50796b651f72..7085a118f38c 100644
> --- a/tools/testing/selftests/bpf/prog_tests/module_attach.c
> +++ b/tools/testing/selftests/bpf/prog_tests/module_attach.c
> @@ -50,6 +50,7 @@ void test_module_attach(void)
>         ASSERT_OK(trigger_module_test_read(READ_SZ), "trigger_read");
>
>         ASSERT_EQ(bss->raw_tp_read_sz, READ_SZ, "raw_tp");
> +       ASSERT_EQ(bss->raw_tp_bare_read_sz, READ_SZ+1, "raw_tp_bare");
>         ASSERT_EQ(bss->tp_btf_read_sz, READ_SZ, "tp_btf");
>         ASSERT_EQ(bss->fentry_read_sz, READ_SZ, "fentry");
>         ASSERT_EQ(bss->fentry_manual_read_sz, READ_SZ, "fentry_manual");
> diff --git a/tools/testing/selftests/bpf/progs/test_module_attach.c b/tools/testing/selftests/bpf/progs/test_module_attach.c
> index efd1e287ac17..08aa157afa1d 100644
> --- a/tools/testing/selftests/bpf/progs/test_module_attach.c
> +++ b/tools/testing/selftests/bpf/progs/test_module_attach.c
> @@ -17,6 +17,16 @@ int BPF_PROG(handle_raw_tp,
>         return 0;
>  }
>
> +__u32 raw_tp_bare_read_sz = 0;
> +
> +SEC("raw_tp/bpf_testmod_test_read_bare")
> +int BPF_PROG(handle_raw_tp_bare,
> +            struct task_struct *task, struct bpf_testmod_test_read_ctx *read_ctx)
> +{
> +       raw_tp_bare_read_sz = BPF_CORE_READ(read_ctx, len);
> +       return 0;
> +}
> +
>  __u32 tp_btf_read_sz = 0;
>
>  SEC("tp_btf/bpf_testmod_test_read")
> --
> 2.25.1
>