Re: [PATCH bpf-next v2] selftests/bpf: Switch test_vmlinux to use hrtimer_range_start_ns.

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On 7/1/20 10:53 AM, Hao Luo wrote:
The test_vmlinux test uses hrtimer_nanosleep as hook to test tracing
programs. But in a kernel built by clang, which performs more aggresive
inlining, that function gets inlined into its caller SyS_nanosleep.
Therefore, even though fentry and kprobe do hook on the function,
they aren't triggered by the call to nanosleep in the test.

A possible fix is switching to use a function that is less likely to
be inlined, such as hrtimer_range_start_ns. The EXPORT_SYMBOL functions
shouldn't be inlined based on the description of [1], therefore safe
to use for this test. Also the arguments of this function include the
duration of sleep, therefore suitable for test verification.

[1] af3b56289be1 time: don't inline EXPORT_SYMBOL functions

Tested:
  In a clang build kernel, before this change, the test fails:

  test_vmlinux:PASS:skel_open 0 nsec
  test_vmlinux:PASS:skel_attach 0 nsec
  test_vmlinux:PASS:tp 0 nsec
  test_vmlinux:PASS:raw_tp 0 nsec
  test_vmlinux:PASS:tp_btf 0 nsec
  test_vmlinux:FAIL:kprobe not called
  test_vmlinux:FAIL:fentry not called

  After switching to hrtimer_range_start_ns, the test passes:

  test_vmlinux:PASS:skel_open 0 nsec
  test_vmlinux:PASS:skel_attach 0 nsec
  test_vmlinux:PASS:tp 0 nsec
  test_vmlinux:PASS:raw_tp 0 nsec
  test_vmlinux:PASS:tp_btf 0 nsec
  test_vmlinux:PASS:kprobe 0 nsec
  test_vmlinux:PASS:fentry 0 nsec

Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx>
Acked-by: Andrii Nakryiko <andriin@xxxxxx>

Thanks!
Acked-by: Yonghong Song <yhs@xxxxxx>



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