On Tue, Jun 30, 2020 at 1:47 PM Hao Luo haoluo@google.com wrote:
The test_vmlinux test uses hrtimer_nanosleep as hook to test tracing programs. But it seems Clang may have done an aggressive optimization, causing fentry and kprobe to not hook on this function properly on a Clang build kernel.
A possible fix is switching to use a more reliable function, e.g. the ones exported to kernel modules such as hrtimer_range_start_ns. After we switch to using hrtimer_range_start_ns, the test passes again even on a clang build kernel.
Tested: In a clang build kernel, the test fail even when the flags {fentry, kprobe}_called are set unconditionally in handle__kprobe() and handle__fentry(), which implies the programs do not hook on hrtimer_nanosleep() properly. This could be because clang's code transformation is too aggressive.
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 we switch 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@google.com
Took me a bit of jumping around to find how it is related to nanosleep call :) But seems like it's unconditionally called, so should be fine.
Acked-by: Andrii Nakryiko andriin@fb.com
tools/testing/selftests/bpf/progs/test_vmlinux.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)
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