Messages in this thread Patch in this message | | | Subject | Re: [PATCH bpf-next] selftests/bpf: Switch test_vmlinux to use hrtimer_range_start_ns. | From | Yonghong Song <> | Date | Tue, 30 Jun 2020 13:36:57 -0700 |
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On 6/30/20 11:49 AM, Hao Luo 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.
Could you explain why it does not on clang built kernel? How did you build the kernel? Did you use [thin]lto?
hrtimer_nanosleep is a global function who is called in several different files. I am curious how clang optimization can make function disappear, or make its function signature change, or rename the function?
> > 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> > --- > tools/testing/selftests/bpf/progs/test_vmlinux.c | 16 ++++++++-------- > 1 file changed, 8 insertions(+), 8 deletions(-) > > diff --git a/tools/testing/selftests/bpf/progs/test_vmlinux.c b/tools/testing/selftests/bpf/progs/test_vmlinux.c > index 5611b564d3b1..29fa09d6a6c6 100644 > --- a/tools/testing/selftests/bpf/progs/test_vmlinux.c > +++ b/tools/testing/selftests/bpf/progs/test_vmlinux.c > @@ -63,20 +63,20 @@ int BPF_PROG(handle__tp_btf, struct pt_regs *regs, long id) > return 0; > } > > -SEC("kprobe/hrtimer_nanosleep") > -int BPF_KPROBE(handle__kprobe, > - ktime_t rqtp, enum hrtimer_mode mode, clockid_t clockid) > +SEC("kprobe/hrtimer_start_range_ns") > +int BPF_KPROBE(handle__kprobe, struct hrtimer *timer, ktime_t tim, u64 delta_ns, > + const enum hrtimer_mode mode) > { > - if (rqtp == MY_TV_NSEC) > + if (tim == MY_TV_NSEC) > kprobe_called = true; > return 0; > } > > -SEC("fentry/hrtimer_nanosleep") > -int BPF_PROG(handle__fentry, > - ktime_t rqtp, enum hrtimer_mode mode, clockid_t clockid) > +SEC("fentry/hrtimer_start_range_ns") > +int BPF_PROG(handle__fentry, struct hrtimer *timer, ktime_t tim, u64 delta_ns, > + const enum hrtimer_mode mode) > { > - if (rqtp == MY_TV_NSEC) > + if (tim == MY_TV_NSEC) > fentry_called = true; > return 0; > } >
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