On Thu, Mar 10, 2022 at 4:05 PM Yonghong Song <yhs@xxxxxx> wrote: > > Building selftests/bpf with latest clang compiler (clang15 built > from source), I hit the following compilation error: > /.../prog_tests/send_signal.c:43:16: error: variable 'j' set but not used [-Werror,-Wunused-but-set-variable] > volatile int j = 0; > ^ > 1 error generated. > The problem also exists with clang13 and clang14. clang12 is okay. > > In send_signal.c, we have the following code > volatile int j = 0; > ... > for (int i = 0; i < 100000000 && !sigusr1_received; i++) > j /= i + 1; > to burn cpu cycles so bpf_send_signal() helper can be tested > in nmi mode. > > Slightly changing 'j /= i + 1' to 'j /= i + j' or 'j++' can > fix the problem. Further investigation indicated this should be > a clang bug ([1]). The upstream fix will be proposed later. But it is > a good idea to workaround the issue to unblock people who build > kernel/selftests with clang. > > [1] https://discourse.llvm.org/t/strange-clang-unused-but-set-variable-error-with-volatile-variables/60841 > > Signed-off-by: Yonghong Song <yhs@xxxxxx> > --- > tools/testing/selftests/bpf/prog_tests/send_signal.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/tools/testing/selftests/bpf/prog_tests/send_signal.c b/tools/testing/selftests/bpf/prog_tests/send_signal.c > index def50f1c5c31..05e303119151 100644 > --- a/tools/testing/selftests/bpf/prog_tests/send_signal.c > +++ b/tools/testing/selftests/bpf/prog_tests/send_signal.c > @@ -65,7 +65,7 @@ static void test_send_signal_common(struct perf_event_attr *attr, > > /* wait a little for signal handler */ > for (int i = 0; i < 100000000 && !sigusr1_received; i++) > - j /= i + 1; > + j /= i + j; `+ 1` was there to avoid division by zero. Let's make it `i + j + 1` then. > > buf[0] = sigusr1_received ? '2' : '0'; > ASSERT_EQ(sigusr1_received, 1, "sigusr1_received"); > -- > 2.30.2 >
