On 3/10/22 4:17 PM, Andrii Nakryiko wrote:
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.
Good point. Previously I did this 'i + 1 + j' and run the selftests and it works fine. And for preparing the final patch, I removed "+ 1" to simplify the code but didn't actually run the test which is not great.
Will fix in v2.
buf[0] = sigusr1_received ? '2' : '0'; ASSERT_EQ(sigusr1_received, 1, "sigusr1_received"); -- 2.30.2
