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selftests/bpf: fix a clang compilation error for send_signal.c #2694

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selftests/bpf: fix a clang compilation error for send_signal.c #2694

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Commits on Mar 11, 2022

  1. adding ci files

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  2. selftests/bpf: fix a clang compilation error for send_signal.c 

    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 + 1' 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@fb.com>
    @yonghong-song
    yonghong-song authored and Nobody committed Mar 11, 2022
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