On 8/18/19 9:34 PM, Nathan Chancellor wrote:
> r369217 in clang added a new warning about potential misuse of the xor
> operator as an exponentiation operator:
>
> ../lib/test_bpf.c:870:13: warning: result of '10 ^ 300' is 294; did you
> mean '1e300'? [-Wxor-used-as-pow]
> { { 4, 10 ^ 300 }, { 20, 10 ^ 300 } },
> ~~~^~~~~
> 1e300
> ../lib/test_bpf.c:870:13: note: replace expression with '0xA ^ 300' to
> silence this warning
> ../lib/test_bpf.c:870:31: warning: result of '10 ^ 300' is 294; did you
> mean '1e300'? [-Wxor-used-as-pow]
> { { 4, 10 ^ 300 }, { 20, 10 ^ 300 } },
> ~~~^~~~~
> 1e300
> ../lib/test_bpf.c:870:31: note: replace expression with '0xA ^ 300' to
> silence this warning
>
> The commit link for this new warning has some good logic behind wanting
> to add it but this instance appears to be a false positive. Adopt its
> suggestion to silence the warning but not change the code. According to
> the differential review link in the clang commit, GCC may eventually
> adopt this warning as well.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/643
> Link: https://github.com/llvm/llvm-project/commit/920890e26812f808a74c60ebc14cc636dac661c1
> Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Verified that latest trunk clang indeed has this warning, and below
change indeed fixed the warning in the correct way.
Acked-by: Yonghong Song <yhs@xxxxxx>
> ---
>
> I highly doubt that 1e300 was intented but if it was (or something else
> was), please let me know. Commit history wasn't entirely clear on why
> this expression was used over just a raw number.
>
> lib/test_bpf.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/test_bpf.c b/lib/test_bpf.c
> index c41705835cba..5ef3eccee27c 100644
> --- a/lib/test_bpf.c
> +++ b/lib/test_bpf.c
> @@ -867,7 +867,7 @@ static struct bpf_test tests[] = {
> },
> CLASSIC,
> { },
> - { { 4, 10 ^ 300 }, { 20, 10 ^ 300 } },
> + { { 4, 0xA ^ 300 }, { 20, 0xA ^ 300 } },
> },
> {
> "SPILL_FILL",
>
