linux-kernel - [PATCH] test_bpf: Fix a new clang warning about xor-ing two numbers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20190819043419.68223-1-natechancellor@gmail.com>
Date:   Sun, 18 Aug 2019 21:34:20 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        Yonghong Song <yhs@...com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] test_bpf: Fix a new clang warning about xor-ing two numbers

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@...il.com>
---

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",
-- 
2.23.0