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Date:   Thu,  2 Jun 2022 21:17:01 -0700
Message-Id: <20220603041701.2799595-1-irogers@google.com>
Mime-Version: 1.0
Subject: [PATCH] libbpf: Fix is_pow_of_2
From:   Ian Rogers <irogers@google.com>
To:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>, netdev@vger.kernel.org,
        bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Yuze Chi <chiyuze@google.com>, Ian Rogers <irogers@google.com>
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From: Yuze Chi <chiyuze@google.com>

There is a missing not. Consider a power of 2 number like 4096:

x && (x & (x - 1))
4096 && (4096 & (4096 - 1))
4096 && (4096 & 4095)
4096 && 0
0

with the not this is:
x && !(x & (x - 1))
4096 && !(4096 & (4096 - 1))
4096 && !(4096 & 4095)
4096 && !0
4096 && 1
1

Reported-by: Yuze Chi <chiyuze@google.com>
Signed-off-by: Yuze Chi <chiyuze@google.com>
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/lib/bpf/libbpf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 3f4f18684bd3..fd0414ea00df 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4956,7 +4956,7 @@ static void bpf_map__destroy(struct bpf_map *map);
 
 static bool is_pow_of_2(size_t x)
 {
-	return x && (x & (x - 1));
+	return x && !(x & (x - 1));
 }
 
 static size_t adjust_ringbuf_sz(size_t sz)
-- 
2.36.1.255.ge46751e96f-goog