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Date: Thu, 7 May 2020 23:39:54 -0700 From: Ian Rogers <irogers@...gle.com> To: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, Andrii Nakryiko <andriin@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...omium.org>, netdev@...r.kernel.org, bpf@...r.kernel.org, linux-kernel@...r.kernel.org Cc: Ian Rogers <irogers@...gle.com> Subject: [PATCH] libbpf hashmap: fix undefined behavior in hash_bits If bits is 0, the case when the map is empty, then the >> is the size of the register which is undefined behavior - on x86 it is the same as a shift by 0. Fix by handling the 0 case explicitly. Signed-off-by: Ian Rogers <irogers@...gle.com> --- tools/lib/bpf/hashmap.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h index d5ef212a55ba..781db653d16c 100644 --- a/tools/lib/bpf/hashmap.h +++ b/tools/lib/bpf/hashmap.h @@ -19,6 +19,8 @@ static inline size_t hash_bits(size_t h, int bits) { /* shuffle bits and return requested number of upper bits */ + if (bits == 0) + return 0; return (h * 11400714819323198485llu) >> (__WORDSIZE - bits); } -- 2.26.2.645.ge9eca65c58-goog
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