[PATCH] libbpf hashmap: fix undefined behavior in hash_bits

[Ian Rogers]

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@xxxxxxxxxx>
---
 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