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From:   Song Liu <songliubraving@fb.com>
To:     Andrii Nakryiko <andrii.nakryiko@gmail.com>
CC:     Ian Rogers <irogers@google.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin Lau <kafai@fb.com>, "Yonghong Song" <yhs@fb.com>,
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        John Fastabend <john.fastabend@gmail.com>,
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        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] libbpf hashmap: Fix undefined behavior in hash_bits
Thread-Topic: [PATCH v2] libbpf hashmap: Fix undefined behavior in hash_bits
Thread-Index: AQHWrkQcbGvCsMR2DkaqEAjiMgI9kamvLAUAgAAFQYA=
Date:   Thu, 29 Oct 2020 22:57:42 +0000
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> On Oct 29, 2020, at 3:38 PM, Andrii Nakryiko <andrii.nakryiko@gmail.com> =
wrote:
>=20
> On Thu, Oct 29, 2020 at 3:38 PM Ian Rogers <irogers@google.com> wrote:
>>=20
>> 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 and guarding calls to
>> hash_bits for empty maps in hashmap__for_each_key_entry and
>> hashmap__for_each_entry_safe.
>>=20
>> Suggested-by: Andrii Nakryiko <andriin@fb.com>,
>> Signed-off-by: Ian Rogers <irogers@google.com>
>> ---
>=20
> Looks good. Thanks and sorry for unnecessary iterations.
>=20
> Acked-by: Andrii Nakryiko <andrii@kernel.org>

Acked-by: Song Liu <songliubraving@fb.com>=