Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220603041701.2799595-1-irogers@google.com> <20220619171248.GC3362@bug>
In-Reply-To: <20220619171248.GC3362@bug>
From:   Zvi Effron <zeffron@riotgames.com>
Date:   Tue, 21 Jun 2022 18:03:27 -0500
Message-ID: <CAC1LvL0rZcEHe_ZHDcB38XD49FmdURg4+yKHP0O=J7=4Xx8M3Q@mail.gmail.com>
Subject: Re: [PATCH] libbpf: Fix is_pow_of_2
To:     Pavel Machek <pavel@ucw.cz>
Cc:     Ian Rogers <irogers@google.com>,
        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,
        Yuze Chi <chiyuze@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Sun, Jun 19, 2022 at 12:13 PM Pavel Machek <pavel@ucw.cz> wrote:
>
> Hi!
>
> > From: Yuze Chi <chiyuze@google.com>
> >
> > +++ 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));
> > }
>
> I'm pretty sure we have this test in macro in includes somewhere... should we use
> that instead?

I went looking for a macro that provided this check and could not find one. I
did find the inlined static function is_power_of_2 in log2.h, though, that we
could use.

> Pavel
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html