linux-kernel - Re: [PATCH bpf-next v2 0/5] cleanup for data casting

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Message-ID: <df76c412-d9e4-b89d-1bd3-eefb50280f57@gmail.com>
Date:   Tue, 19 Jul 2022 14:48:22 +0100
From:   Edward Cree <ecree.xilinx@...il.com>
To:     Pu Lehui <pulehui@...wei.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 0/5] cleanup for data casting

>> On Mon, Jul 18, 2022 at 5:59 AM Pu Lehui <pulehui@...wei.com> wrote:
>>> Previously, we found that memory address casting in libbpf
>>> was not appropriate [0]. Memory addresses are conceptually
>>> unsigned, (unsigned long) casting makes more sense. With the
>>> suggestion of Daniel, we applied this cleanup to the entire
>>> bpf, and there is no functional change.
Fwiw, pointers in C aren't necessarily unsigned; some versions of
 gcc have treated them as signed and — if no object can straddle
 the sign boundary — it's even allowed by the standard. [1]
(And at a hardware level, a memory address is just a pattern of
 bits on an address bus, which isn't arithmetic at all.)

-ed

[1]: https://yarchive.net/comp/linux/signed_pointers.html