linux-kernel - Re: [RFC][PATCH] rcu: Use typeof(p) instead of typeof(*p) *

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Message-ID: <CAHk-=whFhTofNk5G6dYFoFJC10EKzGdZVQdQygXHXWm_jodwBQ@mail.gmail.com>
Date:   Tue, 5 Oct 2021 14:27:49 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jan Engelhardt <jengelh@...i.de>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Paul <paulmck@...ux.vnet.ibm.com>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        "Joel Fernandes, Google" <joel@...lfernandes.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>, rcu <rcu@...r.kernel.org>,
        netfilter-devel <netfilter-devel@...r.kernel.org>,
        coreteam <coreteam@...filter.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [RFC][PATCH] rcu: Use typeof(p) instead of typeof(*p) *

On Tue, Oct 5, 2021 at 2:09 PM Jan Engelhardt <jengelh@...i.de> wrote:
>
> Illegal.
> https://en.cppreference.com/w/c/language/conversion
> subsection "Pointer conversion"
> "No other guarantees are offered"

Well, we happily end up casting pointers to 'unsigned long' and back,
and doing bit games on the low bits of a pointer value.

So it's not like the kernel deeply cares about theoretical portability.

But I do discourage casting when not required, just because as much
static type checking we can possibly have is good when we can do it.

              Linus