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

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Date:   Wed, 6 Oct 2021 00:26:45 +0200 (CEST)
From:   Jan Engelhardt <jengelh@...i.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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 Tuesday 2021-10-05 23:27, Linus Torvalds wrote:
>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,

Yes, that wiki had only a succinct summary of pointer-pointer conversions.
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf section 6.3.2.3
(pdfpage 59) has the details, including pointer-integer conversions.

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

All things considered, that's good enough.
Needless to say, how many times has the compiler changed and then
someone complaind and someone else replied "standard told you so". ;-)