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

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Message-ID: <srqsppq-p657-43qq-np31-pq5pp03271r6@vanv.qr>
Date:   Tue, 5 Oct 2021 21:06:36 +0200 (CEST)
From:   Jan Engelhardt <jengelh@...i.de>
To:     Steven Rostedt <rostedt@...dmis.org>
cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.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 20:40, Steven Rostedt wrote:
>> 
>> >>>> typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p);  
>> 
>> #define static_cast(type, expr) ((struct { type x; }){(expr)}.x)
>> typeof(p) p1 = (typeof(p) __force)static_cast(void *, READ_ONCE(p));
>> 
>> Let the name not fool you; it's absolutely _not_ the same as C++'s 
>> static_cast, but still: it does emit a warning when you do pass an 
>> integer, which is better than no warning at all in that case.
>> 
>>  *flies away*
>
>Are you suggesting I should continue this exercise ;-)

“After all, why not?”

typeof(p) p1 = (typeof(p) __force)READ_ONCE(p) +
               BUILD_BUG_ON_EXPR(__builtin_classify_type(p) != 5);