linux-kernel - Re: Subject: [PATCH] [PATCH] time: tick-sched: use bool for tick

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Date:   Tue, 10 Apr 2018 18:30:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joe Perches <joe@...ches.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>, yuankuiz@...eaurora.org,
        Linux PM <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        aulmck@...ux.vnet.ibm.com, Ingo Molnar <mingo@...nel.org>,
        Len Brown <len.brown@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        apw@...onical.com
Subject: Re: Subject: [PATCH] [PATCH] time: tick-sched: use bool for
 tick_stopped

On Tue, Apr 10, 2018 at 08:14:54AM -0700, Joe Perches wrote:
> Whinging about bool <foo> : <x> seems entirely sensible
> and straightforward to do.
> 
> I'm not so sure about bool in structs as a patch context
> could be adding a bool to local stack definitions and
> there's no real ability to determine if the bool is in a
> struct or on the stack.
> 
> Also, I think there's nothing really wrong with using
> bool in structs.  Steven Rostedt's rationale in
> https://lkml.org/lkml/2017/11/21/207 isn't really right
> as sizeof(int) is 4 not 1 and sizeof(bool) is 1 on arches
> without alignment issues.  I believe when using gcc,
> sizeof(bool) is always 1 and there may be alignment padding
> added on some arches.  Dunno.

C std simply does not define sizeof(_Bool) and leaves it up to
architecture ABI, therefore I refuse to use _Bool in composite types,
because I care about layout.

Also, not all architectures can do byte addressing, see Alpha <EV56
and for those _Bool would have to be a whole word (the existence of such
architectures likely influenced the vague definition of _Bool in the
first place).

> But I think the battle is already lost anyway.
> 
> git grep -P  '(?<!static|extern)\s+bool\s+\w+\s*;' include | wc -l
> 1543

Yes I know, doesn't mean we shouldn't discourage it for new code; also Linus.