From: Peter Zijlstra <peterz@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Joe Perches <joe@perches.com>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Andy Whitcroft <apw@canonical.com>,
yuankuiz@codeaurora.org, Linux PM <linux-pm@vger.kernel.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Frederic Weisbecker <fweisbec@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
paulmck@linux.vnet.ibm.com, Ingo Molnar <mingo@kernel.org>,
Len Brown <len.brown@intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] checkpatch: Add a --strict test for structs with bool member definitions
Date: Wed, 11 Apr 2018 10:15:02 +0200 [thread overview]
Message-ID: <20180411081502.GJ4082@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180410150011.df9e036f57b5bcac7ac19686@linux-foundation.org>
On Tue, Apr 10, 2018 at 03:00:11PM -0700, Andrew Morton wrote:
> On Tue, 10 Apr 2018 14:53:51 -0700 Joe Perches <joe@perches.com> wrote:
>
> > On Tue, 2018-04-10 at 14:39 -0700, Andrew Morton wrote:
> > > On Tue, 10 Apr 2018 11:19:54 -0700 Joe Perches <joe@perches.com> wrote:
> > >
> > > > A struct with a bool member can have different sizes on various
> > > > architectures because neither bool size nor alignment is standardized.
> > >
> > > What's wrong with bools in structs?
> >
> > See above.
>
> Yeah, but so what? `long' has different sizes on different
> architectures too.
Right, so we have ILP32/LP64 for all our 32/64 bit archs respectively.
So only 2 possible variations to consider, and if you know your bitness
you know your layout.
(+- some really unfortunate alignment exceptions, the worst of which
Arnd recently removed, hooray!)
But neither says anything about sizeof(_Bool), and the standard leaves
it undefined and only mandates it is large enough to store either 0 or
1 (and I suspect this vagueness is because there are architectures that
either have no byte addressibility or it's more expensive than word
addressibility).
Typically GCC chooses a single byte to represent _Bool, but there are no
guarantees. This means that when you care about structure layout (as we
all really should) things go wobbly when you use _Bool.
If GCC were to guarantee a 1 byte _Bool for all Linux ABIs we could
reconsider.
next prev parent reply other threads:[~2018-04-11 8:15 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-10 7:33 Subject: [PATCH] [PATCH] time: tick-sched: use bool for tick_stopped yuankuiz
2018-04-10 7:45 ` yuankuiz
2018-04-10 8:51 ` yuankuiz
2018-04-10 8:54 ` yuankuiz
2018-04-10 7:55 ` Subject: [PATCH] " Thomas Gleixner
2018-04-10 8:12 ` yuankuiz
2018-04-10 8:00 ` Rafael J. Wysocki
2018-04-10 8:15 ` yuankuiz
2018-04-10 9:10 ` Thomas Gleixner
2018-04-10 10:07 ` yuankuiz
2018-04-10 11:06 ` Thomas Gleixner
2018-04-10 14:08 ` yuankuiz
2018-04-10 14:49 ` yuankuiz
2018-04-10 23:09 ` yuankuiz
2018-04-10 23:20 ` yuankuiz
2018-04-20 1:47 ` yuankuiz
2018-04-20 6:44 ` yuankuiz
2018-04-20 19:24 ` Joe Perches
2018-04-25 7:01 ` yuankuiz
2018-04-10 11:26 ` Peter Zijlstra
2018-04-10 12:07 ` Thomas Gleixner
2018-04-10 12:26 ` Peter Zijlstra
2018-04-10 12:33 ` Subject: [PATCH] " Peter Zijlstra
2018-04-10 15:14 ` Joe Perches
2018-04-10 16:30 ` Peter Zijlstra
2018-04-10 15:41 ` [PATCH] checkpatch: whinge about bool bitfields Joe Perches
2018-04-10 18:19 ` [PATCH] checkpatch: Add a --strict test for structs with bool member definitions Joe Perches
2018-04-10 21:39 ` Andrew Morton
2018-04-10 21:53 ` Joe Perches
2018-04-10 22:00 ` Andrew Morton
2018-04-11 8:15 ` Peter Zijlstra [this message]
2018-04-11 16:29 ` Andrew Morton
2018-04-11 16:51 ` Joe Perches
2018-04-12 6:22 ` Julia Lawall
2018-04-12 6:42 ` Joe Perches
2018-04-12 7:03 ` Julia Lawall
2018-04-12 8:13 ` Peter Zijlstra
2018-04-14 21:19 ` Julia Lawall
2018-04-17 9:07 ` yuankuiz
2018-04-18 18:38 ` Joe Perches
2018-04-19 4:40 ` Julia Lawall
2018-04-19 4:51 ` Joe Perches
2018-04-19 5:16 ` Julia Lawall
2018-04-19 6:48 ` yuankuiz
2018-04-19 10:42 ` yuankuiz
2018-04-20 1:31 ` yuankuiz
2018-04-11 17:00 ` Peter Zijlstra
2018-04-12 7:47 ` Ingo Molnar
2018-04-12 8:11 ` Peter Zijlstra
2018-04-12 9:35 ` Andrea Parri
2018-04-12 11:50 ` Peter Zijlstra
2018-04-12 12:01 ` Joe Perches
2018-04-12 12:08 ` Peter Zijlstra
2018-04-12 12:38 ` Joe Perches
2018-04-12 16:47 ` Andrew Morton
2018-04-12 11:52 ` Kalle Valo
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