linux-kernel - Re: [PATCH 01/10] compiler.h: add statically

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Message-ID: <CAMZ6Rq+n0vG9zObF-kY-Xo+iP_Y3P8A6_nEfB8F=UhqeQBepRw@mail.gmail.com>
Date: Fri, 6 Dec 2024 00:25:34 +0900
From: Vincent Mailhol <mailhol.vincent@...adoo.fr>
To: David Laight <David.Laight@...lab.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, 
	Luc Van Oostenryck <luc.vanoostenryck@...il.com>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Yury Norov <yury.norov@...il.com>, 
	Rasmus Villemoes <linux@...musvillemoes.dk>, Kees Cook <kees@...nel.org>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Jani Nikula <jani.nikula@...ux.intel.com>, 
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>, 
	Tvrtko Ursulin <tursulin@...ulin.net>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Suzuki K Poulose <suzuki.poulose@....com>, 
	Mike Leach <mike.leach@...aro.org>, James Clark <james.clark@...aro.org>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Rikard Falkeborn <rikard.falkeborn@...il.com>, 
	Martin Uecker <Martin.Uecker@....uni-goettingen.de>, 
	"linux-sparse@...r.kernel.org" <linux-sparse@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"llvm@...ts.linux.dev" <llvm@...ts.linux.dev>, 
	"linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>, 
	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>, 
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, 
	"coresight@...ts.linaro.org" <coresight@...ts.linaro.org>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 01/10] compiler.h: add statically_false()

On Thu. 5 Dec 2024 at 03:30, David Laight <David.Laight@...lab.com> wrote:
> From: Vincent Mailhol
> > Sent: 02 December 2024 17:33
> >
> > From: Vincent Mailhol <mailhol.vincent@...adoo.fr>
> >
> > For completion, add statically_false() which is the equivalent of
> > statically_true() except that it will return true only if the input is
> > known to be false at compile time.
>
> This is pretty much pointless.
> It is just as easy to invert the condition at the call site.

To start with, I will argue that:

  statically_false(foo)

is more pretty than

  statically_true(!(foo))

In addition, the simple negation !(foo) only works if foo is a
boolean. If it is an integer, you would get the -Wint-in-bool-context
warning. Thus you would have to write:

  statically_true((foo) == 0)

Anyone using this in a global header basically does not know what type
of argument they are getting. So, the (foo) == 0 trick is a must. But
because it is ugly, better to encapsulate it once for all. The
statically_false() is just cleaner and less error prone.

That said, I am not strongly opposed to removing statically_false(),
but in that case, I would also remove is_const_false(). For me, these
come as a pair, either we have both or we have none. Only having one
of these looked unbalanced.


Yours sincerely,
Vincent Mailhol