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

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Message-Id: <20241203-is_constexpr-refactor-v1-1-4e4cbaecc216@wanadoo.fr>
Date: Tue, 03 Dec 2024 02:33:23 +0900
From: Vincent Mailhol via B4 Relay <devnull+mailhol.vincent.wanadoo.fr@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>, 
 David Laight <David.Laight@...lab.com>, 
 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>
Cc: linux-sparse@...r.kernel.org, linux-kernel@...r.kernel.org, 
 llvm@...ts.linux.dev, linux-hardening@...r.kernel.org, 
 intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, 
 coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org, 
 Vincent Mailhol <mailhol.vincent@...adoo.fr>
Subject: [PATCH 01/10] compiler.h: add statically_false()

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.

The == operator is used instead of the ! negation to prevent a
-Wint-in-bool-context compiler warning when the argument is not a
boolean. For example:

  statically_false(var * 0)

Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
---
 include/linux/compiler.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 469a64dd6495fefab2c85ffc279568a657b72660..a2a56a50dd85227a4fdc62236a2710ca37c5ba52 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -314,6 +314,7 @@ static inline void *offset_to_ptr(const int *off)
  * values to determine that the condition is statically true.
  */
 #define statically_true(x) (__builtin_constant_p(x) && (x))
+#define statically_false(x) (__builtin_constant_p(x) && (x) == 0)

 /*
  * This is needed in functions which generate the stack canary, see

-- 
2.45.2