From e1edc277e6f6dfb372216522dfc57f9381c39e35 Mon Sep 17 00:00:00 2001
From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Date: Mon, 8 Nov 2021 18:32:46 -0800
Subject: [PATCH] linux/container_of.h: switch to static_assert
_Static_assert() is evaluated already in the compiler's frontend, and
gives a somehat more to-the-point error, compared to the BUILD_BUG_ON
macro, which only fires after the optimizer has had a chance to
eliminate calls to functions marked with __attribute__((error)). In
theory, this might make builds a tiny bit faster.
There's also a little less gunk in the error message emitted:
lib/sort.c: In function `foo':
include/linux/build_bug.h:78:41: error: static assertion failed: "pointer type mismatch in container_of()"
78 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
compared to
lib/sort.c: In function `foo':
include/linux/compiler_types.h:322:38: error: call to `__compiletime_assert_2' declared with attribute error: pointer type mismatch in container_of()
322 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
While at it, fix the copy-pasto in container_of_safe().
Link: https://lkml.kernel.org/r/20211015090530.2774079-1-linux@rasmusvillemoes.dk
Link: https://lore.kernel.org/lkml/20211014132331.GA4811@kernel.org/T/
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
include/linux/container_of.h | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/include/linux/container_of.h b/include/linux/container_of.h
index dd56019838c67..2f4944b791b81 100644
--- a/include/linux/container_of.h
+++ b/include/linux/container_of.h
@@ -16,9 +16,9 @@
*/
#define container_of(ptr, type, member) ({ \
void *__mptr = (void *)(ptr); \
- BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
- !__same_type(*(ptr), void), \
- "pointer type mismatch in container_of()"); \
+ static_assert(__same_type(*(ptr), ((type *)0)->member) || \
+ __same_type(*(ptr), void), \
+ "pointer type mismatch in container_of()"); \
((type *)(__mptr - offsetof(type, member))); })
/**
@@ -31,9 +31,9 @@
*/
#define container_of_safe(ptr, type, member) ({ \
void *__mptr = (void *)(ptr); \
- BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
- !__same_type(*(ptr), void), \
- "pointer type mismatch in container_of()"); \
+ static_assert(__same_type(*(ptr), ((type *)0)->member) || \
+ __same_type(*(ptr), void), \
+ "pointer type mismatch in container_of_safe()"); \
IS_ERR_OR_NULL(__mptr) ? ERR_CAST(__mptr) : \
((type *)(__mptr - offsetof(type, member))); })
--
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