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>

diff --git a/include/linux/container_of.h b/include/linux/container_of.h
index dd56019838c67cdc5adef2b87bbcaad3dd2ff8e6..2f4944b791b814b8c43a8fcc153fc8b52b48ff91 100644 (file)
--- 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))); })