From: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Subject: include: drop pointless __compiler_offsetof indirection
(1) compiler_types.h is unconditionally included via an -include flag
(see scripts/Makefile.lib), and it defines __compiler_offsetof
unconditionally. So testing for definedness of __compiler_offsetof is
mostly pointless.
(2) Every relevant compiler provides __builtin_offsetof (even sparse
has had that for 14 years), and if for whatever reason one would end
up picking up the poor man's fallback definition (C file compiler with
completely custom CFLAGS?), newer clang versions won't treat the
result as an Integer Constant Expression, so if used in place where
such is required (static initializer or static_assert), one would get
errors like
t.c:11:16: error: static_assert expression is not an integral constant expression
t.c:11:16: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
t.c:4:33: note: expanded from macro 'offsetof'
#define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)
So just define offsetof unconditionally and directly in terms of
__builtin_offsetof.
Link: https://lkml.kernel.org/r/20220202102147.326672-1-linux@xxxxxxxxxxxxxxxxxx
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/compiler_types.h | 2 --
include/linux/stddef.h | 6 +-----
2 files changed, 1 insertion(+), 7 deletions(-)
--- a/include/linux/compiler_types.h~include-drop-pointless-__compiler_offsetof-indirection
+++ a/include/linux/compiler_types.h
@@ -138,8 +138,6 @@ struct ftrace_likely_data {
*/
#define __naked __attribute__((__naked__)) notrace
-#define __compiler_offsetof(a, b) __builtin_offsetof(a, b)
-
/*
* Prefer gnu_inline, so that extern inline functions do not emit an
* externally visible function. This makes extern inline behave as per gnu89
--- a/include/linux/stddef.h~include-drop-pointless-__compiler_offsetof-indirection
+++ a/include/linux/stddef.h
@@ -13,11 +13,7 @@ enum {
};
#undef offsetof
-#ifdef __compiler_offsetof
-#define offsetof(TYPE, MEMBER) __compiler_offsetof(TYPE, MEMBER)
-#else
-#define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)
-#endif
+#define offsetof(TYPE, MEMBER) __builtin_offsetof(TYPE, MEMBER)
/**
* sizeof_field() - Report the size of a struct field in bytes
_
