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@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-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/compiler_types.h b/include/linux/compiler_types.h
index 4b3915ce38a4d04a12231e99db280c0051ba157d..232dbd97f8b1ec3bd08f22a7641a3087fefb31a5 100644 (file)
--- a/include/linux/compiler_types.h
+++ b/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

diff --git a/include/linux/stddef.h b/include/linux/stddef.h
index ca507bd5f80824000306b6bfa186097cb7703a39..929d67710cc51e5fd5efe5e012ea2e13eb4dadcd 100644 (file)
--- a/include/linux/stddef.h
+++ b/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