+ include-drop-pointless-__compiler_offsetof-indirection.patch added to -mm tree

+ include-drop-pointless-__compiler_offsetof-indirection.patch added to -mm tree

[Andrew Morton]

The patch titled
     Subject: include: drop pointless __compiler_offsetof indirection
has been added to the -mm tree.  Its filename is
     include-drop-pointless-__compiler_offsetof-indirection.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/include-drop-pointless-__compiler_offsetof-indirection.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/include-drop-pointless-__compiler_offsetof-indirection.patch

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------------------------------------------------------
From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
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@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>
---

 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
@@ -137,8 +137,6 @@ 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
_

Patches currently in -mm which might be from linux@rasmusvillemoes.dk are

include-drop-pointless-__compiler_offsetof-indirection.patch