Merge branch 'rwonce/rework' of git://git.kernel.org/pub/scm/linux/kernel/git/will/linux

Pull READ/WRITE_ONCE rework from Will Deacon:
 "This the READ_ONCE rework I've been working on for a while, which
  bumps the minimum GCC version and improves code-gen on arm64 when
  stack protector is enabled"

[ Side note: I'm _really_ tempted to raise the minimum gcc version to
  4.9, so that we can just say that we require _Generic() support.

  That would allow us to more cleanly handle a lot of the cases where we
  depend on very complex macros with 'sizeof' or __builtin_choose_expr()
  with __builtin_types_compatible_p() etc.

  This branch has a workaround for sparse not handling _Generic(),
  either, but that was already fixed in the sparse development branch,
  so it's really just gcc-4.9 that we'd require.   - Linus ]

* 'rwonce/rework' of git://git.kernel.org/pub/scm/linux/kernel/git/will/linux:
  compiler_types.h: Use unoptimized __unqual_scalar_typeof for sparse
  compiler_types.h: Optimize __unqual_scalar_typeof compilation time
  compiler.h: Enforce that READ_ONCE_NOCHECK() access size is sizeof(long)
  compiler-types.h: Include naked type in __pick_integer_type() match
  READ_ONCE: Fix comment describing 2x32-bit atomicity
  gcov: Remove old GCC 3.4 support
  arm64: barrier: Use '__unqual_scalar_typeof' for acquire/release macros
  locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros
  READ_ONCE: Drop pointer qualifiers when reading from scalar types
  READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses
  READ_ONCE: Simplify implementations of {READ,WRITE}_ONCE()
  arm64: csum: Disable KASAN for do_csum()
  fault_inject: Don't rely on "return value" from WRITE_ONCE()
  net: tls: Avoid assigning 'const' pointer to non-const pointer
  netfilter: Avoid assigning 'const' pointer to non-const pointer
  compiler/gcc: Raise minimum GCC version for kernel builds to 4.8

1 files changed, 47 insertions, 0 deletions

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 6fcf73200b67..d4e1956f903f 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -218,6 +218,53 @@ struct ftrace_likely_data {
 /* Are two types/vars the same type (ignoring qualifiers)? */
 #define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
 
+/*
+ * __unqual_scalar_typeof(x) - Declare an unqualified scalar type, leaving
+ *			       non-scalar types unchanged.
+ */
+#if (defined(CONFIG_CC_IS_GCC) && CONFIG_GCC_VERSION < 40900) || defined(__CHECKER__)
+/*
+ * We build this out of a couple of helper macros in a vain attempt to
+ * help you keep your lunch down while reading it.
+ */
+#define __pick_scalar_type(x, type, otherwise)					\
+	__builtin_choose_expr(__same_type(x, type), (type)0, otherwise)
+
+/*
+ * 'char' is not type-compatible with either 'signed char' or 'unsigned char',
+ * so we include the naked type here as well as the signed/unsigned variants.
+ */
+#define __pick_integer_type(x, type, otherwise)					\
+	__pick_scalar_type(x, type,						\
+		__pick_scalar_type(x, unsigned type,				\
+			__pick_scalar_type(x, signed type, otherwise)))
+
+#define __unqual_scalar_typeof(x) typeof(					\
+	__pick_integer_type(x, char,						\
+		__pick_integer_type(x, short,					\
+			__pick_integer_type(x, int,				\
+				__pick_integer_type(x, long,			\
+					__pick_integer_type(x, long long, x))))))
+#else
+/*
+ * If supported, prefer C11 _Generic for better compile-times. As above, 'char'
+ * is not type-compatible with 'signed char', and we define a separate case.
+ */
+#define __scalar_type_to_expr_cases(type)				\
+		unsigned type:	(unsigned type)0,			\
+		signed type:	(signed type)0
+
+#define __unqual_scalar_typeof(x) typeof(				\
+		_Generic((x),						\
+			 char:	(char)0,				\
+			 __scalar_type_to_expr_cases(char),		\
+			 __scalar_type_to_expr_cases(short),		\
+			 __scalar_type_to_expr_cases(int),		\
+			 __scalar_type_to_expr_cases(long),		\
+			 __scalar_type_to_expr_cases(long long),	\
+			 default: (x)))
+#endif
+
 /* Is this type a native word size -- useful for atomic operations */
 #define __native_word(t) \
 	(sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || \