Merge tag 'compiler-attributes-for-linus-4.20-rc1' of https://github.com/ojeda/linux

Pull compiler attribute updates from Miguel Ojeda:
 "This is an effort to disentangle the include/linux/compiler*.h headers
  and bring them up to date.

  The main idea behind the series is to use feature checking macros
  (i.e. __has_attribute) instead of compiler version checks (e.g.
  GCC_VERSION), which are compiler-agnostic (so they can be shared,
  reducing the size of compiler-specific headers) and version-agnostic.

  Other related improvements have been performed in the headers as well,
  which on top of the use of __has_attribute it has amounted to a
  significant simplification of these headers (e.g. GCC_VERSION is now
  only guarding a few non-attribute macros).

  This series should also help the efforts to support compiling the
  kernel with clang and icc. A fair amount of documentation and comments
  have also been added, clarified or removed; and the headers are now
  more readable, which should help kernel developers in general.

  The series was triggered due to the move to gcc >= 4.6. In turn, this
  series has also triggered Sparse to gain the ability to recognize
  __has_attribute on its own.

  Finally, the __nonstring variable attribute series has been also
  applied on top; plus two related patches from Nick Desaulniers for
  unreachable() that came a bit afterwards"

* tag 'compiler-attributes-for-linus-4.20-rc1' of https://github.com/ojeda/linux:
  compiler-gcc: remove comment about gcc 4.5 from unreachable()
  compiler.h: update definition of unreachable()
  Compiler Attributes: ext4: remove local __nonstring definition
  Compiler Attributes: auxdisplay: panel: use __nonstring
  Compiler Attributes: enable -Wstringop-truncation on W=1 (gcc >= 8)
  Compiler Attributes: add support for __nonstring (gcc >= 8)
  Compiler Attributes: add MAINTAINERS entry
  Compiler Attributes: add Doc/process/programming-language.rst
  Compiler Attributes: remove uses of __attribute__ from compiler.h
  Compiler Attributes: KENTRY used twice the "used" attribute
  Compiler Attributes: use feature checks instead of version checks
  Compiler Attributes: add missing SPDX ID in compiler_types.h
  Compiler Attributes: remove unneeded sparse (__CHECKER__) tests
  Compiler Attributes: homogenize __must_be_array
  Compiler Attributes: remove unneeded tests
  Compiler Attributes: always use the extra-underscores syntax
  Compiler Attributes: remove unused attributes

1 files changed, 7 insertions, 68 deletions

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 90ddfefb6c2b..c0f5db3a9621 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -68,31 +68,20 @@
  */
 #define uninitialized_var(x) x = x
 
-#ifdef __CHECKER__
-#define __must_be_array(a)	0
-#else
-/* &a[0] degrades to a pointer: a different type from an array */
-#define __must_be_array(a)	BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
-#endif
-
 #ifdef RETPOLINE
-#define __noretpoline __attribute__((indirect_branch("keep")))
+#define __noretpoline __attribute__((__indirect_branch__("keep")))
 #endif
 
 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
 
-#define __optimize(level)	__attribute__((__optimize__(level)))
-
 #define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
 
-#ifndef __CHECKER__
-#define __compiletime_warning(message) __attribute__((warning(message)))
-#define __compiletime_error(message) __attribute__((error(message)))
+#define __compiletime_warning(message) __attribute__((__warning__(message)))
+#define __compiletime_error(message) __attribute__((__error__(message)))
 
-#ifdef LATENT_ENTROPY_PLUGIN
+#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
 #define __latent_entropy __attribute__((latent_entropy))
 #endif
-#endif /* __CHECKER__ */
 
 /*
  * calling noreturn functions, __builtin_unreachable() and __builtin_trap()
@@ -107,10 +96,6 @@
  * Mark a position in code as unreachable.  This can be used to
  * suppress control flow warnings after asm blocks that transfer
  * control elsewhere.
- *
- * Early snapshots of gcc 4.5 don't support this and we can't detect
- * this in the preprocessor, but we can live with this because they're
- * unreleased.  Really, we need to have autoconf for the kernel.
  */
 #define unreachable() \
 	do {					\
@@ -119,9 +104,6 @@
 		__builtin_unreachable();	\
 	} while (0)
 
-/* Mark a function definition as prohibited from being cloned. */
-#define __noclone	__attribute__((__noclone__, __optimize__("no-tracer")))
-
 #if defined(RANDSTRUCT_PLUGIN) && !defined(__CHECKER__)
 #define __randomize_layout __attribute__((randomize_layout))
 #define __no_randomize_layout __attribute__((no_randomize_layout))
@@ -131,32 +113,6 @@
 #endif
 
 /*
- * When used with Link Time Optimization, gcc can optimize away C functions or
- * variables which are referenced only from assembly code.  __visible tells the
- * optimizer that something else uses this function or variable, thus preventing
- * this.
- */
-#define __visible	__attribute__((externally_visible))
-
-/* gcc version specific checks */
-
-#if GCC_VERSION >= 40900 && !defined(__CHECKER__)
-/*
- * __assume_aligned(n, k): Tell the optimizer that the returned
- * pointer can be assumed to be k modulo n. The second argument is
- * optional (default 0), so we use a variadic macro to make the
- * shorthand.
- *
- * Beware: Do not apply this to functions which may return
- * ERR_PTRs. Also, it is probably unwise to apply it to functions
- * returning extra information in the low bits (but in that case the
- * compiler should see some alignment anyway, when the return value is
- * massaged by 'flags = ptr & 3; ptr &= ~3;').
- */
-#define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
-#endif
-
-/*
  * GCC 'asm goto' miscompiles certain code sequences:
  *
  *   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
@@ -187,39 +143,22 @@
 #define KASAN_ABI_VERSION 3
 #endif
 
-#if GCC_VERSION >= 40902
 /*
- * Tell the compiler that address safety instrumentation (KASAN)
- * should not be applied to that function.
- * Conflicts with inlining: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
+ * Because __no_sanitize_address conflicts with inlining:
+ *   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
+ * we do one or the other. 
  */
-#define __no_sanitize_address __attribute__((no_sanitize_address))
 #ifdef CONFIG_KASAN
 #define __no_sanitize_address_or_inline					\
 	__no_sanitize_address __maybe_unused notrace
 #else
 #define __no_sanitize_address_or_inline inline
 #endif
-#endif
 
 #if GCC_VERSION >= 50100
-/*
- * Mark structures as requiring designated initializers.
- * https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html
- */
-#define __designated_init __attribute__((designated_init))
 #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
 #endif
 
-#if !defined(__noclone)
-#define __noclone	/* not needed */
-#endif
-
-#if !defined(__no_sanitize_address)
-#define __no_sanitize_address
-#define __no_sanitize_address_or_inline inline
-#endif
-
 /*
  * Turn individual warnings and errors on and off locally, depending
  * on version.