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, 13 insertions, 11 deletions

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 4170fcee5adb..18c80cfa4fc4 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -23,8 +23,8 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 #define __branch_check__(x, expect, is_constant) ({                     \
                         long ______r;                                   \
                         static struct ftrace_likely_data                \
-                                __attribute__((__aligned__(4)))         \
-                                __attribute__((section("_ftrace_annotated_branch"))) \
+                                __aligned(4)                            \
+                                __section("_ftrace_annotated_branch")   \
                                 ______f = {                             \
                                 .data.func = __func__,                  \
                                 .data.file = __FILE__,                  \
@@ -59,8 +59,8 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
         ({                                                              \
                 int ______r;                                            \
                 static struct ftrace_branch_data                        \
-                        __attribute__((__aligned__(4)))                 \
-                        __attribute__((section("_ftrace_branch")))      \
+                        __aligned(4)                                    \
+                        __section("_ftrace_branch")                     \
                         ______f = {                                     \
                                 .func = __func__,                       \
                                 .file = __FILE__,                       \
@@ -115,7 +115,10 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 # define ASM_UNREACHABLE
 #endif
 #ifndef unreachable
-# define unreachable() do { annotate_reachable(); do { } while (1); } while (0)
+# define unreachable() do {             \
+        annotate_unreachable();         \
+        __builtin_unreachable();        \
+} while (0)
 #endif
 
 /*
@@ -137,7 +140,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
         extern typeof(sym) sym;                                 \
         static const unsigned long __kentry_##sym               \
         __used                                                  \
-        __attribute__((section("___kentry" "+" #sym ), used))   \
+        __section("___kentry" "+" #sym )                        \
         = (unsigned long)&sym;
 #endif
 
@@ -278,7 +281,7 @@ unsigned long read_word_at_a_time(const void *addr)
  * visible to the compiler.
  */
 #define __ADDRESSABLE(sym) \
-        static void * __attribute__((section(".discard.addressable"), used)) \
+        static void * __section(".discard.addressable") __used \
                 __PASTE(__addressable_##sym, __LINE__) = (void *)&sym;
 
 /**
@@ -331,10 +334,6 @@ static inline void *offset_to_ptr(const int *off)
 #endif /* __KERNEL__ */
 #endif /* __ASSEMBLY__ */
 
-#ifndef __optimize
-# define __optimize(level)
-#endif
-
 /* Compile time object size, -1 for unknown */
 #ifndef __compiletime_object_size
 # define __compiletime_object_size(obj) -1
@@ -376,4 +375,7 @@ static inline void *offset_to_ptr(const int *off)
         compiletime_assert(__native_word(t),                            \
                 "Need native word sized stores/loads for atomicity.")
 
+/* &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 /* __LINUX_COMPILER_H */