Compiler Attributes: use feature checks instead of version checks

Instead of using version checks per-compiler to define (or not)
each attribute, use __has_attribute to test for them, following
the cleanup started with commit 815f0ddb346c
("include/linux/compiler*.h: make compiler-*.h mutually exclusive"),
which is supported on gcc >= 5, clang >= 2.9 and icc >= 17.
In the meantime, to support 4.6 <= gcc < 5, we implement
__has_attribute by hand.

All the attributes that can be unconditionally defined and directly
map to compiler attribute(s) (even if optional) have been moved
to a new file include/linux/compiler_attributes.h

In an effort to make the file as regular as possible, comments
stating the purpose of attributes have been removed. Instead,
links to the compiler docs have been added (i.e. to gcc and,
if available, to clang as well). In addition, they have been sorted.

Finally, if an attribute is optional (i.e. if it is guarded
by __has_attribute), the reason has been stated for future reference.

Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # on top of v4.19-rc5, clang 7
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>

1 files changed, 0 insertions, 51 deletions

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 1ca6a51cfaa9..cfac027e1625 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -108,9 +108,6 @@
                 __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))
@@ -120,32 +117,6 @@
 #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
-/*
- * __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
@@ -176,32 +147,10 @@
 #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
- */
-#define __no_sanitize_address __attribute__((__no_sanitize_address__))
-#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
-#endif
-
 /*
  * Turn individual warnings and errors on and off locally, depending
  * on version.