compiler.h: bring back annotate_unreachable

bfb1a7c ("x86/bug: Merge annotate_reachable() into _BUG_FLAGS() asm")
removed annotate_reachable, since it's folded in to the BUG_FLAGS macro
on x86 now.

However, we use it on arm64, so it needs to stick around for a while
longer.

Signed-off-by: Frank van der Linden <[email protected]>

Author: fllinden

include/linux/compiler.h

@@ -117,6 +117,14 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
  */
 #define __stringify_label(n) #n
 
+#define __annotate_reachable(c) ({					\
+	asm volatile(__stringify_label(c) ":\n\t"			\
+		     ".pushsection .discard.reachable\n\t"		\
+		     ".long " __stringify_label(c) "b - .\n\t"		\
+		     ".popsection\n\t" : : "i" (c));			\
+})
+#define annotate_reachable() __annotate_reachable(__COUNTER__)
+
 #define __annotate_unreachable(c) ({					\
 	asm volatile(__stringify_label(c) ":\n\t"			\
 		     ".pushsection .discard.unreachable\n\t"		\
@@ -135,6 +143,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 #define __annotate_jump_table __section(".rodata..c_jump_table")
 
 #else
+#define annotate_reachable()
 #define annotate_unreachable()
 # define ASM_REACHABLE
 #define __annotate_jump_table