compiler.h: use compiler barrier for reachable annotations

Partial revert of
commit dcce50e ("compiler.h: Fix annotation macro misplacement with Clang")

volatile is not a compiler barrier.

Signed-off-by: Nick Desaulniers <[email protected]>

Author: nickdesaulniers

include/linux/compiler.h

@@ -112,24 +112,27 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 #ifdef CONFIG_STACK_VALIDATION
 /*
  * These macros help objtool understand GCC code flow for unreachable code.
- * The __COUNTER__ based labels are a hack to make each instance of the macros
- * unique, to convince GCC not to merge duplicate inline asm statements.
+ * The __COUNTER__ based labels are to make each instance of the macros unique,
+ * to convince GCC not to merge duplicate inline asm statements. This was
+ * recommended by GCC developers in
+ * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104236#c4. %= output templates
+ * are not a substitute to prevent asm statements from appearing as duplicates.
  */
 #define __stringify_label(n) #n
 
 #define __annotate_reachable(c) ({					\
-	asm volatile(__stringify_label(c) ":\n\t"			\
+	asm (__stringify_label(c) ":\n\t"				\
 		     ".pushsection .discard.reachable\n\t"		\
 		     ".long " __stringify_label(c) "b - .\n\t"		\
-		     ".popsection\n\t" : : "i" (c));			\
+		     ".popsection" ::: "memory");			\
 })
 #define annotate_reachable() __annotate_reachable(__COUNTER__)
 
 #define __annotate_unreachable(c) ({					\
-	asm volatile(__stringify_label(c) ":\n\t"			\
+	asm (__stringify_label(c) ":\n\t"				\
 		     ".pushsection .discard.unreachable\n\t"		\
 		     ".long " __stringify_label(c) "b - .\n\t"		\
-		     ".popsection\n\t" : : "i" (c));			\
+		     ".popsection" ::: "memory");			\
 })
 #define annotate_unreachable() __annotate_unreachable(__COUNTER__)