objtool: Refactor sibling call detection logic

Simplify the sibling call detection logic a bit.

Signed-off-by: Josh Poimboeuf <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Tested-by: Nick Desaulniers <[e-mail]>
Acked-by: Peter Zijlstra (Intel) <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

tools/objtool/check.c

···
 	for (insn = next_insn_same_sec(file, insn); insn;		\
 	     insn = next_insn_same_sec(file, insn))
 
+static bool is_sibling_call(struct instruction *insn)
+{
+	/* An indirect jump is either a sibling call or a jump to a table. */
+	if (insn->type == INSN_JUMP_DYNAMIC)
+		return list_empty(&insn->alts);
+
+	if (insn->type != INSN_JUMP_CONDITIONAL &&
+	    insn->type != INSN_JUMP_UNCONDITIONAL)
+		return false;
+
+	/* add_jump_destinations() sets insn->call_dest for sibling calls. */
+	return !!insn->call_dest;
+}
+
 /*
  * This checks to see if the given function is a "noreturn" function.
  *
···
 	 * of the sibling call returns.
 	 */
 	func_for_each_insn_all(file, func, insn) {
-		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
+		if (is_sibling_call(insn)) {
 			struct instruction *dest = insn->jump_dest;
 
 			if (!dest)
 				/* sibling call to another file */
 				return false;
 
-			if (dest->func && dest->func->pfunc != insn->func->pfunc) {
-
-				/* local sibling call */
-				if (recursion == 5) {
-					/*
-					 * Infinite recursion: two functions
-					 * have sibling calls to each other.
-					 * This is a very rare case.  It means
-					 * they aren't dead ends.
-					 */
-					return false;
-				}
-
-				return __dead_end_function(file, dest->func,
-							   recursion + 1);
+			/* local sibling call */
+			if (recursion == 5) {
+				/*
+				 * Infinite recursion: two functions have
+				 * sibling calls to each other.  This is a very
+				 * rare case.  It means they aren't dead ends.
+				 */
+				return false;
 			}
-		}
 
-		if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
-			/* sibling call */
-			return false;
+			return __dead_end_function(file, dest->func, recursion+1);
+		}
 	}
 
 	return true;
···
 			insn->retpoline_safe = true;
 			continue;
 		} else {
-			/* sibling call */
+			/* external sibling call */
 			insn->call_dest = rela->sym;
-			insn->jump_dest = NULL;
 			continue;
 		}
 
···
 			} else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 				   insn->jump_dest->offset == insn->jump_dest->func->offset) {
 
-				/* sibling class */
+				/* internal sibling call */
 				insn->call_dest = insn->jump_dest->func;
-				insn->jump_dest = NULL;
 			}
 		}
 	}
···
 	return false;
 }
 
-static inline const char *insn_dest_name(struct instruction *insn)
+static inline const char *call_dest_name(struct instruction *insn)
 {
 	if (insn->call_dest)
 		return insn->call_dest->name;
···
 {
 	if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
 		WARN_FUNC("call to %s() with UACCESS enabled",
-				insn->sec, insn->offset, insn_dest_name(insn));
+				insn->sec, insn->offset, call_dest_name(insn));
 		return 1;
 	}
 
 	if (state->df) {
 		WARN_FUNC("call to %s() with DF set",
-				insn->sec, insn->offset, insn_dest_name(insn));
+				insn->sec, insn->offset, call_dest_name(insn));
 		return 1;
 	}
 
···
 
 		case INSN_JUMP_CONDITIONAL:
 		case INSN_JUMP_UNCONDITIONAL:
-			if (func && !insn->jump_dest) {
+			if (func && is_sibling_call(insn)) {
 				ret = validate_sibling_call(insn, &state);
 				if (ret)
 					return ret;
 
-			} else if (insn->jump_dest &&
-				   (!func || !insn->jump_dest->func ||
-				    insn->jump_dest->func->pfunc == func)) {
+			} else if (insn->jump_dest) {
 				ret = validate_branch(file, func,
 						      insn->jump_dest, state);
 				if (ret) {
···
 			break;
 
 		case INSN_JUMP_DYNAMIC:
-			if (func && list_empty(&insn->alts)) {
+			if (func && is_sibling_call(insn)) {
 				ret = validate_sibling_call(insn, &state);
 				if (ret)
 					return ret;