1 files changed, 39 insertions, 2 deletions

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 9cd028aa1509..2e458eb45586 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -851,8 +851,14 @@ static int add_switch_table(struct objtool_file *file, struct symbol *func,
  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
  *
+ *    As of GCC 7 there are quite a few more of these and the 'in between' code
+ *    is significant. Esp. with KASAN enabled some of the code between the mov
+ *    and jmpq uses .rodata itself, which can confuse things.
+ *
  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
  *    ensure the same register is used in the mov and jump instructions.
+ *
+ *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
  */
 static struct rela *find_switch_table(struct objtool_file *file,
 				      struct symbol *func,
@@ -874,12 +880,25 @@ static struct rela *find_switch_table(struct objtool_file *file,
 						text_rela->addend + 4);
 		if (!rodata_rela)
 			return NULL;
+
 		file->ignore_unreachables = true;
 		return rodata_rela;
 	}
 
 	/* case 3 */
-	func_for_each_insn_continue_reverse(file, func, insn) {
+	/*
+	 * Backward search using the @first_jump_src links, these help avoid
+	 * much of the 'in between' code. Which avoids us getting confused by
+	 * it.
+	 */
+	for (insn = list_prev_entry(insn, list);
+
+	     &insn->list != &file->insn_list &&
+	     insn->sec == func->sec &&
+	     insn->offset >= func->offset;
+
+	     insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
+
 		if (insn->type == INSN_JUMP_DYNAMIC)
 			break;
 
@@ -909,14 +928,32 @@ static struct rela *find_switch_table(struct objtool_file *file,
 	return NULL;
 }
 
+
 static int add_func_switch_tables(struct objtool_file *file,
 				  struct symbol *func)
 {
-	struct instruction *insn, *prev_jump = NULL;
+	struct instruction *insn, *last = NULL, *prev_jump = NULL;
 	struct rela *rela, *prev_rela = NULL;
 	int ret;
 
 	func_for_each_insn(file, func, insn) {
+		if (!last)
+			last = insn;
+
+		/*
+		 * Store back-pointers for unconditional forward jumps such
+		 * that find_switch_table() can back-track using those and
+		 * avoid some potentially confusing code.
+		 */
+		if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
+		    insn->offset > last->offset &&
+		    insn->jump_dest->offset > insn->offset &&
+		    !insn->jump_dest->first_jump_src) {
+
+			insn->jump_dest->first_jump_src = insn;
+			last = insn->jump_dest;
+		}
+
 		if (insn->type != INSN_JUMP_DYNAMIC)
 			continue;