1 files changed, 48 insertions, 5 deletions

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index b00b1896547e..a8cb69a26576 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -852,8 +852,14 @@ 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,
@@ -875,12 +881,25 @@ 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;
 
@@ -910,14 +929,32 @@ 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;
 
@@ -1899,13 +1936,19 @@ static bool ignore_unreachable_insn(struct instruction *insn)
                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
                         return true;
 
-                if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
-                        insn = insn->jump_dest;
-                        continue;
+                if (insn->type == INSN_JUMP_UNCONDITIONAL) {
+                        if (insn->jump_dest &&
+                            insn->jump_dest->func == insn->func) {
+                                insn = insn->jump_dest;
+                                continue;
+                        }
+
+                        break;
                 }
 
                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
                         break;
+
                 insn = list_next_entry(insn, list);
         }