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-rw-r--r--tools/objtool/check.c41
-rw-r--r--tools/objtool/check.h1
2 files changed, 40 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;
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index dbadb304a410..23a1d065cae1 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -47,6 +47,7 @@ struct instruction {
bool alt_group, visited, dead_end, ignore, hint, save, restore, ignore_alts;
struct symbol *call_dest;
struct instruction *jump_dest;
+ struct instruction *first_jump_src;
struct list_head alts;
struct symbol *func;
struct stack_op stack_op;