3 files changed, 70 insertions, 9 deletions

diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
index 21aeca874edb..b0d7dc3d71b5 100644
--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -31,8 +31,9 @@
 #define INSN_RETURN		6
 #define INSN_CONTEXT_SWITCH	7
 #define INSN_STACK		8
-#define INSN_NOP		9
-#define INSN_OTHER		10
+#define INSN_BUG		9
+#define INSN_NOP		10
+#define INSN_OTHER		11
 #define INSN_LAST		INSN_OTHER
 
 enum op_dest_type {
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index a36c2eba64e7..e4b400b67e41 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -382,20 +382,27 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
 
 	case 0x0f:
 
-		if (op2 >= 0x80 && op2 <= 0x8f)
+		if (op2 >= 0x80 && op2 <= 0x8f) {
+
 			*type = INSN_JUMP_CONDITIONAL;
-		else if (op2 == 0x05 || op2 == 0x07 || op2 == 0x34 ||
-			 op2 == 0x35)
+
+		} else if (op2 == 0x05 || op2 == 0x07 || op2 == 0x34 ||
+			   op2 == 0x35) {
 
 			/* sysenter, sysret */
 			*type = INSN_CONTEXT_SWITCH;
 
-		else if (op2 == 0x0d || op2 == 0x1f)
+		} else if (op2 == 0x0b || op2 == 0xb9) {
+
+			/* ud2 */
+			*type = INSN_BUG;
+
+		} else if (op2 == 0x0d || op2 == 0x1f) {
 
 			/* nopl/nopw */
 			*type = INSN_NOP;
 
-		else if (op2 == 0xa0 || op2 == 0xa8) {
+		} else if (op2 == 0xa0 || op2 == 0xa8) {
 
 			/* push fs/gs */
 			*type = INSN_STACK;
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 3436a942b606..d07bf4a62b45 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -296,7 +296,7 @@ static int decode_instructions(struct objtool_file *file)
 }
 
 /*
- * Find all uses of the unreachable() macro, which are code path dead ends.
+ * Mark "ud2" instructions and manually annotated dead ends.
  */
 static int add_dead_ends(struct objtool_file *file)
 {
@@ -305,9 +305,20 @@ static int add_dead_ends(struct objtool_file *file)
 	struct instruction *insn;
 	bool found;
 
+	/*
+	 * By default, "ud2" is a dead end unless otherwise annotated, because
+	 * GCC 7 inserts it for certain divide-by-zero cases.
+	 */
+	for_each_insn(file, insn)
+		if (insn->type == INSN_BUG)
+			insn->dead_end = true;
+
+	/*
+	 * Check for manually annotated dead ends.
+	 */
 	sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 	if (!sec)
-		return 0;
+		goto reachable;
 
 	list_for_each_entry(rela, &sec->rela_list, list) {
 		if (rela->sym->type != STT_SECTION) {
@@ -340,6 +351,48 @@ static int add_dead_ends(struct objtool_file *file)
 		insn->dead_end = true;
 	}
 
+reachable:
+	/*
+	 * These manually annotated reachable checks are needed for GCC 4.4,
+	 * where the Linux unreachable() macro isn't supported.  In that case
+	 * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
+	 * not a dead end.
+	 */
+	sec = find_section_by_name(file->elf, ".rela.discard.reachable");
+	if (!sec)
+		return 0;
+
+	list_for_each_entry(rela, &sec->rela_list, list) {
+		if (rela->sym->type != STT_SECTION) {
+			WARN("unexpected relocation symbol type in %s", sec->name);
+			return -1;
+		}
+		insn = find_insn(file, rela->sym->sec, rela->addend);
+		if (insn)
+			insn = list_prev_entry(insn, list);
+		else if (rela->addend == rela->sym->sec->len) {
+			found = false;
+			list_for_each_entry_reverse(insn, &file->insn_list, list) {
+				if (insn->sec == rela->sym->sec) {
+					found = true;
+					break;
+				}
+			}
+
+			if (!found) {
+				WARN("can't find reachable insn at %s+0x%x",
+				     rela->sym->sec->name, rela->addend);
+				return -1;
+			}
+		} else {
+			WARN("can't find reachable insn at %s+0x%x",
+			     rela->sym->sec->name, rela->addend);
+			return -1;
+		}
+
+		insn->dead_end = false;
+	}
+
 	return 0;
 }