Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull objtool fixes from Ingo Molnar:
"A handful of objtool fixes related to unreachable code, plus a build
fix for out of tree modules"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
objtool: Enclose contents of unreachable() macro in a block
objtool: Prevent GCC from merging annotate_unreachable()
objtool: Improve detection of BUG() and other dead ends
objtool: Fix CONFIG_STACK_VALIDATION=y warning for out-of-tree modules

Makefile

···
 endif
 export mod_sign_cmd
 
+ifdef CONFIG_STACK_VALIDATION
+  has_libelf := $(call try-run,\
+		echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -,1,0)
+  ifeq ($(has_libelf),1)
+    objtool_target := tools/objtool FORCE
+  else
+    $(warning "Cannot use CONFIG_STACK_VALIDATION, please install libelf-dev, libelf-devel or elfutils-libelf-devel")
+    SKIP_STACK_VALIDATION := 1
+    export SKIP_STACK_VALIDATION
+  endif
+endif
+
 
 ifeq ($(KBUILD_EXTMOD),)
 core-y		+= kernel/ certs/ mm/ fs/ ipc/ security/ crypto/ block/
···
 
 # All the preparing..
 prepare: prepare0 prepare-objtool
-
-ifdef CONFIG_STACK_VALIDATION
-  has_libelf := $(call try-run,\
-		echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -,1,0)
-  ifeq ($(has_libelf),1)
-    objtool_target := tools/objtool FORCE
-  else
-    $(warning "Cannot use CONFIG_STACK_VALIDATION, please install libelf-dev, libelf-devel or elfutils-libelf-devel")
-    SKIP_STACK_VALIDATION := 1
-    export SKIP_STACK_VALIDATION
-  endif
-endif
 
 PHONY += prepare-objtool
 prepare-objtool: $(objtool_target)

arch/x86/kernel/vmlinux.lds.S

···
 	/DISCARD/ : {
 		*(.eh_frame)
 		*(__func_stack_frame_non_standard)
+		*(__unreachable)
 	}
 }
 

include/linux/compiler-gcc.h

···
 #endif
 #endif
 
+#ifdef CONFIG_STACK_VALIDATION
+#define annotate_unreachable() ({					\
+	asm("%c0:\t\n"							\
+	    ".pushsection __unreachable, \"a\"\t\n"			\
+	    ".long %c0b\t\n"						\
+	    ".popsection\t\n" : : "i" (__LINE__));			\
+})
+#else
+#define annotate_unreachable()
+#endif
+
 /*
  * Mark a position in code as unreachable.  This can be used to
  * suppress control flow warnings after asm blocks that transfer
···
  * this in the preprocessor, but we can live with this because they're
  * unreleased.  Really, we need to have autoconf for the kernel.
  */
-#define unreachable() __builtin_unreachable()
+#define unreachable() \
+	do { annotate_unreachable(); __builtin_unreachable(); } while (0)
 
 /* Mark a function definition as prohibited from being cloned. */
 #define __noclone	__attribute__((__noclone__, __optimize__("no-tracer")))

tools/objtool/arch.h

···
 #define INSN_CALL_DYNAMIC	8
 #define INSN_RETURN		9
 #define INSN_CONTEXT_SWITCH	10
-#define INSN_BUG		11
-#define INSN_NOP		12
-#define INSN_OTHER		13
+#define INSN_NOP		11
+#define INSN_OTHER		12
 #define INSN_LAST		INSN_OTHER
 
 int arch_decode_instruction(struct elf *elf, struct section *sec,

tools/objtool/arch/x86/decode.c

···
 			 op2 == 0x35)
 			/* sysenter, sysret */
 			*type = INSN_CONTEXT_SWITCH;
-		else if (op2 == 0x0b || op2 == 0xb9)
-			/* ud2 */
-			*type = INSN_BUG;
 		else if (op2 == 0x0d || op2 == 0x1f)
 			/* nopl/nopw */
 			*type = INSN_NOP;

tools/objtool/builtin-check.c

···
 	unsigned int len, state;
 	unsigned char type;
 	unsigned long immediate;
-	bool alt_group, visited;
+	bool alt_group, visited, dead_end;
 	struct symbol *call_dest;
 	struct instruction *jump_dest;
 	struct list_head alts;
···
 				if (!insn->func)
 					insn->func = func;
 		}
+	}
+
+	return 0;
+}
+
+/*
+ * Find all uses of the unreachable() macro, which are code path dead ends.
+ */
+static int add_dead_ends(struct objtool_file *file)
+{
+	struct section *sec;
+	struct rela *rela;
+	struct instruction *insn;
+	bool found;
+
+	sec = find_section_by_name(file->elf, ".rela__unreachable");
+	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 .rela__unreachable");
+			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 unreachable insn at %s+0x%x",
+				     rela->sym->sec->name, rela->addend);
+				return -1;
+			}
+		} else {
+			WARN("can't find unreachable insn at %s+0x%x",
+			     rela->sym->sec->name, rela->addend);
+			return -1;
+		}
+
+		insn->dead_end = true;
 	}
 
 	return 0;
···
 	if (ret)
 		return ret;
 
+	ret = add_dead_ends(file);
+	if (ret)
+		return ret;
+
 	add_ignores(file);
 
 	ret = add_jump_destinations(file);
···
 
 			return 0;
 
-		case INSN_BUG:
-			return 0;
-
 		default:
 			break;
 		}
+
+		if (insn->dead_end)
+			return 0;
 
 		insn = next_insn_same_sec(file, insn);
 		if (!insn) {