init: Mark [arch_call_]rest_init() __noreturn

In preparation for improving objtool's handling of weak noreturn
functions, mark start_kernel(), arch_call_rest_init(), and rest_init()
__noreturn.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/7194ed8a989a85b98d92e62df660f4a90435a723.1681342859.git.jpoimboe@kernel.org

arch/s390/kernel/setup.c

@@ -396,7 +396,7 @@ int __init arch_early_irq_init(void)
 	return 0;
 }
 
-void __init arch_call_rest_init(void)
+void __init __noreturn arch_call_rest_init(void)
 {
 	unsigned long stack;
 

include/linux/start_kernel.h

@@ -9,7 +9,7 @@
    up something else. */
 
 extern asmlinkage void __init start_kernel(void);
-extern void __init arch_call_rest_init(void);
-extern void __ref rest_init(void);
+extern void __init __noreturn arch_call_rest_init(void);
+extern void __ref __noreturn rest_init(void);
 
 #endif /* _LINUX_START_KERNEL_H */

init/main.c

@@ -683,7 +683,7 @@ static void __init setup_command_line(char *command_line)
 
 static __initdata DECLARE_COMPLETION(kthreadd_done);
 
-noinline void __ref rest_init(void)
+noinline void __ref __noreturn rest_init(void)
 {
 	struct task_struct *tsk;
 	int pid;
@@ -889,7 +889,7 @@ static int __init early_randomize_kstack_offset(char *buf)
 early_param("randomize_kstack_offset", early_randomize_kstack_offset);
 #endif
 
-void __init __weak arch_call_rest_init(void)
+void __init __weak __noreturn arch_call_rest_init(void)
 {
 	rest_init();
 }

tools/objtool/check.c

@@ -202,6 +202,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"__reiserfs_panic",
 		"__stack_chk_fail",
 		"__ubsan_handle_builtin_unreachable",
+		"arch_call_rest_init",
 		"arch_cpu_idle_dead",
 		"cpu_bringup_and_idle",
 		"cpu_startup_entry",
@@ -217,6 +218,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"machine_real_restart",
 		"make_task_dead",
 		"panic",
+		"rest_init",
 		"rewind_stack_and_make_dead",
 		"sev_es_terminate",
 		"snp_abort",