[LibOS] Add noreturn function attribute where appropriate

Add noreturn function attribute to __shim_do_execve_rtld(),
execute_elf_object(), __shim_ipc_helper(), shim_ipc_helper_end()

LibOS/shim/include/shim_utils.h

@@ -210,9 +210,9 @@ int check_elf_object (struct shim_handle * file);
 int load_elf_object (struct shim_handle * file, void * addr, size_t mapped);
 int load_elf_interp (struct shim_handle * exec);
 int free_elf_interp (void);
-void execute_elf_object (struct shim_handle * exec,
-                         int * argcp, const char ** argp,
-                         elf_auxv_t * auxp);
+noreturn void execute_elf_object (struct shim_handle * exec,
+                                  int * argcp, const char ** argp,
+                                  elf_auxv_t * auxp);
 int remove_loaded_libraries (void);
 
 /* gdb debugging support */

LibOS/shim/src/elf/shim_rtld.c

@@ -1554,9 +1554,9 @@ int register_library (const char * name, unsigned long load_address)
     return 0;
 }
 
-void execute_elf_object (struct shim_handle * exec,
-                         int * argcp, const char ** argp,
-                         ElfW(auxv_t) * auxp)
+noreturn void execute_elf_object (struct shim_handle * exec,
+                                  int * argcp, const char ** argp,
+                                  ElfW(auxv_t) * auxp)
 {
     struct link_map * exec_map = __search_map_by_handle(exec);
     assert(exec_map);
@@ -1611,6 +1611,8 @@ void execute_elf_object (struct shim_handle * exec,
 #else
 # error "architecture not supported"
 #endif
+    while (true)
+        /* nothing */;
 }
 
 BEGIN_CP_FUNC(library)

LibOS/shim/src/ipc/shim_ipc_helper.c

@@ -805,7 +805,7 @@ next:
 #define IPC_HELPER_STACK_SIZE       (allocsize * 4)
 #define IPC_HELPER_LIST_INIT_SIZE   32
 
-static void shim_ipc_helper_end(struct shim_thread * self)
+noreturn static void shim_ipc_helper_end(struct shim_thread * self)
 {
     /* Put our handle map reference */
     if (self->handle_map)
@@ -831,7 +831,7 @@ static void shim_ipc_helper_end(struct shim_thread * self)
     DkThreadExit();
 }
 
-static void __shim_ipc_helper (void * dummy)
+noreturn static void __shim_ipc_helper (void * dummy)
 {
     struct shim_thread * self = get_cur_thread();
     void * stack = self->stack;

LibOS/shim/src/sys/shim_exec.c

@@ -73,7 +73,7 @@ struct execve_rtld_arg
     elf_auxv_t *  new_auxp;
 };
 
-static void __shim_do_execve_rtld (struct execve_rtld_arg * __arg)
+noreturn static void __shim_do_execve_rtld (struct execve_rtld_arg * __arg)
 {
     struct execve_rtld_arg arg;
     memcpy(&arg, __arg, sizeof(arg));
@@ -169,8 +169,7 @@ retry_dump_vmas:
 
     debug("execve: start execution\n");
     execute_elf_object(cur_thread->exec, new_argcp, new_argp, new_auxp);
-
-    return;
+    /* NOTREACHED */
 
 error:
     debug("execve: failed %d\n", ret);

Pal/src/db_process.c

@@ -63,6 +63,8 @@ noreturn void DkProcessExit (PAL_NUM exitcode)
     ENTER_PAL_CALL(DkProcessExit);
     _DkProcessExit(exitcode);
     _DkRaiseFailure(PAL_ERROR_NOTKILLABLE);
+    while (true)
+        /* nothing */;
     LEAVE_PAL_CALL();
 }
 

Pal/src/db_threading.c

@@ -81,7 +81,8 @@ noreturn void DkThreadExit (void)
     ENTER_PAL_CALL(DkThreadExit);
     _DkThreadExit();
     _DkRaiseFailure(PAL_ERROR_NOTKILLABLE);
-    while (1) {}
+    while (true)
+        /* nothing */;
     LEAVE_PAL_CALL();
 }