Index: sys/compat/freebsd32/freebsd32_misc.c
===================================================================
--- sys/compat/freebsd32/freebsd32_misc.c
+++ sys/compat/freebsd32/freebsd32_misc.c
@@ -337,7 +337,6 @@
 {
 	char *argp, *envp;
 	u_int32_t *p32, arg;
-	size_t length;
 	int error;
 
 	bzero(args, sizeof(*args));
@@ -355,19 +354,9 @@
 	/*
 	 * Copy the file name.
 	 */
-	if (fname != NULL) {
-		args->fname = args->buf;
-		error = (segflg == UIO_SYSSPACE) ?
-		    copystr(fname, args->fname, PATH_MAX, &length) :
-		    copyinstr(fname, args->fname, PATH_MAX, &length);
-		if (error != 0)
-			goto err_exit;
-	} else
-		length = 0;
-
-	args->begin_argv = args->buf + length;
-	args->endp = args->begin_argv;
-	args->stringspace = ARG_MAX;
+	error = exec_args_add_fname(args, fname, segflg);
+	if (error != 0)
+		goto err_exit;
 
 	/*
 	 * extract arguments first
@@ -380,15 +369,10 @@
 		if (arg == 0)
 			break;
 		argp = PTRIN(arg);
-		error = copyinstr(argp, args->endp, args->stringspace, &length);
-		if (error) {
-			if (error == ENAMETOOLONG)
-				error = E2BIG;
+		error = exec_args_add_arg_str(args, (void *)argp,
+		    UIO_USERSPACE);
+		if (error != 0)
 			goto err_exit;
-		}
-		args->stringspace -= length;
-		args->endp += length;
-		args->argc++;
 	}
 			
 	args->begin_envv = args->endp;
@@ -405,16 +389,10 @@
 			if (arg == 0)
 				break;
 			envp = PTRIN(arg);
-			error = copyinstr(envp, args->endp, args->stringspace,
-			    &length);
-			if (error) {
-				if (error == ENAMETOOLONG)
-					error = E2BIG;
+			error = exec_args_add_env_str(args, (void *)envp,
+			    UIO_USERSPACE);
+			if (error != 0)
 				goto err_exit;
-			}
-			args->stringspace -= length;
-			args->endp += length;
-			args->envc++;
 		}
 	}
 
Index: sys/kern/kern_exec.c
===================================================================
--- sys/kern/kern_exec.c
+++ sys/kern/kern_exec.c
@@ -1170,7 +1170,6 @@
 {
 	u_long argp, envp;
 	int error;
-	size_t length;
 
 	bzero(args, sizeof(*args));
 	if (argv == NULL)
@@ -1187,19 +1186,9 @@
 	/*
 	 * Copy the file name.
 	 */
-	if (fname != NULL) {
-		args->fname = args->buf;
-		error = (segflg == UIO_SYSSPACE) ?
-		    copystr(fname, args->fname, PATH_MAX, &length) :
-		    copyinstr(fname, args->fname, PATH_MAX, &length);
-		if (error != 0)
-			goto err_exit;
-	} else
-		length = 0;
-
-	args->begin_argv = args->buf + length;
-	args->endp = args->begin_argv;
-	args->stringspace = ARG_MAX;
+	error = exec_args_add_fname(args, fname, segflg);
+	if (error != 0)
+		goto err_exit;
 
 	/*
 	 * extract arguments first
@@ -1212,16 +1201,10 @@
 		}
 		if (argp == 0)
 			break;
-		error = copyinstr((void *)(uintptr_t)argp, args->endp,
-		    args->stringspace, &length);
-		if (error != 0) {
-			if (error == ENAMETOOLONG) 
-				error = E2BIG;
+		error = exec_args_add_arg_str(args, (void *)argp,
+		    UIO_USERSPACE);
+		if (error != 0)
 			goto err_exit;
-		}
-		args->stringspace -= length;
-		args->endp += length;
-		args->argc++;
 	}
 
 	args->begin_envv = args->endp;
@@ -1238,16 +1221,10 @@
 			}
 			if (envp == 0)
 				break;
-			error = copyinstr((void *)(uintptr_t)envp,
-			    args->endp, args->stringspace, &length);
-			if (error != 0) {
-				if (error == ENAMETOOLONG)
-					error = E2BIG;
+			error = exec_args_add_env_str(args, (void *)envp,
+			    UIO_USERSPACE);
+			if (error != 0)
 				goto err_exit;
-			}
-			args->stringspace -= length;
-			args->endp += length;
-			args->envc++;
 		}
 	}
 
@@ -1459,6 +1436,89 @@
 		fdescfree_remapped(args->fdp);
 }
 
+/*
+ * A set to functions to fill struct image args.
+ *
+ * NOTE: exec_args_add_fname() must be called (possiably with a NULL
+ * fname) before any _arg_ or _env_ functions.  All _arg_ calls should be
+ * made before any _env_ calls.
+ *
+ * exec_args_add_fname() - install path to be executed
+ * exec_args_add_arg_str() - append an argument string
+ * exec_args_add_env_str() - append an env string
+ */
+int
+exec_args_add_fname(struct image_args *args, char *fname,
+    enum uio_seg segflg)
+{
+	int error;
+	size_t length;
+
+	KASSERT(args->fname == NULL, ("fname already appended"));
+	KASSERT(args->endp == NULL, ("already appending to args"));
+
+	if (fname != NULL) {
+		args->fname = args->buf;
+		error = (segflg == UIO_SYSSPACE) ?
+		    copystr(fname, args->fname, PATH_MAX, &length) :
+		    copyinstr(fname, args->fname, PATH_MAX, &length);
+		if (error != 0)
+			return (error == ENAMETOOLONG ? E2BIG : error);
+	} else
+		length = 0;
+
+	/* Set up for _arg_*()/_env_*() */
+	args->endp = args->buf + length;
+	/* begin_argv and begin_envv must be set and updated */
+	args->begin_argv = args->begin_envv = args->endp;
+	/* Actually (exec_map_entry_size - length) which is >= ARG_MAX */
+	args->stringspace = ARG_MAX;
+
+	return (0);
+}
+
+int
+exec_args_add_arg_str(struct image_args *args, char *argp, enum uio_seg segflg)
+{
+	int error;
+	size_t length;
+
+	KASSERT(args->begin_argv != NULL, ("begin_argp not initialzed"));
+	KASSERT(args->begin_envv == args->endp, ("appending args after env"));
+
+	error = (segflg == UIO_SYSSPACE) ?
+	    copystr(argp, args->endp, args->stringspace, &length) :
+	    copyinstr(argp, args->endp, args->stringspace, &length);
+	if (error != 0)
+		return (error == ENAMETOOLONG ? E2BIG : error);
+	args->stringspace -= length;
+	args->endp += length;
+	args->begin_envv += length;
+	args->argc++;
+
+	return (0);
+}
+
+int
+exec_args_add_env_str(struct image_args *args, char *envp, enum uio_seg segflg)
+{
+	int error;
+	size_t length;
+
+	KASSERT(args->begin_envv != NULL, ("begin_envv not initialzed"));
+
+	error = (segflg == UIO_SYSSPACE) ?
+	    copystr(envp, args->endp, args->stringspace, &length) :
+	    copyinstr(envp, args->endp, args->stringspace, &length);
+	if (error != 0)
+		return (error == ENAMETOOLONG ? E2BIG : error);
+	args->stringspace -= length;
+	args->endp += length;
+	args->envc++;
+
+	return (0);
+}
+
 /*
  * Copy strings out to the new process address space, constructing new arg
  * and env vector tables. Return a pointer to the base so that it can be used
Index: sys/sys/imgact.h
===================================================================
--- sys/sys/imgact.h
+++ sys/sys/imgact.h
@@ -96,6 +96,12 @@
 struct vmspace;
 
 int	exec_alloc_args(struct image_args *);
+int	exec_args_add_arg_str(struct image_args *args, char *argp,
+	    enum uio_seg segflg);
+int	exec_args_add_env_str(struct image_args *args, char *envp,
+	    enum uio_seg segflg);
+int	exec_args_add_fname(struct image_args *args, char *fname,
+	    enum uio_seg segflg);
 int	exec_check_permissions(struct image_params *);
 register_t *exec_copyout_strings(struct image_params *);
 void	exec_free_args(struct image_args *);