diff --git a/tools/build/Makefile b/tools/build/Makefile
--- a/tools/build/Makefile
+++ b/tools/build/Makefile
@@ -212,8 +212,8 @@
 	-DHAVE_DIRFD -DHAVE_SYSCONF
 # Provide getprogname/setprograme
 SRCS+=	progname.c
-# Stub implementations of fflagstostr/strtofflags
-SRCS+=	fflags.c
+# Provide fflagstostr/strtofflags for mtree and makefs
+SRCS+=	strtofflags.c
 
 # macOS has a standalone cross-build implementation, but Linux can use the same
 # ELF one as FreeBSD
diff --git a/tools/build/cross-build/fflags.c b/tools/build/cross-build/fflags.c
deleted file mode 100644
--- a/tools/build/cross-build/fflags.c
+++ /dev/null
@@ -1,62 +0,0 @@
-/*-
- * SPDX-License-Identifier: BSD-2-Clause
- *
- * Copyright 2018-2020 Alex Richardson <arichardson@FreeBSD.org>
- *
- * This software was developed by SRI International and the University of
- * Cambridge Computer Laboratory (Department of Computer Science and
- * Technology) under DARPA contract HR0011-18-C-0016 ("ECATS"), as part of the
- * DARPA SSITH research programme.
- *
- * This software was developed by SRI International and the University of
- * Cambridge Computer Laboratory under DARPA/AFRL contract (FA8750-10-C-0237)
- * ("CTSRD"), as part of the DARPA CRASH research programme.
- *
- * This work was supported by Innovate UK project 105694, "Digital Security by
- * Design (DSbD) Technology Platform Prototype".
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#include <string.h>
-#include <unistd.h>
-
-char *
-fflagstostr(u_long flags __unused)
-{
-	return strdup("");
-}
-
-int
-strtofflags(char **stringp __unused, u_long *setp, u_long *clrp)
-{
-	/* On linux just ignore the file flags for now */
-	/*
-	 * XXX: this will prevent makefs from setting noschg on libc, etc.
-	 * so we should really find a way to support flags in disk images.
-	 */
-	if (setp)
-		*setp = 0;
-	if (clrp)
-		*clrp = 0;
-	return (0); /* success */
-}
diff --git a/tools/build/cross-build/include/linux/sys/stat.h b/tools/build/cross-build/include/linux/sys/stat.h
--- a/tools/build/cross-build/include/linux/sys/stat.h
+++ b/tools/build/cross-build/include/linux/sys/stat.h
@@ -66,5 +66,25 @@
 #define ALLPERMS (S_ISUID | S_ISGID | S_ISTXT | S_IRWXU | S_IRWXG | S_IRWXO)
 #endif
 
+#define	UF_SETTABLE	0x0000ffff
+#define	UF_NODUMP	0x00000001
+#define	UF_IMMUTABLE	0x00000002
+#define	UF_APPEND	0x00000004
+#define	UF_OPAQUE	0x00000008
+#define	UF_NOUNLINK	0x00000010
+#define	UF_SYSTEM	0x00000080
+#define	UF_SPARSE	0x00000100
+#define	UF_OFFLINE	0x00000200
+#define	UF_REPARSE	0x00000400
+#define	UF_ARCHIVE	0x00000800
+#define	UF_READONLY	0x00001000
+#define	UF_HIDDEN	0x00008000
+#define	SF_SETTABLE	0xffff0000
+#define	SF_ARCHIVED	0x00010000
+#define	SF_IMMUTABLE	0x00020000
+#define	SF_APPEND	0x00040000
+#define	SF_NOUNLINK	0x00100000
+#define	SF_SNAPSHOT	0x00200000
+
 /* This include is needed for OpenZFS bootstrap */
 #include <sys/mount.h>