diff --git a/plat/msdos86/include/sys/types.h b/plat/msdos86/include/sys/types.h
index 6a0c3d3db..005f48eb0 100644
--- a/plat/msdos86/include/sys/types.h
+++ b/plat/msdos86/include/sys/types.h
@@ -1,7 +1,7 @@
 #ifndef _SYS_TYPES_H
 #define _SYS_TYPES_H
 
-typedef int pid_t;
+typedef long pid_t;
 typedef int mode_t;
 typedef long time_t;
 typedef long suseconds_t;
diff --git a/plat/msdos86/libsys/getpid.s b/plat/msdos86/libsys/getpid.s
new file mode 100644
index 000000000..009c4f9f4
--- /dev/null
+++ b/plat/msdos86/libsys/getpid.s
@@ -0,0 +1,27 @@
+#
+! $Source$
+! $State$
+! $Revision$
+
+! Declare segments (the order is important).
+
+.sect .text
+.sect .rom
+.sect .data
+.sect .bss
+
+.sect .text
+
+! Get the current process identifier.  For MS-DOS, use the Program Segment
+! Prefix (PSP) segment as the PID.
+!
+! (Note that pid_t is a 32-bit type.  This is to allow for PSP addresses
+! above 0x7FFF:0.)
+
+.define _getpid
+_getpid:
+	movb ah, 0x51
+	int 0x21
+	xchg bx, ax
+	xor dx, dx
+	ret
diff --git a/plat/msdos86/libsys/libsys.h b/plat/msdos86/libsys/libsys.h
index ddba5cda6..3488c332e 100644
--- a/plat/msdos86/libsys/libsys.h
+++ b/plat/msdos86/libsys/libsys.h
@@ -49,5 +49,10 @@ extern ssize_t _sys_rawread(int, char *, size_t);
 extern ssize_t _sys_rawwrite(int, const char *, size_t);
 extern int _sys_isopen(int);
 extern int _sys_isreadyr(int);
+extern int _sys_exists(const char *);
+extern int _sys_rawcreat(const char *, unsigned);
+extern int _sys_rawopen(const char *, int);
+extern off_t _sys_rawlseek(int, off_t, int);
+
 
 #endif
diff --git a/plat/msdos86/libsys/lseek.c b/plat/msdos86/libsys/lseek.c
new file mode 100644
index 000000000..db996a1dd
--- /dev/null
+++ b/plat/msdos86/libsys/lseek.c
@@ -0,0 +1,26 @@
+/* $Source$
+ * $State$
+ * $Revision$
+ */
+
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+#include "libsys.h"
+
+off_t lseek(int fd, off_t offset, int whence)
+{
+	off_t newoff;
+
+	if (whence != SEEK_SET && whence != SEEK_CUR && whence != SEEK_END)
+	{
+		errno = EINVAL;
+		return -1L;
+	}
+
+	newoff = _sys_rawlseek(fd, offset, whence);
+	if (newoff != -1L)
+		_sys_seteof(fd, 0);
+
+	return newoff;
+}
diff --git a/plat/msdos86/libsys/open.c b/plat/msdos86/libsys/open.c
new file mode 100644
index 000000000..038ab004b
--- /dev/null
+++ b/plat/msdos86/libsys/open.c
@@ -0,0 +1,101 @@
+/* $Source$
+ * $State$
+ * $Revision$
+ */
+
+/*
+ * Derived from dos-open.c for newlib-ia16 which was written for the
+ * gcc-ia16 toolchain.
+ *
+ * Copyright (c) 2018 Bart Oldeman
+ * Copyright (c) 2019--2021 TK Chia
+ *
+ * The authors hereby grant permission to use, copy, modify, distribute,
+ * and license this software and its documentation for any purpose, provided
+ * that existing copyright notices are retained in all copies and that this
+ * notice is included verbatim in any distributions. No written agreement,
+ * license, or royalty fee is required for any of the authorized uses.
+ * Modifications to this software may be copyrighted by their authors
+ * and need not follow the licensing terms described here, provided that
+ * the new terms are clearly indicated on the first page of each file where
+ * they apply.
+ */
+
+#include <errno.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <unistd.h>
+#include "libsys.h"
+
+int open(const char* pathname, int flags, ...)
+{
+	int fd = -1, binmode;
+	off_t ret;
+
+	if ((flags & ~(O_ACCMODE | O_CREAT | O_TRUNC | O_APPEND
+		       | O_TEXT | O_BINARY)))
+	{
+		/* bail out if there are unknown flags */
+		errno = EINVAL;
+		return -1;
+	}
+
+	binmode = flags & (O_TEXT | O_BINARY);
+	if (binmode != O_TEXT && binmode != O_BINARY && binmode != 0)
+	{
+		/* bail out if both O_TEXT and O_BINARY are specified (!) */
+		errno = EINVAL;
+		return -1;
+	}
+
+	if ((flags & O_CREAT))
+	{
+		/* special but common case O_WRONLY | O_CREAT | O_TRUNC
+		 * should be handled by only calling _sys_rawcreat */
+		int fileexists = 0;
+		if (!(flags & O_TRUNC))
+			fileexists = _sys_exists(pathname);
+		if (!fileexists)
+		{
+			va_list ap;
+			mode_t mode;
+
+			va_start(ap, flags);
+			mode = va_arg(ap, mode_t);
+			va_end(ap);
+
+			fd = _sys_rawcreat(pathname, mode & 0200 ? 0 : 1);
+			if (fd != -1)
+			{
+				if ((flags & O_ACCMODE) == O_WRONLY)
+					return fd;
+				close(fd);
+				fd = -1;
+			}
+		}
+	}
+
+	/* try to open file with mode */
+	if (fd == -1)
+		fd = _sys_rawopen(pathname, flags & O_ACCMODE);
+	if (fd == -1)
+		return fd;
+	ret = 0;
+
+	/* handle O_TRUNC and O_APPEND */
+	if ((flags & O_TRUNC))
+		ret = _sys_rawwrite(fd, NULL, 0);
+	else if ((flags & O_APPEND))
+		ret = _sys_rawlseek(fd, 0L, SEEK_END);
+	if (ret == -1)
+	{
+		close(fd);
+		return -1;
+	}
+
+	/* handle O_TEXT and O_BINARY, and reset "end of file encountered" */
+	_sys_setmode(fd, binmode == O_BINARY ? O_BINARY : O_TEXT);
+	_sys_seteof(fd, 0);
+
+	return fd;
+}
diff --git a/plat/msdos86/libsys/sys_exists.s b/plat/msdos86/libsys/sys_exists.s
new file mode 100644
index 000000000..e282ef687
--- /dev/null
+++ b/plat/msdos86/libsys/sys_exists.s
@@ -0,0 +1,25 @@
+#
+! $Source$
+! $State$
+! $Revision$
+
+! Declare segments (the order is important).
+
+.sect .text
+.sect .rom
+.sect .data
+.sect .bss
+
+.sect .text
+
+! Say whether a file exists with the given name.
+
+.define __sys_exists
+__sys_exists:
+	mov bx, sp
+	mov dx, 2(bx)
+	mov ax, 0x4300
+	int 0x21
+	sbb ax, ax
+	inc ax
+	ret
diff --git a/plat/msdos86/libsys/sys_rawcreat.s b/plat/msdos86/libsys/sys_rawcreat.s
new file mode 100644
index 000000000..67bc34e59
--- /dev/null
+++ b/plat/msdos86/libsys/sys_rawcreat.s
@@ -0,0 +1,24 @@
+#
+! $Source$
+! $State$
+! $Revision$
+
+! Declare segments (the order is important).
+
+.sect .text
+.sect .rom
+.sect .data
+.sect .bss
+
+.sect .text
+
+! Create or truncate a file.
+
+.define __sys_rawcreat
+__sys_rawcreat:
+	movb ah, 0x3c
+	mov bx, sp
+	mov dx, 2(bx)
+	mov cx, 4(bx)
+	int 0x21
+	jmp .sys_axret
diff --git a/plat/msdos86/libsys/sys_rawlseek.s b/plat/msdos86/libsys/sys_rawlseek.s
new file mode 100644
index 000000000..992c4c655
--- /dev/null
+++ b/plat/msdos86/libsys/sys_rawlseek.s
@@ -0,0 +1,26 @@
+#
+! $Source$
+! $State$
+! $Revision$
+
+! Declare segments (the order is important).
+
+.sect .text
+.sect .rom
+.sect .data
+.sect .bss
+
+.sect .text
+
+! Move the current file position for a file descriptor.
+
+.define __sys_rawlseek
+__sys_rawlseek:
+	movb ah, 0x42
+	mov bx, sp
+	mov dx, 4(bx)
+	mov cx, 6(bx)
+	movb al, 8(bx)
+	mov bx, 2(bx)
+	int 0x21
+	jmp .sys_dxaxret
diff --git a/plat/msdos86/libsys/sys_rawopen.s b/plat/msdos86/libsys/sys_rawopen.s
new file mode 100644
index 000000000..301e2fded
--- /dev/null
+++ b/plat/msdos86/libsys/sys_rawopen.s
@@ -0,0 +1,24 @@
+#
+! $Source$
+! $State$
+! $Revision$
+
+! Declare segments (the order is important).
+
+.sect .text
+.sect .rom
+.sect .data
+.sect .bss
+
+.sect .text
+
+! Open an existing file.
+
+.define __sys_rawopen
+__sys_rawopen:
+	movb ah, 0x3d
+	mov bx, sp
+	mov dx, 2(bx)
+	movb al, 4(bx)
+	int 0x21
+	jmp .sys_axret
diff --git a/plat/msdos86/libsys/sys_seterrno.c b/plat/msdos86/libsys/sys_seterrno.c
index 779e600f5..b135aea33 100644
--- a/plat/msdos86/libsys/sys_seterrno.c
+++ b/plat/msdos86/libsys/sys_seterrno.c
@@ -33,9 +33,9 @@ static const signed char err_map[] =
 
 /*
  * Map an MS-DOS 2+ system error code to an `errno' value and store that in
- * `errno'.  Return -1.
+ * `errno'.  Return a longword -1.
  */
-int _sys_seterrno(unsigned dos_err)
+long _sys_seterrno(unsigned dos_err)
 {
 	if (dos_err < sizeof(err_map) / sizeof(err_map[0]))
 		errno = err_map[dos_err];
diff --git a/plat/msdos86/libsys/sys_xret.s b/plat/msdos86/libsys/sys_xret.s
index a5b65116a..57f407ef4 100644
--- a/plat/msdos86/libsys/sys_xret.s
+++ b/plat/msdos86/libsys/sys_xret.s
@@ -13,20 +13,26 @@
 .sect .text
 
 ! .sys_zret: if the carry flag is set, then set `errno' from the DOS error
-! code in ax, and return -1.  If the carry flag is clear, just return zero.
+! code in ax, and return a shortword -1.  If the carry flag is clear, just
+! return a shortword zero.
 !
 ! .sys_axret: if the carry flag is set, then set `errno' from the DOS error
-! code in ax, and return -1.  If the carry flag is clear, just return ax as
-! a return value.
+! code in ax, and return a shortword -1.  If the carry flag is clear, just
+! return ax as a return value.
+!
+! .sys_dxaxret: same as .sys_axret, but return a longword -1 or dx:ax as a
+! return value.
 
 .extern .sys_zret
 .extern .sys_axret
+.extern .sys_dxaxret
 .sys_zret:
 	jc error
 	xor ax, ax
 no_error:
 	ret
 .sys_axret:
+.sys_dxaxret:
 	jnc no_error
 error:
 	push ax