diff --git a/kernel/Makefile b/kernel/Makefile
index 4752efee0..8b54d2c56 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -91,7 +91,7 @@ SRCS+= profile.c do_sprofile.c
 
 debug.d: extracted-errno.h extracted-mfield.h extracted-mtype.h
 
-CLEANFILES+=extracted-errno.h extracted-mfield.h extracted-mtype.h
+CLEANFILES+=extracted-errno.h extracted-mfield.h extracted-mtype.h procoffsets.h
 
 extracted-errno.h: extract-errno.sh ../include/errno.h
 	${_MKTARGET_CREATE}
diff --git a/kernel/arch/i386/Makefile.inc b/kernel/arch/i386/Makefile.inc
index 28acb0457..407ea69b8 100644
--- a/kernel/arch/i386/Makefile.inc
+++ b/kernel/arch/i386/Makefile.inc
@@ -2,7 +2,8 @@
 # Makefile for arch-dependent kernel code
 .include <bsd.own.mk>
 
-.PATH:	${.CURDIR}/arch/${ARCH}
+HERE=${.CURDIR}/arch/${ARCH}
+.PATH:	${HERE}
 SRCS+=	arch_do_vmctl.c \
 	arch_clock.c \
 	do_int86.c \
@@ -27,6 +28,20 @@ SRCS+=	arch_do_vmctl.c \
 	arch_system.c \
 	pre_init.c
 
+apic_asm.d klib.d mpx.d: procoffsets.h
+
+# It's OK to hardcode the arch as i386 here as this and procoffsets.cf
+# are i386-specific.
+TMP=procoffsets.h.tmp
+INCLS=../include/arch/i386/include/
+PROCOFFSETSCF=procoffsets.cf
+
+procoffsets.h: $(PROCOFFSETSCF) kernel.h proc.h $(INCLS)/stackframe.h $(INCLS)/archtypes.h
+	${_MKTARGET_CREATE}
+	cat ${HERE}/$(PROCOFFSETSCF) | \
+	  ${TOOL_GENASSYM} -- ${CC} ${CFLAGS} ${CPPFLAGS} ${PROF} >$TMP && \
+	  mv -f $TMP $@ 
+
 .ifdef CONFIG_SMP
 SRCS += arch_smp.c trampoline.S
 .endif
diff --git a/kernel/arch/i386/procoffsets.cf b/kernel/arch/i386/procoffsets.cf
new file mode 100644
index 000000000..9584de24b
--- /dev/null
+++ b/kernel/arch/i386/procoffsets.cf
@@ -0,0 +1,29 @@
+
+include "kernel.h"
+include "proc.h"
+
+struct proc
+member GSREG p_reg.gs
+member FSREG p_reg.fs
+member ESREG p_reg.es
+member DSREG p_reg.ds
+member DIREG p_reg.di
+member SIREG p_reg.si
+member BPREG p_reg.fp
+member STREG p_reg.st
+member BXREG p_reg.bx
+member DXREG p_reg.dx
+member CXREG p_reg.cx
+member AXREG p_reg.retreg
+member RETADR p_reg.retadr
+member PCREG p_reg.pc
+member CSREG p_reg.cs
+member PSWREG p_reg.psw
+member SPREG p_reg.sp
+member SSREG p_reg.ss
+member FP_SAVE_AREA_P p_fpu_state
+member P_LDT_SEL p_seg.p_ldt_sel
+member P_CR3 p_seg.p_cr3
+member P_CR3_V p_seg.p_cr3_v
+member P_LDT p_seg.p_ldt
+
diff --git a/kernel/arch/i386/sconst.h b/kernel/arch/i386/sconst.h
index 5f2bd6e09..c0108185e 100644
--- a/kernel/arch/i386/sconst.h
+++ b/kernel/arch/i386/sconst.h
@@ -2,39 +2,7 @@
 #define __SCONST_H__
 
 #include "kernel/const.h"
-
-/* Miscellaneous constants used in assembler code. */
-	W = _WORD_SIZE	/* Machine word size. */
-
-/* Offsets in struct proc. They MUST match proc.h. */
-	P_STACKBASE = 0
-	GSREG = P_STACKBASE
-	FSREG = GSREG+2	/* 386 introduces FS and GS segments*/
-	ESREG = FSREG+2
-	DSREG = ESREG+2
-	DIREG = DSREG+2
-	SIREG = DIREG+W
-	BPREG = SIREG+W
-	STREG = BPREG+W	/* hole for another SP*/
-	BXREG = STREG+W
-	DXREG = BXREG+W
-	CXREG = DXREG+W
-	AXREG = CXREG+W
-	RETADR = AXREG+W	/* return address for save() call*/
-	PCREG = RETADR+W
-	CSREG = PCREG+W
-	PSWREG = CSREG+W
-	SPREG = PSWREG+W
-	SSREG = SPREG+W
-	P_STACKTOP = SSREG+W
-	FP_SAVE_AREA_P = P_STACKTOP
-	P_LDT_SEL = FP_SAVE_AREA_P + 532
-	P_CR3 = P_LDT_SEL+W
-	P_CR3_V = P_CR3+4
-	P_LDT = P_CR3_V+W
-	P_MISC_FLAGS = P_LDT + 50
-	Msize = 9	/* size of a message in 32-bit words*/
-
+#include "kernel/procoffsets.h"
 
 /*
  * offset to current process pointer right after trap, we assume we always have
diff --git a/tools/nbsd_ports b/tools/nbsd_ports
index b3ed779e1..e23b85638 100644
--- a/tools/nbsd_ports
+++ b/tools/nbsd_ports
@@ -2,6 +2,7 @@
 # Timestamp in UTC,minixpath,netbsdpath
 # minixpath:  path in Minix source tree (starting from /usr/src/)
 # netbsdpath: path in BSD source tree (starting from src/)
+2011/01/17 18:11:10,usr.bin/genassym
 2012/02/10 16:16:12,usr.bin/su
 2011/12/25 06:09:09,sys/arch/i386/stand
 2012/02/10 16:16:12,share/zoneinfo
diff --git a/usr.bin/Makefile b/usr.bin/Makefile
index a301a2f68..a7a987e19 100644
--- a/usr.bin/Makefile
+++ b/usr.bin/Makefile
@@ -4,7 +4,7 @@
 
 # NetBSD imports
 SUBDIR= indent m4 stat tic sed mkdep uniq seq du man \
-	apropos chpass newgrp passwd bzip2 bzip2recover gzip su
+	apropos chpass newgrp passwd bzip2 bzip2recover gzip su genassym
 
 # Non-NetBSD imports
 SUBDIR+= ministat
diff --git a/usr.bin/genassym/Makefile b/usr.bin/genassym/Makefile
new file mode 100644
index 000000000..74de3c7e0
--- /dev/null
+++ b/usr.bin/genassym/Makefile
@@ -0,0 +1,6 @@
+#	$NetBSD: Makefile,v 1.1 2005/06/05 18:19:54 thorpej Exp $
+
+MAN=		genassym.1
+SCRIPTS=	genassym.sh
+
+.include <bsd.prog.mk>
diff --git a/usr.bin/genassym/genassym.1 b/usr.bin/genassym/genassym.1
new file mode 100644
index 000000000..701284926
--- /dev/null
+++ b/usr.bin/genassym/genassym.1
@@ -0,0 +1,92 @@
+.\"	$NetBSD: genassym.1,v 1.5 2010/04/13 09:01:10 jruoho Exp $
+.\"
+.\" Copyright (c) 1997 Matthias Pfaller.
+.\" All rights reserved.
+.\"
+.\" 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 ``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 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.
+.\"
+.Dd April 13, 2010
+.Dt GENASSYM 1
+.Os
+.Sh NAME
+.Nm genassym
+.Nd emit an assym.h file
+.Sh SYNOPSIS
+.Nm genassym
+.Op Fl c
+.Op Fl f
+.Ar C compiler invocation
+.Sh DESCRIPTION
+.Nm
+is a shell script normally used during the kernel build process to
+create an assym.h file.
+This file defines a number of cpp constants derived from the configuration
+information
+.Nm
+reads from stdin. The generated file is used by kernel sources
+written in assembler to gain access to information (e.g. structure
+offsets and sizes) normally only known to the C compiler.
+.Pp
+Arguments to
+.Nm
+are usually of the form
+.Ar ${CC} ${CFLAGS} ${CPPFLAGS}
+where
+.Ar ${CC}
+is the C compiler used to compile the kernel, while
+.Ar ${CFLAGS}
+and
+.Ar ${CPPFLAGS}
+are flag arguments to the C compiler. The script creates a C source file
+from its input. Then the C compiler is called according to the script's
+arguments to compile this file.
+.Pp
+Normally
+.Nm
+instructs the C compiler to create an assembler source from the constructed
+C source. The resulting file is then processed to extract the information
+needed to create the assym.h file. The
+.Fl c
+flag instructs
+.Nm
+to create slightly different code, generate an executable from this code
+and run it. In both cases the assym.h file is written to stdout.
+The
+.Fl f
+flag instructs
+.Nm
+to create forth code.
+.Sh DIAGNOSTICS
+Either self-explanatory, or generated by one of the programs
+called from the script.
+.Sh SEE ALSO
+.Xr genassym.cf 5
+.Sh HISTORY
+The
+.Nm
+command appeared in
+.Nx 1.3
+as
+.Dq genassym.sh
+in
+.Pa /usr/src/sys/kern .
+It became a userland utility in
+.Nx 4.0 .
diff --git a/usr.bin/genassym/genassym.sh b/usr.bin/genassym/genassym.sh
new file mode 100644
index 000000000..1cf2166b8
--- /dev/null
+++ b/usr.bin/genassym/genassym.sh
@@ -0,0 +1,207 @@
+#!/bin/sh -
+#	$NetBSD: genassym.sh,v 1.6 2009/11/28 20:30:01 dsl Exp $
+#
+# Copyright (c) 1997 Matthias Pfaller.
+# All rights reserved.
+#
+# 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 ``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 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.
+#
+
+progname=${0}
+: ${AWK:=awk}
+
+ccode=0		# generate temporary C file, compile it, execute result
+fcode=0		# generate Forth code
+
+usage()
+{
+
+	echo "usage: ${progname} [-c | -f] -- compiler command" >&2
+}
+
+while getopts cf i
+do
+	case "$i" in
+	c)
+		ccode=1
+		;;
+	f)
+		fcode=1
+		;;
+	esac
+done
+shift $(($OPTIND - 1))
+if [ $# -eq 0 ]; then
+	usage
+	exit 1
+fi
+
+# Deal with any leading environment settings..
+
+while [ "$1" ]
+do
+	case "$1" in
+	*=*)
+		eval export "$1"
+		shift
+		;;
+	*)
+		break
+		;;
+	esac
+done
+
+genassym_temp=/tmp/genassym.$$
+
+if ! mkdir $genassym_temp; then
+	echo "${progname}: unable to create temporary directory" >&2
+	exit 1
+fi
+trap "rm -rf $genassym_temp" 0 1 2 3 15
+
+$AWK '
+BEGIN {
+	printf("#define	offsetof(type, member) ((size_t)(&((type *)0)->member))\n");
+	defining = 0;
+	type = "long";
+	asmtype = "n";
+	asmprint = "";
+}
+
+{
+	doing_member = 0;
+}
+
+$0 ~ /^[ \t]*#.*/ || $0 ~ /^[ \t]*$/ {
+	# Just ignore comments and empty lines
+	next;
+}
+
+$0 ~ /^config[ \t]/ {
+	type = $2;
+	asmtype = $3;
+	asmprint = $4;
+	next;
+}
+
+/^include[ \t]/ {
+	if (defining != 0) {
+		defining = 0;
+		printf("}\n");
+	}
+	printf("#%s\n", $0);
+	next;
+}
+
+$0 ~ /^if[ \t]/ ||
+$0 ~ /^ifdef[ \t]/ ||
+$0 ~ /^ifndef[ \t]/ ||
+$0 ~ /^else/ ||
+$0 ~ /^elif[ \t]/ ||
+$0 ~ /^endif/ {
+	printf("#%s\n", $0);
+	next;
+}
+
+/^struct[ \t]/ {
+	structname = $2;
+	$0 = "define " structname "_SIZEOF sizeof(struct " structname ")";
+	# fall through
+}
+
+/^member[ \t]/ {
+	if (NF > 2)
+		$0 = "define " $2 " offsetof(struct " structname ", " $3 ")";
+	else
+		$0 = "define " $2 " offsetof(struct " structname ", " $2 ")";
+	doing_member = 1;
+	# fall through
+}
+
+/^export[ \t]/ {
+	$0 = "define " $2 " " $2;
+	# fall through
+}
+
+/^define[ \t]/ {
+	if (defining == 0) {
+		defining = 1;
+		printf("void f" FNR "(void);\n");
+		printf("void f" FNR "(void) {\n");
+		if (ccode)
+			call[FNR] = "f" FNR;
+		defining = 1;
+	}
+	value = $0
+	gsub("^define[ \t]+[A-Za-z_][A-Za-z_0-9]*[ \t]+", "", value)
+	if (ccode)
+		printf("printf(\"#define " $2 " %%ld\\n\", (%s)" value ");\n", type);
+	else if (fcode) {
+		if (doing_member)
+			printf("__asm(\"XYZZY : %s d# %%%s0 + ;\" : : \"%s\" (%s));\n", $2, asmprint, asmtype, value);
+		else
+			printf("__asm(\"XYZZY d# %%%s0 constant %s\" : : \"%s\" (%s));\n", asmprint, $2, asmtype, value);
+	} else
+		printf("__asm(\"XYZZY %s %%%s0\" : : \"%s\" (%s));\n", $2, asmprint, asmtype, value);
+	next;
+}
+
+/^quote[ \t]/ {
+	gsub("^quote[ \t]+", "");
+	print;
+	next;
+}
+
+{
+	printf("syntax error in line %d\n", FNR) >"/dev/stderr";
+	exit(1);
+}
+
+END {
+	if (defining != 0) {
+		defining = 0;
+		printf("}\n");
+	}
+	if (ccode) {
+		printf("int main(int argc, char **argv) {");
+		for (i in call)
+			printf(call[i] "();");
+		printf("return(0); }\n");
+	}
+}
+' ccode=$ccode fcode=$fcode > ${genassym_temp}/assym.c || exit 1
+
+if [ $ccode = 1 ] ; then
+	"$@" ${genassym_temp}/assym.c -o ${genassym_temp}/genassym && \
+	    ${genassym_temp}/genassym
+elif [ $fcode = 1 ]; then
+	# Kill all of the "#" and "$" modifiers; locore.s already
+	# prepends the correct "constant" modifier.
+	"$@" -S ${genassym_temp}/assym.c -o - | sed -e 's/\$//g' | \
+	    sed -n 's/.*XYZZY//gp'
+else
+	# Kill all of the "#" and "$" modifiers; locore.s already
+	# prepends the correct "constant" modifier.
+	"$@" -S ${genassym_temp}/assym.c -o - > \
+	    ${genassym_temp}/genassym.out && \
+	    sed -e 's/#//g' -e 's/\$//g' < ${genassym_temp}/genassym.out | \
+	    sed -n 's/.*XYZZY/#define/gp'
+fi