diff --git a/sim/common/ChangeLog b/sim/common/ChangeLog
index 134111fe2e..5d4fb35355 100644
--- a/sim/common/ChangeLog
+++ b/sim/common/ChangeLog
@@ -1,3 +1,9 @@
+2000-12-13  Ben Elliston  <bje@redhat.com>
+
+	* cgen.sh: Set prefix/PREFIX (append ISA if applicable). Factor
+	sed expressions into $sedscript, substituting @prefix@/@PREFIX@.
+	(defs): New action.
+
 2000-12-12  Geoffrey Keating  <geoffk@redhat.com>
 
 	* sim-endian.h: Don't have parameters on macro definitions which
diff --git a/sim/common/cgen.sh b/sim/common/cgen.sh
index 58449af7f3..14fa247773 100644
--- a/sim/common/cgen.sh
+++ b/sim/common/cgen.sh
@@ -1,8 +1,8 @@
 #! /bin/sh
 # Generate CGEN simulator files.
 #
-# Usage: /bin/sh cgen.sh {"arch"|"cpu"|"decode"|"cpu-decode"} srcdir \
-#	cgen cgendir cgenflags \
+# Usage: /bin/sh cgen.sh {"arch"|"cpu"|"decode"|"defs"|"cpu-decode"} \
+#	srcdir cgen cgendir cgenflags \
 #	arch archflags cpu mach suffix extrafiles
 #
 # We store the generated files in the source directory until we decide to
@@ -21,21 +21,30 @@ arch=$6
 archflags=$7
 cpu=$8
 isa=$9
-# bring parms past 9 portably into view
+# portably bring parameters beyond $9 into view
 shift ; mach=$9
 shift ; suffix=$9
 shift ; extrafiles=$9
 
 rootdir=${srcdir}/../..
 
+if test -z "$isa" ; then
+  isa=all
+  prefix=$cpu
+else
+  prefix=${cpu}_$isa
+fi
+
 lowercase='abcdefghijklmnopqrstuvwxyz'
 uppercase='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
 ARCH=`echo ${arch} | tr "${lowercase}" "${uppercase}"`
 CPU=`echo ${cpu} | tr "${lowercase}" "${uppercase}"`
+PREFIX=`echo ${prefix} | tr "${lowercase}" "${uppercase}"`
 
-if test -z "$isa" ; then
-  isa=all
-fi
+sedscript="\
+-e s/@ARCH@/${ARCH}/g -e s/@arch@/${arch}/g \
+-e s/@CPU@/${CPU}/g -e s/@cpu@/${cpu}/g \
+-e s/@PREFIX@/${PREFIX}/g -e s/@prefix@/${prefix}/g"
 
 case $action in
 arch)
@@ -53,11 +62,11 @@ arch)
 		-A tmp-arch.h1 \
 		-B tmp-arch.c1 \
 		-N tmp-all.h1
-	sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" < tmp-arch.h1 > tmp-arch.h
+	sed $sedscript < tmp-arch.h1 > tmp-arch.h
 	${rootdir}/move-if-change tmp-arch.h ${srcdir}/arch.h
-	sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" < tmp-arch.c1 > tmp-arch.c
+	sed $sedscript < tmp-arch.c1 > tmp-arch.c
 	${rootdir}/move-if-change tmp-arch.c ${srcdir}/arch.c
-	sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" < tmp-all.h1 > tmp-all.h
+	sed $sedscript < tmp-all.h1 > tmp-all.h
 	${rootdir}/move-if-change tmp-all.h ${srcdir}/cpuall.h
 
 	rm -f tmp-arch.h1 tmp-arch.c1 tmp-all.h1
@@ -102,30 +111,30 @@ cpu | decode | cpu-decode)
 
 	case $action in
 	*cpu*)
-		sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" -e "s/@CPU@/${CPU}/g" -e "s/@cpu@/${cpu}/g" < tmp-cpu.h1 > tmp-cpu.h
+		sed $sedscript < tmp-cpu.h1 > tmp-cpu.h
 		${rootdir}/move-if-change tmp-cpu.h ${srcdir}/cpu${suffix}.h
-		sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" -e "s/@CPU@/${CPU}/g" -e "s/@cpu@/${cpu}/g" < tmp-cpu.c1 > tmp-cpu.c
+		sed $sedscript < tmp-cpu.c1 > tmp-cpu.c
 		${rootdir}/move-if-change tmp-cpu.c ${srcdir}/cpu${suffix}.c
-		sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" -e "s/@CPU@/${CPU}/g" -e "s/@cpu@/${cpu}/g" < tmp-mod.c1 > tmp-mod.c
+		sed $sedscript < tmp-mod.c1 > tmp-mod.c
 		${rootdir}/move-if-change tmp-mod.c ${srcdir}/model${suffix}.c
 		if test -f tmp-ext.c1 ; then \
-			sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" -e "s/@CPU@/${CPU}/g" -e "s/@cpu@/${cpu}/g" < tmp-ext.c1 > tmp-ext.c ; \
+			sed $sedscript < tmp-ext.c1 > tmp-ext.c ; \
 			${rootdir}/move-if-change tmp-ext.c ${srcdir}/extract${suffix}.c ; \
 		fi
 		if test -f tmp-read.c1 ; then \
-			sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" -e "s/@CPU@/${CPU}/g" -e "s/@cpu@/${cpu}/g" < tmp-read.c1 > tmp-read.c ; \
+			sed $sedscript < tmp-read.c1 > tmp-read.c ; \
 			${rootdir}/move-if-change tmp-read.c ${srcdir}/read${suffix}.c ; \
 		fi
 		if test -f tmp-write.c1 ; then \
-			sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" -e "s/@CPU@/${CPU}/g" -e "s/@cpu@/${cpu}/g" < tmp-write.c1 > tmp-write.c ; \
+			sed $sedscript < tmp-write.c1 > tmp-write.c ; \
 			${rootdir}/move-if-change tmp-write.c ${srcdir}/write${suffix}.c ; \
 		fi
 		if test -f tmp-sem.c1 ; then \
-			sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" -e "s/@CPU@/${CPU}/g" -e "s/@cpu@/${cpu}/g" < tmp-sem.c1 > tmp-sem.c ; \
+			sed $sedscript < tmp-sem.c1 > tmp-sem.c ; \
 			${rootdir}/move-if-change tmp-sem.c ${srcdir}/sem${suffix}.c ; \
 		fi
 		if test -f tmp-semsw.c1 ; then \
-			sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" -e "s/@CPU@/${CPU}/g" -e "s/@cpu@/${cpu}/g" < tmp-semsw.c1 > tmp-semsw.c ; \
+			sed $sedscript < tmp-semsw.c1 > tmp-semsw.c ; \
 			${rootdir}/move-if-change tmp-semsw.c ${srcdir}/sem${suffix}-switch.c ; \
 		fi
 
@@ -137,9 +146,9 @@ cpu | decode | cpu-decode)
 
 	case $action in
 	*decode*)
-		sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" -e "s/@CPU@/${CPU}/g" -e "s/@cpu@/${cpu}/g" < tmp-dec.h1 > tmp-dec.h
+		sed $sedscript < tmp-dec.h1 > tmp-dec.h
 		${rootdir}/move-if-change tmp-dec.h ${srcdir}/decode${suffix}.h
-		sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" -e "s/@CPU@/${CPU}/g" -e "s/@cpu@/${cpu}/g" < tmp-dec.c1 > tmp-dec.c
+		sed $sedscript < tmp-dec.c1 > tmp-dec.c
 		${rootdir}/move-if-change tmp-dec.c ${srcdir}/decode${suffix}.c
 
 		rm -f tmp-dec.h1 tmp-dec.c1
@@ -148,6 +157,21 @@ cpu | decode | cpu-decode)
 
 	;;
 
+defs)
+	rm -f tmp-defs.h1 tmp-defs.h
+	
+	${cgen} -s ${cgendir}/cgen-sim.scm \
+		-s ${cgendir} \
+		${cgenflags} \
+		-f "${archflags}" \
+		-m ${mach} \
+		-a ${arch} \
+		-i ${isa} \
+		-G tmp-defs.h1
+	sed $sedscript < tmp-defs.h1 > tmp-defs.h
+	${rootdir}/move-if-change tmp-defs.h ${srcdir}/defs${suffix}.h
+	;;
+
 desc)
 	rm -f tmp-desc.h1 tmp-desc.h
 	rm -f tmp-desc.c1 tmp-desc.c
@@ -163,19 +187,18 @@ desc)
 		-H tmp-desc.h1 \
 		-C tmp-desc.c1 \
 		-O tmp-opc.h1
-	sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" < tmp-desc.h1 > tmp-desc.h
+	sed $sedscript < tmp-desc.h1 > tmp-desc.h
 	${rootdir}/move-if-change tmp-desc.h ${srcdir}/${arch}-desc.h
-	sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" \
-		-e "s/@prefix@/${arch}/" < tmp-desc.c1 > tmp-desc.c
+	sed $sedscript < tmp-desc.c1 > tmp-desc.c
 	${rootdir}/move-if-change tmp-desc.c ${srcdir}/${arch}-desc.c
-	sed -e "s/@ARCH@/${ARCH}/g" -e "s/@arch@/${arch}/g" < tmp-opc.h1 > tmp-opc.h
+	sed $sedscript < tmp-opc.h1 > tmp-opc.h
 	${rootdir}/move-if-change tmp-opc.h ${srcdir}/${arch}-opc.h
 
 	rm -f tmp-desc.h1 tmp-desc.c1 tmp-opc.h1
 	;;
 
 *)
-	echo "cgen.sh: bad action: ${action}" >&2
+	echo "`basename $0`: unknown action: ${action}" >&2
 	exit 1
 	;;