diff --git a/Makefile b/Makefile
index 637e8baaf..98f36bef3 100644
--- a/Makefile
+++ b/Makefile
@@ -50,15 +50,17 @@ include util/opt/build.mk
 include util/ncgg/build.mk
 include util/arch/build.mk
 include util/misc/build.mk
+include util/led/build.mk
+include util/topgen/build.mk
 
 include lang/cem/build.mk
 
 include mach/proto/as/build.mk
 include mach/proto/ncg/build.mk
+include mach/proto/top/build.mk
 
 include plat/linux/liblinux/build.mk
 
-include mach/build.mk
 include mach/i80/build.mk
 include mach/i386/build.mk
 include mach/i86/build.mk
diff --git a/lang/cem/libcc.ansi/build.mk b/lang/cem/libcc.ansi/build.mk
index 727d04718..a9434ceb4 100644
--- a/lang/cem/libcc.ansi/build.mk
+++ b/lang/cem/libcc.ansi/build.mk
@@ -254,6 +254,14 @@ $(call ackfile, lang/cem/libcc.ansi/time/misc.c)
 $(call acklibrary, $(LIBDIR)/$(PLATFORM)/libc.a)
 $(call installto, $(PLATIND)/$(PLATFORM)/libc.a)
 
+# CRT
+
+$(call reset)
+$(eval objdir := $(PLATFORM))
+$(eval ackflags += -Ih)
+$(call ackfile, lang/cem/libcc.ansi/head_ac.e)
+$(call installto, $(PLATIND)/$(PLATFORM)/c-ansi.o)
+
 endef
 
 build-runtime-libcc-ansi = $(eval $(build-runtime-libcc-ansi-impl))
diff --git a/mach/build.mk b/mach/build.mk
deleted file mode 100644
index 368e6b0ca..000000000
--- a/mach/build.mk
+++ /dev/null
@@ -1,12 +0,0 @@
-define build-architecture-impl
-	$(eval ARCHITECTURE_$(ARCH) := \
-			$(PLATDEP)/$(ARCH)/as \
-			$(PLATDEP)/$(ARCH)/ncg)
-
-	$(eval PLATFORM := $(ARCH))
-    $(call build-as)
-    $(call build-ncg)
-endef
-
-build-architecture = $(eval $(build-architecture-impl))
-
diff --git a/mach/i386/build.mk b/mach/i386/build.mk
index f4670cc2f..acd5e51eb 100644
--- a/mach/i386/build.mk
+++ b/mach/i386/build.mk
@@ -1,8 +1,53 @@
-ARCH := i386
-OPTIMISATION := -O
+arch-libem-i386 = \
+	adi.s \
+	and.s \
+	blm.s \
+	cii.s \
+	cms.s \
+	com.s \
+	csa4.s \
+	csb4.s \
+	cuu.s \
+	dup.s \
+	dvi.s \
+	dvu.s \
+	error.s \
+	exg.s \
+	fp8087.s \
+	fat.s \
+	gto.s \
+	iaar.s \
+	ilar.s \
+	inn.s \
+	ior.s \
+	isar.s \
+	lar4.s \
+	loi.s \
+	mli.s \
+	mon.s \
+	ngi.s \
+	nop.s \
+	print.s \
+	rck.s \
+	rmi.s \
+	rmu.s \
+	rol.s \
+	ror.s \
+	sar4.s \
+	sbi.s \
+	set.s \
+	sli.s \
+	sri.s \
+	sti.s \
+	strhp.s \
+	trp.s \
+	unknown.s \
+	xor.s
 
-D := mach/i386
-
-$(eval $(call build-architecture))
+arch-libend-i386 = \
+	edata.s \
+	em_end.s \
+	end.s \
+	etext.s
 
 
diff --git a/mach/i80/build.mk b/mach/i80/build.mk
index bd3cfc2b3..ce9b07c67 100644
--- a/mach/i80/build.mk
+++ b/mach/i80/build.mk
@@ -1,8 +1,47 @@
-ARCH := i80
-OPTIMISATION := -O
+arch-libem-i80 = \
+	aar2.s \
+	adi4.s \
+	and.s \
+	blm.s \
+	cii.s \
+	cmi4.s \
+	cms.s \
+	com.s \
+	csa.s \
+	csb.s \
+	dup.s \
+	dvi2.s \
+	exg.s \
+	flp.s \
+	inn.s \
+	ior.s \
+	lar2.s \
+	mli2.s \
+	mli4.s \
+	mlu2.s \
+	ngi4.s \
+	nop.s \
+	rol4.s \
+	ror4.s \
+	sar2.s \
+	sbi4.s \
+	set.s \
+	set2.s \
+	sli2.s \
+	sli4.s \
+	sri2.s \
+	sri4.s \
+	xor.s \
+	loi.s \
+	sti.s \
+	dvi4.s \
+	rck.s
 
-D := mach/i80
-
-$(eval $(call build-architecture))
+arch-libend-i80 = \
+	edata.s \
+	em_end.s \
+	end.s \
+	etext.s
 
+arch-top-i80 = yes
 
diff --git a/mach/i86/build.mk b/mach/i86/build.mk
index 2f999023d..1613b651f 100644
--- a/mach/i86/build.mk
+++ b/mach/i86/build.mk
@@ -1,8 +1,68 @@
-ARCH := i86
-OPTIMISATION := -O
+arch-libem-i86 := \
+	adi.s \
+	and.s \
+	cii.s \
+	cms.s \
+	cmi4.s \
+	cmu4.s \
+	com.s \
+	csa2.s \
+	csb2.s \
+	csa4.s \
+	csb4.s \
+	cuu.s \
+	dup.s \
+	dvi.s \
+	dvi4.s \
+	dvu.s \
+	dvu4.s \
+	exg.s \
+	fp8087.s \
+	gto.s \
+	iaar.s \
+	ilar.s \
+	inn.s \
+	ior.s \
+	isar.s \
+	lar2.s \
+	loi.s \
+	mli.s \
+	mli4.s \
+	mon.s \
+	ngi.s \
+	nop.s \
+	rck.s \
+	rmi.s \
+	rmi4.s \
+	rmu.s \
+	rmu4.s \
+	rol.s \
+	ror.s \
+	sar2.s \
+	sbi.s \
+	set.s \
+	sli.s \
+	sri.s \
+	sti.s \
+	strhp.s \
+	xor.s \
+	error.s \
+	unknown.s \
+	fat.s \
+	trp.s \
+	print.s \
+	ret6.s \
+	ret8.s \
+	lfr6.s \
+	lfr8.s \
+	retarea.s \
+	blm.s \
+	return.s
 
-D := mach/i86
-
-$(eval $(call build-architecture))
+arch-libend-i86 = \
+	edata.s \
+	em_end.s \
+	end.s \
+	etext.s
 
 
diff --git a/mach/m68020/build.mk b/mach/m68020/build.mk
index 2ddaf85a0..5dac37653 100644
--- a/mach/m68020/build.mk
+++ b/mach/m68020/build.mk
@@ -1,8 +1,33 @@
-ARCH := m68020
-OPTIMISATION := -O6
+arch-libem-m68020 = \
+	fp68881.s \
+	aar.s \
+	lar.s \
+	sar.s \
+	csa.s \
+	csb.s \
+	shp.s \
+	set.s \
+	inn.s \
+	fat.s \
+	trp.s \
+	trpstr.c \
+	mon.s \
+	nop.s \
+	dia.s \
+	cii.s \
+	cuu.s \
+	cmi.s \
+	cms.s \
+	cmu.s \
+	cvf.s \
+	exg.s \
+	los.s \
+	sts.s
 
-D := mach/m68020
-
-$(eval $(call build-architecture))
+arch-libend-m68020 = \
+	edata.s \
+	em_end.s \
+	end.s \
+	etext.s
 
 
diff --git a/mach/powerpc/build.mk b/mach/powerpc/build.mk
index 75cbeb5d0..e69de29bb 100644
--- a/mach/powerpc/build.mk
+++ b/mach/powerpc/build.mk
@@ -1,8 +0,0 @@
-ARCH := powerpc
-OPTIMISATION := -O
-
-D := mach/powerpc
-
-$(eval $(call build-architecture))
-
-
diff --git a/mach/proto/as/build.mk b/mach/proto/as/build.mk
index f7b56ca66..039630f75 100644
--- a/mach/proto/as/build.mk
+++ b/mach/proto/as/build.mk
@@ -35,8 +35,8 @@ $(OBJDIR)/$D/preprocessed-comm2.y: mach/proto/as/comm2.y $(CPPANSI)
 		mach/proto/as/comm2.y > $$@
 
 	$(call file, $(LIBOBJECT))
-    $(call cprogram, $(BINDIR)/$(ARCH)/as)
-    $(call installto, $(PLATDEP)/$(ARCH)/as)
+    $(call cprogram, $(BINDIR)/$(PLATFORM)/as)
+    $(call installto, $(PLATDEP)/$(PLATFORM)/as)
 endef
 
 build-as = $(eval $(build-as-impl))
diff --git a/mach/proto/ncg/build.mk b/mach/proto/ncg/build.mk
index f3782322b..d37c623d4 100644
--- a/mach/proto/ncg/build.mk
+++ b/mach/proto/ncg/build.mk
@@ -37,8 +37,8 @@ $(call cfile, $(OBJDIR)/$D/tables.c)
 $(call file, $(LIBEM_DATA))
 $(call file, $(LIBFLT_ARITH))
 
-$(call cprogram, $(BINDIR)/$(ARCH)/ncg)
-$(call installto, $(PLATDEP)/$(ARCH)/ncg)
+$(call cprogram, $(BINDIR)/$(PLATFORM)/ncg)
+$(call installto, $(PLATDEP)/$(PLATFORM)/ncg)
 
 endef
 
diff --git a/mach/proto/top/build.mk b/mach/proto/top/build.mk
new file mode 100644
index 000000000..56f41c276
--- /dev/null
+++ b/mach/proto/top/build.mk
@@ -0,0 +1,15 @@
+define build-top-impl
+	$(call reset)
+	$(eval cflags += -I$(OBJDIR)/$(PLATFORM)/top)
+
+	$(call cfile, mach/proto/top/queue.c)
+	$(call cfile, mach/proto/top/top.c)
+	$(eval $q: $(OBJDIR)/$(PLATFORM)/top/gen.h)
+
+	$(call topgen, $(OBJDIR)/$(PLATFORM)/top, mach/$(ARCH)/top/table)
+
+	$(call cprogram, $(OBJDIR)/$(PLATFORM)/top/top)
+	$(call installto, $(PLATDEP)/$(PLATFORM)/top)
+endef
+
+build-top = $(eval $(build-top-impl))
diff --git a/plat/build.mk b/plat/build.mk
index 3a80c438d..3f8994fc9 100644
--- a/plat/build.mk
+++ b/plat/build.mk
@@ -14,15 +14,48 @@ define build-platform-impl
 	$(eval PLATFORM_$(PLATFORM) := \
 			$(PLATIND)/descr/$(PLATFORM) \
 			$(PLATFORM_HEADERS_$(PLATFORM)) \
+			$(PLATDEP)/$(PLATFORM)/as \
+			$(PLATDEP)/$(PLATFORM)/ncg \
 			$(ARCHITECTURE_$(ARCH)))
 
 	$(foreach f, $(platform-headers), $(call build-platform-headers, $f))
 
+	# libsys
+
 	$(call reset)
 	$(foreach f, $(platform-libsys), $(call ackfile, $D/libsys/$f))
 	$(call acklibrary, $(LIBDIR)/$(PLATFORM)/libsys.a)
 	$(call installto, $(PLATIND)/$(PLATFORM)/libsys.a)
 
+    # libem
+
+    $(call reset)
+    $(eval objdir := $(PLATFORM))
+    $(eval ackflags += -Ih)
+    $(foreach f, $(arch-libem-$(ARCH)), $(call ackfile, mach/$(ARCH)/libem/$f))
+    $(call acklibrary, $(LIBDIR)/$(PLATFORM)/libem.a)
+    $(call installto, $(PLATIND)/$(PLATFORM)/libem.a)
+
+    # libend
+
+    $(call reset)
+    $(eval objdir := $(PLATFORM))
+    $(eval ackflags += -Ih)
+    $(foreach f, $(arch-libend-$(ARCH)), $(call ackfile, mach/$(ARCH)/libend/$f))
+    $(call acklibrary, $(LIBDIR)/$(PLATFORM)/libend.a)
+    $(call installto, $(PLATIND)/$(PLATFORM)/libend.a)
+
+    # The tools themselves
+
+    $(call build-as)
+    $(call build-ncg)
+
+	# Build top only if the architecture asks for it.
+
+	$(if $(arch-top-$(ARCH)), $(call build-top))
+
+    # Language runtimes
+
     $(foreach runtime, $(RUNTIMES), $(build-runtime-$(runtime)))
 endef
 
diff --git a/plat/cpm/build.mk b/plat/cpm/build.mk
index 2f8836956..54ed3d839 100644
--- a/plat/cpm/build.mk
+++ b/plat/cpm/build.mk
@@ -30,5 +30,13 @@ platform-libsys := \
 
 $(eval $(call build-platform))
 
+define build-cpm-boot-impl
+	$(call reset)
+	$(call ackfile, $D/boot.s)
+	$(call installto, $(PLATIND)/$(PLATFORM)/boot.o)
+endef
+
+$(eval $(build-cpm-boot-impl))
+
 
 
diff --git a/plat/cpm/descr b/plat/cpm/descr
index 436dc40cc..a72f50276 100644
--- a/plat/cpm/descr
+++ b/plat/cpm/descr
@@ -10,7 +10,7 @@ var f=4
 var d=8
 var ARCH=i80
 var PLATFORM=cpm
-var PLATFORMDIR={EM}/lib/ack/{PLATFORM}
+var PLATFORMDIR={EM}/share/ack/{PLATFORM}
 var CPP_F=-D__unix
 var ALIGN=-a0:1 -a1:1 -a2:1 -a3:1 -b0:0x0100
 var MACHOPT_F=-m8
@@ -23,7 +23,7 @@ var C_INCLUDES=-I{EM}/share/ack/{PLATFORM}/include -I{EM}/share/ack/include/ansi
 name be
 	from .m.g
 	to .s
-	program {EM}/lib/ack/{ARCH}/ncg
+	program {EM}/lib/ack/{PLATFORM}/ncg
 	args <
 	stdout
 	need .e
@@ -31,7 +31,7 @@ end
 name asopt
 	from .s
 	to .so
-	program {EM}/lib/ack/{ARCH}/top
+	program {EM}/lib/ack/{PLATFORM}/top
 	args
 	optimizer
 	stdin
@@ -40,7 +40,7 @@ end
 name as
 	from .s.so
 	to .o
-	program {EM}/lib/ack/{ARCH}/as
+	program {EM}/lib/ack/{PLATFORM}/as
 	args - -o > <
 	prep cond
 end
diff --git a/plat/linux386/build.mk b/plat/linux386/build.mk
index 760cc69f6..f35fa6be7 100644
--- a/plat/linux386/build.mk
+++ b/plat/linux386/build.mk
@@ -15,3 +15,14 @@ platform-libsys := \
 $(eval $(call build-platform))
 $(eval $(call build-liblinux))
 
+define build-linux386-boot-impl
+	$(call reset)
+	$(call ackfile, $D/boot.s)
+	$(call installto, $(PLATIND)/$(PLATFORM)/boot.o)
+endef
+
+$(eval $(build-linux386-boot-impl))
+
+
+
+
diff --git a/plat/linux386/descr b/plat/linux386/descr
index a0d23ad3b..ff2b26dfb 100644
--- a/plat/linux386/descr
+++ b/plat/linux386/descr
@@ -27,7 +27,7 @@ var C_INCLUDES=-I{PLATFORMDIR}/include -I{EM}/share/ack/include/ansi
 name be
 	from .m.g
 	to .s
-	program {EM}/lib/ack/{ARCH}/ncg
+	program {EM}/lib/ack/{PLATFORM}/ncg
 	mapflag -gdb GF=-gdb
 	args {GF?} <
 	stdout
@@ -36,7 +36,7 @@ end
 name as
 	from .s.so
 	to .o
-	program {EM}/lib/ack/{ARCH}/as
+	program {EM}/lib/ack/{PLATFORM}/as
 	args - -o > <
 	prep cond
 end
diff --git a/plat/linux68k/build.mk b/plat/linux68k/build.mk
index b230b2500..7a1e7223b 100644
--- a/plat/linux68k/build.mk
+++ b/plat/linux68k/build.mk
@@ -15,4 +15,11 @@ platform-libsys := \
 $(eval $(call build-platform))
 $(eval $(call build-liblinux))
 
+define build-linux68k-boot-impl
+	$(call reset)
+	$(call ackfile, $D/boot.s)
+	$(call installto, $(PLATIND)/$(PLATFORM)/boot.o)
+endef
+
+$(eval $(build-linux68k-boot-impl))
 
diff --git a/plat/linux68k/descr b/plat/linux68k/descr
index 124955b55..14f973d52 100644
--- a/plat/linux68k/descr
+++ b/plat/linux68k/descr
@@ -27,7 +27,7 @@ var C_INCLUDES=-I{PLATFORMDIR}/include -I{EM}/share/ack/include/ansi
 name be
 	from .m.g
 	to .s
-	program {EM}/lib/ack/{ARCH}/ncg
+	program {EM}/lib/ack/{PLATFORM}/ncg
 	mapflag -gdb GF=-gdb
 	args {GF?} <
 	stdout
@@ -36,7 +36,7 @@ end
 name as
 	from .s.so
 	to .o
-	program {EM}/lib/ack/{ARCH}/as
+	program {EM}/lib/ack/{PLATFORM}/as
 	args - -o > <
 	prep cond
 end
diff --git a/plat/linuxppc/build.mk b/plat/linuxppc/build.mk
index 515d498a6..d19fa5aa3 100644
--- a/plat/linuxppc/build.mk
+++ b/plat/linuxppc/build.mk
@@ -16,4 +16,16 @@ platform-libsys := \
 $(eval $(call build-platform))
 $(eval $(call build-liblinux))
 
+define build-linuxppc-boot-impl
+	$(call reset)
+	$(call ackfile, $D/boot.s)
+	$(call installto, $(PLATIND)/$(PLATFORM)/boot.o)
+endef
+
+$(eval $(build-linuxppc-boot-impl))
+
+
+
+
+
 
diff --git a/plat/pc86/build.mk b/plat/pc86/build.mk
index 8a7ec92f1..1ae9e5f49 100644
--- a/plat/pc86/build.mk
+++ b/plat/pc86/build.mk
@@ -28,4 +28,11 @@ platform-libsys := \
 
 $(eval $(call build-platform))
 
+define build-pc86-boot-impl
+	$(call reset)
+	$(call ackfile, $D/boot.s)
+	$(call installto, $(PLATIND)/$(PLATFORM)/boot.o)
+endef
+
+$(eval $(build-pc86-boot-impl))
 
diff --git a/plat/pc86/descr b/plat/pc86/descr
index f02ab3eed..a3f11fc4f 100644
--- a/plat/pc86/descr
+++ b/plat/pc86/descr
@@ -23,7 +23,7 @@ var C_INCLUDES=-I{PLATFORMDIR}/include -I{EM}/share/ack/include/ansi
 name be
 	from .m.g
 	to .s
-	program {EM}/lib/ack/{ARCH}/ncg
+	program {EM}/lib/ack/{PLATFORM}/ncg
 	args <
 	stdout
 	need .e
@@ -31,7 +31,7 @@ end
 name as
 	from .s.so
 	to .o
-	program {EM}/lib/ack/{ARCH}/as
+	program {EM}/lib/ack/{PLATFORM}/as
 	args - -o > <
 	prep cond
 end
diff --git a/util/LLgen/build.mk b/util/LLgen/build.mk
index 44b63f891..3c40d1886 100644
--- a/util/LLgen/build.mk
+++ b/util/LLgen/build.mk
@@ -46,6 +46,7 @@ $o: $1/Lpars.h
 $1/Lpars.h: $2 $(LLGEN)
 	@echo LLGEN $1/Lpars.c
 	@mkdir -p $(dir $o)
+	$(hide) $(RM) $o $1/Lpars.h
 	$(hide) cd $(dir $o) && $(LLGEN) $(abspath $2)
 
 $(foreach f,$o,$(call cfile,$f))
diff --git a/util/amisc/build.mk b/util/amisc/build.mk
index e7f71e33f..03f44b5e9 100644
--- a/util/amisc/build.mk
+++ b/util/amisc/build.mk
@@ -19,4 +19,5 @@ $(call build-simple-tool,ashow)
 $(call build-simple-tool,asize)
 $(call build-simple-tool,aslod)
 $(call build-simple-tool,astrip)
+$(call build-simple-tool,aelflod)
 
diff --git a/util/data/build.mk b/util/data/build.mk
index c9b601da1..424712956 100644
--- a/util/data/build.mk
+++ b/util/data/build.mk
@@ -22,6 +22,9 @@ $(call cfile, $(OBJDIR)/$D/em_flag.c)
 $(call cfile, $(OBJDIR)/$D/em_pseu.c)
 $(call cfile, $(OBJDIR)/$D/em_mnem.c)
 $(call cfile, $D/em_ptyp.c)
+
+$(eval $q: $g)
+
 $(call clibrary, $(LIBDIR)/libem_data.a)
 $(eval LIBEM_DATA := $q)
 
diff --git a/util/led/build.mk b/util/led/build.mk
new file mode 100644
index 000000000..d96dd35c6
--- /dev/null
+++ b/util/led/build.mk
@@ -0,0 +1,34 @@
+D := util/led
+
+define build-led-impl
+	$(call reset)
+	$(call cfile, $D/archive.c)
+	$(call cfile, $D/error.c)
+	$(call cfile, $D/extract.c)
+	$(call cfile, $D/finish.c)
+	$(call cfile, $D/main.c)
+	$(call cfile, $D/memory.c)
+	$(call cfile, $D/output.c)
+	$(call cfile, $D/read.c)
+	$(call cfile, $D/relocate.c)
+	$(call cfile, $D/save.c)
+	$(call cfile, $D/scan.c)
+	$(call cfile, $D/sym.c)
+	$(call cfile, $D/write.c)
+
+	$(call file, $(LIBSTRING))
+	$(call file, $(LIBOBJECT))
+
+	$(call cprogram, $(BINDIR)/em_led)
+	$(call installto, $(PLATDEP)/em_led)
+
+	$(call reset)
+	$(eval q := $D/ack.out.5)
+	$(call installto, $(INSDIR)/share/man/man5/ack.out.5)
+
+	$(call reset)
+	$(eval q := $D/led.6)
+	$(call installto, $(INSDIR)/share/man/man6/led.6)
+endef
+
+$(eval $(build-led-impl))
diff --git a/util/ncgg/build.mk b/util/ncgg/build.mk
index 97576794d..c3a7f31fa 100644
--- a/util/ncgg/build.mk
+++ b/util/ncgg/build.mk
@@ -32,6 +32,8 @@ $(OBJDIR)/$D/enterkeyw.c: $D/cvtkeywords $D/keywords
 	$(hide) cd $$(dir $$@) && sh $(abspath $D/cvtkeywords) $(abspath $D/keywords)
 $(call cfile, $(OBJDIR)/$D/enterkeyw.c)
 
+$(eval $q: $(INCDIR)/em_spec.h)
+
 $(call file, $(LIBEM_DATA))
 $(call cprogram, $(BINDIR)/ncgg)
 $(eval NCGG := $o)
diff --git a/util/topgen/build.mk b/util/topgen/build.mk
new file mode 100644
index 000000000..4ef15c278
--- /dev/null
+++ b/util/topgen/build.mk
@@ -0,0 +1,50 @@
+D := util/topgen
+
+# Rule to build topgen.
+
+define build-topgen-impl
+	$(call reset)
+	$(eval cflags += -I$(OBJDIR)/$D -I$D)
+
+	$(call cfile, $D/LLlex.c)
+	$(call cfile, $D/hash.c)
+	$(call cfile, $D/main.c)
+	$(call cfile, $D/pattern.c)
+	$(call cfile, $D/symtab.c)
+	$(eval $q: $(OBJDIR)/$D/Lpars.h)
+
+	$(call llgen, $(OBJDIR)/$D, $D/topgen.g)
+
+	$(call file, $(LIBASSERT))
+	$(call file, $(LIBPRINT))
+	$(call file, $(LIBALLOC))
+	$(call file, $(LIBSYSTEM))
+	$(call file, $(LIBSTRING))
+
+	$(call cprogram, $(BINDIR)/topgen)
+	TOPGEN := $o
+endef
+
+$(eval $(build-topgen-impl))
+
+# Rule to invoke to *use* LLgen.
+#
+#  $1: directory to put output files
+#  $2: input files
+#
+# Output files are *not* compiled (gen.c is expected to be included by
+# something).
+
+define topgen-impl
+$(eval CLEANABLES += $1/gen.h $1/gen.c)
+
+$1/gen.h: $1/gen.c
+$1/gen.c: $2 $(TOPGEN)
+	@echo TOPGEN $$@
+	@mkdir -p $$(dir $$@)
+	$(hide) $(RM) $1/gen.h $1/gen.c
+	$(hide) cd $$(dir $$@) && $(abspath $(TOPGEN)) $(abspath $2)
+
+endef
+
+topgen = $(eval $(call topgen-impl,$1,$2))