Add simple cross compile mechanism for flisp/libsupport (+ dependencies) (#30526)

This makes some incremental progress towards #30338 in the build system.
In particular, it allows compiling a separate boostrap version of flisp
and its dependencies for an architecture different from the target.
The immediate use case here is to build libjulia for wasm. Of course,
there's still the enormous problem of building the system image itself,
but luckily wasm is largely memory-layout-identical to linux32, so doing
that limited bootstrap is fairly easy after this change (though the subject
of a different PR).

The mechanism here is to use the out-of-tree build support to create
separate host/ subdirectories for the build directories of interest.
These have a special make variable set that tell it to include a
different Make.user (or in the absence thereof use the host defaults).

Author: Keno

Make.inc

@@ -126,11 +126,19 @@ endif
 
 # we include twice to pickup user definitions better
 # include from JULIAHOME first so that BUILDROOT can override
-ifeq (exists, $(shell [ -e $(JULIAHOME)/Make.user ] && echo exists ))
-include $(JULIAHOME)/Make.user
+MAYBE_HOST :=
+ifneq ($(BUILDING_HOST_TOOLS),1)
+MAKE_USER_FNAME = Make.user
+else
+MAYBE_HOST := /host
+MAKE_USER_FNAME = Make.host.user
+endif
+
+ifeq (exists, $(shell [ -e $(JULIAHOME)/$(MAKE_USER_FNAME) ] && echo exists ))
+include $(JULIAHOME)/$(MAKE_USER_FNAME)
 endif
-ifeq (exists, $(shell [ -e $(BUILDROOT)/Make.user ] && echo exists ))
-include $(BUILDROOT)/Make.user
+ifeq (exists, $(shell [ -e $(BUILDROOT)/$(MAKE_USER_FNAME) ] && echo exists ))
+include $(BUILDROOT)/$(MAKE_USER_FNAME)
 endif
 
 # disable automatic Makefile rules
@@ -236,8 +244,12 @@ sysconfdir := $(prefix)/etc
 endif
 
 # Directories where things get built into
-build_prefix := $(BUILDROOT)/usr
+build_prefix := $(BUILDROOT)/usr$(MAYBE_HOST)
+ifeq ($(BUILDING_HOST_TOOLS), 1)
+build_staging := $(BUILDROOT)/usr-host-staging
+else
 build_staging := $(build_prefix)-staging
+endif
 build_bindir := $(build_prefix)/bin
 build_depsbindir := $(build_prefix)/tools
 build_libdir := $(build_prefix)/lib
@@ -571,11 +583,11 @@ else
 LOCALBASE ?= /usr
 endif
 
-ifeq (exists, $(shell [ -e $(JULIAHOME)/Make.user ] && echo exists ))
-include $(JULIAHOME)/Make.user
+ifeq (exists, $(shell [ -e $(JULIAHOME)/$(MAKE_USER_FNAME) ] && echo exists ))
+include $(JULIAHOME)/$(MAKE_USER_FNAME)
 endif
-ifeq (exists, $(shell [ -e $(BUILDROOT)/Make.user ] && echo exists ))
-include $(BUILDROOT)/Make.user
+ifeq (exists, $(shell [ -e $(BUILDROOT)/$(MAKE_USER_FNAME) ] && echo exists ))
+include $(BUILDROOT)/$(MAKE_USER_FNAME)
 endif
 
 # A bit of a kludge to work around libraries linking to FreeBSD's outdated system libgcc_s
@@ -1064,7 +1076,7 @@ else ifneq ($(USEMSVC), 1)
 endif
 
 ifeq ($(OS), Linux)
-OSLIBS += -Wl,--no-as-needed -ldl -lrt -lpthread -Wl,--export-dynamic,--as-needed,--no-whole-archive $(LIBUNWIND)
+OSLIBS += -Wl,--no-as-needed -ldl -lrt -lpthread -Wl,--export-dynamic,--as-needed,--no-whole-archive
 # Detect if ifunc is supported
 IFUNC_DETECT_SRC := 'void (*f0(void))(void) { return (void(*)(void))0L; }; void f(void) __attribute__((ifunc("f0")));'
 ifeq (supported, $(shell echo $(IFUNC_DETECT_SRC) | $(CC) -Werror -x c - -S -o /dev/null > /dev/null 2>&1 && echo supported))

Makefile

@@ -9,7 +9,7 @@ all: debug release
 # sort is used to remove potential duplicates
 DIRS := $(sort $(build_bindir) $(build_depsbindir) $(build_libdir) $(build_private_libdir) $(build_libexecdir) $(build_includedir) $(build_includedir)/julia $(build_sysconfdir)/julia $(build_datarootdir)/julia $(build_datarootdir)/julia/stdlib $(build_man1dir))
 ifneq ($(BUILDROOT),$(JULIAHOME))
-BUILDDIRS := $(BUILDROOT) $(addprefix $(BUILDROOT)/,base src src/clangsa ui doc deps stdlib test test/embedding test/llvmpasses)
+BUILDDIRS := $(BUILDROOT) $(addprefix $(BUILDROOT)/,base src src/flisp src/support src/clangsa ui doc deps stdlib test test/embedding test/llvmpasses)
 BUILDDIRMAKE := $(addsuffix /Makefile,$(BUILDDIRS)) $(BUILDROOT)/sysimage.mk
 DIRS := $(DIRS) $(BUILDDIRS)
 $(BUILDDIRMAKE): | $(BUILDDIRS)

deps/Makefile

@@ -14,6 +14,8 @@ include $(SRCDIR)/tools/common.mk
 include $(SRCDIR)/tools/git-external.mk
 include $(SRCDIR)/tools/bb-install.mk
 
+BUILDDIR := $(BUILDDIR)$(MAYBE_HOST)
+
 # Special comments:
 #
 # all targets in here should follow the same structure,

deps/libuv.mk

@@ -25,8 +25,9 @@ ifneq ($(VERBOSE), 0)
 UV_MFLAGS += V=1
 endif
 
+LIBUV_BUILDDIR := $(BUILDDIR)/$(LIBUV_SRC_DIR)
 
-$(BUILDDIR)/$(LIBUV_SRC_DIR)/build-configured: $(SRCCACHE)/$(LIBUV_SRC_DIR)/source-extracted
+$(LIBUV_BUILDDIR)/build-configured: $(SRCCACHE)/$(LIBUV_SRC_DIR)/source-extracted
 	touch -c $(SRCCACHE)/$(LIBUV_SRC_DIR)/aclocal.m4 # touch a few files to prevent autogen from getting called
 	touch -c $(SRCCACHE)/$(LIBUV_SRC_DIR)/Makefile.in
 	touch -c $(SRCCACHE)/$(LIBUV_SRC_DIR)/configure
@@ -35,11 +36,11 @@ $(BUILDDIR)/$(LIBUV_SRC_DIR)/build-configured: $(SRCCACHE)/$(LIBUV_SRC_DIR)/sour
 	$(dir $<)/configure --with-pic $(CONFIGURE_COMMON) $(UV_FLAGS)
 	echo 1 > $@
 
-$(BUILDDIR)/$(LIBUV_SRC_DIR)/build-compiled: $(BUILDDIR)/$(LIBUV_SRC_DIR)/build-configured
+$(LIBUV_BUILDDIR)/build-compiled: $(LIBUV_BUILDDIR)/build-configured
 	$(MAKE) -C $(dir $<) $(UV_MFLAGS)
 	echo 1 > $@
 
-$(BUILDDIR)/$(LIBUV_SRC_DIR)/build-checked: $(BUILDDIR)/$(LIBUV_SRC_DIR)/build-compiled
+$(LIBUV_BUILDDIR)/build-checked: $(LIBUV_BUILDDIR)/build-compiled
 ifeq ($(OS),$(BUILD_OS))
 	-$(MAKE) -C $(dir $@) check
 endif
@@ -51,16 +52,16 @@ $(eval $(call staged-install, \
 	$$(INSTALL_NAME_CMD)libuv.$$(SHLIB_EXT) $$(build_shlibdir)/libuv.$$(SHLIB_EXT)))
 
 clean-libuv:
-	-rm -rf $(BUILDDIR)/$(LIBUV_SRC_DIR)/build-configured $(BUILDDIR)/$(LIBUV_SRC_DIR)/build-compiled
-	-$(MAKE) -C $(BUILDDIR)/$(LIBUV_SRC_DIR) clean
+	-rm -rf $(LIBUV_BUILDDIR)/build-configured $(LIBUV_BUILDDIR)/build-compiled
+	-$(MAKE) -C $(LIBUV_BUILDDIR) clean
 
 
 get-libuv: $(LIBUV_SRC_FILE)
 extract-libuv: $(SRCCACHE)/$(LIBUV_SRC_DIR)/source-extracted
-configure-libuv: $(BUILDDIR)/$(LIBUV_SRC_DIR)/build-configured
-compile-libuv: $(BUILDDIR)/$(LIBUV_SRC_DIR)/build-compiled
+configure-libuv: $(LIBUV_BUILDDIR)/build-configured
+compile-libuv: $(LIBUV_BUILDDIR)/build-compiled
 fastcheck-libuv: #none
-check-libuv: $(BUILDDIR)/$(LIBUV_SRC_DIR)/build-checked
+check-libuv: $(LIBUV_BUILDDIR)/build-checked
 
 else # USE_BINARYBUILDER_LIBUV
 LIBUV_BB_URL_BASE := https://github.com/JuliaPackaging/Yggdrasil/releases/download/LibUV-v2+$(LIBUV_VER)-julia+$(LIBUV_BB_REL)

deps/utf8proc.mk

@@ -7,12 +7,13 @@ UTF8PROC_OBJ_LIB    := $(build_libdir)/libutf8proc.a
 UTF8PROC_OBJ_HEADER := $(build_includedir)/utf8proc.h
 UTF8PROC_CFLAGS     := -O2
 UTF8PROC_MFLAGS     := CC="$(CC)" CFLAGS="$(CFLAGS) $(UTF8PROC_CFLAGS)" PICFLAG="$(fPIC)" AR="$(AR)"
+UTF8PROC_BUILDDIR   := $(BUILDDIR)/$(UTF8PROC_SRC_DIR)
 
-$(BUILDDIR)/$(UTF8PROC_SRC_DIR)/build-compiled: $(BUILDDIR)/$(UTF8PROC_SRC_DIR)/source-extracted
+$(UTF8PROC_BUILDDIR)/build-compiled: $(UTF8PROC_BUILDDIR)/source-extracted
 	$(MAKE) -C $(dir $<) $(UTF8PROC_MFLAGS) libutf8proc.a
 	echo 1 > $@
 
-$(BUILDDIR)/$(UTF8PROC_SRC_DIR)/build-checked: $(BUILDDIR)/$(UTF8PROC_SRC_DIR)/build-compiled
+$(UTF8PROC_BUILDDIR)/build-checked: $(UTF8PROC_BUILDDIR)/build-compiled
 ifeq ($(OS),$(BUILD_OS))
 	$(MAKE) -C $(dir $@) $(UTF8PROC_MFLAGS) check
 endif
@@ -32,9 +33,9 @@ clean-utf8proc:
 	-$(MAKE) -C $(BUILDDIR)/$(UTF8PROC_SRC_DIR) clean
 
 get-utf8proc: $(UTF8PROC_SRC_FILE)
-extract-utf8proc: $(BUILDDIR)/$(UTF8PROC_SRC_DIR)/source-extracted
+extract-utf8proc: $(UTF8PROC_BUILDDIR)/source-extracted
 configure-utf8proc: extract-utf8proc
-compile-utf8proc: $(BUILDDIR)/$(UTF8PROC_SRC_DIR)/build-compiled
+compile-utf8proc: $(UTF8PROC_BUILDDIR)/build-compiled
 # utf8proc tests disabled since they require a download
 fastcheck-utf8proc: #check-utf8proc
-check-utf8proc: $(BUILDDIR)/$(UTF8PROC_SRC_DIR)/build-checked
+check-utf8proc: $(UTF8PROC_BUILDDIR)/build-checked

src/.gitignore

@@ -18,3 +18,5 @@
 /libjulia-release.so
 /libjulia-release.dylib
 /julia_version.h
+/flisp/host
+/support/host

src/Makefile

@@ -108,7 +108,7 @@ FLAGS += -DLLVM_SHLIB
 endif # USE_LLVM_SHLIB == 1
 endif
 
-COMMON_LIBS := -L$(build_shlibdir) -L$(build_libdir) $(LIBUV) $(LIBUTF8PROC) $(NO_WHOLE_ARCHIVE) $(LLVMLINK) $(OSLIBS)
+COMMON_LIBS := -L$(build_shlibdir) -L$(build_libdir) $(LIBUV) $(LIBUTF8PROC) $(NO_WHOLE_ARCHIVE) $(LLVMLINK) $(OSLIBS) $(LIBUNWIND)
 DEBUG_LIBS := $(WHOLE_ARCHIVE) $(BUILDDIR)/flisp/libflisp-debug.a $(WHOLE_ARCHIVE) $(BUILDDIR)/support/libsupport-debug.a $(COMMON_LIBS)
 RELEASE_LIBS := $(WHOLE_ARCHIVE) $(BUILDDIR)/flisp/libflisp.a $(WHOLE_ARCHIVE) $(BUILDDIR)/support/libsupport.a $(COMMON_LIBS)
 
@@ -121,8 +121,13 @@ SHIPFLAGS += $(FLAGS)
 SHIPFLAGS += "-DJL_SYSTEM_IMAGE_PATH=\"$(build_private_libdir_rel)/sys.$(SHLIB_EXT)\""
 DEBUGFLAGS += "-DJL_SYSTEM_IMAGE_PATH=\"$(build_private_libdir_rel)/sys-debug.$(SHLIB_EXT)\""
 
-FLISP_EXECUTABLE_debug := $(BUILDDIR)/flisp/flisp-debug$(EXE)
-FLISP_EXECUTABLE_release := $(BUILDDIR)/flisp/flisp$(EXE)
+ifeq ($(USE_CROSS_FLISP), 1)
+FLISPDIR := $(BUILDDIR)/flisp/host
+else
+FLISPDIR := $(BUILDDIR)/flisp
+endif
+FLISP_EXECUTABLE_debug := $(FLISPDIR)/flisp-debug$(EXE)
+FLISP_EXECUTABLE_release := $(FLISPDIR)/flisp$(EXE)
 ifeq ($(OS),WINNT)
 FLISP_EXECUTABLE := $(FLISP_EXECUTABLE_release)
 else
@@ -232,10 +237,14 @@ $(BUILDDIR)/support/libsupport-debug.a: $(addprefix $(SRCDIR)/support/,*.h *.c *
 	$(MAKE) -C $(SRCDIR)/support debug BUILDDIR='$(abspath $(BUILDDIR)/support)'
 
 $(FLISP_EXECUTABLE_release): $(BUILDDIR)/flisp/libflisp.a
+	$(MAKE) -C $(BUILDDIR)/flisp $(subst $(abspath $(BUILDDIR)/flisp)/,,$(abspath $(FLISP_EXECUTABLE_release)))
+
+$(FLISP_EXECUTABLE_debug): $(BUILDDIR)/flisp/libflisp-debug.a
+	$(MAKE) -C $(BUILDDIR)/flisp $(subst $(abspath $(BUILDDIR)/flisp)/,,$(abspath $(FLISP_EXECUTABLE_debug)))
+
 $(BUILDDIR)/flisp/libflisp.a: $(addprefix $(SRCDIR)/flisp/,*.h *.c) $(BUILDDIR)/support/libsupport.a
 	$(MAKE) -C $(SRCDIR)/flisp BUILDDIR='$(abspath $(BUILDDIR)/flisp)'
 
-$(FLISP_EXECUTABLE_debug): $(BUILDDIR)/flisp/libflisp-debug.a
 $(BUILDDIR)/flisp/libflisp-debug.a: $(addprefix $(SRCDIR)/,flisp/*.h flisp/*.c) $(BUILDDIR)/support/libsupport-debug.a
 	$(MAKE) -C $(SRCDIR)/flisp debug BUILDDIR='$(abspath $(BUILDDIR)/flisp)'
 

src/flisp/Makefile

@@ -1,4 +1,5 @@
-JULIAHOME := $(abspath ../..)
+SRCDIR := $(abspath $(dir $(lastword $(MAKEFILE_LIST))))
+JULIAHOME := $(abspath $(SRCDIR)/../..)
 BUILDDIR := .
 include $(JULIAHOME)/Make.inc
 
@@ -15,21 +16,30 @@ SRCS := flisp.c builtins.c string.c equalhash.c table.c iostream.c \
         julia_extensions.c
 
 LLTDIR := ../support
+LLTSRCDIR := $(SRCDIR)/$(LLTDIR)
+NATIVE_BUILDDIR :=
+ifeq ($(BUILDING_HOST_TOOLS), 1)
+NATIVE_BUILDDIR := $(BUILDDIR)/..
+LLT_BUILDDIR := $(BUILDDIR)/../$(LLTDIR)/host
+else
+NATIVE_BUILDDIR := $(BUILDDIR)
+LLT_BUILDDIR := $(BUILDDIR)/$(LLTDIR)
+endif
 
 HEADERS := $(wildcard *.h) $(LIBUV_INC)/uv.h $(wildcard $(LLTDIR)/*.h)
 
 OBJS := $(SRCS:%.c=$(BUILDDIR)/%.o)
 DOBJS := $(SRCS:%.c=$(BUILDDIR)/%.dbg.obj)
-LLT_release := $(BUILDDIR)/$(LLTDIR)/libsupport.a
-LLT_debug := $(BUILDDIR)/$(LLTDIR)/libsupport-debug.a
+LLT_release := $(LLT_BUILDDIR)/libsupport.a
+LLT_debug := $(LLT_BUILDDIR)/libsupport-debug.a
 LIBFILES_release := $(LLT_release) $(LIBUV) $(LIBUTF8PROC)
 LIBFILES_debug := $(LLT_debug) $(LIBUV) $(LIBUTF8PROC)
 LIBS :=
 ifneq ($(OS),WINNT)
 LIBS += -lpthread
 endif
 
-FLAGS := -I$(LLTDIR) $(JCFLAGS) $(HFILEDIRS:%=-I%) \
+FLAGS := -I$(LLTSRCDIR) $(JCFLAGS) $(HFILEDIRS:%=-I%) \
         -I$(LIBUV_INC) -I$(UTF8PROC_INC) -I$(build_includedir) $(LIBDIRS:%=-L%) \
         -DLIBRARY_EXPORTS -DUTF8PROC_EXPORTS
 ifneq ($(USEMSVC), 1)
@@ -52,20 +62,22 @@ debug: $(BUILDDIR)/$(EXENAME)-debug$(EXE)
 $(BUILDDIR):
 	mkdir -p $(BUILDDIR)
 
-$(BUILDDIR)/%.o: %.c $(HEADERS) | $(BUILDDIR)
+$(BUILDDIR)/%.o: $(SRCDIR)/%.c $(HEADERS) | $(BUILDDIR)
 	@$(call PRINT_CC, $(CC) $(JCPPFLAGS) $(SHIPFLAGS) $(DISABLE_ASSERTIONS) -c $< -o $@)
-$(BUILDDIR)/%.dbg.obj: %.c $(HEADERS) | $(BUILDDIR)
+$(BUILDDIR)/%.dbg.obj: $(SRCDIR)/%.c $(HEADERS) | $(BUILDDIR)
 	@$(call PRINT_CC, $(CC) $(JCPPFLAGS) $(DEBUGFLAGS) -c $< -o $@)
 
-$(BUILDDIR)/flisp.o:   flisp.c cvalues.c types.c flisp.h print.c read.c equal.c
-$(BUILDDIR)/flisp.dbg.obj:  flisp.c cvalues.c types.c flisp.h print.c read.c equal.c
-$(BUILDDIR)/flmain.o:  flmain.c flisp.h
-$(BUILDDIR)/flmain.dbg.obj: flmain.c flisp.h
+FLISP_SRCS := $(flisp.c cvalues.c types.c flisp.h print.c read.c equal.c:%=$(SRCDIR)/%)
+FLMAIN_SRCS := $(flmain.c flisp.h:%=$(SRCDIR)/%)
+$(BUILDDIR)/flisp.o: $(FLISP_SRCS)
+$(BUILDDIR)/flisp.dbg.obj: $(FLISP_SRCS)
+$(BUILDDIR)/flmain.o: $(FLMAIN_SRCS)
+$(BUILDDIR)/flmain.dbg.obj: $(FLMAIN_SRCS)
 
-$(LLT_release): $(LLTDIR)/*.h $(LLTDIR)/*.c
-	$(MAKE) -C $(LLTDIR) BUILDDIR='$(abspath $(BUILDDIR)/$(LLTDIR))'
-$(LLT_debug): $(LLTDIR)/*.h $(LLTDIR)/*.c
-	$(MAKE) debug -C $(LLTDIR) BUILDDIR='$(abspath $(BUILDDIR)/$(LLTDIR))'
+$(LLT_release): $(LLTSRCDIR)/*.h $(LLTSRCDIR)/*.c
+	$(MAKE) -C $(NATIVE_BUILDDIR)/$(LLTDIR) $(subst $(abspath $(NATIVE_BUILDDIR)/$(LLTDIR))/,,$(abspath $(LLT_release)))
+$(LLT_debug): $(LLTSRCDIR)/*.h $(LLTSRCDIR)/*.c
+	$(MAKE) -C $(NATIVE_BUILDDIR)/$(LLTDIR) $(subst $(abspath $(NATIVE_BUILDDIR)/$(LLTDIR))/,,$(abspath $(LLT_debug)))
 
 $(BUILDDIR)/$(LIBTARGET)-debug.a: $(DOBJS) | $(BUILDDIR)
 	rm -rf $@
@@ -87,8 +99,19 @@ $(BUILDDIR)/$(EXENAME)-debug$(EXE): $(DOBJS) $(LIBFILES_debug) $(BUILDDIR)/$(LIB
 $(BUILDDIR)/$(EXENAME)$(EXE): $(OBJS) $(LIBFILES_release) $(BUILDDIR)/$(LIBTARGET).a $(BUILDDIR)/flmain.o | $(BUILDDIR)/flisp.boot
 	@$(call PRINT_LINK, $(CCLD) $(SHIPFLAGS) $(JLDFLAGS) $(OBJS) $(BUILDDIR)/flmain.o -o $@ $(BUILDDIR)/$(LIBTARGET).a $(LIBFILES_release) $(LIBS) $(OSLIBS))
 
-ifneq ($(BUILDDIR),.)
-$(BUILDDIR)/flisp.boot: flisp.boot | $(BUILDDIR)
+$(BUILDDIR)/host/Makefile:
+	mkdir -p $(BUILDDIR)/host
+	@# add Makefiles to the build directories for convenience (pointing back to the source location of each)
+	@echo '# -- This file is automatically generated in julia/src/flisp/Makefile -- #' > $@
+	@echo 'BUILDDIR=$(BUILDDIR)/host' >> $@
+	@echo 'BUILDING_HOST_TOOLS=1' >> $@
+	@echo 'include $(SRCDIR)/Makefile' >> $@
+
+$(BUILDDIR)/host/$(EXENAME): $(BUILDDIR)/host/Makefile
+	make -C $(BUILDDIR)/host $(EXENAME)
+
+ifneq ($(BUILDDIR)$(BUILDING_HOST_TOOLS),.)
+$(BUILDDIR)/flisp.boot: $(SRCDIR)/flisp.boot | $(BUILDDIR)
 	cp $< $@
 endif
 
@@ -103,5 +126,6 @@ clean:
 	rm -f $(BUILDDIR)/*.a
 	rm -f $(BUILDDIR)/$(EXENAME)$(EXE)
 	rm -f $(BUILDDIR)/$(EXENAME)-debug$(EXE)
+	rm -f $(BUILDDIR)/host/*
 
 .PHONY: flisp-deps

src/support/Makefile

@@ -1,4 +1,5 @@
-JULIAHOME := $(abspath ../..)
+SRCDIR := $(abspath $(dir $(lastword $(MAKEFILE_LIST))))
+JULIAHOME := $(abspath $(SRCDIR)/../..)
 BUILDDIR := .
 include $(JULIAHOME)/Make.inc
 
@@ -40,24 +41,32 @@ default: release
 $(BUILDDIR):
 	mkdir -p $(BUILDDIR)
 
-$(BUILDDIR)/%.o: %.c $(HEADERS) | $(BUILDDIR)
+$(BUILDDIR)/%.o: $(SRCDIR)/%.c $(HEADERS) | $(BUILDDIR)
 	@$(call PRINT_CC, $(CC) $(JCPPFLAGS) $(JCFLAGS) $(SHIPFLAGS) $(DISABLE_ASSERTIONS) -c $< -o $@)
-$(BUILDDIR)/%.dbg.obj: %.c $(HEADERS) | $(BUILDDIR)
+$(BUILDDIR)/%.dbg.obj: $(SRCDIR)/%.c $(HEADERS) | $(BUILDDIR)
 	@$(call PRINT_CC, $(CC) $(JCPPFLAGS) $(JCFLAGS) $(DEBUGFLAGS) -c $< -o $@)
 ifneq ($(USEMSVC), 1)
-$(BUILDDIR)/%.o: %.S | $(BUILDDIR)
+$(BUILDDIR)/%.o: $(SRCDIR)/%.S | $(BUILDDIR)
 	@$(call PRINT_CC, $(CC) $(JCPPFLAGS) $(SHIPFLAGS) -c $< -o $@)
-$(BUILDDIR)/%.dbg.obj: %.S | $(BUILDDIR)
+$(BUILDDIR)/%.dbg.obj: $(SRCDIR)/%.S | $(BUILDDIR)
 	@$(call PRINT_CC, $(CC) $(JCPPFLAGS) $(DEBUGFLAGS) -c $< -o $@)
 else
-$(BUILDDIR)/%.o: %.S | $(BUILDDIR)
+$(BUILDDIR)/%.o: $(SRCDIR)/%.S | $(BUILDDIR)
 	@$(call PRINT_CC, $(CPP) -P $(JCPPFLAGS) $(SHIPFLAGS) $<)
 	@$(call PRINT_CC, $(AS) $(JCPPFLAGS) $(SHIPFLAGS) -Fo $@ -c $*.i)
-$(BUILDDIR)/%.dbg.obj: %.S | $(BUILDDIR)
+$(BUILDDIR)/%.dbg.obj: $(SRCDIR)/%.S | $(BUILDDIR)
 	@$(call PRINT_CC, $(CPP) -P $(JCPPFLAGS) $(DEBUGFLAGS) $<)
 	@$(call PRINT_CC, $(AS) $(JCPPFLAGS) $(DEBUGFLAGS) -Fo $@ -c $*.i)
 endif
 
+$(BUILDDIR)/host/Makefile:
+	mkdir -p $(BUILDDIR)/host
+	@# add Makefiles to the build directories for convenience (pointing back to the source location of each)
+	@echo '# -- This file is automatically generated in julia/Makefile -- #' > $@
+	@echo 'BUILDDIR=$(BUILDDIR)/host' >> $@
+	@echo 'BUILDING_HOST_TOOLS=1' >> $@
+	@echo 'include $(SRCDIR)/Makefile' >> $@
+
 release: $(BUILDDIR)/libsupport.a
 debug: $(BUILDDIR)/libsupport-debug.a
 
@@ -69,6 +78,12 @@ $(BUILDDIR)/libsupport-debug.a: $(DOBJS) | $(BUILDDIR)
 	rm -rf $@
 	@$(call PRINT_LINK, $(AR) -rcs $@ $^)
 
+$(BUILDDIR)/host/libsupport.a: $(BUILDDIR)/host/Makefile
+	$(MAKE) -C $(BUILDDIR)/host libsupport.a
+
+$(BUILDDIR)/host/libsupport-debug.a: $(BUILDDIR)/host/Makefile
+	$(MAKE) -C $(BUILDDIR)/host libsupport-debug.a
+
 clean:
 	rm -f $(BUILDDIR)/*.o
 	rm -f $(BUILDDIR)/*.dbg.obj
@@ -77,3 +92,4 @@ clean:
 	rm -f $(BUILDDIR)/core*
 	rm -f $(BUILDDIR)/libsupport.a
 	rm -f $(BUILDDIR)/libsupport-debug.a
+	rm -f $(BUILDDIR)/host/*