egor duda writes:

Hi!

I've created a patch to busybox' build system to allow building it in
separate tree in a manner similar to kbuild from kernel version 2.6.

That is, one runs command like
'make O=/build/some/where/for/specific/target/and/options'
and everything is built in this exact directory, provided that it exists.

I understand that applyingc such invasive changes during 'release
candidates' stage of development is at best unwise. So, i'm currently
asking for comments about this patch, starting from whether such thing
is needed at all to whether it coded properly.

'make check' should work now, and one make creates Makefile in build
directory, so one can run 'make' in build directory after that.

One possible caveat is that if we build in some directory other than
source one, the source directory should be 'distclean'ed first.

egor

Makefile

@@ -22,37 +22,112 @@
 #--------------------------------------------------------------
 noconfig_targets := menuconfig config oldconfig randconfig \
 	defconfig allyesconfig allnoconfig clean distclean \
-	release tags
-TOPDIR=./
-include Rules.mak
+	release tags  
+
+ifndef TOPDIR
+TOPDIR=$(CURDIR)/
+endif
+ifndef top_srcdir
+top_srcdir=$(CURDIR)
+endif
+ifndef top_builddir
+top_builddir=$(CURDIR)
+endif
+
+srctree=$(top_srcdir)
+vpath %/Config.in $(srctree)
+
+include $(top_builddir)/Rules.mak
 
 DIRS:=applets archival archival/libunarchive coreutils console-tools \
 	debianutils editors findutils init miscutils modutils networking \
 	networking/libiproute networking/udhcp procps loginutils shell \
 	sysklogd util-linux libpwdgrp coreutils/libcoreutils libbb
 
+SRC_DIRS:=$(patsubst %,$(top_srcdir)/%,$(DIRS))
+
 ifeq ($(strip $(CONFIG_SELINUX)),y)
 CFLAGS += -I/usr/include/selinux
 LIBRARIES += -lsecure
 endif
 
-CONFIG_CONFIG_IN = sysdeps/$(TARGET_OS)/Config.in
-CONFIG_DEFCONFIG = sysdeps/$(TARGET_OS)/defconfig
+CONFIG_CONFIG_IN = $(top_srcdir)/sysdeps/$(TARGET_OS)/Config.in
+CONFIG_DEFCONFIG = $(top_srcdir)/sysdeps/$(TARGET_OS)/defconfig
+
+ALL_DIRS:= $(DIRS) scripts/config
+ALL_MAKEFILES:=$(patsubst %,%/Makefile,$(ALL_DIRS))
+
+ifeq ($(KBUILD_SRC),)
+
+ifdef O
+  ifeq ("$(origin O)", "command line")
+    KBUILD_OUTPUT := $(O)
+  endif
+endif
+
+# That's our default target when none is given on the command line
+.PHONY: _all
+_all:
+
+ifneq ($(KBUILD_OUTPUT),)
+# Invoke a second make in the output directory, passing relevant variables
+# check that the output directory actually exists
+saved-output := $(KBUILD_OUTPUT)
+KBUILD_OUTPUT := $(shell cd $(KBUILD_OUTPUT) && /bin/pwd)
+$(if $(wildcard $(KBUILD_OUTPUT)),, \
+     $(error output directory "$(saved-output)" does not exist))
+
+.PHONY: $(MAKECMDGOALS)
+
+$(filter-out _all,$(MAKECMDGOALS)) _all: $(KBUILD_OUTPUT)/Rules.mak $(KBUILD_OUTPUT)/Makefile
+	$(MAKE) -C $(KBUILD_OUTPUT) \
+	top_srcdir=$(CURDIR) \
+	top_builddir=$(KBUILD_OUTPUT) \
+	TOPDIR=$(KBUILD_OUTPUT)	\
+	KBUILD_SRC=$(CURDIR) \
+	-f $(CURDIR)/Makefile $@
+
+$(KBUILD_OUTPUT)/Rules.mak:
+	@echo > $@
+	@echo top_srcdir=$(CURDIR) >> $@
+	@echo top_builddir=$(KBUILD_OUTPUT) >> $@
+	@echo include $(top_srcdir)/Rules.mak >> $@
+
+$(KBUILD_OUTPUT)/Makefile:
+	@echo > $@
+	@echo top_srcdir=$(CURDIR) >> $@
+	@echo top_builddir=$(KBUILD_OUTPUT) >> $@
+	@echo KBUILD_SRC='$$(top_srcdir)' >> $@
+	@echo include '$$(KBUILD_SRC)'/Makefile >> $@
+
+# Leave processing to above invocation of make
+skip-makefile := 1
+endif # ifneq ($(KBUILD_OUTPUT),)
+endif # ifeq ($(KBUILD_SRC),)
+
+ifeq ($(skip-makefile),)
+
+_all: all
 
 ifeq ($(strip $(HAVE_DOT_CONFIG)),y)
 
 all: busybox busybox.links doc
 
-# In this section, we need .config
--include .config.cmd
-include $(patsubst %,%/Makefile.in, $(DIRS))
--include $(TOPDIR).depend
+all_tree:	$(ALL_MAKEFILES)
 
-busybox: .depend include/config.h $(libraries-y)
+$(ALL_MAKEFILES): %/Makefile: $(top_srcdir)/%/Makefile
+	d=`dirname $@`; [ -d "$$d" ] || mkdir -p "$$d"; cp $< $@
+
+# In this section, we need .config
+-include $(top_builddir)/.config.cmd
+include $(patsubst %,%/Makefile.in, $(SRC_DIRS))
+-include $(top_builddir)/.depend
+
+busybox: $(ALL_MAKEFILES) .depend include/config.h $(libraries-y)
 	$(CC) $(LDFLAGS) -o $@ -Wl,--start-group $(libraries-y) $(LIBRARIES) -Wl,--end-group
 	$(STRIPCMD) $@
 
-busybox.links: applets/busybox.mkll include/config.h
+busybox.links: $(top_srcdir)/applets/busybox.mkll include/config.h $(top_srcdir)/include/applets.h
 	- $(SHELL) $^ >$@
 
 install: applets/install.sh busybox busybox.links
@@ -75,14 +150,18 @@ uninstall: busybox.links
 install-hardlinks: applets/install.sh busybox busybox.links
 	$(SHELL) $< $(PREFIX) --hardlinks
 
+check: busybox
+	bindir=$(top_builddir) srcdir=$(top_srcdir)/testsuite \
+	$(top_srcdir)/testsuite/runtest
 
 # Documentation Targets
 doc: docs/busybox.pod docs/BusyBox.txt docs/BusyBox.1 docs/BusyBox.html
 
-docs/busybox.pod : docs/busybox_header.pod include/usage.h docs/busybox_footer.pod
-	- ( cat docs/busybox_header.pod; \
-	    docs/autodocifier.pl include/usage.h; \
-	    cat docs/busybox_footer.pod ) > docs/busybox.pod
+docs/busybox.pod : $(top_srcdir)/docs/busybox_header.pod $(top_srcdir)/include/usage.h $(top_srcdir)/docs/busybox_footer.pod
+	-mkdir -p docs
+	- ( cat $(top_srcdir)/docs/busybox_header.pod; \
+	    $(top_srcdir)/docs/autodocifier.pl $(top_srcdir)/include/usage.h; \
+	    cat $(top_srcdir)/docs/busybox_footer.pod ) > docs/busybox.pod
 
 docs/BusyBox.txt: docs/busybox.pod
 	@echo
@@ -99,7 +178,7 @@ docs/BusyBox.1: docs/busybox.pod
 docs/BusyBox.html: docs/busybox.net/BusyBox.html
 	- mkdir -p docs
 	-@ rm -f docs/BusyBox.html
-	-@ ln -s busybox.net/BusyBox.html docs/BusyBox.html
+	-@ cp docs/busybox.net/BusyBox.html docs/BusyBox.html
 
 docs/busybox.net/BusyBox.html: docs/busybox.pod
 	-@ mkdir -p docs/busybox.net
@@ -108,20 +187,19 @@ docs/busybox.net/BusyBox.html: docs/busybox.pod
 	-@ rm -f pod2htm*
 
 # The nifty new buildsystem stuff
-scripts/mkdep: scripts/mkdep.c
-	$(HOSTCC) $(HOSTCFLAGS) -o scripts/mkdep scripts/mkdep.c
+scripts/mkdep: $(top_srcdir)/scripts/mkdep.c
+	$(HOSTCC) $(HOSTCFLAGS) -o $@ $<
 
-scripts/split-include: scripts/split-include.c
-	$(HOSTCC) $(HOSTCFLAGS) -o scripts/split-include scripts/split-include.c
+scripts/split-include: $(top_srcdir)/scripts/split-include.c
+	$(HOSTCC) $(HOSTCFLAGS) -o $@ $<
 
 .depend: scripts/mkdep
 	rm -f .depend .hdepend;
 	mkdir -p include/config;
-	$(HOSTCC) $(HOSTCFLAGS) -o scripts/mkdep scripts/mkdep.c
 	scripts/mkdep -I include -- \
-		`find -name \*.c -print | sed -e "s,^./,,"` >> .depend;
+	  `find $(top_srcdir) -name \*.c -print | sed -e "s,^./,,"` >> .depend;
 	scripts/mkdep -I include -- \
-		`find -name \*.h -print | sed -e "s,^./,,"` >> .hdepend;
+	  `find $(top_srcdir) -name \*.h -print | sed -e "s,^./,,"` >> .hdepend;
 
 depend dep: include/config.h .depend
 
@@ -130,13 +208,10 @@ include/config/MARKER: depend scripts/split-include
 	@ touch include/config/MARKER
 
 include/config.h: .config
-	@if [ ! -x ./scripts/config/conf ] ; then \
+	@if [ ! -x $(top_builddir)/scripts/config/conf ] ; then \
 	    $(MAKE) -C scripts/config conf; \
 	fi;
-	@./scripts/config/conf -o $(CONFIG_CONFIG_IN)
-
-%.o: %.c
-	$(CC) $(CFLAGS) $(EXTRA_CFLAGS) -c -o $@ $<
+	@$(top_builddir)/scripts/config/conf -o $(CONFIG_CONFIG_IN)
 
 finished2:
 	@echo
@@ -150,12 +225,16 @@ all: menuconfig
 # configuration
 # ---------------------------------------------------------------------------
 
-scripts/config/conf:
+$(ALL_MAKEFILES): %/Makefile: $(top_srcdir)/%/Makefile
+	d=`dirname $@`; [ -d "$$d" ] || mkdir -p "$$d"; cp $< $@
+
+scripts/config/conf: scripts/config/Makefile Rules.mak
 	$(MAKE) -C scripts/config conf
 	-@if [ ! -f .config ] ; then \
 		cp $(CONFIG_DEFCONFIG) .config; \
 	fi
-scripts/config/mconf:
+
+scripts/config/mconf: scripts/config/Makefile Rules.mak
 	$(MAKE) -C scripts/config ncurses conf mconf
 	-@if [ ! -f .config ] ; then \
 		cp $(CONFIG_DEFCONFIG) .config; \
@@ -187,9 +266,6 @@ allnoconfig: scripts/config/conf
 defconfig: scripts/config/conf
 	@./scripts/config/conf -d $(CONFIG_CONFIG_IN)
 
-check: busybox
-	cd testsuite && ./runtest
-
 clean:
 	- rm -f docs/busybox.dvi docs/busybox.ps \
 	    docs/busybox.pod docs/busybox.net/busybox.html \
@@ -232,7 +308,8 @@ tags:
 
 endif # ifeq ($(strip $(HAVE_DOT_CONFIG)),y)
 
+endif # ifeq ($(skip-makefile),)
+
 .PHONY: dummy subdirs release distclean clean config oldconfig \
-	menuconfig tags check test depend
-
+	menuconfig tags check test depend buildtree