[XEN PATCH v8 12/47] build: build everything from the root dir, use obj=$subdir

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

A subdirectory is now built by setting "$(obj)" instead of changing
directory. "$(obj)" should always be set when using "Rules.mk" and
thus a shortcut "$(build)" is introduced and should be used.

A new variable "$(need-builtin)" is introduce. It is to be used
whenever a "built_in.o" is wanted from a subdirectory. "built_in.o"
isn't the main target anymore, and thus only needs to depends on the
objects that should be part of "built_in.o".

Introduce $(srctree) and $(objtree) to replace $(BASEDIR) in cases a
relative path is better, and $(abs_srctree) and $(abs_objtree) which
have an absolute path.

DEPS is updated as the existing macro to deal with it doesn't know
about $(obj).

There's some changes in "Rules.mk" which in addition to deal with
"$(obj)" also make it's looks more like "Makefile.build" from Linux
v5.12.

test/Makefile doesn't need special handling in order to build
everything under test/, Rules.mk will visit test/livepatch via
$(subdir-y), thus "tests" "all" and "build" target are removed.
"subtree-force-update" target isn't useful so it is removed as well.

test/livepatch/Makefile doesn't need default target anymore, Rules.mk
will build everything in $(extra-y) and thus all *.livepatch.

Adjust cloc recipe: dependency files generated by CC will now have the
full path to the source file, so we don't need to prepend the
subdirectory. This fix some issue with source not been parsed by cloc
before. Also source from tools/kconfig would be listed with changes in
this patch so adjust the find command to stop listing the "tools"
directory and thus kconfig. With a default build of Xen on X86, they
are a few new files parsed by cloc:
    arch/x86/x86_64/compat/mm.c
    arch/x86/x86_64/mm.c
    common/compat/domain.c
    common/compat/memory.c
    common/compat/xlat.c

Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
Acked-by: Bob Eshleman <bobbyeshleman@xxxxxxxxx>
---

Notes:
    v8:
    - rebased
    - move check for $(obj) in Rules.mk earlier
    - use $(sort ) when adding directories in $(subdir-y)
    - fix missing space between "DEPS" and ":="
    - use -iquote when adding '.' for xen/arch/x86/usercopy.o
    - introduce also abs_srctree and abs_objtree
      those were in patch "build: replace $(BASEDIR) by $(objtree)"
    - reworked cmd_objcopy_fix_sym, we don't need to do anything for old
      version of clang, and for recent version of clang the change is the
      same a for gcc.
    - adjust "cloc" recipe
    - add some more $(Q) to silent $(MAKE) $(build)=...
    
    v7:
    - Spell "Makefile.build" as "Rules.mk" in the warning in Rules.mk about
      undefined $(obj).
    - use $(srctree) for include/xen/config.h
    - handle $(nocov-y) and $(noubsan-y), needed to add $(obj)/

 xen/Makefile                |  36 ++++++----
 xen/Rules.mk                | 138 ++++++++++++++++++++++++------------
 xen/arch/arm/Makefile       |   4 +-
 xen/arch/arm/Rules.mk       |   5 --
 xen/arch/arm/arch.mk        |   4 +-
 xen/arch/riscv/arch.mk      |   4 +-
 xen/arch/x86/Makefile       |  11 +--
 xen/arch/x86/Rules.mk       |   4 +-
 xen/arch/x86/arch.mk        |  12 ++--
 xen/arch/x86/boot/Makefile  |   8 +--
 xen/build.mk                |  12 +++-
 xen/include/Makefile        |   6 +-
 xen/scripts/Kbuild.include  |   6 ++
 xen/test/Makefile           |   7 +-
 xen/test/livepatch/Makefile |   6 --
 xen/xsm/flask/Makefile      |   2 +-
 xen/xsm/flask/ss/Makefile   |   2 +-
 17 files changed, 162 insertions(+), 105 deletions(-)

diff --git a/xen/Makefile b/xen/Makefile
index 6afae6ced37c..88997244368c 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -22,6 +22,15 @@ export CHECKPOLICY   ?= checkpolicy
 export BASEDIR := $(CURDIR)
 export XEN_ROOT := $(BASEDIR)/..
 
+abs_objtree := $(CURDIR)
+abs_srctree := $(CURDIR)
+
+export abs_srctree abs_objtree
+
+srctree := .
+objtree := .
+export srctree objtree
+
 # Do not use make's built-in rules and variables
 MAKEFLAGS += -rR
 
@@ -47,7 +56,7 @@ export KCONFIG_CONFIG ?= .config
 
 export CC CXX LD
 
-export TARGET := $(BASEDIR)/xen
+export TARGET := xen
 
 .PHONY: default
 default: build
@@ -250,7 +259,7 @@ endif
 CFLAGS += -nostdinc -fno-builtin -fno-common
 CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
 $(call cc-option-add,CFLAGS,CC,-Wvla)
-CFLAGS += -pipe -D__XEN__ -include $(BASEDIR)/include/xen/config.h
+CFLAGS += -pipe -D__XEN__ -include $(srctree)/include/xen/config.h
 CFLAGS-$(CONFIG_DEBUG_INFO) += -g
 
 ifneq ($(CONFIG_CC_IS_CLANG),y)
@@ -352,10 +361,10 @@ _install: $(TARGET)$(CONFIG_XEN_INSTALL_SUFFIX)
 
 .PHONY: tests
 tests:
-       $(MAKE) -f $(BASEDIR)/Rules.mk -C test tests
+       $(Q)$(MAKE) $(build)=test
 .PHONY: install-tests
 install-tests:
-       $(MAKE) -f $(BASEDIR)/Rules.mk -C test install
+       $(Q)$(MAKE) $(build)=test install
 
 .PHONY: _uninstall
 _uninstall: D=$(DESTDIR)
@@ -411,16 +420,16 @@ $(TARGET).gz: $(TARGET)
 
 $(TARGET): FORCE
        $(MAKE) -C tools
-       $(MAKE) -f $(BASEDIR)/Rules.mk include/xen/compile.h
+       $(Q)$(MAKE) $(build)=. include/xen/compile.h
        [ -e arch/$(TARGET_ARCH)/efi ] && for f in $$(cd common/efi; echo 
*.[ch]); \
                do test -r arch/$(TARGET_ARCH)/efi/$$f || \
                   ln -nsf ../../../common/efi/$$f arch/$(TARGET_ARCH)/efi/; \
                done; \
                true
-       $(MAKE) -f $(BASEDIR)/Rules.mk -C include
-       $(MAKE) -f $(BASEDIR)/Rules.mk -C arch/$(TARGET_ARCH) include
-       $(MAKE) -f $(BASEDIR)/Rules.mk 
arch/$(TARGET_ARCH)/include/asm/asm-offsets.h
-       $(MAKE) -f $(BASEDIR)/Rules.mk $@
+       $(Q)$(MAKE) $(build)=include all
+       $(Q)$(MAKE) $(build)=arch/$(TARGET_ARCH) include
+       $(Q)$(MAKE) $(build)=. arch/$(TARGET_ARCH)/include/asm/asm-offsets.h
+       $(Q)$(MAKE) $(build)=. $@
 
 SUBDIRS = xsm arch/$(TARGET_ARCH) common drivers lib test
 define all_sources
@@ -467,19 +476,18 @@ _MAP:
        $(NM) -n $(TARGET)-syms | grep -v '\(compiled\)\|\(\.o$$\)\|\( [aUw] 
\)\|\(\.\.ng$$\)\|\(LASH[RL]DI\)' > System.map
 
 %.o %.i %.s: %.c FORCE
-       $(MAKE) -f $(BASEDIR)/Rules.mk -C $(*D) $(@F)
+       $(Q)$(MAKE) $(build)=$(*D) $(*D)/$(@F)
 
 %.o %.s: %.S FORCE
-       $(MAKE) -f $(BASEDIR)/Rules.mk -C $(*D) $(@F)
+       $(Q)$(MAKE) $(build)=$(*D) $(*D)/$(@F)
 
 %/: FORCE
-       $(MAKE) -f $(BASEDIR)/Rules.mk -C $* built_in.o built_in_bin.o
+       $(Q)$(MAKE) $(build)=$* need-builtin=1
 
 .PHONY: cloc
 cloc:
-       find . -name '*.o.d' | while read f; do \
+       find . -name tools -prune -o -name '*.o.d' -print | while read f; do \
            for sf in $$(grep -o "[a-zA-Z0-9_/-]*\.[cS]" $$f); do \
-               sf="$$(dirname $$f)/$$sf"; \
                test -f "$$sf" && echo "$$sf"; \
            done; \
        done | cloc --list-file=-
diff --git a/xen/Rules.mk b/xen/Rules.mk
index 14b6e7fdd721..32a97e012060 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -3,19 +3,29 @@
 # Makefile and are consumed by Rules.mk
 #
 
-obj := .
+ifndef obj
+$(warning kbuild: Rules.mk is included improperly)
+endif
+
 src := $(obj)
 
+PHONY := __build
+__build:
+
 -include $(BASEDIR)/include/config/auto.conf
 
 include $(XEN_ROOT)/Config.mk
 include $(BASEDIR)/scripts/Kbuild.include
 
 # Initialise some variables
+obj-y :=
 lib-y :=
 targets :=
+subdir-y :=
 CFLAGS-y :=
 AFLAGS-y :=
+nocov-y :=
+noubsan-y :=
 
 SPECIAL_DATA_SECTIONS := rodata $(foreach a,1 2 4 8 16, \
                                             $(foreach w,1 2 4, \
@@ -50,27 +60,54 @@ cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $< $@
 quiet_cmd_binfile = BINFILE $@
 cmd_binfile = $(SHELL) $(BASEDIR)/tools/binfile $(BINFILE_FLAGS) $@ $(2)
 
-define gendep
-    ifneq ($(1),$(subst /,:,$(1)))
-        DEPS += $(dir $(1)).$(notdir $(1)).d
-    endif
-endef
-$(foreach o,$(filter-out %/,$(obj-y) $(obj-bin-y) $(extra-y)),$(eval $(call 
gendep,$(o))))
+# Figure out what we need to build from the various variables
+# ===========================================================================
+
+# Libraries are always collected in one lib file.
+# Filter out objects already built-in
+lib-y := $(filter-out $(obj-y), $(sort $(lib-y)))
+
+# Subdirectories we need to descend into
+subdir-y := $(sort $(subdir-y) $(patsubst %/,%,$(filter %/, $(obj-y))))
 
 # Handle objects in subdirs
-# ---------------------------------------------------------------------------
-# o if we encounter foo/ in $(obj-y), replace it by foo/built_in.o
-#   and add the directory to the list of dirs to descend into: $(subdir-y)
-subdir-y := $(subdir-y) $(filter %/, $(obj-y))
+# - if we encounter foo/ in $(obj-y), replace it by foo/built_in.o
+ifdef need-builtin
 obj-y    := $(patsubst %/, %/built_in.o, $(obj-y))
+else
+obj-y    := $(filter-out %/, $(obj-y))
+endif
 
-# $(subdir-obj-y) is the list of objects in $(obj-y) which uses dir/ to
-# tell kbuild to descend
-subdir-obj-y := $(filter %/built_in.o, $(obj-y))
+# Add subdir path
 
-# Libraries are always collected in one lib file.
-# Filter out objects already built-in
-lib-y := $(filter-out $(obj-y), $(sort $(lib-y)))
+extra-y         := $(addprefix $(obj)/,$(extra-y))
+targets         := $(addprefix $(obj)/,$(targets))
+lib-y           := $(addprefix $(obj)/,$(lib-y))
+obj-y           := $(addprefix $(obj)/,$(obj-y))
+obj-bin-y       := $(addprefix $(obj)/,$(obj-bin-y))
+subdir-y        := $(addprefix $(obj)/,$(subdir-y))
+nocov-y         := $(addprefix $(obj)/,$(nocov-y))
+noubsan-y       := $(addprefix $(obj)/,$(noubsan-y))
+
+# subdir-builtin may contain duplications. Use $(sort ...)
+subdir-builtin := $(sort $(filter %/built_in.o, $(obj-y)))
+
+targets-for-builtin := $(extra-y)
+
+ifneq ($(strip $(lib-y)),)
+    targets-for-builtin += $(obj)/lib.a
+endif
+
+ifdef need-builtin
+    targets-for-builtin += $(obj)/built_in.o
+    ifneq ($(strip $(obj-bin-y)),)
+        ifeq ($(CONFIG_LTO),y)
+            targets-for-builtin += $(obj)/built_in_bin.o
+        endif
+    endif
+endif
+
+targets += $(targets-for-builtin)
 
 $(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): CFLAGS-y += 
-DINIT_SECTIONS_ONLY
 
@@ -122,29 +159,28 @@ quiet_cmd_cc_builtin = CC      $@
 cmd_cc_builtin = \
     $(CC) $(XEN_CFLAGS) -c -x c /dev/null -o $@
 
+# To build objects in subdirs, we need to descend into the directories
+$(subdir-builtin): $(obj)/%/built_in.o: $(obj)/% ;
+
 quiet_cmd_ld_builtin = LD      $@
 ifeq ($(CONFIG_LTO),y)
 cmd_ld_builtin = \
-    $(LD_LTO) -r -o $@ $(filter $(obj-y),$(real-prereqs))
+    $(LD_LTO) -r -o $@ $(real-prereqs)
 else
 cmd_ld_builtin = \
-    $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter $(obj-y),$(real-prereqs))
+    $(LD) $(XEN_LDFLAGS) -r -o $@ $(real-prereqs)
 endif
 
-built_in.o: $(obj-y) $(if $(strip $(lib-y)),lib.a) $(extra-y) FORCE
+$(obj)/built_in.o: $(obj-y) FORCE
        $(call if_changed,$(if $(strip $(obj-y)),ld_builtin,cc_builtin))
 
-lib.a: $(lib-y) FORCE
+$(obj)/lib.a: $(lib-y) FORCE
        $(call if_changed,ar)
 
-targets += built_in.o
-ifneq ($(strip $(lib-y)),)
-targets += lib.a
-endif
-targets += $(filter-out $(subdir-obj-y), $(obj-y) $(lib-y)) $(extra-y)
-targets += $(MAKECMDGOALS)
+targets += $(filter-out $(subdir-builtin), $(obj-y))
+targets += $(lib-y) $(MAKECMDGOALS)
 
-built_in_bin.o: $(obj-bin-y) $(extra-y)
+$(obj)/built_in_bin.o: $(obj-bin-y)
 ifeq ($(strip $(obj-bin-y)),)
        $(CC) $(a_flags) -c -x assembler /dev/null -o $@
 else
@@ -155,23 +191,15 @@ endif
 PHONY += FORCE
 FORCE:
 
-%/built_in.o %/lib.a: FORCE
-       $(MAKE) -f $(BASEDIR)/Rules.mk -C $* built_in.o
-
-%/built_in_bin.o: FORCE
-       $(MAKE) -f $(BASEDIR)/Rules.mk -C $* built_in_bin.o
-
-SRCPATH := $(patsubst $(BASEDIR)/%,%,$(CURDIR))
-
 quiet_cmd_cc_o_c = CC      $@
 ifeq ($(CONFIG_ENFORCE_UNIQUE_SYMBOLS),y)
     cmd_cc_o_c = $(CC) $(c_flags) -c $< -o $(dot-target).tmp -MQ $@
-    ifeq ($(CONFIG_CC_IS_CLANG)$(call clang-ifversion,-lt,400,y),yy)
-        cmd_objcopy_fix_sym = $(OBJCOPY) --redefine-sym $<=$(SRCPATH)/$< 
$(dot-target).tmp $@
+    ifneq ($(CONFIG_CC_IS_CLANG)$(call clang-ifversion,-lt,400,y),yy)
+        cmd_objcopy_fix_sym = \
+           $(OBJCOPY) --redefine-sym $(<F)=$< $(dot-target).tmp $@ && rm -f 
$(dot-target).tmp
     else
-        cmd_objcopy_fix_sym = $(OBJCOPY) --redefine-sym $(<F)=$(SRCPATH)/$< 
$(dot-target).tmp $@
+        cmd_objcopy_fix_sym = mv -f $(dot-target).tmp $@
     endif
-    cmd_objcopy_fix_sym += && rm -f $(dot-target).tmp
 else
     cmd_cc_o_c = $(CC) $(c_flags) -c $< -o $@
 endif
@@ -181,13 +209,13 @@ define rule_cc_o_c
     $(call cmd,objcopy_fix_sym)
 endef
 
-%.o: %.c FORCE
+$(obj)/%.o: $(src)/%.c FORCE
        $(call if_changed_rule,cc_o_c)
 
 quiet_cmd_cc_o_S = CC      $@
 cmd_cc_o_S = $(CC) $(a_flags) -c $< -o $@
 
-%.o: %.S FORCE
+$(obj)/%.o: $(src)/%.S FORCE
        $(call if_changed,cc_o_S)
 
 
@@ -205,7 +233,7 @@ define cmd_obj_init_o
     $(OBJCOPY) $(foreach s,$(SPECIAL_DATA_SECTIONS),--rename-section 
.$(s)=.init.$(s)) $< $@
 endef
 
-$(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): %.init.o: %.o FORCE
+$(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): $(obj)/%.init.o: 
$(obj)/%.o FORCE
        $(call if_changed,obj_init_o)
 
 quiet_cmd_cpp_i_c = CPP     $@
@@ -217,19 +245,21 @@ cmd_cc_s_c = $(CC) $(filter-out -Wa$(comma)%,$(c_flags)) 
-S $< -o $@
 quiet_cmd_cpp_s_S = CPP     $@
 cmd_cpp_s_S = $(CPP) $(call cpp_flags,$(a_flags)) -MQ $@ -o $@ $<
 
-%.i: %.c FORCE
+$(obj)/%.i: $(src)/%.c FORCE
        $(call if_changed,cpp_i_c)
 
-%.s: %.c FORCE
+$(obj)/%.s: $(src)/%.c FORCE
        $(call if_changed,cc_s_c)
 
-%.s: %.S FORCE
+$(obj)/%.s: $(src)/%.S FORCE
        $(call if_changed,cpp_s_S)
 
 # Linker scripts, .lds.S -> .lds
 quiet_cmd_cpp_lds_S = LDS     $@
 cmd_cpp_lds_S = $(CPP) -P $(call cpp_flags,$(a_flags)) -D__LINKER__ -MQ $@ -o 
$@ $<
 
+targets := $(filter-out $(PHONY), $(targets))
+
 # Add intermediate targets:
 # When building objects with specific suffix patterns, add intermediate
 # targets that the final targets are derived from.
@@ -239,7 +269,18 @@ intermediate_targets = $(foreach sfx, $(2), \
 # %.init.o <- %.o
 targets += $(call intermediate_targets, .init.o, .o)
 
--include $(DEPS_INCLUDE)
+# Build
+# ---------------------------------------------------------------------------
+
+__build: $(targets-for-builtin) $(subdir-y)
+       @:
+
+# Descending
+# ---------------------------------------------------------------------------
+
+PHONY += $(subdir-y)
+$(subdir-y):
+       $(Q)$(MAKE) $(build)=$@ need-builtin=$(if $(filter $@/built_in.o, 
$(subdir-builtin)),1)
 
 # Read all saved command lines and dependencies for the $(targets) we
 # may be building above, using $(if_changed{,_dep}). As an
@@ -250,6 +291,9 @@ existing-targets := $(wildcard $(sort $(targets)))
 
 -include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
 
+DEPS := $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).d)
+-include $(DEPS_INCLUDE)
+
 # Declare the contents of the PHONY variable as phony.  We keep that
 # information in a variable so we can use it in if_changed and friends.
 .PHONY: $(PHONY)
diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
index c993ce72a341..fd24f0212ffa 100644
--- a/xen/arch/arm/Makefile
+++ b/xen/arch/arm/Makefile
@@ -95,12 +95,12 @@ $(TARGET)-syms: $(BASEDIR)/prelink.o $(obj)/xen.lds
            $(BASEDIR)/common/symbols-dummy.o -o $(@D)/.$(@F).0
        $(NM) -pa --format=sysv $(@D)/.$(@F).0 \
                | $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort 
>$(@D)/.$(@F).0.S
-       $(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).0.o
+       $(MAKE) $(build)=$(@D) $(@D)/.$(@F).0.o
        $(LD) $(XEN_LDFLAGS) -T $(obj)/xen.lds -N $< \
            $(@D)/.$(@F).0.o -o $(@D)/.$(@F).1
        $(NM) -pa --format=sysv $(@D)/.$(@F).1 \
                | $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort 
>$(@D)/.$(@F).1.S
-       $(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).1.o
+       $(MAKE) $(build)=$(@D) $(@D)/.$(@F).1.o
        $(LD) $(XEN_LDFLAGS) -T $(obj)/xen.lds -N $< $(build_id_linker) \
            $(@D)/.$(@F).1.o -o $@
        $(NM) -pa --format=sysv $(@D)/$(@F) \
diff --git a/xen/arch/arm/Rules.mk b/xen/arch/arm/Rules.mk
index 290609487605..e69de29bb2d1 100644
--- a/xen/arch/arm/Rules.mk
+++ b/xen/arch/arm/Rules.mk
@@ -1,5 +0,0 @@
-# head.o is built by descending into arch/arm/$(TARGET_SUBARCH), depends on the
-# part of $(ALL_OBJS) that will eventually recurse into $(TARGET_SUBARCH)/ and
-# build head.o
-arch/arm/$(TARGET_SUBARCH)/head.o: arch/arm/built_in.o
-arch/arm/$(TARGET_SUBARCH)/head.o: ;
diff --git a/xen/arch/arm/arch.mk b/xen/arch/arm/arch.mk
index ba3f140e2ea7..4e3f7014305e 100644
--- a/xen/arch/arm/arch.mk
+++ b/xen/arch/arm/arch.mk
@@ -1,8 +1,8 @@
 ########################################
 # arm-specific definitions
 
-CFLAGS += -I$(BASEDIR)/include
-CFLAGS += -I$(BASEDIR)/arch/$(TARGET_ARCH)/include
+CFLAGS += -I$(srctree)/include
+CFLAGS += -I$(srctree)/arch/$(TARGET_ARCH)/include
 
 $(call cc-options-add,CFLAGS,CC,$(EMBEDDED_EXTRA_CFLAGS))
 $(call cc-option-add,CFLAGS,CC,-Wnested-externs)
diff --git a/xen/arch/riscv/arch.mk b/xen/arch/riscv/arch.mk
index 39ae6ffea94d..694ba053ceab 100644
--- a/xen/arch/riscv/arch.mk
+++ b/xen/arch/riscv/arch.mk
@@ -11,5 +11,5 @@ riscv-march-$(CONFIG_RISCV_ISA_C)       := $(riscv-march-y)c
 # -mcmodel=medlow would force Xen into the lower half.
 
 CFLAGS += -march=$(riscv-march-y) -mstrict-align -mcmodel=medany
-CFLAGS += -I$(BASEDIR)/include
-CFLAGS += -I$(BASEDIR)/arch/$(TARGET_ARCH)/include
+CFLAGS += -I$(srctree)/include
+CFLAGS += -I$(srctree)/arch/$(TARGET_ARCH)/include
diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index f9af39ba6138..6f18daf9105c 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -80,6 +80,9 @@ endif
 extra-y += asm-macros.i
 extra-y += xen.lds
 
+# Allows usercopy.c to include itself
+$(obj)/usercopy.o: CFLAGS-y += -iquote .
+
 ifneq ($(CONFIG_HVM),y)
 $(obj)/x86_emulate.o: CFLAGS-y += -Wno-unused-label
 endif
@@ -129,13 +132,13 @@ $(TARGET)-syms: $(BASEDIR)/prelink.o $(obj)/xen.lds
        $(NM) -pa --format=sysv $(@D)/.$(@F).0 \
                | $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort \
                >$(@D)/.$(@F).0.S
-       $(MAKE) -f $(BASEDIR)/Rules.mk efi-y= $(@D)/.$(@F).0.o
+       $(MAKE) $(build)=$(@D) efi-y= $(@D)/.$(@F).0.o
        $(LD) $(XEN_LDFLAGS) -T $(obj)/xen.lds -N $< $(build_id_linker) \
            $(@D)/.$(@F).0.o -o $(@D)/.$(@F).1
        $(NM) -pa --format=sysv $(@D)/.$(@F).1 \
                | $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort 
$(syms-warn-dup-y) \
                >$(@D)/.$(@F).1.S
-       $(MAKE) -f $(BASEDIR)/Rules.mk efi-y= $(@D)/.$(@F).1.o
+       $(MAKE) $(build)=$(@D) efi-y= $(@D)/.$(@F).1.o
        $(LD) $(XEN_LDFLAGS) -T $(obj)/xen.lds -N $< $(build_id_linker) \
            $(@D)/.$(@F).1.o -o $@
        $(NM) -pa --format=sysv $(@D)/$(@F) \
@@ -199,14 +202,14 @@ endif
        $(MKRELOC) $(foreach base,$(VIRT_BASE) 
$(ALT_BASE),$(@D)/.$(@F).$(base).0) >$(@D)/.$(@F).0r.S
        $(NM) -pa --format=sysv $(@D)/.$(@F).$(VIRT_BASE).0 \
                | $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort 
>$(@D)/.$(@F).0s.S
-       $(MAKE) -f $(BASEDIR)/Rules.mk efi-y= $(@D)/.$(@F).0r.o 
$(@D)/.$(@F).0s.o
+       $(MAKE) $(build)=$(@D) efi-y= .$(@F).0r.o .$(@F).0s.o
        $(foreach base, $(VIRT_BASE) $(ALT_BASE), \
                  $(LD) $(call EFI_LDFLAGS,$(base)) -T $(obj)/efi.lds -N $< \
                        $(@D)/.$(@F).0r.o $(@D)/.$(@F).0s.o $(note_file_option) 
-o $(@D)/.$(@F).$(base).1 &&) :
        $(MKRELOC) $(foreach base,$(VIRT_BASE) 
$(ALT_BASE),$(@D)/.$(@F).$(base).1) >$(@D)/.$(@F).1r.S
        $(NM) -pa --format=sysv $(@D)/.$(@F).$(VIRT_BASE).1 \
                | $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort 
>$(@D)/.$(@F).1s.S
-       $(MAKE) -f $(BASEDIR)/Rules.mk efi-y= $(@D)/.$(@F).1r.o 
$(@D)/.$(@F).1s.o
+       $(MAKE) $(build)=$(@D) efi-y= .$(@F).1r.o .$(@F).1s.o
        $(LD) $(call EFI_LDFLAGS,$(VIRT_BASE)) -T $(obj)/efi.lds -N $< \
                        $(@D)/.$(@F).1r.o $(@D)/.$(@F).1s.o $(note_file_option) 
-o $@
        $(NM) -pa --format=sysv $(@D)/$(@F) \
diff --git a/xen/arch/x86/Rules.mk b/xen/arch/x86/Rules.mk
index 56fe22c979ea..2d12c2dca208 100644
--- a/xen/arch/x86/Rules.mk
+++ b/xen/arch/x86/Rules.mk
@@ -2,9 +2,9 @@
 # x86-specific definitions
 
 ifneq ($(filter -DHAVE_AS_QUOTED_SYM,$(XEN_CFLAGS)),)
-object_label_flags = '-D__OBJECT_LABEL__=$(subst $(BASEDIR)/,,$(CURDIR))/$@'
+object_label_flags = '-D__OBJECT_LABEL__=$@'
 else
-object_label_flags = '-D__OBJECT_LABEL__=$(subst /,$$,$(subst -,_,$(subst 
$(BASEDIR)/,,$(CURDIR))/$@))'
+object_label_flags = '-D__OBJECT_LABEL__=$(subst /,$$,$(subst -,_,$@))'
 endif
 c_flags += $(object_label_flags) $(CFLAGS-stack-boundary)
 a_flags += $(object_label_flags) $(CFLAGS-stack-boundary)
diff --git a/xen/arch/x86/arch.mk b/xen/arch/x86/arch.mk
index c830dc5b3a7c..5152de343082 100644
--- a/xen/arch/x86/arch.mk
+++ b/xen/arch/x86/arch.mk
@@ -3,10 +3,10 @@
 
 export XEN_IMG_OFFSET := 0x200000
 
-CFLAGS += -I$(BASEDIR)/include
-CFLAGS += -I$(BASEDIR)/arch/$(TARGET_ARCH)/include
-CFLAGS += -I$(BASEDIR)/arch/x86/include/asm/mach-generic
-CFLAGS += -I$(BASEDIR)/arch/x86/include/asm/mach-default
+CFLAGS += -I$(srctree)/include
+CFLAGS += -I$(srctree)/arch/$(TARGET_ARCH)/include
+CFLAGS += -I$(srctree)/arch/x86/include/asm/mach-generic
+CFLAGS += -I$(srctree)/arch/x86/include/asm/mach-default
 CFLAGS += -DXEN_IMG_OFFSET=$(XEN_IMG_OFFSET)
 
 # Prevent floating-point variables from creeping into Xen.
@@ -87,7 +87,7 @@ efi-nr-fixups := $(shell $(OBJDUMP) -p $(efi-check-o:.o=.efi) 
| grep '^[[:blank:
 ifeq ($(efi-nr-fixups),2)
 MKRELOC := :
 else
-MKRELOC := efi/mkreloc
+MKRELOC := arch/x86/efi/mkreloc
 # If the linker produced fixups but not precisely two of them, we need to
 # disable it doing so.  But if it didn't produce any fixups, it also wouldn't
 # recognize the option.
@@ -103,6 +103,6 @@ export EFI_LDFLAGS
 endif
 
 # Set up the assembler include path properly for older toolchains.
-CFLAGS += -Wa,-I$(BASEDIR)/include
+CFLAGS += -Wa,-I$(srctree)/include
 
 ALL_OBJS-y := arch/x86/boot/built_in.o arch/x86/efi/built_in.o $(ALL_OBJS-y)
diff --git a/xen/arch/x86/boot/Makefile b/xen/arch/x86/boot/Makefile
index 0aec8a464364..ba732e4a88c3 100644
--- a/xen/arch/x86/boot/Makefile
+++ b/xen/arch/x86/boot/Makefile
@@ -1,8 +1,8 @@
 obj-bin-y += head.o
 
-DEFS_H_DEPS = $(src)/defs.h $(BASEDIR)/include/xen/stdbool.h
+DEFS_H_DEPS = $(abs_srctree)/$(src)/defs.h $(abs_srctree)/include/xen/stdbool.h
 
-CMDLINE_DEPS = $(DEFS_H_DEPS) $(src)/video.h \
+CMDLINE_DEPS = $(DEFS_H_DEPS) $(abs_srctree)/$(src)/video.h \
               $(BASEDIR)/include/xen/kconfig.h \
               $(BASEDIR)/include/generated/autoconf.h
 
@@ -17,7 +17,7 @@ RELOC_DEPS = $(DEFS_H_DEPS) \
 $(obj)/head.o: $(obj)/cmdline.S $(obj)/reloc.S
 
 $(obj)/cmdline.S: $(src)/cmdline.c $(CMDLINE_DEPS) $(src)/build32.lds
-       $(MAKE) -f build32.mk -C $(obj) $(@F) CMDLINE_DEPS="$(CMDLINE_DEPS)"
+       $(MAKE) -f $(abs_srctree)/$(src)/build32.mk -C $(obj) $(@F) 
CMDLINE_DEPS="$(CMDLINE_DEPS)"
 
 $(obj)/reloc.S: $(src)/reloc.c $(RELOC_DEPS) $(src)/build32.lds
-       $(MAKE) -f build32.mk -C $(obj) $(@F) RELOC_DEPS="$(RELOC_DEPS)"
+       $(MAKE) -f $(abs_srctree)/$(src)/build32.mk -C $(obj) $(@F) 
RELOC_DEPS="$(RELOC_DEPS)"
diff --git a/xen/build.mk b/xen/build.mk
index 740945333a97..bf0c9710241a 100644
--- a/xen/build.mk
+++ b/xen/build.mk
@@ -59,6 +59,16 @@ arch/$(TARGET_ARCH)/include/asm/asm-offsets.h: asm-offsets.s
          echo ""; \
          echo "#endif") <$< >$@
 
+build-dirs := $(patsubst %/built_in.o,%,$(filter %/built_in.o,$(ALL_OBJS) 
$(ALL_LIBS)))
+
+# The actual objects are generated when descending,
+# make sure no implicit rule kicks in
+$(sort $(ALL_OBJS) $(ALL_LIBS)): $(build-dirs) ;
+
+PHONY += $(build-dirs)
+$(build-dirs): FORCE
+       $(Q)$(MAKE) $(build)=$@ need-builtin=1
+
 ifeq ($(CONFIG_LTO),y)
 # Gather all LTO objects together
 prelink_lto.o: $(ALL_OBJS) $(ALL_LIBS)
@@ -75,4 +85,4 @@ endif
 targets += prelink.o
 
 $(TARGET): prelink.o FORCE
-       $(MAKE) -f $(BASEDIR)/Rules.mk -C arch/$(TARGET_ARCH) $@
+       $(Q)$(MAKE) $(build)=arch/$(TARGET_ARCH) $@
diff --git a/xen/include/Makefile b/xen/include/Makefile
index d2f5a956a11a..cd40d5b4c923 100644
--- a/xen/include/Makefile
+++ b/xen/include/Makefile
@@ -61,7 +61,7 @@ $(obj)/compat/.xlat/%.h: $(obj)/compat/%.h 
$(obj)/compat/.xlat/%.lst $(BASEDIR)/
        export PYTHON=$(PYTHON); \
        while read what name; do \
                $(SHELL) $(BASEDIR)/tools/get-fields.sh "$$what" compat_$$name 
$< || exit $$?; \
-       done <$(patsubst compat/%,compat/.xlat/%,$(basename $<)).lst >$@.new
+       done <$(patsubst $(obj)/compat/%,$(obj)/compat/.xlat/%,$(basename 
$<)).lst >$@.new
        mv -f $@.new $@
 
 .PRECIOUS: $(obj)/compat/.xlat/%.lst
@@ -86,8 +86,8 @@ PUBLIC_HEADERS := $(filter-out $(src)/public/arch-% 
$(src)/public/dom0_ops.h, $(
 PUBLIC_C99_HEADERS := $(src)/public/io/9pfs.h $(src)/public/io/pvcalls.h
 PUBLIC_ANSI_HEADERS := $(filter-out $(src)/public/%ctl.h $(src)/public/xsm/% 
$(src)/public/%hvm/save.h $(PUBLIC_C99_HEADERS), $(PUBLIC_HEADERS))
 
-public/io/9pfs.h-prereq := string
-public/io/pvcalls.h-prereq := string
+$(src)/public/io/9pfs.h-prereq := string
+$(src)/public/io/pvcalls.h-prereq := string
 
 $(obj)/headers.chk: $(PUBLIC_ANSI_HEADERS) $(src)/Makefile
        for i in $(filter %.h,$^); do \
diff --git a/xen/scripts/Kbuild.include b/xen/scripts/Kbuild.include
index b4b77f85d8d5..a333c3961db6 100644
--- a/xen/scripts/Kbuild.include
+++ b/xen/scripts/Kbuild.include
@@ -61,6 +61,12 @@ cc-ifversion = $(shell [ $(CONFIG_GCC_VERSION)0 $(1) $(2)000 
] && echo $(3) || e
 
 clang-ifversion = $(shell [ $(CONFIG_CLANG_VERSION)0 $(1) $(2)000 ] && echo 
$(3) || echo $(4))
 
+###
+# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.build obj=
+# Usage:
+# $(Q)$(MAKE) $(build)=dir
+build := -f $(srctree)/Rules.mk obj
+
 # Shorthand for $(MAKE) clean
 # Usage:
 # $(MAKE) $(clean) dir
diff --git a/xen/test/Makefile b/xen/test/Makefile
index 41e4d7bdb78b..080763c80766 100644
--- a/xen/test/Makefile
+++ b/xen/test/Makefile
@@ -1,13 +1,10 @@
 
-tests all: build
-
-
 ifneq ($(XEN_TARGET_ARCH),x86_32)
 # Xen 32-bit x86 hypervisor no longer supported, so has no test livepatches
 subdir-y += livepatch
 endif
 
-install build subtree-force-update uninstall: %:
+install uninstall: %:
        set -e; for s in $(subdir-y); do \
-               $(MAKE) -f $(BASEDIR)/Rules.mk -C $$s $*; \
+               $(MAKE) $(build)=$$s $*; \
        done
diff --git a/xen/test/livepatch/Makefile b/xen/test/livepatch/Makefile
index 69fadccd01ea..afb8d589ecae 100644
--- a/xen/test/livepatch/Makefile
+++ b/xen/test/livepatch/Makefile
@@ -11,9 +11,6 @@ endif
 CODE_ADDR=$(shell nm --defined $(1) | grep $(2) | awk '{print "0x"$$1}')
 CODE_SZ=$(shell nm --defined -S $(1) | grep $(2) | awk '{ print "0x"$$2}')
 
-.PHONY: default
-build default: livepatch
-
 extra-y += xen_hello_world.livepatch
 xen_hello_world-objs := xen_hello_world_func.o xen_hello_world.o note.o 
xen_note.o modinfo.o
 $(obj)/xen_hello_world.o: $(obj)/config.h
@@ -156,9 +153,6 @@ LIVEPATCHES := $(filter %.livepatch,$(extra-y))
 
 LIVEPATCH_DEBUG_DIR ?= $(DEBUG_DIR)/xen-livepatch
 
-.PHONY: livepatch
-livepatch: $(LIVEPATCHES)
-
 install: $(addprefix $(obj)/,$(LIVEPATCHES))
        $(INSTALL_DIR) $(DESTDIR)$(LIVEPATCH_DEBUG_DIR)
        $(INSTALL_DATA) $(addprefix $(obj)/,$(LIVEPATCHES)) 
$(DESTDIR)$(LIVEPATCH_DEBUG_DIR)
diff --git a/xen/xsm/flask/Makefile b/xen/xsm/flask/Makefile
index 51fd37f6c4d5..49cf730cf098 100644
--- a/xen/xsm/flask/Makefile
+++ b/xen/xsm/flask/Makefile
@@ -40,7 +40,7 @@ $(obj)/flask-policy.S: $(BASEDIR)/tools/binfile FORCE
        $(call if_changed,binfile,$(obj)/policy.bin xsm_flask_init_policy)
 targets += flask-policy.S
 
-FLASK_BUILD_DIR := $(CURDIR)
+FLASK_BUILD_DIR := $(abs_objtree)/$(obj)
 POLICY_SRC := $(FLASK_BUILD_DIR)/xenpolicy-$(XEN_FULLVERSION)
 
 $(obj)/policy.bin: FORCE
diff --git a/xen/xsm/flask/ss/Makefile b/xen/xsm/flask/ss/Makefile
index d32b9e07138e..aba1339f3808 100644
--- a/xen/xsm/flask/ss/Makefile
+++ b/xen/xsm/flask/ss/Makefile
@@ -8,4 +8,4 @@ obj-y += services.o
 obj-y += conditional.o
 obj-y += mls.o
 
-CFLAGS-y += -I../include
+CFLAGS-y += -I$(srctree)/xsm/flask/include
-- 
Anthony PERARD