kbuild: resync top Makefile, mkmakefile, tags.sh with Linux 5.7-rc4

The prologue of the build system is not specific to Linux or Barebox.
Paritially resync with Linux 5.7-rc4

- In Linux, $(objtree) is always '.', and $(srctree) might be relative.
  I am keeping both absolute for now to avoid unexpected breakage.

- I did not resync single target for now. We need to touch
  Makefile.build a lot if we want to resync it.

- 'export CDPATH=' is Barebox-only code, which was added by
  commit 6cc8d0544658 ("Makefile: disable CDPATH"). Keep it.

- KBUILD_SRC no longer exists in the upstream Linux. I replaced it
  with building_out_of_srctree.

- scripts/mkmakefile does not contain anything specific to Linux or
  Barebox. Resync it with Linux 5.7-rc4

- scripts/tags was imported from Linux 3.6 with some cherry-picks on
  top of that. Resync it with Linux 5.7-rc4

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 345 insertions, 260 deletions

diff --git a/Makefile b/Makefile
index be9f2a211a..837ae47e22 100644
--- a/Makefile
+++ b/Makefile
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
 VERSION = 2020
 PATCHLEVEL = 04
 SUBLEVEL = 0
@@ -10,11 +11,9 @@ NAME = None
 # Comments in this file are targeted only to the developer, do not
 # expect to learn how to build the kernel reading this file.
 
-# Do not:
-# o  use make's built-in rules and variables
-#    (this increases performance and avoids hard-to-debug behaviour);
-# o  print "Entering directory ...";
-MAKEFLAGS += -rR --no-print-directory
+# That's our default target when none is given on the command line
+PHONY := _all
+_all:
 
 # We are using a recursive build, so we need to do a little thinking
 # to get the ordering right.
@@ -22,8 +21,8 @@ MAKEFLAGS += -rR --no-print-directory
 # Most importantly: sub-Makefiles should only ever modify files in
 # their own directory. If in some directory we have a dependency on
 # a file in another dir (which doesn't happen often, but it's often
-# unavoidable when linking the built-in.o targets which finally
-# turn into barebox), we will call a sub make in that other dir, and
+# unavoidable when linking the built-in.a targets which finally
+# turn into vmlinux), we will call a sub make in that other dir, and
 # after that we are sure that everything which is in that other dir
 # is now up to date.
 #
@@ -32,6 +31,45 @@ MAKEFLAGS += -rR --no-print-directory
 # descending is started. They are now explicitly listed as the
 # prepare rule.
 
+ifneq ($(sub_make_done),1)
+
+# Do not use make's built-in rules and variables
+# (this increases performance and avoids hard-to-debug behaviour)
+MAKEFLAGS += -rR
+
+# Avoid funny character set dependencies
+unexport LC_ALL
+LC_COLLATE=C
+LC_NUMERIC=C
+export LC_COLLATE LC_NUMERIC
+
+# Avoid interference with shell env settings
+unexport GREP_OPTIONS
+
+# Beautify output
+# ---------------------------------------------------------------------------
+#
+# Normally, we echo the whole command before executing it. By making
+# that echo $($(quiet)$(cmd)), we now have the possibility to set
+# $(quiet) to choose other forms of output instead, e.g.
+#
+#         quiet_cmd_cc_o_c = Compiling $(RELDIR)/$@
+#         cmd_cc_o_c       = $(CC) $(c_flags) -c -o $@ $<
+#
+# If $(quiet) is empty, the whole command will be printed.
+# If it is set to "quiet_", only the short version will be printed.
+# If it is set to "silent_", nothing will be printed at all, since
+# the variable $(silent_cmd_cc_o_c) doesn't exist.
+#
+# A simple variant is to prefix commands with $(Q) - that's useful
+# for commands that shall be hidden in non-verbose mode.
+#
+#	$(Q)ln $@ :<
+#
+# If KBUILD_VERBOSE equals 0 then the above command will be hidden.
+# If KBUILD_VERBOSE equals 1 then the above command is displayed.
+# If KBUILD_VERBOSE equals 2 then give the reason why each target is rebuilt.
+#
 # To put more focus on warnings, be less verbose as default
 # Use 'make V=1' to see the full commands
 
@@ -42,6 +80,119 @@ ifndef KBUILD_VERBOSE
   KBUILD_VERBOSE = 0
 endif
 
+ifeq ($(KBUILD_VERBOSE),1)
+  quiet =
+  Q =
+else
+  quiet=quiet_
+  Q = @
+endif
+
+# If the user is running make -s (silent mode), suppress echoing of
+# commands
+
+ifneq ($(findstring s,$(filter-out --%,$(MAKEFLAGS))),)
+  quiet=silent_
+endif
+
+export quiet Q KBUILD_VERBOSE
+
+# Kbuild will save output files in the current working directory.
+# This does not need to match to the root of the kernel source tree.
+#
+# For example, you can do this:
+#
+#  cd /dir/to/store/output/files; make -f /dir/to/kernel/source/Makefile
+#
+# If you want to save output files in a different location, there are
+# two syntaxes to specify it.
+#
+# 1) O=
+# Use "make O=dir/to/store/output/files/"
+#
+# 2) Set KBUILD_OUTPUT
+# Set the environment variable KBUILD_OUTPUT to point to the output directory.
+# export KBUILD_OUTPUT=dir/to/store/output/files/; make
+#
+# The O= assignment takes precedence over the KBUILD_OUTPUT environment
+# variable.
+
+# Do we want to change the working directory?
+ifeq ("$(origin O)", "command line")
+  KBUILD_OUTPUT := $(O)
+endif
+
+ifneq ($(KBUILD_OUTPUT),)
+# Make's built-in functions such as $(abspath ...), $(realpath ...) cannot
+# expand a shell special character '~'. We use a somewhat tedious way here.
+abs_objtree := $(shell mkdir -p $(KBUILD_OUTPUT) && cd $(KBUILD_OUTPUT) && pwd)
+$(if $(abs_objtree),, \
+     $(error failed to create output directory "$(KBUILD_OUTPUT)"))
+
+# $(realpath ...) resolves symlinks
+abs_objtree := $(realpath $(abs_objtree))
+else
+abs_objtree := $(CURDIR)
+endif # ifneq ($(KBUILD_OUTPUT),)
+
+ifeq ($(abs_objtree),$(CURDIR))
+# Suppress "Entering directory ..." unless we are changing the work directory.
+MAKEFLAGS += --no-print-directory
+else
+need-sub-make := 1
+endif
+
+abs_srctree := $(realpath $(dir $(lastword $(MAKEFILE_LIST))))
+
+ifneq ($(words $(subst :, ,$(abs_srctree))), 1)
+$(error source directory cannot contain spaces or colons)
+endif
+
+ifneq ($(abs_srctree),$(abs_objtree))
+# Look for make include files relative to root of kernel src
+#
+# This does not become effective immediately because MAKEFLAGS is re-parsed
+# once after the Makefile is read. We need to invoke sub-make.
+MAKEFLAGS += --include-dir=$(abs_srctree)
+need-sub-make := 1
+endif
+
+ifneq ($(filter 3.%,$(MAKE_VERSION)),)
+# 'MAKEFLAGS += -rR' does not immediately become effective for GNU Make 3.x
+# We need to invoke sub-make to avoid implicit rules in the top Makefile.
+need-sub-make := 1
+# Cancel implicit rules for this Makefile.
+$(lastword $(MAKEFILE_LIST)): ;
+endif
+
+export abs_srctree abs_objtree
+export sub_make_done := 1
+
+ifeq ($(need-sub-make),1)
+
+PHONY += $(MAKECMDGOALS) sub-make
+
+$(filter-out _all sub-make $(lastword $(MAKEFILE_LIST)), $(MAKECMDGOALS)) _all: sub-make
+	@:
+
+# Invoke a second make in the output directory, passing relevant variables
+sub-make:
+	$(Q)$(MAKE) -C $(abs_objtree) -f $(abs_srctree)/Makefile $(MAKECMDGOALS)
+
+endif # need-sub-make
+endif # sub_make_done
+
+# We process the rest of the Makefile if this is the final invocation of make
+ifeq ($(need-sub-make),)
+
+# CDPATH can have sideeffects; disable, since we do know where we want to cd to
+export CDPATH=
+
+# Do not print "Entering directory ...",
+# but we want to display it when entering to the output directory
+# so that IDEs/editors are able to understand relative filenames.
+MAKEFLAGS += --no-print-directory
+
 # Call a source code checker (by default, "sparse") as part of the
 # C compilation.
 #
@@ -49,8 +200,8 @@ endif
 # Use 'make C=2' to enable checking of *all* source files, regardless
 # of whether they are re-compiled or not.
 #
-# See the file "Documentation/sparse.txt" for more details, including
-# where to get the "sparse" utility.
+# See the file "Documentation/dev-tools/sparse.rst" for more details,
+# including where to get the "sparse" utility.
 
 ifeq ("$(origin C)", "command line")
   KBUILD_CHECKSRC = $(C)
@@ -59,91 +210,108 @@ ifndef KBUILD_CHECKSRC
   KBUILD_CHECKSRC = 0
 endif
 
-# Use make M=dir to specify directory of external module to build
-# Old syntax make ... SUBDIRS=$PWD is still supported
-# Setting the environment variable KBUILD_EXTMOD take precedence
-ifdef SUBDIRS
-  KBUILD_EXTMOD ?= $(SUBDIRS)
-endif
+# Use make M=dir or set the environment variable KBUILD_EXTMOD to specify the
+# directory of external module to build. Setting M= takes precedence.
 ifeq ("$(origin M)", "command line")
   KBUILD_EXTMOD := $(M)
 endif
 
+export KBUILD_CHECKSRC KBUILD_EXTMOD
 
-# kbuild supports saving output files in a separate directory.
-# To locate output files in a separate directory two syntaxes are supported.
-# In both cases the working directory must be the root of the kernel src.
-# 1) O=
-# Use "make O=dir/to/store/output/files/"
-#
-# 2) Set KBUILD_OUTPUT
-# Set the environment variable KBUILD_OUTPUT to point to the directory
-# where the output files shall be placed.
-# export KBUILD_OUTPUT=dir/to/store/output/files/
-# make
-#
-# The O= assignment takes precedence over the KBUILD_OUTPUT environment
-# variable.
+ifeq ($(abs_srctree),$(abs_objtree))
+        # building in the source tree
+	building_out_of_srctree :=
+else
+	building_out_of_srctree := 1
+endif
 
+srctree		:= $(abs_srctree)
+objtree		:= $(abs_objtree)
+src		:= $(srctree)
+obj		:= $(objtree)
 
-# KBUILD_SRC is set on invocation of make in OBJ directory
-# KBUILD_SRC is not intended to be used by the regular user (for now)
-ifeq ($(KBUILD_SRC),)
+VPATH		:= $(srctree)
 
-# OK, Make called in directory where kernel src resides
-# Do we want to locate output files in a separate directory?
-ifeq ("$(origin O)", "command line")
-  KBUILD_OUTPUT := $(O)
-endif
+export building_out_of_srctree srctree objtree VPATH
 
-# That's our default target when none is given on the command line
-PHONY := _all
-_all:
+# To make sure we do not include .config for any of the *config targets
+# catch them early, and hand them over to scripts/kconfig/Makefile
+# It is allowed to specify more targets when calling make, including
+# mixing *config targets and build targets.
+# For example 'make oldconfig all'.
+# Detect when mixed targets is specified, and make a second invocation
+# of make so .config is not included in this case either (for *config).
 
-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 mkdir -p $(KBUILD_OUTPUT) && cd $(KBUILD_OUTPUT) \
-								&& /bin/pwd)
-$(if $(KBUILD_OUTPUT),, \
-     $(error failed to create output directory "$(saved-output)"))
+version_h := include/generated/version.h
 
-PHONY += $(MAKECMDGOALS) sub-make
+clean-targets := %clean mrproper cleandocs
+no-dot-config-targets := $(clean-targets) \
+			 cscope gtags TAGS tags help% %docs \
+			 $(version_h) kernelversion outputmakefile
+no-sync-config-targets := $(no-dot-config-targets) install %install \
+			   kernelrelease
 
-$(filter-out _all sub-make,$(MAKECMDGOALS)) _all: sub-make
-	@:
+config-build	:=
+mixed-build	:=
+need-config	:= 1
+may-sync-config	:= 1
 
-sub-make: FORCE
-	$(if $(KBUILD_VERBOSE:1=),@)$(MAKE) -C $(KBUILD_OUTPUT) \
-	KBUILD_SRC=$(CURDIR) \
-	KBUILD_EXTMOD="$(KBUILD_EXTMOD)" -f $(CURDIR)/Makefile \
-	$(filter-out _all sub-make,$(MAKECMDGOALS))
+ifneq ($(filter $(no-dot-config-targets), $(MAKECMDGOALS)),)
+	ifeq ($(filter-out $(no-dot-config-targets), $(MAKECMDGOALS)),)
+		need-config :=
+	endif
+endif
 
-# Leave processing to above invocation of make
-skip-makefile := 1
-endif # ifneq ($(KBUILD_OUTPUT),)
-endif # ifeq ($(KBUILD_SRC),)
+ifneq ($(filter $(no-sync-config-targets), $(MAKECMDGOALS)),)
+	ifeq ($(filter-out $(no-sync-config-targets), $(MAKECMDGOALS)),)
+		may-sync-config :=
+	endif
+endif
 
-# We process the rest of the Makefile if this is the final invocation of make
-ifeq ($(skip-makefile),)
+ifneq ($(KBUILD_EXTMOD),)
+	may-sync-config :=
+endif
 
-# If building an external module we do not care about the all: rule
-# but instead _all depend on modules
-PHONY += all
-_all: all
+ifeq ($(KBUILD_EXTMOD),)
+        ifneq ($(filter config %config,$(MAKECMDGOALS)),)
+		config-build := 1
+                ifneq ($(words $(MAKECMDGOALS)),1)
+			mixed-build := 1
+                endif
+        endif
+endif
 
-# CDPATH can have sideeffects; disable, since we do know where we want to cd to
-export CDPATH=
+# For "make -j clean all", "make -j mrproper defconfig all", etc.
+ifneq ($(filter $(clean-targets),$(MAKECMDGOALS)),)
+        ifneq ($(filter-out $(clean-targets),$(MAKECMDGOALS)),)
+		mixed-build := 1
+        endif
+endif
 
-srctree		:= $(if $(KBUILD_SRC),$(KBUILD_SRC),$(CURDIR))
-objtree		:= $(CURDIR)
-src		:= $(srctree)
-obj		:= $(objtree)
+ifdef mixed-build
+# ===========================================================================
+# We're called with mixed targets (*config and build targets).
+# Handle them one by one.
 
-VPATH		:= $(srctree)$(if $(KBUILD_EXTMOD),:$(KBUILD_EXTMOD))
+PHONY += $(MAKECMDGOALS) __build_one_by_one
 
-export srctree objtree VPATH
+$(filter-out __build_one_by_one, $(MAKECMDGOALS)): __build_one_by_one
+	@:
+
+__build_one_by_one:
+	$(Q)set -e; \
+	for i in $(MAKECMDGOALS); do \
+		$(MAKE) -f $(srctree)/Makefile $$i; \
+	done
+
+else # !mixed-build
+
+include scripts/Kbuild.include
+
+# Read KERNELRELEASE from include/config/kernel.release (if it exists)
+KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
+KERNELVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)
+export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION
 
 # Cross compiling and selecting different set of gcc/bin-utils
 # ---------------------------------------------------------------------------
@@ -202,80 +370,6 @@ KBUILD_HOSTCXXFLAGS := -Wall -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS)
 KBUILD_HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
 KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
 
-# Decide whether to build built-in, modular, or both.
-# Normally, just do built-in.
-
-KBUILD_MODULES :=
-KBUILD_BUILTIN := 1
-
-#	If we have only "make modules", don't compile built-in objects.
-#	When we're building modules with modversions, we need to consider
-#	the built-in objects during the descend as well, in order to
-#	make sure the checksums are up to date before we record them.
-
-ifeq ($(MAKECMDGOALS),modules)
-  KBUILD_BUILTIN := $(if $(CONFIG_MODVERSIONS),1)
-endif
-
-#	If we have "make <whatever> modules", compile modules
-#	in addition to whatever we do anyway.
-#	Just "make" or "make all" shall build modules as well
-
-ifneq ($(filter all _all modules,$(MAKECMDGOALS)),)
-  KBUILD_MODULES := 1
-endif
-
-export KBUILD_MODULES KBUILD_BUILTIN
-export KBUILD_CHECKSRC KBUILD_SRC
-
-# Beautify output
-# ---------------------------------------------------------------------------
-#
-# Normally, we echo the whole command before executing it. By making
-# that echo $($(quiet)$(cmd)), we now have the possibility to set
-# $(quiet) to choose other forms of output instead, e.g.
-#
-#         quiet_cmd_cc_o_c = Compiling $(RELDIR)/$@
-#         cmd_cc_o_c       = $(CC) $(c_flags) -c -o $@ $<
-#
-# If $(quiet) is empty, the whole command will be printed.
-# If it is set to "quiet_", only the short version will be printed.
-# If it is set to "silent_", nothing will be printed at all, since
-# the variable $(silent_cmd_cc_o_c) doesn't exist.
-#
-# A simple variant is to prefix commands with $(Q) - that's useful
-# for commands that shall be hidden in non-verbose mode.
-#
-#	$(Q)ln $@ :<
-#
-# If KBUILD_VERBOSE equals 0 then the above command will be hidden.
-# If KBUILD_VERBOSE equals 1 then the above command is displayed.
-
-ifeq ($(KBUILD_VERBOSE),1)
-  quiet =
-  Q =
-else
-  quiet=quiet_
-  Q = @
-endif
-
-# If the user is running make -s (silent mode), suppress echoing of
-# commands
-
-ifneq ($(findstring s,$(MAKEFLAGS)),)
-  quiet=silent_
-endif
-
-export quiet Q KBUILD_VERBOSE
-
-
-# Look for make include files relative to root of kernel src
-MAKEFLAGS += --include-dir=$(srctree)
-
-# We need some generic definitions.
-include $(srctree)/scripts/Kbuild.include
-include $(srctree)/scripts/Makefile.lib
-
 # Make variables (CC, etc...)
 
 AS		= $(CROSS_COMPILE)as
@@ -296,6 +390,7 @@ KALLSYMS	= scripts/kallsyms
 PERL		= perl
 PYTHON3		= python3
 CHECK		= sparse
+BASH		= bash
 
 CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ -Wbitwise $(CF)
 CFLAGS_KERNEL	=
@@ -311,7 +406,7 @@ export MODVERDIR := $(if $(KBUILD_EXTMOD),$(firstword $(KBUILD_EXTMOD))/).tmp_ve
 # Use LINUXINCLUDE when you must reference the include/ directory.
 # Needed to be compatible with the O= option
 LINUXINCLUDE    := -Iinclude -I$(srctree)/dts/include \
-                   $(if $(KBUILD_SRC), -I$(srctree)/include) \
+                   $(if $(building_out_of_srctree), -I$(srctree)/include) \
 		   -I$(srctree)/arch/$(SRCARCH)/include \
 		   -I$(objtree)/arch/$(SRCARCH)/include \
                    -include $(srctree)/include/linux/kconfig.h
@@ -330,12 +425,7 @@ LDFLAGS_barebox	:= -Map barebox.map
 LDFLAGS_barebox += $(call ld-option, --no-dynamic-linker)
 LDFLAGS_pbl += $(call ld-option, --no-dynamic-linker)
 
-# Read KERNELRELEASE from include/config/kernel.release (if it exists)
-KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
-KERNELVERSION = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)
-
-export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION
-export ARCH SRCARCH CONFIG_SHELL HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC
+export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC
 export CPP AR NM STRIP OBJCOPY OBJDUMP MAKE AWK GENKSYMS PERL PYTHON3 UTS_MACHINE
 export LEX YACC
 export HOSTCXX CHECK CHECKFLAGS
@@ -351,78 +441,45 @@ export CFLAGS_UBSAN
 
 # Files to ignore in find ... statements
 
-RCS_FIND_IGNORE := \( -name SCCS -o -name BitKeeper -o -name .svn -o -name CVS -o -name .pc -o -name .hg -o -name .git \) -prune -o
-export RCS_TAR_IGNORE := --exclude SCCS --exclude BitKeeper --exclude .svn --exclude CVS --exclude .pc --exclude .hg --exclude .git
+export RCS_FIND_IGNORE := \( -name SCCS -o -name BitKeeper -o -name .svn -o    \
+			  -name CVS -o -name .pc -o -name .hg -o -name .git \) \
+			  -prune -o
+export RCS_TAR_IGNORE := --exclude SCCS --exclude BitKeeper --exclude .svn \
+			 --exclude CVS --exclude .pc --exclude .hg --exclude .git
 
 # ===========================================================================
 # Rules shared between *config targets and build targets
 
-# Basic helpers built in scripts/
+# Basic helpers built in scripts/basic/
 PHONY += scripts_basic
 scripts_basic:
 	$(Q)$(MAKE) $(build)=scripts/basic
 
-# To avoid any implicit rule to kick in, define an empty command.
-scripts/basic/%: scripts_basic ;
-
 PHONY += outputmakefile
+# Before starting out-of-tree build, make sure the source tree is clean.
 # outputmakefile generates a Makefile in the output directory, if using a
 # separate output directory. This allows convenient use of make in the
 # output directory.
+# At the same time when output Makefile generated, generate .gitignore to
+# ignore whole output directory
 outputmakefile:
-ifneq ($(KBUILD_SRC),)
-	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkmakefile \
-	    $(srctree) $(objtree) $(VERSION) $(PATCHLEVEL)
-endif
-
-# To make sure we do not include .config for any of the *config targets
-# catch them early, and hand them over to scripts/kconfig/Makefile
-# It is allowed to specify more targets when calling make, including
-# mixing *config targets and build targets.
-# For example 'make oldconfig all'.
-# Detect when mixed targets is specified, and make a second invocation
-# of make so .config is not included in this case either (for *config).
-
-no-dot-config-targets := clean mrproper distclean \
-			 cscope TAGS tags help %docs check% \
-			 include/generated/version.h headers_% \
-			 kernelrelease kernelversion
-
-config-targets := 0
-mixed-targets  := 0
-dot-config     := 1
-
-ifneq ($(filter $(no-dot-config-targets), $(MAKECMDGOALS)),)
-	ifeq ($(filter-out $(no-dot-config-targets), $(MAKECMDGOALS)),)
-		dot-config := 0
-	endif
-endif
-
-ifneq ($(filter config %config,$(MAKECMDGOALS)),)
-        config-targets := 1
-	ifneq ($(filter-out config %config,$(MAKECMDGOALS)),)
-		mixed-targets := 1
-	endif
+ifdef building_out_of_srctree
+	$(Q)if [ -f $(srctree)/.config -o \
+		 -d $(srctree)/include/config -o \
+		 -d $(srctree)/arch/$(SRCARCH)/include/generated ]; then \
+		echo >&2 "***"; \
+		echo >&2 "*** The source tree is not clean, please run 'make$(if $(findstring command line, $(origin ARCH)), ARCH=$(ARCH)) mrproper'"; \
+		echo >&2 "*** in $(abs_srctree)";\
+		echo >&2 "***"; \
+		false; \
+	fi
+	$(Q)ln -fsn $(srctree) source
+	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkmakefile $(srctree)
+	$(Q)test -e .gitignore || \
+	{ echo "# this is build directory, ignore it"; echo "*"; } > .gitignore
 endif
 
-ifeq ($(mixed-targets),1)
-# ===========================================================================
-# We're called with mixed targets (*config and build targets).
-# Handle them one by one.
-
-PHONY += $(MAKECMDGOALS) __build_one_by_one
-
-$(filter-out __build_one_by_one, $(MAKECMDGOALS)): __build_one_by_one
-	@:
-
-__build_one_by_one:
-	$(Q)set -e; \
-	for i in $(MAKECMDGOALS); do \
-		$(MAKE) -f $(srctree)/Makefile $$i; \
-	done
-
-else
-ifeq ($(config-targets),1)
+ifdef config-build
 # ===========================================================================
 # *config targets only - make sure prerequisites are updated, and descend
 # in scripts/kconfig to make the *config target
@@ -433,34 +490,65 @@ ifeq ($(config-targets),1)
 include $(srctree)/arch/$(SRCARCH)/Makefile
 export KBUILD_DEFCONFIG
 
-config: scripts_basic outputmakefile FORCE
+config: outputmakefile scripts_basic FORCE
 	$(Q)$(MAKE) $(build)=scripts/kconfig $@
 
-%config: scripts_basic outputmakefile FORCE
+%config: outputmakefile scripts_basic FORCE
 	$(Q)$(MAKE) $(build)=scripts/kconfig $@
 
-else
+else #!config-build
 # ===========================================================================
 # Build targets only - this includes barebox, arch specific targets, clean
 # targets and others. In general all targets except *config targets.
 
-# Additional helpers built in scripts/
-# Carefully list dependencies so we do not try to build scripts twice
-# in parallel
-PHONY += scripts
-scripts: scripts_basic
-	$(Q)$(MAKE) $(build)=$(@)
+# If building an external module we do not care about the all: rule
+# but instead _all depend on modules
+PHONY += all
+ifeq ($(KBUILD_EXTMOD),)
+_all: all
+else
+_all: modules
+endif
+
+# Decide whether to build built-in, modular, or both.
+# Normally, just do built-in.
+
+KBUILD_MODULES :=
+KBUILD_BUILTIN := 1
+
+# If we have only "make modules", don't compile built-in objects.
+# When we're building modules with modversions, we need to consider
+# the built-in objects during the descend as well, in order to
+# make sure the checksums are up to date before we record them.
+
+ifeq ($(MAKECMDGOALS),modules)
+  KBUILD_BUILTIN := $(if $(CONFIG_MODVERSIONS),1)
+endif
+
+# If we have "make <whatever> modules", compile modules
+# in addition to whatever we do anyway.
+# Just "make" or "make all" shall build modules as well
+
+ifneq ($(filter all _all modules,$(MAKECMDGOALS)),)
+  KBUILD_MODULES := 1
+endif
+
+export KBUILD_MODULES KBUILD_BUILTIN
 
-ifeq ($(dot-config),1)
+ifdef need-config
 include include/config/auto.conf
 endif
 
+# We need some generic definitions.
+include $(srctree)/scripts/Makefile.lib
+
 # Objects we will link into barebox / subdirs we need to visit
 common-y		:= common/ drivers/ commands/ lib/ crypto/ net/ fs/ firmware/
 
 include $(srctree)/arch/$(SRCARCH)/Makefile
 
-ifeq ($(dot-config),1)
+ifdef need-config
+ifdef may-sync-config
 # Read in dependencies to all Kconfig* files, make sure to run syncconfig if
 # changes are detected. This should be included after arch/$(SRCARCH)/Makefile
 # because some architectures define CROSS_COMPILE there.
@@ -484,7 +572,23 @@ $(KCONFIG_CONFIG):
 # (Note: use the grouped target '&:' when we bump to GNU Make 4.3)
 %/auto.conf %/auto.conf.cmd: $(KCONFIG_CONFIG)
 	$(Q)$(MAKE) -f $(srctree)/Makefile syncconfig
-endif # $(dot-config)
+else # !may-sync-config
+# External modules and some install targets need include/generated/autoconf.h
+# and include/config/auto.conf but do not care if they are up-to-date.
+# Use auto.conf to trigger the test
+PHONY += include/config/auto.conf
+
+include/config/auto.conf:
+	$(Q)test -e include/generated/autoconf.h -a -e $@ || (		\
+	echo >&2;							\
+	echo >&2 "  ERROR: Kernel configuration is invalid.";		\
+	echo >&2 "         include/generated/autoconf.h or $@ are missing.";\
+	echo >&2 "         Run 'make oldconfig && make prepare' on kernel src to fix it.";	\
+	echo >&2 ;							\
+	/bin/false)
+
+endif # may-sync-config
+endif # need-config
 
 KBUILD_CFLAGS		+= -ggdb3
 
@@ -800,6 +904,13 @@ include/config/kernel.release: FORCE
 	$(Q)rm -f $@
 	$(Q)echo $(KERNELVERSION)$(localversion) > $@
 
+# Additional helpers built in scripts/
+# Carefully list dependencies so we do not try to build scripts twice
+# in parallel
+PHONY += scripts
+scripts: scripts_basic
+	$(Q)$(MAKE) $(build)=$(@)
+
 # Things we need to do before we recursively start building the kernel
 # or the modules are listed in "prepare".
 # A multi level approach is used. prepareN is processed before prepareN-1.
@@ -807,42 +918,20 @@ include/config/kernel.release: FORCE
 # version.h and scripts_basic is processed / created.
 
 # Listed in dependency order
-PHONY += prepare archprepare prepare0 prepare1 prepare2 prepare3
-
-# prepare-all is deprecated, use prepare as valid replacement
-PHONY += prepare-all
-
-# prepare3 is used to check if we are building in a separate output directory,
-# and if so do:
-# 1) Check that make has not been executed in the kernel src $(srctree)
-prepare3: include/config/kernel.release
-ifneq ($(KBUILD_SRC),)
-	@echo '  Using $(srctree) as source for barebox'
-	$(Q)if [ -f $(srctree)/.config -o -d $(srctree)/include/config ]; then \
-		echo "  $(srctree) is not clean, please run 'make mrproper'";\
-		echo "  in the '$(srctree)' directory.";\
-		false; \
-	fi;
-endif
-
-# prepare2 creates a makefile if using a separate output directory
-prepare2: prepare3 outputmakefile
+PHONY += prepare archprepare prepare0
 
-prepare1: prepare2 include/generated/version.h include/generated/utsrelease.h \
-                   include/config.h
+archprepare: outputmakefile scripts_basic include/config/kernel.release \
+	$(version_h) include/generated/utsrelease.h include/config.h
 
+prepare0: archprepare FORCE
 ifneq ($(KBUILD_MODULES),)
 	$(Q)mkdir -p $(MODVERDIR)
 	$(Q)rm -f $(MODVERDIR)/*
 endif
-
-archprepare: prepare1 scripts_basic
-
-prepare0: archprepare FORCE
 	$(Q)$(MAKE) $(build)=.
 
 # All the preparing..
-prepare prepare-all: prepare0
+prepare: prepare0
 
 # Leave this as default for preprocessing barebox.lds.S, which is now
 # done in arch/$(SRCARCH)/kernel/Makefile
@@ -1095,9 +1184,9 @@ help:
 # Generate tags for editors
 # ---------------------------------------------------------------------------
 quiet_cmd_tags = GEN     $@
-      cmd_tags = $(CONFIG_SHELL) $(srctree)/scripts/tags.sh $@
+      cmd_tags = $(BASH) $(srctree)/scripts/tags.sh $@
 
-tags TAGS cscope: FORCE
+tags TAGS cscope gtags: FORCE
 	$(call cmd,tags)
 
 SPHINXBUILD   = sphinx-build
@@ -1109,9 +1198,6 @@ docs: FORCE
 	@$(SPHINXBUILD) -b html -d $(objtree)/doctrees $(srctree)/Documentation \
 		$(objtree)/Documentation/html
 
-endif #ifeq ($(config-targets),1)
-endif #ifeq ($(mixed-targets),1)
-
 # Single targets
 # ---------------------------------------------------------------------------
 # Single targets are compatible with:
@@ -1175,14 +1261,13 @@ ifneq ($(cmd_files),)
   include $(cmd_files)
 endif
 
-endif	# skip-makefile
+endif # config-build
+endif # mixed-build
+endif # need-sub-make
 
 PHONY += FORCE
 FORCE:
 
-# Cancel implicit rules on top Makefile, `-rR' will apply to sub-makes.
-Makefile: ;
-
 # 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)