Commit 11b3d517 authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

kbuild: support building external modules in a separate build directory 



There has been a long-standing request to support building external
modules in a separate build directory.

This commit introduces a new environment variable, KBUILD_EXTMOD_OUTPUT,
and its shorthand Make variable, MO.

A simple usage:

 $ make -C <kernel-dir> M=<module-src-dir> MO=<module-build-dir>

Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
Reviewed-by: default avatarNicolas Schier <nicolas@fjasle.eu>
parent bad6beb2

Documentation/kbuild/kbuild.rst

+7 −1
Original line number Diff line number Diff line
@@ -137,12 +137,18 @@ Specify the output directory when building the kernel. 
This variable can also be used to point to the kernel output directory when

building external modules against a pre-built kernel in a separate build

directory. Please note that this does NOT specify the output directory for the

external modules themselves.

external modules themselves. (Use KBUILD_EXTMOD_OUTPUT for that purpose.)



The output directory can also be specified using "O=...".



Setting "O=..." takes precedence over KBUILD_OUTPUT.



KBUILD_EXTMOD_OUTPUT

--------------------

Specify the output directory for external modules.



Setting "MO=..." takes precedence over KBUILD_EXTMOD_OUTPUT.



KBUILD_EXTRA_WARN

-----------------

Specify the extra build checks. The same value can be assigned by passing

Documentation/kbuild/modules.rst

+7 −1
Original line number Diff line number Diff line
@@ -66,7 +66,10 @@ Options 
	of the kernel output directory if the kernel was built in a separate

	build directory.)



	make -C $KDIR M=$PWD

	You can optionally pass MO= option if you want to build the modules in

	a separate directory.



	make -C $KDIR M=$PWD [MO=$BUILD_DIR]



	-C $KDIR

		The directory that contains the kernel and relevant build
@@ -80,6 +83,9 @@ Options 
		directory where the external module (kbuild file) is

		located.



	MO=$BUILD_DIR

		Specifies a separate output directory for the external module.



Targets

-------

Makefile

+18 −2
Original line number Diff line number Diff line
@@ -134,6 +134,10 @@ ifeq ("$(origin M)", "command line") 
  KBUILD_EXTMOD := $(M)

endif



ifeq ("$(origin MO)", "command line")

  KBUILD_EXTMOD_OUTPUT := $(MO)

endif



$(if $(word 2, $(KBUILD_EXTMOD)), \

	$(error building multiple external modules is not supported))
@@ -187,7 +191,7 @@ ifdef KBUILD_EXTMOD 
    else

        objtree := $(CURDIR)

    endif

    output := $(KBUILD_EXTMOD)

    output := $(or $(KBUILD_EXTMOD_OUTPUT),$(KBUILD_EXTMOD))

    # KBUILD_EXTMOD might be a relative path. Remember its absolute path before

    # Make changes the working directory.

    srcroot := $(realpath $(KBUILD_EXTMOD))
@@ -645,6 +649,7 @@ quiet_cmd_makefile = GEN Makefile 
	} > Makefile



outputmakefile:

ifeq ($(KBUILD_EXTMOD),)

	@if [ -f $(srctree)/.config -o \

		 -d $(srctree)/include/config -o \

		 -d $(srctree)/arch/$(SRCARCH)/include/generated ]; then \
@@ -654,7 +659,16 @@ outputmakefile: 
		echo >&2 "***"; \

		false; \

	fi

	$(Q)ln -fsn $(srctree) source

else

	@if [ -f $(srcroot)/modules.order ]; then \

		echo >&2 "***"; \

		echo >&2 "*** The external module source tree is not clean."; \

		echo >&2 "*** Please run 'make -C $(abs_srctree) M=$(realpath $(srcroot)) clean'"; \

		echo >&2 "***"; \

		false; \

	fi

endif

	$(Q)ln -fsn $(srcroot) source

	$(call cmd,makefile)

	$(Q)test -e .gitignore || \

	{ echo "# this is build directory, ignore it"; echo "*"; } > .gitignore
@@ -1940,6 +1954,8 @@ KBUILD_MODULES := 1 


endif



prepare: outputmakefile



# Preset locale variables to speed up the build process. Limit locale

# tweaks to this spot to avoid wrong language settings when running

# make menuconfig etc.

scripts/Makefile.host

+3 −5
Original line number Diff line number Diff line
@@ -96,12 +96,10 @@ hostrust_flags = --out-dir $(dir $@) --emit=dep-info=$(depfile) \ 
                 $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \

                 $(HOSTRUSTFLAGS_$(target-stem))



# $(objtree)/$(obj) for including generated headers from checkin source files

ifeq ($(KBUILD_EXTMOD),)

# $(obj) for including generated headers from checkin source files

ifdef building_out_of_srctree

hostc_flags   += -I $(objtree)/$(obj)

hostcxx_flags += -I $(objtree)/$(obj)

endif

hostc_flags   += -I $(obj)

hostcxx_flags += -I $(obj)

endif



#####

scripts/Makefile.lib

+0 −2
Original line number Diff line number Diff line
@@ -213,13 +213,11 @@ endif 


# $(src) for including checkin headers from generated source files

# $(obj) for including generated headers from checkin source files

ifeq ($(KBUILD_EXTMOD),)

ifdef building_out_of_srctree

_c_flags   += $(addprefix -I, $(src) $(obj))

_a_flags   += $(addprefix -I, $(src) $(obj))

_cpp_flags += $(addprefix -I, $(src) $(obj))

endif

endif



# If $(is-kernel-object) is 'y', this object will be linked to vmlinux or modules

is-kernel-object = $(or $(part-of-builtin),$(part-of-module))