On Tue, Sep 17, 2024 at 11:16:47PM +0900, Masahiro Yamada wrote:
> 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: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> ---
>
> Documentation/kbuild/kbuild.rst | 8 +++++-
> Documentation/kbuild/modules.rst | 5 +++-
> Makefile | 44 +++++++++++++++++++++++---------
> 3 files changed, 43 insertions(+), 14 deletions(-)
>
> diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
> index 716f6fb70829..66a9dc44ea28 100644
> --- a/Documentation/kbuild/kbuild.rst
> +++ b/Documentation/kbuild/kbuild.rst
> @@ -132,12 +132,18 @@ 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 using kernel build artifacts 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
> diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/modules.rst
> index 3a6e7bdc0889..03347e13eeb5 100644
> --- a/Documentation/kbuild/modules.rst
> +++ b/Documentation/kbuild/modules.rst
> @@ -95,7 +95,7 @@ executed to make module versioning work.
> of the kernel output directory if the kernel was built in a separate
> build directory.)
>
> - make -C $KDIR M=$PWD
> + make -C $KDIR M=$PWD [MO=$BUILD_DIR]
>
> -C $KDIR
> The directory that contains the kernel and relevant build
> @@ -109,6 +109,9 @@ executed to make module versioning work.
> directory where the external module (kbuild file) is
> located.
>
> + MO=$BUILD_DIR
> + Speficies a separate output directory for the external module.
s/Speficies/Specifies/
> +
> 2.3 Targets
> ===========
>
> diff --git a/Makefile b/Makefile
> index 9fbf7ef6e394..b654baa0763a 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -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))
Should we also check against multiple output directories?
>
> @@ -187,7 +191,11 @@ 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.
> + export abs_extmodtree := $(realpath $(KBUILD_EXTMOD))
> + $(if $(abs_extmodtree),,$(error specified external module directory "$(KBUILD_EXTMOD)" does not exist))
> else
> objtree := .
> output := $(KBUILD_OUTPUT)
> @@ -246,7 +254,6 @@ else # need-sub-make
> ifeq ($(abs_srctree),$(CURDIR))
> # building in the source tree
> srctree := .
> - building_out_of_srctree :=
> else
> ifeq ($(abs_srctree)/,$(dir $(CURDIR)))
> # building in a subdirectory of the source tree
> @@ -254,22 +261,23 @@ else
> else
> srctree := $(abs_srctree)
> endif
> - building_out_of_srctree := 1
> endif
>
> ifneq ($(KBUILD_ABS_SRCTREE),)
> srctree := $(abs_srctree)
> endif
>
> -VPATH :=
> +export srctree
>
> -ifeq ($(KBUILD_EXTMOD),)
> -ifdef building_out_of_srctree
> -VPATH := $(srctree)
> -endif
> -endif
> +_vpath = $(or $(abs_extmodtree),$(srctree))
>
> -export building_out_of_srctree srctree VPATH
> +ifeq ($(realpath $(_vpath)),$(CURDIR))
Just a style consistency question: 'ifeq (,)' with a space after ',' (as a few
lines above) or without as used here?
> +building_out_of_srctree :=
> +VPATH :=
> +else
> +export building_out_of_srctree := 1
> +export VPATH := $(_vpath)
> +endif
>
> # To make sure we do not include .config for any of the *config targets
> # catch them early, and hand them over to scripts/kconfig/Makefile
> @@ -550,7 +558,7 @@ USERINCLUDE := \
> LINUXINCLUDE := \
> -I$(srctree)/arch/$(SRCARCH)/include \
> -I$(objtree)/arch/$(SRCARCH)/include/generated \
> - $(if $(building_out_of_srctree),-I$(srctree)/include) \
> + -I$(srctree)/include \
> -I$(objtree)/include \
> $(USERINCLUDE)
>
> @@ -640,6 +648,7 @@ quiet_cmd_makefile = GEN Makefile
> } > Makefile
>
> outputmakefile:
> +ifeq ($(KBUILD_EXTMOD),)
> @if [ -f $(srctree)/.config -o \
> -d $(srctree)/include/config -o \
> -d $(srctree)/arch/$(SRCARCH)/include/generated ]; then \
> @@ -649,7 +658,16 @@ outputmakefile:
> echo >&2 "***"; \
> false; \
> fi
> - $(Q)ln -fsn $(srctree) source
> +else
> + @if [ -f $(KBUILD_EXTMOD)/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 $(KBUILD_EXTMOD)) clean'"; \
> + echo >&2 "***"; \
> + false; \
> + fi
> +endif
> + $(Q)ln -fsn $(_vpath) source
> $(call cmd,makefile)
> $(Q)test -e .gitignore || \
> { echo "# this is build directory, ignore it"; echo "*"; } > .gitignore
> @@ -1926,6 +1944,8 @@ 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.
> --
> 2.43.0
>
Thanks, this feature is really appreciated by a lot of my colleagues, and I think you found quite a nice solution!
I'm a bit surprised, that there are not some more testers ...
Reviewed-by: Nicolas Schier <nicolas@xxxxxxxxx>
