linux-kernel - Re: [PATCH v2] Add MO(mod objs) variable to process ext modules with subdirs

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Message-ID: <5628d83f-cc05-46b4-997a-2309701d3a77@infradead.org>
Date: Fri, 5 Apr 2024 09:22:00 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Valerii Chernous <vchernou@...co.com>,
 Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor
 <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>
Cc: xe-linux-external@...co.com, Jonathan Corbet <corbet@....net>,
 linux-kbuild@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Add MO(mod objs) variable to process ext modules with
 subdirs

Hi--

On 4/5/24 3:01 AM, Valerii Chernous wrote:
> The change allow to build external modules with nested makefiles.
> With current unofficial way(using "src" variable) it is possible to build
> external(out of tree) kernel module with separating source and build

                                           separate

> artifacts dirs but with nested makefiles it doesn't work properly.
> Build system trap to recursion inside makefiles, artifacts output dir
> path grow with each iteration until exceed max path len and build failed

                                                                    failed.

> Providing "MO" variable and using "override" directive with declaring
> "src" variable solve the problem

                 solves the problem.

> Usage example:
> make -C KERNEL_SOURCE_TREE MO=BUILD_OUT_DIR M=EXT_MOD_SRC_DIR modules
> 
> Cc: xe-linux-external@...co.com
> Cc: Valerii Chernous <vchernou@...co.com>
> Signed-off-by: Valerii Chernous <vchernou@...co.com>
> ---
>  Documentation/kbuild/kbuild.rst  | 14 +++++++++++++-
>  Documentation/kbuild/modules.rst | 16 +++++++++++++++-
>  Makefile                         | 17 +++++++++++++++++
>  scripts/Makefile.build           |  7 +++++++
>  4 files changed, 52 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
> index 9c8d1d046ea5..63e1a71a3b9a 100644
> --- a/Documentation/kbuild/kbuild.rst
> +++ b/Documentation/kbuild/kbuild.rst
> @@ -121,10 +121,22 @@ Setting "V=..." takes precedence over KBUILD_VERBOSE.
>  KBUILD_EXTMOD
>  -------------
>  Set the directory to look for the kernel source when building external
> -modules.
> +modules. In case of using separate sources and module artifatcs directories

                                                         artifacts

> +(KBUILD_EXTMOD + KBUILD_EXTMOD_SRC), KBUILD_EXTMOD working as output
> +artifacts directory

             directory.

>  
>  Setting "M=..." takes precedence over KBUILD_EXTMOD.
>  
> +KBUILD_EXTMOD_SRC
> +-------------

Extend the underline to the same length as the title.

> +Set the external module source directory in case when separate module
> +sources and build artifacts directories required. Working in pair with

                                           are required.
or
                                           are used.

> +KBUILD_EXTMOD. If KBUILD_EXTMOD_SRC is set then KBUILD_EXTMOD working as

                                                                 works as
or
                                                                 is used as

> +module build artifacts directory

                          directory.

> +
> +Setting "MO=..." takes precedence over KBUILD_EXTMOD.
> +Setting "M=..." takes precedence over KBUILD_EXTMOD_SRC.
> +
>  KBUILD_OUTPUT
>  -------------
>  Specify the output directory when building the kernel.
> diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/modules.rst
> index a1f3eb7a43e2..135be2fc798e 100644
> --- a/Documentation/kbuild/modules.rst
> +++ b/Documentation/kbuild/modules.rst
> @@ -79,6 +79,14 @@ executed to make module versioning work.
>  	The kbuild system knows that an external module is being built
>  	due to the "M=<dir>" option given in the command.
>  
> +	To build an external module with separate src and artifacts dirs use::
> +
> +		$ make -C <path_to_kernel_src> M=$PWD MO=<output_dir>
> +
> +	The kbuild system knows that an external module with separate sources
> +	and build artifacts dirs is being built due to the "M=<dir>" and
> +	"MO=<output_dir>" options given in the command.
> +
>  	To build against the running kernel use::
>  
>  		$ make -C /lib/modules/`uname -r`/build M=$PWD
> @@ -93,7 +101,7 @@ executed to make module versioning work.
>  
>  	($KDIR refers to the path of the kernel source directory.)
>  
> -	make -C $KDIR M=$PWD
> +	make -C $KDIR M=$PWD MO=<module_output_dir>
>  
>  	-C $KDIR
>  		The directory where the kernel source is located.
> @@ -106,6 +114,12 @@ executed to make module versioning work.
>  		directory where the external module (kbuild file) is
>  		located.
>  
> +	MO=<module_output_dir>
> +		Informs kbuild that an external module build artifacts

         drop                       an

> +		should be placed into specific dir(<module_output_dir>)

		                                                      ).

> +		This parameter optional, without it "M" working as

                     parameter is optional. Without it "M" works as both

> +		source provider and build output location

		                                 location.

> +
>  2.3 Targets
>  ===========
>  
> diff --git a/Makefile b/Makefile
> index 4bef6323c47d..3d45a41737a6 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -142,6 +142,7 @@ ifeq ("$(origin M)", "command line")
>    KBUILD_EXTMOD := $(M)
>  endif
>  
> +define kbuild_extmod_check_TEMPLATE
>  $(if $(word 2, $(KBUILD_EXTMOD)), \
>  	$(error building multiple external modules is not supported))
>  
> @@ -152,9 +153,25 @@ $(foreach x, % :, $(if $(findstring $x, $(KBUILD_EXTMOD)), \
>  ifneq ($(filter %/, $(KBUILD_EXTMOD)),)
>  KBUILD_EXTMOD := $(shell dirname $(KBUILD_EXTMOD).)
>  endif
> +endef
> +$(eval $(call kbuild_extmod_check_TEMPLATE))
>  
>  export KBUILD_EXTMOD
>  
> +# Use make M=src_dir MO=ko_dir or set the environment variables:
> +# KBUILD_EXTMOD_SRC, KBUILD_EXTMOD to specify separate directories of
> +# external module sources and build artifacts.
> +ifeq ("$(origin MO)", "command line")
> +ifeq ($(KBUILD_EXTMOD),)
> +	$(error Ext module objects without module sources is not supported))
> +endif
> +KBUILD_EXTMOD_SRC := $(KBUILD_EXTMOD)
> +KBUILD_EXTMOD := $(MO)
> +$(eval $(call kbuild_extmod_check_TEMPLATE))
> +endif
> +
> +export KBUILD_EXTMOD_SRC
> +
>  # backward compatibility
>  KBUILD_EXTRA_WARN ?= $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)
>  
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index baf86c0880b6..a293950e2e07 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -3,7 +3,14 @@
>  # Building
>  # ==========================================================================
>  
> +ifeq ($(KBUILD_EXTMOD_SRC),)
>  src := $(obj)
> +else ifeq ($(KBUILD_EXTMOD),$(obj))
> +override src := $(KBUILD_EXTMOD_SRC)
> +else
> +src_subdir := $(patsubst $(KBUILD_EXTMOD)/%,%,$(obj))
> +override src := $(KBUILD_EXTMOD_SRC)/$(src_subdir)
> +endif
>  
>  PHONY := $(obj)/
>  $(obj)/:

-- 
#Randy