From nobody Sun Nov 24 00:57:31 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CBC991531E1; Sun, 10 Nov 2024 01:37:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731202636; cv=none; b=eMyxE4hjlyrFuLQN0IJ9ARxr6WbnI3WWQ8BSlFQnmqyDcgENMChjvcccRtzh3zTgX6ZCDQPG2luax3m0o9icgBBxAPDoO3lADuAEctY5eJ7nUxRgmcAwW1YxLOLi51VpBlozqaU2lXoN0fl6qRMGE/JqVYjecsJMUk2I4wooDmo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731202636; c=relaxed/simple; bh=JnWxdVvEakJui+gj8y0AxBpvkUHKa2A9Zi/L+iOkT1Q=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ElVZnibyjkgk1bmpLtvkkU/Iv8FYdp0lwQVrgG463APoXO3oAa2W8jhFsY2BA3rYA03Bs+Gem4a4JSDFRh6xrG3dD+vbuUlDmleIvVVClpnWh4JmvP1OjXkL8dLITiOInUfAXjO91a49qbX8R4Y86cAyRnAGeV9Q8mzjPlYINQI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bwaaGq2H; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bwaaGq2H" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8D4A0C4CED4; Sun, 10 Nov 2024 01:37:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1731202636; bh=JnWxdVvEakJui+gj8y0AxBpvkUHKa2A9Zi/L+iOkT1Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bwaaGq2HqiVB2ahWcOSdWO3oIJXB7Eg6GV61J+xbFylFN/twskGjDMCQccPPIldvI zS0AxzPzUaaV/bw1hlYH+M74PtywkLUgBmISlhKQyFACz962upk1J4iuF6uhL8QKnL xy3mlAamzLiMZRvFiAqQItnFPAeTmxb9wzxzQrz/M5ul1BqXMQ+1T53dc9O7mp75oP m+zaJzb2Sje2GMiWQ/5XADl2KZK75KQhtD9hjFRlOL7DABkghTsk+SUjUxgHlIKtm9 j/tqReUhKCoTZ2r41ztMH5Kyhf4ksju/aRIIHqCqkRNs4F1fL/VRW+FBOEhWPfSVkC ODb2gw/ITRmKg== From: Masahiro Yamada To: linux-kbuild@vger.kernel.org Cc: linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, cocci@inria.fr, Masahiro Yamada , Nicolas Schier Subject: [PATCH v2 11/11] kbuild: allow to start building external modules in any directory Date: Sun, 10 Nov 2024 10:34:39 +0900 Message-ID: <20241110013649.34903-12-masahiroy@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20241110013649.34903-1-masahiroy@kernel.org> References: <20241110013649.34903-1-masahiroy@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Unless an explicit O=3D option is provided, external module builds must start from the kernel directory. This can be achieved by using the -C option: $ make -C /path/to/kernel M=3D/path/to/external/module This commit allows starting external module builds from any directory, so you can also do the following: $ make -f /path/to/kernel/Makefile M=3D/path/to/external/module The key difference is that the -C option changes the working directory and parses the Makefile located there, while the -f option only specifies the Makefile to use. As shown in the examples in Documentation/kbuild/modules.rst, external modules usually have a wrapper Makefile that allows you to build them without specifying any make arguments. The Makefile typically contains a rule as follows: KDIR ?=3D /path/to/kernel default: $(MAKE) -C $(KDIR) M=3D$(CURDIR) $(MAKECMDGOALS) The log will appear as follows: $ make make -C /path/to/kernel M=3D/path/to/external/module make[1]: Entering directory '/path/to/kernel' make[2]: Entering directory '/path/to/external/module' CC [M] helloworld.o MODPOST Module.symvers CC [M] helloworld.mod.o CC [M] .module-common.o LD [M] helloworld.ko make[2]: Leaving directory '/path/to/external/module' make[1]: Leaving directory '/path/to/kernel' This changes the working directory twice because the -C option first switches to the kernel directory, and then Kbuild internally recurses back to the external module directory. With this commit, the wrapper Makefile can directly include the kernel Makefile: KDIR ?=3D /path/to/kernel export KBUILD_EXTMOD :=3D $(realpath $(dir $(lastword $(MAKEFILE_LIST))= )) include $(KDIR)/Makefile This avoids unnecessary sub-make invocations: $ make CC [M] helloworld.o MODPOST Module.symvers CC [M] helloworld.mod.o CC [M] .module-common.o LD [M] helloworld.ko Signed-off-by: Masahiro Yamada Reviewed-by: Nicolas Schier --- Changes in v2: - Fix typos in the commit description (s/exernal/external/) - Fix `uname -r` to $(shell uname -r) in Example 3 Documentation/kbuild/modules.rst | 21 +++++++++++++++++++++ Makefile | 8 ++++++-- 2 files changed, 27 insertions(+), 2 deletions(-) diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/module= s.rst index a01f3754c7fc..101de236cd0c 100644 --- a/Documentation/kbuild/modules.rst +++ b/Documentation/kbuild/modules.rst @@ -59,6 +59,12 @@ Command Syntax =20 $ make -C /lib/modules/`uname -r`/build M=3D$PWD modules_install =20 + Starting from Linux 6.13, you can use the -f option instead of -C. This + will avoid unnecessary change of the working directory. The external + module will be output to the directory where you invoke make. + + $ make -f /lib/modules/`uname -r`/build/Makefile M=3D$PWD + Options ------- =20 @@ -221,6 +227,21 @@ Separate Kbuild File and Makefile consisting of several hundred lines, and here it really pays off to separate the kbuild part from the rest. =20 + Linux 6.13 and later support another way. The external module Makefile + can include the kernel Makefile directly, rather than invoking sub Make. + + Example 3:: + + --> filename: Kbuild + obj-m :=3D 8123.o + 8123-y :=3D 8123_if.o 8123_pci.o + + --> filename: Makefile + KDIR ?=3D /lib/modules/$(shell uname -r)/build + export KBUILD_EXTMOD :=3D $(realpath $(dir $(lastword $(MAKEFILE_LIST)))) + include $(KDIR)/Makefile + + Building Multiple Modules ------------------------- =20 diff --git a/Makefile b/Makefile index df002595341a..0825a9a58ca9 100644 --- a/Makefile +++ b/Makefile @@ -189,9 +189,13 @@ ifdef KBUILD_EXTMOD objtree :=3D $(realpath $(KBUILD_OUTPUT)) $(if $(objtree),,$(error specified kernel directory "$(KBUILD_OUTP= UT)" does not exist)) else - objtree :=3D $(CURDIR) + objtree :=3D $(abs_srctree) endif - output :=3D $(or $(KBUILD_EXTMOD_OUTPUT),$(KBUILD_EXTMOD)) + # If Make is invoked from the kernel directory (either kernel + # source directory or kernel build directory), external modules + # are built in $(KBUILD_EXTMOD) for backward compatibility, + # otherwise, built in the current directory. + output :=3D $(or $(KBUILD_EXTMOD_OUTPUT),$(if $(filter $(CURDIR),$(obj= tree) $(abs_srctree)),$(KBUILD_EXTMOD))) # KBUILD_EXTMOD might be a relative path. Remember its absolute path b= efore # Make changes the working directory. srcroot :=3D $(realpath $(KBUILD_EXTMOD)) --=20 2.43.0