From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.domeneshop.no (smtp.domeneshop.no [194.63.252.55]) (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 B02C01D9588; Fri, 4 Oct 2024 20:05:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=194.63.252.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728072336; cv=none; b=WOMlEMzvkN8iY73cAinOuSaBIcMN1C6Mw1M82Z8l/4EDPreaB1eGDSfIIpGloBnTIP4FhBlNBtQBaxv/60VNaQNFm8eComCO5Ce2Ihulh/Ea3aPbHKLmOoAeS/uNsAKDTXA9wlgboe7Q9q7p7sE4CppY4vaNTvRFiBxj+QUuzYQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728072336; c=relaxed/simple; bh=lnQnwX51KbeTOk7EqjEaYfYznToRgOVeG1zxycB9DWI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Bmh2wp6m180VoZlzIPV/ySYxuuFCqOxgAqQrXLwh6J8YVbT7itkXYzv1Q5YeUdIrdWd6NkOlmAz95lpGX6e4Ox6JfAqunha34rjhFajtb7XlDOKhqaDuUhZr4t/iBKISrhlHAA77I3vIqKltsvZMDPETszI5/0Q/tqzxW/aasws= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=fjasle.eu; spf=pass smtp.mailfrom=fjasle.eu; dkim=pass (2048-bit key) header.d=fjasle.eu header.i=@fjasle.eu header.b=rztRO+h0; arc=none smtp.client-ip=194.63.252.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=fjasle.eu Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=fjasle.eu Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=fjasle.eu header.i=@fjasle.eu header.b="rztRO+h0" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=fjasle.eu; s=ds202307; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:From:Sender:Reply-To:Subject:Date:Message-ID:To:Cc: MIME-Version:Content-Type:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:In-Reply-To:References:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=6WRL0xjAowkqD9cS0vENvWnFkgzMYtUzJr8oCNaqviI=; b=rztRO+h02B1O82cu6Gj2CMMf8j CjC/xddPpd8MT1+u63uQto9PGxfkeejXLeJQI7rGTx8LYsbup61t1OQsFBYE6PK6rPAYgTxuua4Mu BM8cxYzMgu07pQ3/sjXSV2MF8Sfs2iYV57FJES6dHpafyF5h43BXigTTX0HAS8rWn0wkWg+cBRn+B NTDqfGq05EX6jS1+a+QQHvTs5PDRIKzRdvog8MQRgN4EwQcKX5XoH0BRnFbigFJnYywlbiL2WCL7f TWl361PbtIprlmLqaB0XbEF5Fkn18kxbd6wOPcZROQWwJ9qEJ5jH9k8qHEMMb7dxQ+9Cl4wBPuAz7 kU2txdaA==; Received: from [2001:9e8:9c9:1501:3235:adff:fed0:37e6] (port=43060 helo=lindesnes.fjasle.eu) by smtp.domeneshop.no with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1swoYE-00D22o-7N; Fri, 04 Oct 2024 22:05:22 +0200 Date: Fri, 4 Oct 2024 22:05:20 +0200 From: Nicolas Schier To: Masahiro Yamada Cc: linux-kbuild@vger.kernel.org, Miguel Ojeda , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, Nathan Chancellor Subject: Re: [PATCH 23/23] kbuild: allow to start building external module in any directory Message-ID: <20241004-little-rigorous-ammonite-6a8ce2@lindesnes> References: <20240917141725.466514-1-masahiroy@kernel.org> <20240917141725.466514-24-masahiroy@kernel.org> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240917141725.466514-24-masahiroy@kernel.org> On Tue, Sep 17, 2024 at 11:16:51PM +0900, Masahiro Yamada wrote: > Unless an explicit O= 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=/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=/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 ?= /path/to/kernel > default: > $(MAKE) -C $(KDIR) M=$(CURDIR) $(MAKECMDGOALS) > > The log will appear as follows: > > $ make > make -C /path/to/kernel M=/path/to/external/module > make[1]: Entering directory '/path/to/kernel' > make[2]: Entering directory '/path/to/exernal/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/exernal/module' s/exernal/external/, also above. > 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 ?= /path/to/kernel > export KBUILD_EXTMOD = $(CURDIR) > 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 > --- > > Documentation/kbuild/modules.rst | 21 +++++++++++++++++++++ > Makefile | 8 ++++++-- > 2 files changed, 27 insertions(+), 2 deletions(-) > > diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/modules.rst > index 03347e13eeb5..5610cfa426bb 100644 > --- a/Documentation/kbuild/modules.rst > +++ b/Documentation/kbuild/modules.rst > @@ -88,6 +88,12 @@ executed to make module versioning work. > > $ make -C /lib/modules/`uname -r`/build M=$PWD modules_install > > + 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=$PWD > + > 2.2 Options > =========== > > @@ -246,6 +252,21 @@ module 8123.ko, which is built from the following files:: > consisting of several hundred lines, and here it really pays > off to separate the kbuild part from the rest. > > + Linux 6.13 and later support another way. The external module Makefile > + can include the kernel Makefile directly, rather than invoking sub Make. > + > + Example 3:: > + > + --> filename: Kbuild > + obj-m := 8123.o > + 8123-y := 8123_if.o 8123_pci.o > + > + --> filename: Makefile > + KDIR ?= /lib/modules/`uname -r`/build KDIR ?= /lib/modules/$(shell uname -r)/build This patch is another very good idea, thanks! Reviewed-by: Nicolas Schier > + export KBUILD_EXTMOD = $(CURDIR) > + include $(KDIR)/Makefile > + > + > 3.4 Building Multiple Modules > ============================= > > diff --git a/Makefile b/Makefile > index 81603a50c757..88c160ac7b3c 100644 > --- a/Makefile > +++ b/Makefile > @@ -189,9 +189,13 @@ ifdef KBUILD_EXTMOD > objtree := $(realpath $(KBUILD_OUTPUT)) > $(if $(objtree),,$(error specified kernel directory "$(KBUILD_OUTPUT)" does not exist)) > else > - objtree := $(CURDIR) > + objtree := $(abs_srctree) > endif > - output := $(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 := $(or $(KBUILD_EXTMOD_OUTPUT),$(if $(filter $(CURDIR),$(objtree) $(abs_srctree)),$(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)) > -- > 2.43.0 > -- Nicolas