linux-kernel - Re: [PATCH v2 05/11] kbuild: change working directory to external module directory with M=

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Message-ID: <CAK7LNAR0jmafdi7GAxq58AU-=tuWdVas02q=sQXC4zaOg4JcEA@mail.gmail.com>
Date: Thu, 5 Dec 2024 11:48:08 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, cocci@...ia.fr
Subject: Re: [PATCH v2 05/11] kbuild: change working directory to external
 module directory with M=

On Thu, Dec 5, 2024 at 8:35 AM Charlie Jenkins <charlie@...osinc.com> wrote:
>
> On Sun, Nov 10, 2024 at 10:34:33AM +0900, Masahiro Yamada wrote:
> > Currently, Kbuild always operates in the output directory of the kernel,
> > even when building external modules. This increases the risk of external
> > module Makefiles attempting to write to the kernel directory.
> >
> > This commit switches the working directory to the external module
> > directory, allowing the removal of the $(KBUILD_EXTMOD)/ prefix from
> > some build artifacts.
> >
> > The command for building external modules maintains backward
> > compatibility, but Makefiles that rely on working in the kernel
> > directory may break. In such cases, $(objtree) and $(srctree) should
> > be used to refer to the output and source directories of the kernel.
> >
> > The appearance of the build log will change as follows:
> >
> > [Before]
> >
> >   $ make -C /path/to/my/linux M=/path/to/my/externel/module
> >   make: Entering directory '/path/to/my/linux'
> >     CC [M]  /path/to/my/externel/module/helloworld.o
> >     MODPOST /path/to/my/externel/module/Module.symvers
> >     CC [M]  /path/to/my/externel/module/helloworld.mod.o
> >     CC [M]  /path/to/my/externel/module/.module-common.o
> >     LD [M]  /path/to/my/externel/module/helloworld.ko
> >   make: Leaving directory '/path/to/my/linux'
> >
> > [After]
> >
> >   $ make -C /path/to/my/linux M=/path/to/my/externel/module
> >   make: Entering directory '/path/to/my/linux'
> >   make[1]: Entering directory '/path/to/my/externel/module'
> >     CC [M]  helloworld.o
> >     MODPOST Module.symvers
> >     CC [M]  helloworld.mod.o
> >     CC [M]  .module-common.o
> >     LD [M]  helloworld.ko
> >   make[1]: Leaving directory '/path/to/my/externel/module'
> >   make: Leaving directory '/path/to/my/linux'
> >
> > Printing "Entering directory" twice is cumbersome. This will be
> > addressed later.
>
> This change has caused O=<relative directory> to fail.
>
> For example:
>
> make O=build defconfig
> make -j$(nproc) V=1 O=build bindeb-pkg
>
> outputs:
>
> make ARCH=x86 KERNELRELEASE=6.13.0-rc1 KBUILD_BUILD_VERSION=3  run-command KBUILD_RUN_COMMAND='+$(srctree)/scripts/package/builddeb linux-libc-dev'
> dh_installchangelogs -plinux-image-6.13.0-rc1
> ../scripts/package/builddeb linux-headers-6.13.0-rc1
> dh_compress -plinux-image-6.13.0-rc1
> dh_fixperms -plinux-image-6.13.0-rc1
> dh_gencontrol -plinux-image-6.13.0-rc1 -- -fdebian/image.files
> Rebuilding host programs with x86_64-linux-gnu-gcc...
> make[6]: Entering directory '/scratch/kernels/linux/build'
> /scratch/kernels/linux/Makefile:190: *** specified kernel directory "build" does not exist.  Stop.
>
> It is stepping into this directory and then trying to find the directory
> it just stepped into so $(realpath $(KBUILD_OUTPUT)) returns an empty
> string.
>
> Using an absolute directory resolves this problem, but I believe it
> shouldn't be necessary.


Agree.

I will apply the following fixup unless I have a better idea.




diff --git a/scripts/package/install-extmod-build
b/scripts/package/install-extmod-build
index 64d958ee45f3..85af1573db31 100755
--- a/scripts/package/install-extmod-build
+++ b/scripts/package/install-extmod-build
@@ -69,7 +69,7 @@ if [ "${CC}" != "${HOSTCC}" ]; then
        #
        # Use the single-target build to avoid the modpost invocation, which
        # would overwrite Module.symvers.
-       "${MAKE}" HOSTCC="${CC}" KBUILD_EXTMOD="${destdir}" scripts/
+       "${MAKE}" O=. HOSTCC="${CC}" KBUILD_EXTMOD="${destdir}" scripts/

        cat <<-'EOF' >  "${destdir}/scripts/Kbuild"
        subdir-y := basic
@@ -78,7 +78,7 @@ if [ "${CC}" != "${HOSTCC}" ]; then
        EOF

        # Run once again to rebuild scripts/basic/ and scripts/mod/modpost.
-       "${MAKE}" HOSTCC="${CC}" KBUILD_EXTMOD="${destdir}" scripts/
+       "${MAKE}" O=. HOSTCC="${CC}" KBUILD_EXTMOD="${destdir}" scripts/

        rm -f "${destdir}/Kbuild" "${destdir}/scripts/Kbuild"
 fi



--
Best Regards
Masahiro Yamada