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

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Message-ID: <CAK7LNARCz1s2z_mBJgL_S+=o8jWOGSmRb017WLFXaKdp5EDiqw@mail.gmail.com>
Date: Thu, 5 Dec 2024 11:33:33 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Alison Schofield <alison.schofield@...el.com>
Cc: Vishal Verma <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, 
	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 5:51 AM Alison Schofield
<alison.schofield@...el.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.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
>
> With this in v6.13-rc1 the cxl-test module fails depmod.
> It causes depmod  to be invoked from the incorrect place
> (or something doesn't respect INSTALL_MOD_PATH)
>
> Is there something additional that this cxl-test module needs
> to do?
>
> Repro:
> /git/new$ make V=1 M=tools/testing/cxl INSTALL_MOD_PATH=qbuild/mkosi.extra/ modules_install

Kbuild changes the working directory, so you need to specify
an absolute path for INSTALL_MOD_PATH.

INSTALL_MOD_PATH=$(realpath qbuild/mkosi.extra/)




-- 
Best Regards
Masahiro Yamada