linux-kernel - Re: [PATCH RFC] Makefile: Export absolute srctree path for out-of-tree builds

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Message-ID: <CAK7LNAS4yrEvvDOFdHyNxBp9Yzi9=eGRsO+2R-t+NNTOfp=gHg@mail.gmail.com>
Date: Sat, 21 Dec 2024 12:41:21 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Li Zhijian <lizhijian@...itsu.com>
Cc: linux-kbuild@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC] Makefile: Export absolute srctree path for
 out-of-tree builds

On Tue, Dec 17, 2024 at 12:10 PM Li Zhijian <lizhijian@...itsu.com> wrote:
>
> Fixes an issue where out-of-tree kselftest builds fail when building
> the BPF and bpftools components. The failure occurs because the top-level
> Makefile passes a relative srctree path ('..') to its sub-Makefiles, which
> leads to errors in locating necessary files.
>
> For example, the following error is encountered:
>
> ```
> $ make V=1 O=$build/ TARGETS=hid kselftest-all
> ...
> make -C ../tools/testing/selftests all
> make[4]: Entering directory '/path/to/linux/tools/testing/selftests/hid'
> make  -C /path/to/linux/tools/testing/selftests/../../../tools/lib/bpf OUTPUT=/path/to/linux/O/kselftest/hid/tools/build/libbpf/ \
>             EXTRA_CFLAGS='-g -O0'                                      \
>             DESTDIR=/path/to/linux/O/kselftest/hid/tools prefix= all install_headers
> make[5]: Entering directory '/path/to/linux/tools/lib/bpf'
> ...
> make[5]: Entering directory '/path/to/linux/tools/bpf/bpftool'
> Makefile:127: ../tools/build/Makefile.feature: No such file or directory
> make[5]: *** No rule to make target '../tools/build/Makefile.feature'.  Stop.
> ```
>
> To resolve this, the srctree is exported as an absolute path (abs_srctree)
> when performing an out-of-tree build. This ensures that all sub-Makefiles
> have the correct path to the source tree, preventing directory resolution
> errors.

NACK.
This negates 9da0763bdd82572be243fcf5161734f11568960f

This is a recurring topic [1] because kselftest adopts a completely
different build system.
If kselftest cannot do this correctly, please do not hook it to the
top-Makefile.

[1] https://lore.kernel.org/linux-kbuild/cover.1657614127.git.guillaume.tucker@collabora.com/



> Signed-off-by: Li Zhijian <lizhijian@...itsu.com>
> ---
> Request for Additional Testing
>
> We welcome all contributors and CI systems to test this change thoroughly.

This is NACKed. I recommend not wasting CI system resources.






> In theory, this change should not affect in-tree builds. However, to ensure
> stability and compatibility, we encourage testing across different
> configurations.
>
> What has been tested?
> - out-of-tree kernel build
> - out-of-tree kselftest-all
> ---
>  Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index e5b8a8832c0c..36e65806bb5e 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -275,7 +275,8 @@ else ifeq ($(srcroot)/,$(dir $(CURDIR)))
>      srcroot := ..
>  endif
>
> -export srctree := $(if $(KBUILD_EXTMOD),$(abs_srctree),$(srcroot))
> +srctree := $(if $(KBUILD_EXTMOD),$(abs_srctree),$(srcroot))
> +export srctree := $(if $(building_out_of_srctree),$(abs_srctree),$(srctree))
>
>  ifdef building_out_of_srctree
>  export VPATH := $(srcroot)
> --
> 2.44.0
>
>


-- 
Best Regards
Masahiro Yamada