On 21/12/2024 01:14, Quentin Monnet wrote:

2024-12-17 11:10 UTC+0800 ~ Li Zhijian lizhijian@fujitsu.com

...

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.

Another condition to reproduce the failure above is to have have $(srcroot) in the Makefile set to "." or "..", for example when your $build is located right under the root of the repo [0].

[0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Make...

...

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.

Signed-off-by: Li Zhijian lizhijian@fujitsu.com

Request for Additional Testing

We welcome all contributors and CI systems to test this change thoroughly. 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)

The patch does fix the issue in the case you reported.

Maybe I'd write the change differently, though; rather than potentially overwriting $(srctree) before exporting it, let's unroll with ifdef's to make it clearer?

Yes, your code looks better. However, this "absolute source tree" approach was not approved.:)

Thank you!!

ifdef building_out_of_srctree srctree := $(abs_srctree) else ifdef KBUILD_EXTMOD srctree := $(abs_srctree) else srctree := $(srcroot) endif export srctree

(not tested)

Thanks, Quentin

On 21/12/2024 11:41, Masahiro Yamada wrote:

On Tue, Dec 17, 2024 at 12:10 PM Li Zhijian lizhijian@fujitsu.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.

Hi Masahiro,

Thank you for your feedback I understand and agree with your points, thanks again for these information.

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

...

Signed-off-by: Li Zhijian lizhijian@fujitsu.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.

It sounds reasonable. It makes sense to avoid using CI resources on this patch given the current circumstances.

Thanks Zhijian

...

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