[PATCH bpf-next v3] selftests/Makefile: override the srctree for out-of-tree builds

[PATCH bpf-next v3] selftests/Makefile: override the srctree for out-of-tree builds

[Li Zhijian]

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, override the srctree in the kselftests's top Makefile
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.

Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Tested-by: Quentin Monnet <qmo@kernel.org>
---
Cc: Masahiro Yamada <masahiroy@kernel.org>

V3:
  collected Tested-by and rebased on bpf-next

V2:
 - handle srctree in selftests itself rather than the linux' top Makefile # Masahiro Yamada <masahiroy@kernel.org>

V1: https://lore.kernel.org/lkml/20241217031052.69744-1-lizhijian@fujitsu.com/
---
 tools/testing/selftests/Makefile | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 2401e973c359..f04a3b0003f6 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -154,15 +154,19 @@ override LDFLAGS =
 override MAKEFLAGS =
 endif
 
+top_srcdir ?= ../../..
+
 # Append kselftest to KBUILD_OUTPUT and O to avoid cluttering
 # KBUILD_OUTPUT with selftest objects and headers installed
 # by selftests Makefile or lib.mk.
+# Override the `srctree` variable to ensure it is correctly resolved in
+# sub-Makefiles, such as those within `bpf`, when managing targets like
+# `net` and `hid`.
 ifdef building_out_of_srctree
 override LDFLAGS =
+override srctree := $(top_srcdir)
 endif
 
-top_srcdir ?= ../../..
-
 ifeq ("$(origin O)", "command line")
   KBUILD_OUTPUT := $(O)
 endif
-- 
2.44.0

Re: [PATCH bpf-next v3] selftests/Makefile: override the srctree for out-of-tree builds

[Daniel Borkmann]

On 1/15/25 2:47 AM, Li Zhijian 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, override the srctree in the kselftests's top Makefile
> 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.
> 
> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
> Tested-by: Quentin Monnet <qmo@kernel.org>

[...]
>   tools/testing/selftests/Makefile | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)

Shuah, want to pick this up given its the top-level Makefile or want us to
route it via bpf-next with your Ack? Fwiw, BPF CI went through fine.

Re: [PATCH bpf-next v3] selftests/Makefile: override the srctree for out-of-tree builds

[Zhijian Li (Fujitsu)]

ping...


On 15/01/2025 23:06, Daniel Borkmann wrote:
> On 1/15/25 2:47 AM, Li Zhijian 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, override the srctree in the kselftests's top Makefile
>> 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.
>>
>> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
>> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
>> Tested-by: Quentin Monnet <qmo@kernel.org>
> 
> [...]
>>   tools/testing/selftests/Makefile | 8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> Shuah, want to pick this up given its the top-level Makefile or want us to
> route it via bpf-next with your Ack? Fwiw, BPF CI went through fine.