Re: [RFC PATCH 4/6] tools: build kernel selftests in tools_build

[Sasha Levin <sashal@kernel.org>]

On Tue, Oct 13, 2026 at 10:41:00PM +0200, Thomas Weißschuh wrote:
>On 2026-10-11 19:36:43-0400, Sasha Levin wrote:
>> Add a "Kernel selftests" sub-menu with one entry per selftests directory
>> that builds with only a C library and does not write into the source
>> tree. Each is built as "make kselftest-all" builds it, with KHDR_INCLUDES
>> pointing at the UAPI headers installed in the object tree, but by its own
>> make, so the selected ones build in parallel. Selftests whose Makefile
>> does not use KHDR_INCLUDES still build against the C library's copy of
>> the UAPI headers.
>>
>> The selftests do not track header dependencies, so a selftest is built
>> again from scratch when its own directory, a header or makefile any
>> selftest may share, or a kernel source it includes directly (the vDSO
>> test includes the architecture's vDSO code) is newer than its last
>> build.
>>
>> Selftests that need libraries beyond the C library, a vmlinux with BTF,
>> or a sanitizer runtime are left out for now.
>>
>> Assisted-by: LLM
>> Signed-off-by: Sasha Levin <sashal@kernel.org>
>> ---
>>  tools/Kconfig         | 239 ++++++++++++++++++++++++++++++++++++++++++
>>  tools/Makefile.kbuild | 100 ++++++++++++++++++
>>  2 files changed, 339 insertions(+)
>
>(...)
>
>> diff --git a/tools/Makefile.kbuild b/tools/Makefile.kbuild
>> index 62fd494253eca..c31347258d0a9 100644
>> --- a/tools/Makefile.kbuild
>> +++ b/tools/Makefile.kbuild
>> @@ -92,6 +92,106 @@ PHONY += perf
>>  perf: FORCE
>>  	$(call build,$(outdir)/perf,-C $(toolsdir)/perf -f Makefile.perf O=$(outdir)/perf $(perf-flags) $(perf-flags-y),,TOOLS_BUILD_PERF)
>
>(...)
>
>> +# Unlike tools/build, the selftests do not track header dependencies. A
>> +# selftest is built again from scratch when its own directory, a header or
>> +# makefile any selftest may share, or a kernel source it includes directly
>> +# is newer than its last build.
>> +selftest-shared := $(outdir)/selftests/.shared
>> +selftest-extra-vDSO := $(abs_srctree)/arch/$(SRCARCH)
>
>Can we not fix the selftests to properly track header dependencies?
>That has been an annoyance of mine for quite some time.
>It would also get rid of a whole bunch of hackery here.

Ugh... I suppose? The current check is also incomplete: it misses headers
outside the paths it watches, such as include/linux/annotate.h, which the vDSO
test pulls in, or tools/arch/x86/include/uapi, used by ir and proc.

I'll see if I can fix it up... 

-- 
Thanks,
Sasha