linux-kernel - Re: [PATCH] selftests: more general make nesting support

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Date:   Wed, 05 Aug 2020 13:40:15 -0700
From:   Greg Thelen <gthelen@...gle.com>
To:     Shuah Khan <skhan@...uxfoundation.org>,
        Shuah Khan <shuah@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-kselftest@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] selftests: more general make nesting support

Shuah Khan <skhan@...uxfoundation.org> wrote:

> On 8/5/20 1:36 PM, Greg Thelen wrote:
>> On Tue, Jul 28, 2020 at 12:32 AM Greg Thelen <gthelen@...gle.com> wrote:
>>>
>>> selftests can be built from the toplevel kernel makefile (e.g. make
>>> kselftest-all) or directly (make -C tools/testing/selftests all).
>>>
>>> The toplevel kernel makefile explicitly disables implicit rules with
>>> "MAKEFLAGS += -rR", which is passed to tools/testing/selftests.  Some
>>> selftest makefiles require implicit make rules, which is why
>>> commit 67d8712dcc70 ("selftests: Fix build failures when invoked from
>>> kselftest target") reenables implicit rules by clearing MAKEFLAGS if
>>> MAKELEVEL=1.
>>>
>>> So far so good.  However, if the toplevel makefile is called from an
>>> outer makefile then MAKELEVEL will be elevated, which breaks the
>>> MAKELEVEL equality test.
>>> Example wrapped makefile error:
>>>    $ cat ~/Makefile
>>>    all:
>>>          $(MAKE) defconfig
>>>          $(MAKE) kselftest-all
>>>    $ make -sf ~/Makefile
>>>      futex_wait_timeout.c /src/tools/testing/selftests/kselftest_harness.h   /src/tools/testing/selftests/kselftest.h ../include/futextest.h ../include/atomic.h ../include/logging.h -lpthread -lrt -o /src/tools/testing/selftests/futex/functional/futex_wait_timeout
>>>    make[4]: futex_wait_timeout.c: Command not found
>>>
>>> Rather than checking $(MAKELEVEL), check for $(LINK.c), which is a more
>>> direct side effect of "make -R".  This enables arbitrary makefile
>>> nesting.
>>>
>>> Signed-off-by: Greg Thelen <gthelen@...gle.com>
>>> ---
>>>   tools/testing/selftests/Makefile | 8 ++++----
>>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
>>> index 1195bd85af38..289a2e4b3f6f 100644
>>> --- a/tools/testing/selftests/Makefile
>>> +++ b/tools/testing/selftests/Makefile
>>> @@ -84,10 +84,10 @@ endif
>>>   # of the targets gets built.
>>>   FORCE_TARGETS ?=
>>>
>>> -# Clear LDFLAGS and MAKEFLAGS if called from main
>>> -# Makefile to avoid test build failures when test
>>> -# Makefile doesn't have explicit build rules.
>>> -ifeq (1,$(MAKELEVEL))
>>> +# Clear LDFLAGS and MAKEFLAGS when implicit rules are missing.  This provides
>>> +# implicit rules to sub-test Makefiles which avoids build failures in test
>>> +# Makefile that don't have explicit build rules.
>>> +ifeq (,$(LINK.c))
>>>   override LDFLAGS =
>>>   override MAKEFLAGS =
>>>   endif
>>> --
>>> 2.28.0.rc0.142.g3c755180ce-goog
>> 
>> Is there any feedback on this patch?  It's not high priority but something that
>> will help me make more use of selftests.
>> 
>
> No issues with the patch. I will apply it once the merge window ends.
>
> thanks,
> -- Shuah

Great.  Thank you.