Re: [PATCH] selftests: more general make nesting support

[Shuah Khan <skhan@linuxfoundation.org>]

On 8/5/20 1:36 PM, Greg Thelen wrote:
> On Tue, Jul 28, 2020 at 12:32 AM Greg Thelen <gthelen@google.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 $(LINK.c), which is a more
>> direct side effect of "make -R".  This enables arbitrary makefile
>> nesting.
>>
>> Signed-off-by: Greg Thelen <gthelen@google.com>
>> ---
>>   tools/testing/selftests/Makefile | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
>> index 1195bd85af38..289a2e4b3f6f 100644
>> --- a/tools/testing/selftests/Makefile
>> +++ b/tools/testing/selftests/Makefile
>> @@ -84,10 +84,10 @@ endif
>>   # of the targets gets built.
>>   FORCE_TARGETS ?=
>>
>> -# Clear LDFLAGS and MAKEFLAGS if called from main
>> -# Makefile to avoid test build failures when test
>> -# Makefile doesn't have explicit build rules.
>> -ifeq (1,$(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