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

[Greg Thelen <gthelen@google.com>]

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.