From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751820AbdHGSdi (ORCPT ); Mon, 7 Aug 2017 14:33:38 -0400 Received: from mail-pg0-f53.google.com ([74.125.83.53]:33348 "EHLO mail-pg0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751426AbdHGSdg (ORCPT ); Mon, 7 Aug 2017 14:33:36 -0400 Date: Mon, 7 Aug 2017 11:33:33 -0700 From: Matthias Kaehlcke To: Masahiro Yamada Cc: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , Michal Marek , X86 ML , Linux Kbuild mailing list , Linux Kernel Mailing List , Douglas Anderson , Michael Davidson , Greg Hackmann , Nick Desaulniers , Stephen Hines , Kees Cook , Arnd Bergmann , Bernhard =?utf-8?Q?Rosenkr=C3=A4nzer?= Subject: Re: [PATCH 1/2] kbuild: Add macros cc-option-3 and __cc-option-3 Message-ID: <20170807183333.GK84665@google.com> References: <20170721215657.81631-1-mka@chromium.org> <20170802164650.GG84665@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Masahiro, El Mon, Aug 07, 2017 at 10:01:41AM +0900 Masahiro Yamada ha dit: > Hi Matthias, > > Sorry for my late reply. > > 2017-08-03 1:46 GMT+09:00 Matthias Kaehlcke : > > El Fri, Jul 21, 2017 at 02:56:56PM -0700 Matthias Kaehlcke ha dit: > > > >> The macro cc-option receives two parameters (the second may be empty). It > >> returns the first parameter if it is a valid compiler option, otherwise > >> the second one. It is not evaluated if the second parameter is a valid > >> compiler option. This seems to be fine in virtually all cases, however > >> there are scenarios where the second paramater needs to be evaluated too, > >> and an empty value (or a third option) should be returned if it is not > >> valid. > >> > >> The macro cc-option-3 receives three parameters and returns parameter 1 > >> or 2 (in this order) if one of them is found to be a valid compiler > >> option, and otherwise paramater 3. The macro __cc-option-3 works > >> analogously. > > > > Any comment on this? > > > > Thanks > > > > Matthias > > > >> Signed-off-by: Matthias Kaehlcke > >> --- > >> scripts/Kbuild.include | 9 +++++++++ > >> 1 file changed, 9 insertions(+) > >> > >> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include > >> index dd8e2dde0b34..dc83635f2317 100644 > >> --- a/scripts/Kbuild.include > >> +++ b/scripts/Kbuild.include > >> @@ -113,6 +113,11 @@ as-instr = $(call try-run,\ > >> __cc-option = $(call try-run,\ > >> $(1) -Werror $(2) $(3) -c -x c /dev/null -o "$$TMP",$(3),$(4)) > >> > >> +# __cc-option-3 > >> +# Usage: MY_CFLAGS += $(call __cc-option-3,$(CC),$(MY_CFLAGS),\ > >> +# -mpreferred-stack-boundary=2,-mstack-alignment=4,) > >> +__cc-option-3 = $(call __cc-option,$(1),$(2),$(3),$(call __cc-option,$(1),$(2),$(4),$(5))) > >> + > >> # Do not attempt to build with gcc plugins during cc-option tests. > >> # (And this uses delayed resolution so the flags will be up to date.) > >> CC_OPTION_CFLAGS = $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS)) > >> @@ -123,6 +128,10 @@ CC_OPTION_CFLAGS = $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS)) > >> cc-option = $(call __cc-option, $(CC),\ > >> $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS),$(1),$(2)) > >> > >> +# cc-option-3 > >> +# Usage: cflags-y += $(call cc-option-3,-mpreferred-stack-boundary=3,-mstack-alignment=8,) > >> +cc-option-3 = $(call cc-option,$(1),$(call cc-option,$(2),$(3))) > > > I do not like this macro much for the following reasons: > > > [1] > I guess your motivation is to evaluate the second option, > not receive the third option. In this case yes, a future use case could be to support another compiler with different option names, but I suppose we can focus on the present for now. > If this is the demand, I thought it might be nicer to > change cc-option to always evaluate the second option. I considered that, but was reluctant to change current behavior, though in practice it shouldn't make a difference. > (I do no have a good idea for the implementation.) One option could be a variant of the try-run macro, that receives the 'base command' as first parameter: try-run-opt = $(shell set -e; \ TMP="$(TMPOUT).$$$$.tmp"; \ TMPO="$(TMPOUT).$$$$.o"; \ if ($(1) $(2)) >/dev/null 2>&1; \ then echo "$(2)"; \ elif [ -n "${3}" ] && ($(1) $(3)) >/dev/null 2>&1; \ then echo "$(3)"; \ else echo ""; \ fi; \ rm -f "$$TMP" "$$TMPO") __cc-option = $(call try-run-opt,\ $(1) -Werror $(2) -c -x c /dev/null -o "$$TMP",$(3),$(4)) try-run-opt assumes that is is valid to append an option to the end of the base command. For consistency we'd probably want to adapt other suitable xx-option macros as well. Does this look reasonable to you? > cc-option-3 = $(call cc-option,$(1),$(call cc-option,$(2),$(3))) > > evaluates the inner $(call cc-option,) first. > > This works a bit differently from our expectation. > > > For example, let's consider the following case. > > $(call cc-option-3,-Oz,-Os,-O2) > > > I think we generally expect -Oz, -Os are tested in this order. > (If -Oz is supported by the compiler, the test for -Os will be skipped.) > > > In fact, cc-option-3 tests -Os, -Oz in this order > because inner cc-option is evaluated before the outer one. > The test for -Os may or may not be necessary. I agree, running the check for the alternative options always is not desirable.