From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from condef-06.nifty.com (condef-06.nifty.com [202.248.20.71]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9314A3C35 for ; Mon, 5 Sep 2022 09:16:48 +0000 (UTC) Received: from conssluserg-02.nifty.com ([10.126.8.81])by condef-06.nifty.com with ESMTP id 2859AOI9006973 for ; Mon, 5 Sep 2022 18:10:24 +0900 Received: from mail-oo1-f50.google.com (mail-oo1-f50.google.com [209.85.161.50]) (authenticated) by conssluserg-02.nifty.com with ESMTP id 2859A5Mq023251 for ; Mon, 5 Sep 2022 18:10:06 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-02.nifty.com 2859A5Mq023251 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1662369006; bh=4BbPbSzeFLnJFI+hMdkPwj9aQwOKx7JySs0IWqZPQ0E=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=K/mdEeMRVWUJ43uBAY659SEzldpJrYqmzDMddLj0aB0c56GoecW80PmlDDWYOBpfL 9bHh6vsGCFA/d53NC+q3BwVLoFvzDrUKtMgyA3z5iGlNJBpLEaIcyQ0Of/foUdMafK zUOic0nRiESCOt98VhDySaaAXwmn4LntcT8541AJv/6pNJrCT6OZinJjDcgbCVlaNR okCu1UQFRXhzxW4aTnxWqabtQZrmYjiMBpjnShwT8s7LKypx4NZE24sUBg2m2v+Ip7 IDLxZ4oZmMkjpIUx3qQ9CZsDLW2VJES/duDlV3G+bE/05uV9/obzK5bLWM5Uuq4Mxx A1L8Hj+SAmV0w== X-Nifty-SrcIP: [209.85.161.50] Received: by mail-oo1-f50.google.com with SMTP id x10-20020a4a410a000000b004456a27110fso1391259ooa.7 for ; Mon, 05 Sep 2022 02:10:06 -0700 (PDT) X-Gm-Message-State: ACgBeo0tv4S8Q/aZaeNXHi5y5Ao6v1ONcu3QH2mQ8sKYw1DeGFGZq5kb y1lmolka5mwqU0SBFIBtryUGM7Fz2FxGHeooXYw= X-Google-Smtp-Source: AA6agR762y627dWmUGyX6sAQX7gCT5K0+/66Ge89+EYNKHtueHA4CGyB7PqUnbc1v/EXYM/a2gYwd3gnsxX4Rw7avhg= X-Received: by 2002:a4a:9789:0:b0:451:437b:cc58 with SMTP id w9-20020a4a9789000000b00451437bcc58mr6570173ooi.96.1662369004999; Mon, 05 Sep 2022 02:10:04 -0700 (PDT) Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20220831184408.2778264-1-ndesaulniers@google.com> <20220831184408.2778264-3-ndesaulniers@google.com> In-Reply-To: From: Masahiro Yamada Date: Mon, 5 Sep 2022 18:09:28 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 2/5] Makefile.compiler: Use KBUILD_AFLAGS for as-option To: Nathan Chancellor Cc: Nick Desaulniers , Michal Marek , Tom Rix , Linux Kbuild mailing list , Linux Kernel Mailing List , clang-built-linux , X86 ML , Dmitrii Bundin , Fangrui Song , Alexey Alexandrov , Bill Wendling , Greg Thelen Content-Type: text/plain; charset="UTF-8" On Thu, Sep 1, 2022 at 4:53 AM Nathan Chancellor wrote: > > On Wed, Aug 31, 2022 at 11:44:05AM -0700, Nick Desaulniers wrote: > > as-instr uses KBUILD_AFLAGS, but as-option uses KBUILD_CFLAGS. This can > > cause as-option to fail unexpectedly because clang will emit > > -Werror,-Wunused-command-line-argument for various -m and -f flags for > > assembler sources. > > Now that I am looking closer at it, where does that '-Werror' come from? The related commit is c3f0d0bc5b01ad90c45276952802455750444b4f The previous discussion with Arnd is https://lore.kernel.org/linux-kbuild/20170314213724.3836900-1-arnd@arndb.de/ > For cc-option, we add it to elevate clang's warnings about unused '-f', > '-m', and '-W' flags to errors so that we do not add those flags. > However, I do not see '-Werror' in as-option. I am going to assume it > came from CONFIG_WERROR, as I believe Android has that turned on by > default. CONFIG_WERROR is added to CFLAGS. But, I guess it is more correct to do likewise for others. (https://patchwork.kernel.org/project/linux-kbuild/patch/20220905083619.672091-1-masahiroy@kernel.org/) > I think that is the real problem: without '-Werror', the only > error that should come from as-option is when an option isn't supported > by the assembler, as clang will still warn but those will not be fatal > but with '-Werror', those warnings turn fatal, causing all subsequent > as-option calls to fail. Presumably, it is correct to add -Werror to as-option as well. We have no reason to add it to cc-option, but not to as-option. I also believe '-x assembler' should be changed to '-x assembler-with-cpp'. As I mentioned somewhere before, our assembly code (*.S) is always preprocessed. There is no *.s file in the kernel source tree. So, '-x assembler-with-cpp' matches the real situation. One interesting thing is, clang does not warn [-Wunused-command-line-argument] for *.S files. $ clang -fomit-frame-pointer -c -x assembler /dev/null -o /dev/null clang: warning: argument unused during compilation: '-fomit-frame-pointer' [-Wunused-command-line-argument] $ clang -fomit-frame-pointer -c -x assembler-with-cpp /dev/null -o /dev/null The root cause is we are using '-x assembler', which never happens in the kernel tree. To sum up, the code I think correct is: as-option = $(call try-run,\ $(CC) -Werror $(KBUILD_AFLAGS) $(1) -c -x assembler-with-cpp /dev/null -o "$$TMP",$(1),$(2)) > Do not get me wrong, I still believe this is the correct fix but I think > it would be good to describe exactly under which conditions this is a > real issue in case we ever have to revisit this. > > > Callers of as-option (and as-instr) likely want to be adding flags to > > KBUILD_AFLAGS/aflags-y, not KBUILD_CFLAGS/cflags-y. > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/1699 > > Signed-off-by: Nick Desaulniers > > Regardless of changes to the commit message: > > Reviewed-by: Nathan Chancellor > > > --- > > Changes v1 -> v2: > > * Split off changes to arch/x86/boot/compressed/Makefile into parent > > patch, as per Masahiro. > > > > scripts/Makefile.compiler | 6 +++--- > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler > > index 94d0d40cddb3..d1739f0d3ce3 100644 > > --- a/scripts/Makefile.compiler > > +++ b/scripts/Makefile.compiler > > @@ -29,13 +29,13 @@ try-run = $(shell set -e; \ > > fi) > > > > # as-option > > -# Usage: cflags-y += $(call as-option,-Wa$(comma)-isa=foo,) > > +# Usage: aflags-y += $(call as-option,-Wa$(comma)-isa=foo,) > > > > as-option = $(call try-run,\ > > - $(CC) $(KBUILD_CFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2)) > > + $(CC) $(KBUILD_AFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2)) > > > > # as-instr > > -# Usage: cflags-y += $(call as-instr,instr,option1,option2) > > +# Usage: aflags-y += $(call as-instr,instr,option1,option2) > > > > as-instr = $(call try-run,\ > > printf "%b\n" "$(1)" | $(CC) $(KBUILD_AFLAGS) -c -x assembler -o "$$TMP" -,$(2),$(3)) > > -- > > 2.37.2.672.g94769d06f0-goog > > -- Best Regards Masahiro Yamada