From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3361C31E46 for ; Wed, 12 Jun 2019 09:25:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9783D207E0 for ; Wed, 12 Jun 2019 09:25:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2408714AbfFLJZZ (ORCPT ); Wed, 12 Jun 2019 05:25:25 -0400 Received: from foss.arm.com ([217.140.110.172]:48308 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2406207AbfFLJZY (ORCPT ); Wed, 12 Jun 2019 05:25:24 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C883C28; Wed, 12 Jun 2019 02:25:23 -0700 (PDT) Received: from e103592.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AA1123F246; Wed, 12 Jun 2019 02:25:22 -0700 (PDT) Date: Wed, 12 Jun 2019 10:25:20 +0100 From: Dave Martin To: Nathan Chancellor Cc: Catalin Marinas , Will Deacon , Nick Desaulniers , linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, Qian Cai , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2] arm64: Don't unconditionally add -Wno-psabi to KBUILD_CFLAGS Message-ID: <20190612092519.GP28398@e103592.cambridge.arm.com> References: <20190607161201.73430-1-natechancellor@gmail.com> <20190611171931.99705-1-natechancellor@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190611171931.99705-1-natechancellor@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 11, 2019 at 10:19:32AM -0700, Nathan Chancellor wrote: > This is a GCC only option, which warns about ABI changes within GCC, so > unconditionally adding it breaks Clang with tons of: > > warning: unknown warning option '-Wno-psabi' [-Wunknown-warning-option] > > and link time failures: > > ld.lld: error: undefined symbol: __efistub___stack_chk_guard > >>> referenced by arm-stub.c:73 > (/home/nathan/cbl/linux/drivers/firmware/efi/libstub/arm-stub.c:73) > >>> arm-stub.stub.o:(__efistub_install_memreserve_table) > in archive ./drivers/firmware/efi/libstub/lib.a > > These failures come from the lack of -fno-stack-protector, which is > added via cc-option in drivers/firmware/efi/libstub/Makefile. When an > unknown flag is added to KBUILD_CFLAGS, clang will noisily warn that it > is ignoring the option like above, unlike gcc, who will just error. > > $ echo "int main() { return 0; }" > tmp.c > > $ clang -Wno-psabi tmp.c; echo $? > warning: unknown warning option '-Wno-psabi' [-Wunknown-warning-option] > 1 warning generated. > 0 > > $ gcc -Wsometimes-uninitialized tmp.c; echo $? > gcc: error: unrecognized command line option > ‘-Wsometimes-uninitialized’; did you mean ‘-Wmaybe-uninitialized’? > 1 > > For cc-option to work properly with clang and behave like gcc, -Werror > is needed, which was done in commit c3f0d0bc5b01 ("kbuild, LLVMLinux: > Add -Werror to cc-option to support clang"). > > $ clang -Werror -Wno-psabi tmp.c; echo $? > error: unknown warning option '-Wno-psabi' > [-Werror,-Wunknown-warning-option] > 1 > > As a consequence of this, when an unknown flag is unconditionally added > to KBUILD_CFLAGS, it will cause cc-option to always fail and those flags > will never get added: > > $ clang -Werror -Wno-psabi -fno-stack-protector tmp.c; echo $? > error: unknown warning option '-Wno-psabi' > [-Werror,-Wunknown-warning-option] > 1 > > This can be seen when compiling the whole kernel as some warnings that > are normally disabled (see below) show up. The full list of flags > missing from drivers/firmware/efi/libstub are the following (gathered > from diffing .arm64-stub.o.cmd): > > -fno-delete-null-pointer-checks > -Wno-address-of-packed-member > -Wframe-larger-than=2048 > -Wno-unused-const-variable > -fno-strict-overflow > -fno-merge-all-constants > -fno-stack-check > -Werror=date-time > -Werror=incompatible-pointer-types > -ffreestanding > -fno-stack-protector > > Use cc-disable-warning so that it gets disabled for GCC and does nothing > for Clang. > > Fixes: ebcc5928c5d9 ("arm64: Silence gcc warnings about arch ABI drift") > Link: https://github.com/ClangBuiltLinux/linux/issues/511 > Reported-by: Qian Cai > Acked-by: Dave Martin > Reviewed-by: Nick Desaulniers > Signed-off-by: Nathan Chancellor > --- > > v1 -> v2: > > * Improve commit message explanation, I wasn't entirely happy with the > first one; let me know if there are any issues/questions. > > * Carry forward Dave's ack and Nick's review (let me know if you > disagree with the commit messasge rewording). > > arch/arm64/Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index 8fbd583b18e1..e9d2e578cbe6 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -51,7 +51,7 @@ endif > > KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr) $(brokengasinst) > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > -KBUILD_CFLAGS += -Wno-psabi > +KBUILD_CFLAGS += $(call cc-disable-warning, psabi) > KBUILD_AFLAGS += $(lseinstr) $(brokengasinst) > > KBUILD_CFLAGS += $(call cc-option,-mabi=lp64) Looks OK to me. Thanks for the additional explanation. Cheers ---Dave