From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 53B092F21 for ; Thu, 3 Mar 2022 17:30:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 45241C340E9; Thu, 3 Mar 2022 17:30:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1646328655; bh=GCDTpWwAdbUUe92yPSIjZBhj5yfaiPwzu66bwylkoac=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=CLQazQPiBOZrP69PhmqDFy7s/3OGcDUji9CNq78GafEhJcptBOq9ejoyBYJ2f546B WTlZ8u1FFUpD/OSgSZY6He9snfv0gRmz7lyA01z+f8swbsuntwtgqOlSdC95A9rhzD 4EHG/xJLnX+ThYlzbEB371mF/DWMhhm1qjhNHHYZhOO7+PHV6EBURX4/QlJg2a/04b cK6IxzhArX/HTp+RcLIdMrJ/+byFkhr/Hqjfdh68MR5K6wiC4kB9Fz3hjA/9cu5twz SOPBjB6KiiImIA7vzXX5v1kdIK7cVQWHqIsb9S4rGhtqXcJiLS7L+LsHATv9VdVI4o g0bbBtjD2FOMg== Date: Thu, 3 Mar 2022 10:30:47 -0700 From: Nathan Chancellor To: David Gow Cc: Kees Cook , Jeff Dike , Richard Weinberger , Anton Ivanov , Masahiro Yamada , Nick Desaulniers , linux-um@lists.infradead.org, linux-kbuild@vger.kernel.org, linux-kselftest@vger.kernel.org, kunit-dev@googlegroups.com, llvm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] um: clang: Strip out -mno-global-merge from USER_CFLAGS Message-ID: References: <20220303090643.241747-1-davidgow@google.com> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220303090643.241747-1-davidgow@google.com> Hi David, On Thu, Mar 03, 2022 at 05:06:42PM +0800, David Gow wrote: > The things built with USER_CFLAGS don't seem to recognise it as a > compiler option, and print a warning: > clang: warning: argument unused during compilation: '-mno-global-merge' [-Wunused-command-line-argument] > > Fixes: 744814d2fa ("um: Allow builds with Clang") > Signed-off-by: David Gow > --- > > This warning shows up after merging: > https://lore.kernel.org/lkml/20220227184517.504931-6-keescook@chromium.org/ > > I'm not 100% sure why this is necessary, but it does seem to work. All > the attempts to get rid of -mno-global-merge entirely have been met with > skepticism, but I'm guessing that it's not a problem for just the UML > "user" files, as they shouldn't(?) interact too much with modules. Thank you for the patch! I think it is correct, as this flag only works for AArch64 and ARM, as it is only used in Clang::AddAArch64TargetArgs() and Clang::AddARMTargetArgs() in clang/lib/Driver/ToolChains/Clang.cpp, which are obviously never called with UML. I am not sure why we do not see warning during regular kernel builds, maybe something about how UML objects are compiled exposes this? Regardless, I would definitely like to clean up this instance of the warning because I would like to make this warning a hard error so that we do not get cryptic cc-option failures: https://github.com/ClangBuiltLinux/linux/issues/1587 Reviewed-by: Nathan Chancellor One small comment below. > arch/um/Makefile | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/um/Makefile b/arch/um/Makefile > index f2fe63bfd819..320b09cd513c 100644 > --- a/arch/um/Makefile > +++ b/arch/um/Makefile > @@ -75,6 +75,10 @@ USER_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \ > -D_FILE_OFFSET_BITS=64 -idirafter $(srctree)/include \ > -idirafter $(objtree)/include -D__KERNEL__ -D__UM_HOST__ > > +ifdef CONFIG_CC_IS_CLANG Is this ifdef needed? > +USER_CFLAGS := $(patsubst -mno-global-merge,,$(USER_CFLAGS)) > +endif > + > #This will adjust *FLAGS accordingly to the platform. > include $(srctree)/$(ARCH_DIR)/Makefile-os-$(OS) > > -- > 2.35.1.616.g0bdcbb4464-goog > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nPpI2-007JgR-3p for linux-um@lists.infradead.org; Thu, 03 Mar 2022 17:31:00 +0000 Date: Thu, 3 Mar 2022 10:30:47 -0700 From: Nathan Chancellor Subject: Re: [PATCH] um: clang: Strip out -mno-global-merge from USER_CFLAGS Message-ID: References: <20220303090643.241747-1-davidgow@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220303090643.241747-1-davidgow@google.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: David Gow Cc: Kees Cook , Jeff Dike , Richard Weinberger , Anton Ivanov , Masahiro Yamada , Nick Desaulniers , linux-um@lists.infradead.org, linux-kbuild@vger.kernel.org, linux-kselftest@vger.kernel.org, kunit-dev@googlegroups.com, llvm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Hi David, On Thu, Mar 03, 2022 at 05:06:42PM +0800, David Gow wrote: > The things built with USER_CFLAGS don't seem to recognise it as a > compiler option, and print a warning: > clang: warning: argument unused during compilation: '-mno-global-merge' [-Wunused-command-line-argument] > > Fixes: 744814d2fa ("um: Allow builds with Clang") > Signed-off-by: David Gow > --- > > This warning shows up after merging: > https://lore.kernel.org/lkml/20220227184517.504931-6-keescook@chromium.org/ > > I'm not 100% sure why this is necessary, but it does seem to work. All > the attempts to get rid of -mno-global-merge entirely have been met with > skepticism, but I'm guessing that it's not a problem for just the UML > "user" files, as they shouldn't(?) interact too much with modules. Thank you for the patch! I think it is correct, as this flag only works for AArch64 and ARM, as it is only used in Clang::AddAArch64TargetArgs() and Clang::AddARMTargetArgs() in clang/lib/Driver/ToolChains/Clang.cpp, which are obviously never called with UML. I am not sure why we do not see warning during regular kernel builds, maybe something about how UML objects are compiled exposes this? Regardless, I would definitely like to clean up this instance of the warning because I would like to make this warning a hard error so that we do not get cryptic cc-option failures: https://github.com/ClangBuiltLinux/linux/issues/1587 Reviewed-by: Nathan Chancellor One small comment below. > arch/um/Makefile | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/um/Makefile b/arch/um/Makefile > index f2fe63bfd819..320b09cd513c 100644 > --- a/arch/um/Makefile > +++ b/arch/um/Makefile > @@ -75,6 +75,10 @@ USER_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \ > -D_FILE_OFFSET_BITS=64 -idirafter $(srctree)/include \ > -idirafter $(objtree)/include -D__KERNEL__ -D__UM_HOST__ > > +ifdef CONFIG_CC_IS_CLANG Is this ifdef needed? > +USER_CFLAGS := $(patsubst -mno-global-merge,,$(USER_CFLAGS)) > +endif > + > #This will adjust *FLAGS accordingly to the platform. > include $(srctree)/$(ARCH_DIR)/Makefile-os-$(OS) > > -- > 2.35.1.616.g0bdcbb4464-goog > _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um