From: Nathan Chancellor <nathan@kernel.org> To: David Gow <davidgow@google.com> Cc: Kees Cook <keescook@chromium.org>, Jeff Dike <jdike@addtoit.com>, Richard Weinberger <richard@nod.at>, Anton Ivanov <anton.ivanov@cambridgegreys.com>, Masahiro Yamada <masahiroy@kernel.org>, Nick Desaulniers <ndesaulniers@google.com>, 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 Date: Thu, 3 Mar 2022 10:30:47 -0700 [thread overview] Message-ID: <YiD7R2wRxoWxtVq7@dev-arch.thelio-3990X> (raw) 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 <davidgow@google.com> > --- > > 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 <nathan@kernel.org> 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 >
WARNING: multiple messages have this Message-ID (diff)
From: Nathan Chancellor <nathan@kernel.org> To: David Gow <davidgow@google.com> Cc: Kees Cook <keescook@chromium.org>, Jeff Dike <jdike@addtoit.com>, Richard Weinberger <richard@nod.at>, Anton Ivanov <anton.ivanov@cambridgegreys.com>, Masahiro Yamada <masahiroy@kernel.org>, Nick Desaulniers <ndesaulniers@google.com>, 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 Date: Thu, 3 Mar 2022 10:30:47 -0700 [thread overview] Message-ID: <YiD7R2wRxoWxtVq7@dev-arch.thelio-3990X> (raw) 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 <davidgow@google.com> > --- > > 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 <nathan@kernel.org> 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
next prev parent reply other threads:[~2022-03-03 17:30 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-03-03 9:06 [PATCH] um: clang: Strip out -mno-global-merge from USER_CFLAGS David Gow 2022-03-03 9:06 ` David Gow 2022-03-03 17:30 ` Nathan Chancellor [this message] 2022-03-03 17:30 ` Nathan Chancellor 2022-03-03 18:04 ` Kees Cook 2022-03-03 18:26 ` Nathan Chancellor 2022-03-03 18:26 ` Nathan Chancellor 2022-03-03 18:39 ` Nick Desaulniers 2022-03-03 18:39 ` Nick Desaulniers 2022-03-04 11:42 ` Sedat Dilek 2022-03-04 11:42 ` Sedat Dilek 2022-03-04 6:51 ` David Gow 2022-03-04 6:51 ` David Gow
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