From: Nick Desaulniers <ndesaulniers@google.com> To: Will Deacon <will@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com>, Masahiro Yamada <masahiroy@kernel.org>, Arnd Bergmann <arnd@kernel.org>, Fangrui Song <maskray@google.com>, Nathan Chancellor <nathan@kernel.org>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: Re: [PATCH] arm64: drop CROSS_COMPILE for LLVM=1 LLVM_IAS=1 Date: Fri, 2 Jul 2021 10:50:27 -0700 [thread overview] Message-ID: <CAKwvOdk4GLDVrOJsxPBVM+g4sBiYW-64M3rNN6hsBgHP0eYqGg@mail.gmail.com> (raw) In-Reply-To: <20210702112210.GA11084@willie-the-truck> On Fri, Jul 2, 2021 at 4:22 AM Will Deacon <will@kernel.org> wrote: > > On Thu, Jul 01, 2021 at 04:55:05PM -0700, Nick Desaulniers wrote: > > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > > index 7bc37d0a1b68..016873fddcc3 100644 > > --- a/arch/arm64/Makefile > > +++ b/arch/arm64/Makefile > > @@ -34,6 +34,17 @@ $(warning LSE atomics not supported by binutils) > > endif > > endif > > > > +ifneq ($(LLVM),) > > +ifneq ($(LLVM_IAS),) > > +ifeq ($(CROSS_COMPILE),) > > +CLANG_TARGET :=--target=aarch64-linux > > +CLANG_FLAGS += $(CLANG_TARGET) > > +KBUILD_CFLAGS += $(CLANG_TARGET) > > +KBUILD_AFLAGS += $(CLANG_TARGET) > > Do we need to do anything extra for the linker here? I can't see how we > avoid picking up the host copy. That's handled by the top level Makefile when LLVM=1 is set. There is $KBUILD_LDFLAGS, but we don't do anything with it at the moment in terms of which linker we select; $LD controls which linker we use. LLD can figure out the target based on the object files it's given as input, so it doesn't need any `--target=` flag. When clang is invoked as the compiler or assembler, it does need --target. > Have you tested the compat vDSO with this change? I think we'll just end > up passing two --target options, which is hopefully ok, but thought I'd > better check. Good catch. We don't reuse KBUILD_CFLAGS or KBUILD_AFLAGS for the compat vdso for this very reason. In arch/arm64/kernel/vdso32/Makefile you'll see no references to KBUILD_CFLAGS or KBUILD_AFLAGS; instead we use VDSO_CFLAGS and VDSO_AFLAGS in their stead. But, we could (and should) make this same change for the compat vdso, and drop the need for CROSS_COMPILE_COMPAT for LLVM. Let me play around with the changes Arnd suggested and see if I can get that working. I'm a bit nervous about making this depend on something from the top level Makefile on initial glance; these changes start to become tree wide rather than isolated per arch/, but let's see. Maybe at that point we carry a series in the kbuild tree with acks for the arch/ specific changes from the respective maintainers? Either way, I'll send a v2 that nixes CROSS_COMPILE_COMPAT for LLVM. -- Thanks, ~Nick Desaulniers
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From: Nick Desaulniers <ndesaulniers@google.com> To: Will Deacon <will@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com>, Masahiro Yamada <masahiroy@kernel.org>, Arnd Bergmann <arnd@kernel.org>, Fangrui Song <maskray@google.com>, Nathan Chancellor <nathan@kernel.org>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: Re: [PATCH] arm64: drop CROSS_COMPILE for LLVM=1 LLVM_IAS=1 Date: Fri, 2 Jul 2021 10:50:27 -0700 [thread overview] Message-ID: <CAKwvOdk4GLDVrOJsxPBVM+g4sBiYW-64M3rNN6hsBgHP0eYqGg@mail.gmail.com> (raw) In-Reply-To: <20210702112210.GA11084@willie-the-truck> On Fri, Jul 2, 2021 at 4:22 AM Will Deacon <will@kernel.org> wrote: > > On Thu, Jul 01, 2021 at 04:55:05PM -0700, Nick Desaulniers wrote: > > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > > index 7bc37d0a1b68..016873fddcc3 100644 > > --- a/arch/arm64/Makefile > > +++ b/arch/arm64/Makefile > > @@ -34,6 +34,17 @@ $(warning LSE atomics not supported by binutils) > > endif > > endif > > > > +ifneq ($(LLVM),) > > +ifneq ($(LLVM_IAS),) > > +ifeq ($(CROSS_COMPILE),) > > +CLANG_TARGET :=--target=aarch64-linux > > +CLANG_FLAGS += $(CLANG_TARGET) > > +KBUILD_CFLAGS += $(CLANG_TARGET) > > +KBUILD_AFLAGS += $(CLANG_TARGET) > > Do we need to do anything extra for the linker here? I can't see how we > avoid picking up the host copy. That's handled by the top level Makefile when LLVM=1 is set. There is $KBUILD_LDFLAGS, but we don't do anything with it at the moment in terms of which linker we select; $LD controls which linker we use. LLD can figure out the target based on the object files it's given as input, so it doesn't need any `--target=` flag. When clang is invoked as the compiler or assembler, it does need --target. > Have you tested the compat vDSO with this change? I think we'll just end > up passing two --target options, which is hopefully ok, but thought I'd > better check. Good catch. We don't reuse KBUILD_CFLAGS or KBUILD_AFLAGS for the compat vdso for this very reason. In arch/arm64/kernel/vdso32/Makefile you'll see no references to KBUILD_CFLAGS or KBUILD_AFLAGS; instead we use VDSO_CFLAGS and VDSO_AFLAGS in their stead. But, we could (and should) make this same change for the compat vdso, and drop the need for CROSS_COMPILE_COMPAT for LLVM. Let me play around with the changes Arnd suggested and see if I can get that working. I'm a bit nervous about making this depend on something from the top level Makefile on initial glance; these changes start to become tree wide rather than isolated per arch/, but let's see. Maybe at that point we carry a series in the kbuild tree with acks for the arch/ specific changes from the respective maintainers? Either way, I'll send a v2 that nixes CROSS_COMPILE_COMPAT for LLVM. -- Thanks, ~Nick Desaulniers _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-07-02 17:50 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-07-01 23:55 [PATCH] arm64: drop CROSS_COMPILE for LLVM=1 LLVM_IAS=1 Nick Desaulniers 2021-07-01 23:55 ` Nick Desaulniers 2021-07-02 1:05 ` Tom Stellard 2021-07-02 1:05 ` Tom Stellard 2021-07-02 17:37 ` Nick Desaulniers 2021-07-02 17:37 ` Nick Desaulniers 2021-07-02 11:22 ` Will Deacon 2021-07-02 11:22 ` Will Deacon 2021-07-02 17:50 ` Nick Desaulniers [this message] 2021-07-02 17:50 ` Nick Desaulniers 2021-07-02 11:59 ` Arnd Bergmann 2021-07-02 11:59 ` Arnd Bergmann 2021-07-02 18:29 ` Nick Desaulniers 2021-07-02 18:29 ` Nick Desaulniers 2021-07-04 0:47 ` Nathan Chancellor 2021-07-04 0:47 ` Nathan Chancellor 2021-07-07 19:04 ` Nick Desaulniers 2021-07-07 19:04 ` Nick Desaulniers 2021-07-07 19:08 ` Nathan Chancellor 2021-07-07 19:08 ` Nathan Chancellor 2021-07-07 22:44 ` Nick Desaulniers 2021-07-07 22:44 ` Nick Desaulniers
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