linux-kernel - Re: [PATCH v2] arm64: vdso32: drop -no-integrated-as flag

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Message-ID: <a2ddf4d2-110a-9290-f766-3925e451ddef@arm.com>
Date:   Thu, 15 Apr 2021 14:31:06 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH v2] arm64: vdso32: drop -no-integrated-as flag



On 4/14/21 10:45 PM, Nick Desaulniers wrote:
> Clang can assemble these files just fine; this is a relic from the top
> level Makefile conditionally adding this. We no longer need --prefix,
> --gcc-toolchain, or -Qunused-arguments flags either with this change, so
> remove those too.
> 
> To test building:
> $ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- \
>   CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 LLVM_IAS=1 \
>   defconfig arch/arm64/kernel/vdso32/
> 
> Suggested-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

The patch looks fine, but I have one question: the kernel requires as a minimum
Clang/LLVM version 10.0.1. Did you verify that with that version compat vDSOs
still builds and works correctly?

Otherwise:

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@....com>

> ---
> Changes V1 -> V2:
> * Remove --prefix, --gcc-toolchain, COMPAT_GCC_TOOLCHAIN, and
>   COMPAT_GCC_TOOLCHAIN_DIR as per Nathan.
> * Credit Nathan with Suggested-by tag.
> * Remove -Qunused-arguments.
> * Update commit message.
> 
>  arch/arm64/kernel/vdso32/Makefile | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> index 789ad420f16b..3dba0c4f8f42 100644
> --- a/arch/arm64/kernel/vdso32/Makefile
> +++ b/arch/arm64/kernel/vdso32/Makefile
> @@ -10,15 +10,7 @@ include $(srctree)/lib/vdso/Makefile
>  
>  # Same as cc-*option, but using CC_COMPAT instead of CC
>  ifeq ($(CONFIG_CC_IS_CLANG), y)
> -COMPAT_GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE_COMPAT)elfedit))
> -COMPAT_GCC_TOOLCHAIN := $(realpath $(COMPAT_GCC_TOOLCHAIN_DIR)/..)
> -
>  CC_COMPAT_CLANG_FLAGS := --target=$(notdir $(CROSS_COMPILE_COMPAT:%-=%))
> -CC_COMPAT_CLANG_FLAGS += --prefix=$(COMPAT_GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE_COMPAT))
> -CC_COMPAT_CLANG_FLAGS += -no-integrated-as -Qunused-arguments
> -ifneq ($(COMPAT_GCC_TOOLCHAIN),)
> -CC_COMPAT_CLANG_FLAGS += --gcc-toolchain=$(COMPAT_GCC_TOOLCHAIN)
> -endif
>  
>  CC_COMPAT ?= $(CC)
>  CC_COMPAT += $(CC_COMPAT_CLANG_FLAGS)
> 

-- 
Regards,
Vincenzo