linux-kernel - Re: [PATCH v1 1/2] LoongArch: Make LTO case independent in Makefile

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Message-ID: <20250920061536.GA1460394@ax162>
Date: Fri, 19 Sep 2025 23:15:36 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Huacai Chen <chenhuacai@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
	WANG Rui <wangrui@...ngson.cn>, rust-for-linux@...r.kernel.org,
	loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: Re: [PATCH v1 1/2] LoongArch: Make LTO case independent in Makefile

Hi Tiezhu,

On Tue, Sep 09, 2025 at 05:27:06PM +0800, Tiezhu Yang wrote:
> LTO is not only used for Clang, it maybe used for Rust, make LTO case out
> of CONFIG_CC_HAS_ANNOTATE_TABLEJUMP in Makefile.
> 
> This is preparation for later patch, no function changes.
> 
> Suggested-by: WANG Rui <wangrui@...ngson.cn>
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>  arch/loongarch/Makefile | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index a3a9759414f4..9d80af7f75c8 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -102,16 +102,16 @@ KBUILD_CFLAGS			+= $(call cc-option,-mthin-add-sub) $(call cc-option,-Wa$(comma)
>  
>  ifdef CONFIG_OBJTOOL
>  ifdef CONFIG_CC_HAS_ANNOTATE_TABLEJUMP
> +KBUILD_CFLAGS			+= -mannotate-tablejump
> +else
> +KBUILD_CFLAGS			+= -fno-jump-tables # keep compatibility with older compilers
> +endif
> +ifdef CONFIG_LTO_CLANG
>  # The annotate-tablejump option can not be passed to LLVM backend when LTO is enabled.
>  # Ensure it is aware of linker with LTO, '--loongarch-annotate-tablejump' also needs to
>  # be passed via '-mllvm' to ld.lld.
> -KBUILD_CFLAGS			+= -mannotate-tablejump
> -ifdef CONFIG_LTO_CLANG
>  KBUILD_LDFLAGS			+= -mllvm --loongarch-annotate-tablejump
>  endif
> -else
> -KBUILD_CFLAGS			+= -fno-jump-tables # keep compatibility with older compilers
> -endif
>  endif
>  
>  KBUILD_RUSTFLAGS		+= --target=loongarch64-unknown-none-softfloat -Ccode-model=small
> -- 
> 2.42.0
> 

This change is now in -next as commit b15212824a01 ("LoongArch: Make LTO
case independent in Makefile"), where it breaks the build for clang-18,
as '--loongarch-annotate-tablejump' is unimplemented there but there is
no version check before using it.

  $ make -skj"$(nproc)" ARCH=loongarch LLVM=1 mrproper defconfig

  $ scripts/config -d LTO_NONE -e LTO_CLANG_THIN

  $ make -skj"$(nproc)" ARCH=loongarch LLVM=1 olddefconfig vmlinuz.efi
  ld.lld: error: -mllvm: ld.lld: Unknown command line argument '--loongarch-annotate-tablejump'.
  ...

  $ scripts/config -s CC_HAS_ANNOTATE_TABLEJUMP
  undef

Cheers,
Nathan