linux-kernel - Re: [PATCH 4/4] Makefile: lld: set -O2 linker flag when linking with LLD

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Date:   Thu, 7 Feb 2019 23:07:37 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     ndesaulniers@...gle.com
Cc:     yamada.masahiro@...ionext.com, Rui Ueyama <ruiu@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] Makefile: lld: set -O2 linker flag when linking with
 LLD

On Thu, Feb 07, 2019 at 02:01:52PM -0800, ndesaulniers@...gle.com wrote:
> -O2 enables tail merging of string table strings.
> 
> For arm64:
> 0.34% size improvement with lld -O2 over lld for vmlinux.
> 3.30% size improvement with lld -O2 over lld for Image.lz4-dtb.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/343
> Suggested-by: Rui Ueyama <ruiu@...gle.com>
> Suggested-by: Nathan Chancellor <natechancellor@...il.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>

> ---
>  Makefile | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index 6307c17259ea..c07208ec49d4 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -718,6 +718,10 @@ else
>  KBUILD_CFLAGS += -Wno-unused-but-set-variable
>  endif
>  
> +ifdef CONFIG_LD_IS_LLD
> +KBUILD_LDFLAGS += -O2
> +endif
> +
>  KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
>  ifdef CONFIG_FRAME_POINTER
>  KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
> -- 
> 2.20.1.791.gb4d0f1c61a-goog
>