linux-kernel - Re: [PATCH v1] kbuild: Add KBUILD_VMLINUX_LIBS

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Message-ID: <20251121070140.GA780042@ax162>
Date: Fri, 21 Nov 2025 00:01:40 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
	Huacai Chen <chenhuacai@...nel.org>, linux-kbuild@...r.kernel.org,
	linux-efi@...r.kernel.org, loongarch@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] kbuild: Add KBUILD_VMLINUX_LIBS_PRELINK

On Wed, Nov 19, 2025 at 12:27:08PM +0800, Tiezhu Yang wrote:
> In order to only link libstub to the final vmlinux, it can not use the
> current KBUILD_VMLINUX_LIBS, just add KBUILD_VMLINUX_LIBS_PRELINK. This
> is preparation for later patch, no functionality change.
> 
> Link: https://lore.kernel.org/lkml/pq4h7jgndnt6p45lj4kgubxjd5gidfetugcuf5rcxzxxanzetd@6rrlpjnjsmuy/
> Suggested-by: Josh Poimboeuf <jpoimboe@...nel.org>
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
> There is a long discussion in the previous patch:
> https://lore.kernel.org/lkml/20250928085506.4471-1-yangtiezhu@loongson.cn/
> 
> This version is based on 6.18-rc6, split the generic parts out
> into a separate patch to avoid merge conflicts, the other parts
> will send out after the merge window.
> 
>  Makefile                | 1 +
>  scripts/link-vmlinux.sh | 5 ++---
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index d763c2c75cdb..69485f47b794 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1199,6 +1199,7 @@ KBUILD_VMLINUX_OBJS := built-in.a $(patsubst %/, %/lib.a, $(filter %/, $(libs-y)
>  KBUILD_VMLINUX_LIBS := $(filter-out %/, $(libs-y))
>  
>  export KBUILD_VMLINUX_LIBS
> +export KBUILD_VMLINUX_LIBS_PRELINK

This variable name is a little confusing to me since they do get added
to vmlinux during linking, not before. I am not sure of a better one
though, maybe KBUILD_VMLINUX_LIBS_FINAL? It may also make sense to
introduce similar syntax to the existing libs-y syntax, maybe

  final-libs-y

or something like that?

Also, since these objects are no longer in KBUILD_VMLINUX_LIBS, does
this new variable need to be added to any of the other places in the
build system that use KBUILD_VMLINUX_LIBS for things such as build
dependencies?

>  export KBUILD_LDS          := arch/$(SRCARCH)/kernel/vmlinux.lds
>  
>  ifdef CONFIG_TRIM_UNUSED_KSYMS
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 433849ff7529..e72d3254b93f 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -61,12 +61,11 @@ vmlinux_link()
>  	shift
>  
>  	if is_enabled CONFIG_LTO_CLANG || is_enabled CONFIG_X86_KERNEL_IBT; then
> -		# Use vmlinux.o instead of performing the slow LTO link again.
>  		objs=vmlinux.o
> -		libs=
> +		libs="${KBUILD_VMLINUX_LIBS_PRELINK}"
>  	else
>  		objs=vmlinux.a
> -		libs="${KBUILD_VMLINUX_LIBS}"
> +		libs="${KBUILD_VMLINUX_LIBS} ${KBUILD_VMLINUX_LIBS_PRELINK}"
>  	fi
>  
>  	if is_enabled CONFIG_GENERIC_BUILTIN_DTB; then
> -- 
> 2.42.0
>