linux-kernel - Re: [PATCH v3 1/3] objtool/LoongArch: Fix fall through warning about efistub

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Message-ID: <pq4h7jgndnt6p45lj4kgubxjd5gidfetugcuf5rcxzxxanzetd@6rrlpjnjsmuy>
Date: Thu, 18 Sep 2025 17:20:13 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Peter Zijlstra <peterz@...radead.org>, 
	Huacai Chen <chenhuacai@...nel.org>, loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] objtool/LoongArch: Fix fall through warning about
 efistub

On Thu, Sep 18, 2025 at 09:44:24AM +0800, Tiezhu Yang wrote:
> (1) libstub doesn't link to vmlinux.o, only link libstub with vmlinux.o
> during the final vmlinux link.
> 
> ----->8-----
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index a3a9759414f4..919c1970ce14 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -164,7 +164,6 @@ CHECKFLAGS += $(shell $(CC) $(KBUILD_CPPFLAGS)
> $(KBUILD_CFLAGS) -dM -E -x c /dev
>  endif
> 
>  libs-y += arch/loongarch/lib/
> -libs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
> 
>  drivers-y              += arch/loongarch/crypto/
> 
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 51367c2bfc21..c664bfb9b15f 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -69,6 +69,12 @@ vmlinux_link()
>                 libs="${KBUILD_VMLINUX_LIBS}"
>         fi
> 
> +       if [ "${SRCARCH}" = "loongarch" ]; then
> +               if is_enabled CONFIG_EFI_STUB; then
> +                       libs="${libs} drivers/firmware/efi/libstub/lib.a"
> +               fi
> +       fi

Right, though I think it would need to be something more generic so that
other arches can have "post-objtool libs" as well.

For example, arch/loongarch/Makefile could have 

  KBUILD_VMLINUX_LIBS_PRELINK += $(objtree)/drivers/firmware/efi/libstub/lib.a

which can be exported by the top-level Makefile:

  export KBUILD_VMLINUX_LIBS_PRELINK

and then used by scripts/link-vmlinux.sh (untested):

  ${ld} ${ldflags} -o ${output} \
	${wl}--whole-archive ${objs} ${wl}--no-whole-archive \
	${wl}--start-group ${libs} ${KBUILD_VMLINUX_LIBS_PRELINK} ${wl}--end-group \
	${kallsymso} ${btf_vmlinux_bin_o} ${arch_vmlinux_o} ${ldlibs}

-- 
Josh