linux-kernel - Re: [PATCH] LoongArch: Apply dynamic relocations for LLD

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Message-ID: <CAAhV-H72pcXHQi-o71Ct7v+A1BSfNRTSzLrE9KMeS1dwd9KNnw@mail.gmail.com>
Date:   Sun, 26 Nov 2023 22:20:01 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     WANG Rui <wangrui@...ngson.cn>
Cc:     WANG Xuerui <kernel@...0n.name>, Xi Ruoyao <xry111@...111.site>,
        linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev,
        linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev,
        loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] LoongArch: Apply dynamic relocations for LLD

Queued for loongarch-fixes, thanks.

Huacai

On Fri, Nov 24, 2023 at 11:56 AM WANG Rui <wangrui@...ngson.cn> wrote:
>
> For the following assembly code:
>
>      .text
>      .global func
>  func:
>      nop
>
>      .data
>  var:
>      .dword func
>
> When linked with `-pie`, GNU LD populates the `var` variable with the
> pre-relocated value of `func`. However, LLVM LLD does not exhibit the
> same behavior. This issue also arises with the `kernel_entry` in
> arch/loongarch/kernel/head.S:
>
>  _head:
>      .word   MZ_MAGIC                /* "MZ", MS-DOS header */
>      .org    0x8
>      .dword  kernel_entry            /* Kernel entry point */
>
> The correct kernel entry from the MS-DOS header is crucial for jumping
> to vmlinux from zboot. This necessity is why the compressed kernel
> compiled by Clang encounters difficulties in booting.
>
> To address this problem, it is proposed to apply dynamic relocations to
> place with `--apply-dynamic-relocs`.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1962
> Signed-off-by: WANG Rui <wangrui@...ngson.cn>
> ---
>  arch/loongarch/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index 1f0d74403419..05ab85118212 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -83,7 +83,7 @@ endif
>
>  ifeq ($(CONFIG_RELOCATABLE),y)
>  KBUILD_CFLAGS_KERNEL           += -fPIE
> -LDFLAGS_vmlinux                        += -static -pie --no-dynamic-linker -z notext
> +LDFLAGS_vmlinux                        += -static -pie --no-dynamic-linker -z notext $(call ld-option, --apply-dynamic-relocs)
>  endif
>
>  cflags-y += $(call cc-option, -mno-check-zero-division)
> --
> 2.43.0
>
>