linux-kernel - Re: [PATCH 3/5] LoongArch: Support relocation against _GLOBAL_OFFSET_TABLE

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Date:   Thu, 28 Jul 2022 14:41:16 +0800
From:   Xi Ruoyao <xry111@...111.site>
To:     Jinyang He <hejinyang@...ngson.cn>, loongarch@...ts.linux.dev
Cc:     linux-kernel@...r.kernel.org, WANG Xuerui <kernel@...0n.name>,
        Huacai Chen <chenhuacai@...nel.org>
Subject: Re: [PATCH 3/5] LoongArch: Support relocation against
 _GLOBAL_OFFSET_TABLE_

On Thu, 2022-07-28 at 09:02 +0800, Jinyang He wrote:

> Hi, Ruoyao,
> 
> It is possible to create a symbol when linking, which means
> maybe we can add _GLOBAL_OFFSET_TABLE_ in 'module.lds.h'.
> What do you think about it?

Hi Jinyang,

I think you are right, this patch can be replaced with the following,
which is much simpler.

-- >8 --

With the stack-based relocations, the assembler emits three relocations
to push the PC-relative offset of a GOT entry:

    R_LARCH_SOP_PUSH_PCREL _GLOBAL_OFFSET_TABLE_
    R_LARCH_SOP_PUSH_GPREL foo
    R_LARCH_SOP_ADD

In normal relocatable ELF object files, "_GLOBAL_OFFSET_TABLE_" is
undefined in the symtab and the BFD linker generates it on final link.
Define it for kernel modules so we will be able to really use
R_LARCH_SOP_PUSH_GPREL relocation.

Note that we need to use "HIDDEN" to make it a local symbol because each
kernel module has its own GOT and the reference to it should not be
resolved to the GOT in the main kernel image.

Suggested-by: Jinyang He <hejinyang@...ngson.cn>
Signed-off-by: Xi Ruoyao <xry111@...111.site>
---
 arch/loongarch/include/asm/module.lds.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/loongarch/include/asm/module.lds.h b/arch/loongarch/include/asm/module.lds.h
index 57bbd0cedd26..42b7cca0b947 100644
--- a/arch/loongarch/include/asm/module.lds.h
+++ b/arch/loongarch/include/asm/module.lds.h
@@ -4,5 +4,5 @@ SECTIONS {
 	. = ALIGN(4);
 	.plt : { BYTE(0) }
 	.plt.idx : { BYTE(0) }
-	.got : { BYTE(0) }
+	.got : { HIDDEN(_GLOBAL_OFFSET_TABLE_ = .); BYTE(0) }
 }
-- 
2.37.0