linux-kernel - [PATCH AUTOSEL 6.6 45/47] LoongArch: Apply dynamic relocations for LLD

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Message-ID: <20231211135147.380223-45-sashal@kernel.org>
Date:   Mon, 11 Dec 2023 08:50:46 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     WANG Rui <wangrui@...ngson.cn>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        Sasha Levin <sashal@...nel.org>, chenhuacai@...nel.org,
        nathan@...nel.org, loongarch@...ts.linux.dev, llvm@...ts.linux.dev
Subject: [PATCH AUTOSEL 6.6 45/47] LoongArch: Apply dynamic relocations for LLD

From: WANG Rui <wangrui@...ngson.cn>

[ Upstream commit eea673e9d5ea994c60b550ffb684413d3759b3f4 ]

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 relocatable
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>
Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/loongarch/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
index fb0fada43197e..390867fc45b84 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -80,7 +80,7 @@ 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)
-- 
2.42.0