linux-kernel - [PATCH v2] LoongArch: KGDB: Rework arch_kgdb

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Message-ID: <943E06D656E4E707+20250321141001.109916-1-wangyuli@uniontech.com>
Date: Fri, 21 Mar 2025 22:10:01 +0800
From: WangYuli <wangyuli@...ontech.com>
To: chenhuacai@...nel.org,
	kernel@...0n.name
Cc: wangyuli@...ontech.com,
	guanwentao@...ontech.com,
	wentao@...ontech.com,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	zhangqing@...ngson.cn,
	zhoubinbin@...ngson.cn,
	lihui@...ngson.cn,
	rdunlap@...radead.org,
	chenhuacai@...ngson.cn,
	zhanjun@...ontech.com,
	niecheng1@...ontech.com
Subject: [PATCH v2] LoongArch: KGDB: Rework arch_kgdb_breakpoint() implementation

The arch_kgdb_breakpoint() function defines the kgdb_breakinst
symbol using inline assembly.

There's a potential issue where the compiler might inline
arch_kgdb_breakpoint(), which would then define the kgdb_breakinst
symbol multiple times, leading to a linker error.

To prevent this, declare arch_kgdb_breakpoint() as noline.

Fix follow error with LLVM-19 *only* when LTO_CLANG_FULL:
    LD      vmlinux.o
  ld.lld-19: error: ld-temp.o <inline asm>:3:1: symbol 'kgdb_breakinst' is already defined
  kgdb_breakinst: break 2
  ^

Additionally, remove "nop" here because it's meaningless for LoongArch
here.

Fixes: e14dd076964e ("LoongArch: Add basic KGDB & KDB support")
Co-developed-by: Winston Wen <wentao@...ontech.com>
Signed-off-by: Winston Wen <wentao@...ontech.com>
Co-developed-by: Wentao Guan <guanwentao@...ontech.com>
Signed-off-by: Wentao Guan <guanwentao@...ontech.com>
Co-developed-by: Huacai Chen <chenhuacai@...ngson.cn>
Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
Tested-by: Yuli Wang <wangyuli@...ontech.com>
Tested-by: Binbin Zhou <zhoubinbin@...ngson.cn>
Signed-off-by: Yuli Wang <wangyuli@...ontech.com>
---
Changelog:
 *v1->v2:
    1. Drop the nop which is no effect for LoongArch here.
    2. Add "STACK_FRAME_NON_STANDARD" for arch_kgdb_breakpoint() to
avoid the objtool warning.
---
 arch/loongarch/kernel/kgdb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/loongarch/kernel/kgdb.c b/arch/loongarch/kernel/kgdb.c
index 445c452d72a7..38bd0561d7d5 100644
--- a/arch/loongarch/kernel/kgdb.c
+++ b/arch/loongarch/kernel/kgdb.c
@@ -224,13 +224,13 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long pc)
 	regs->csr_era = pc;
 }
 
-void arch_kgdb_breakpoint(void)
+noinline void arch_kgdb_breakpoint(void)
 {
 	__asm__ __volatile__ (			\
 		".globl kgdb_breakinst\n\t"	\
-		"nop\n"				\
 		"kgdb_breakinst:\tbreak 2\n\t"); /* BRK_KDB = 2 */
 }
+STACK_FRAME_NON_STANDARD(arch_kgdb_breakpoint);
 
 /*
  * Calls linux_debug_hook before the kernel dies. If KGDB is enabled,
-- 
2.49.0