linux-kernel - [PATCH v4 1/2] riscv: KGDB: Do not inline arch_kgdb

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Message-ID: <F22359AFB6FF9FD8+20250411073222.56820-1-wangyuli@uniontech.com>
Date: Fri, 11 Apr 2025 15:32:21 +0800
From: WangYuli <wangyuli@...ontech.com>
To: wangyuli@...ontech.com
Cc: alex@...ti.fr,
	aou@...s.berkeley.edu,
	chenhuacai@...nel.org,
	guanwentao@...ontech.com,
	linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	niecheng1@...ontech.com,
	palmer@...belt.com,
	palmerdabbelt@...gle.com,
	paul.walmsley@...ive.com,
	samuel.holland@...ive.com,
	vincent.chen@...ive.com,
	zhanjun@...ontech.com,
	Huacai Chen <chenhuacai@...ngson.cn>
Subject: [PATCH v4 1/2] riscv: KGDB: Do not inline arch_kgdb_breakpoint()

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

There's a potential issue where the compiler might inline
arch_kgdb_breakpoint(), which would then define the kgdb_compiled_break
symbol multiple times, leading to fail to link vmlinux.o.

This isn't merely a potential compilation problem. The intent here
is to determine the global symbol address of kgdb_compiled_break,
and if this function is inlined multiple times, it would logically
be a grave error.

Link: https://lore.kernel.org/all/4b4187c1-77e5-44b7-885f-d6826723dd9a@sifive.com/
Link: https://lore.kernel.org/all/5b0adf9b-2b22-43fe-ab74-68df94115b9a@ghiti.fr/
Link: https://lore.kernel.org/all/23693e7f-4fff-40f3-a437-e06d827278a5@ghiti.fr/
Fixes: fe89bd2be866 ("riscv: Add KGDB support")
Co-developed-by: Huacai Chen <chenhuacai@...ngson.cn>
Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
Signed-off-by: WangYuli <wangyuli@...ontech.com>
---
Changelog:
 *v1->v2:
    1. Add the missing __ASSEMBLY__ check and substitute
".option rvc/norvc" with ".option push/pop".
  v2->v3:
    1. Remove "extern".
    2. Restore the inadvertently deleted .option norvc to prevent
a change in semantics.
  v3->v4:
    1. Replace kgdb_breakinst into kgdb_compiled_break.
    2. Split the origin patch into 2.
---
 arch/riscv/include/asm/kgdb.h | 9 +--------
 arch/riscv/kernel/kgdb.c      | 8 ++++++++
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/include/asm/kgdb.h b/arch/riscv/include/asm/kgdb.h
index 46677daf708b..cc11c4544cff 100644
--- a/arch/riscv/include/asm/kgdb.h
+++ b/arch/riscv/include/asm/kgdb.h
@@ -19,16 +19,9 @@
 
 #ifndef	__ASSEMBLY__
 
+void arch_kgdb_breakpoint(void);
 extern unsigned long kgdb_compiled_break;
 
-static inline void arch_kgdb_breakpoint(void)
-{
-	asm(".global kgdb_compiled_break\n"
-	    ".option norvc\n"
-	    "kgdb_compiled_break: ebreak\n"
-	    ".option rvc\n");
-}
-
 #endif /* !__ASSEMBLY__ */
 
 #define DBG_REG_ZERO "zero"
diff --git a/arch/riscv/kernel/kgdb.c b/arch/riscv/kernel/kgdb.c
index 2e0266ae6bd7..5d1ce8dacaf5 100644
--- a/arch/riscv/kernel/kgdb.c
+++ b/arch/riscv/kernel/kgdb.c
@@ -254,6 +254,14 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long pc)
 	regs->epc = pc;
 }
 
+noinline void arch_kgdb_breakpoint(void)
+{
+	asm(".global kgdb_compiled_break\n"
+	    ".option norvc\n"
+	    "kgdb_compiled_break: ebreak\n"
+	    ".option rvc\n");
+}
+
 void kgdb_arch_handle_qxfer_pkt(char *remcom_in_buffer,
 				char *remcom_out_buffer)
 {
-- 
2.49.0