From 3af4bec9c1db3f003be4d5ae09b6a737e4be1612 Mon Sep 17 00:00:00 2001 From: WangYuli Date: Fri, 11 Apr 2025 15:32:21 +0800 Subject: [PATCH 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 Signed-off-by: Huacai Chen Signed-off-by: WangYuli Link: https://lore.kernel.org/r/F22359AFB6FF9FD8+20250411073222.56820-1-wangyuli@uniontech.com Signed-off-by: Palmer Dabbelt --- 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) { From 550c2aa787d1b06efcb11de1877354502a1237f2 Mon Sep 17 00:00:00 2001 From: WangYuli Date: Fri, 11 Apr 2025 15:32:22 +0800 Subject: [PATCH 2/2] riscv: KGDB: Remove ".option norvc/.option rvc" for kgdb_compiled_break [ Quoting Samuel Holland: ] This is a separate issue, but using ".option rvc" here is a bug. It will unconditionally enable the C extension for the rest of the file, even if the kernel is being built with CONFIG_RISCV_ISA_C=n. [ Quoting Palmer Dabbelt: ] We're just looking at the address of kgdb_compiled_break, so it's fine if it ends up as a c.ebreak. [ Quoting Alexandre Ghiti: ] .option norvc is used to prevent the assembler from using compressed instructions, but it's generally used when we need to ensure the size of the instructions that are used, which is not the case here as noted by Palmer since we only care about the address. So yes it will work fine with C enabled :) So let's just remove them all. Link: https://lore.kernel.org/all/4b4187c1-77e5-44b7-885f-d6826723dd9a@sifive.com/ Link: https://lore.kernel.org/all/mhng-69513841-5068-441d-be8f-2aeebdc56a08@palmer-ri-x1c9a/ Link: https://lore.kernel.org/all/23693e7f-4fff-40f3-a437-e06d827278a5@ghiti.fr/ Fixes: fe89bd2be866 ("riscv: Add KGDB support") Cc: Samuel Holland Cc: Palmer Dabbelt Cc: Alexandre Ghiti Signed-off-by: WangYuli Link: https://lore.kernel.org/r/8B431C6A4626225C+20250411073222.56820-2-wangyuli@uniontech.com Signed-off-by: Palmer Dabbelt --- arch/riscv/kernel/kgdb.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/arch/riscv/kernel/kgdb.c b/arch/riscv/kernel/kgdb.c index 5d1ce8dacaf5..9f3db3503dab 100644 --- a/arch/riscv/kernel/kgdb.c +++ b/arch/riscv/kernel/kgdb.c @@ -257,9 +257,7 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long pc) noinline void arch_kgdb_breakpoint(void) { asm(".global kgdb_compiled_break\n" - ".option norvc\n" - "kgdb_compiled_break: ebreak\n" - ".option rvc\n"); + "kgdb_compiled_break: ebreak\n"); } void kgdb_arch_handle_qxfer_pkt(char *remcom_in_buffer,