linux-kernel - Re: [PATCH v2] riscv: KGDB: Do not inline arch_kgdb

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Message-ID: <5b0adf9b-2b22-43fe-ab74-68df94115b9a@ghiti.fr>
Date: Thu, 3 Apr 2025 11:58:50 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: WangYuli <wangyuli@...ontech.com>, paul.walmsley@...ive.com,
 palmer@...belt.com, aou@...s.berkeley.edu
Cc: chenhuacai@...nel.org, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org, vincent.chen@...ive.com,
 palmerdabbelt@...gle.com, zhanjun@...ontech.com, niecheng1@...ontech.com,
 guanwentao@...ontech.com, Huacai Chen <chenhuacai@...ngson.cn>
Subject: Re: [PATCH v2] riscv: KGDB: Do not inline arch_kgdb_breakpoint()

Hi WangYuli,

On 02/04/2025 09:42, WangYuli wrote:
> 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_breakinst


I guess you meant 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/
> 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: Add the missing __ASSEMBLY__ check and substitute
> ".option rvc/norvc" with ".option push/pop".
> ---
>   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..d9f6a8fc387f 100644
> --- a/arch/riscv/include/asm/kgdb.h
> +++ b/arch/riscv/include/asm/kgdb.h
> @@ -19,16 +19,9 @@
>   
>   #ifndef	__ASSEMBLY__
>   
> +extern void arch_kgdb_breakpoint(void);


The "extern" is not needed here.


>   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..5873d3970360 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 push\n"


Here you forgot .option norvc. But this fix as mentioned by Samuel 
should be in a separate patch.

Thanks,

Alex


> +	    "kgdb_compiled_break: ebreak\n"
> +	    ".option pop\n");
> +}
> +
>   void kgdb_arch_handle_qxfer_pkt(char *remcom_in_buffer,
>   				char *remcom_out_buffer)
>   {