linux-kernel - Re: [PATCH] LoongArch: Avoid using $r0/$r1 as "mask" for csrxchg

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Message-ID: <c491ab26-dc44-4bc9-b481-29b4ba62f658@linux.dev>
Date: Fri, 23 May 2025 14:43:23 +0800
From: Yanteng Si <si.yanteng@...ux.dev>
To: Huacai Chen <chenhuacai@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev, Xuefeng Li <lixuefeng@...ngson.cn>,
 Guo Ren <guoren@...nel.org>, Xuerui Wang <kernel@...0n.name>,
 Jiaxun Yang <jiaxun.yang@...goat.com>, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org, WANG Rui <wangrui@...ngson.cn>
Subject: Re: [PATCH] LoongArch: Avoid using $r0/$r1 as "mask" for csrxchg

在 5/22/25 8:50 PM, Huacai Chen 写道:
> When building kernel with LLVM there are occasionally such errors:
> 
> In file included from ./include/linux/spinlock.h:59:
> In file included from ./include/linux/irqflags.h:17:
> arch/loongarch/include/asm/irqflags.h:38:3: error: must not be $r0 or $r1
>     38 |                 "csrxchg %[val], %[mask], %[reg]\n\t"
>        |                 ^
> <inline asm>:1:16: note: instantiated into assembly here
>      1 |         csrxchg $a1, $ra, 0
>        |                       ^
> 
> The "mask" of the csrxchg instruction should not be $r0 or $r1, but the
> compiler cannot avoid generating such code currently. So force to use t0
> in the inline asm, in order to avoid using $r0/$r1.
> 
> Cc: stable@...r.kernel.org
> Suggested-by: WANG Rui <wangrui@...ngson.cn>
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
Reviewed-by: Yanteng Si <si.yanteng@...ux.dev>

Thanks,
Yanteng
> ---
>   arch/loongarch/include/asm/irqflags.h | 16 ++++++++++++----
>   1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/loongarch/include/asm/irqflags.h b/arch/loongarch/include/asm/irqflags.h
> index 319a8c616f1f..003172b8406b 100644
> --- a/arch/loongarch/include/asm/irqflags.h
> +++ b/arch/loongarch/include/asm/irqflags.h
> @@ -14,40 +14,48 @@
>   static inline void arch_local_irq_enable(void)
>   {
>   	u32 flags = CSR_CRMD_IE;
> +	register u32 mask asm("t0") = CSR_CRMD_IE;
> +
>   	__asm__ __volatile__(
>   		"csrxchg %[val], %[mask], %[reg]\n\t"
>   		: [val] "+r" (flags)
> -		: [mask] "r" (CSR_CRMD_IE), [reg] "i" (LOONGARCH_CSR_CRMD)
> +		: [mask] "r" (mask), [reg] "i" (LOONGARCH_CSR_CRMD)
>   		: "memory");
>   }
>   
>   static inline void arch_local_irq_disable(void)
>   {
>   	u32 flags = 0;
> +	register u32 mask asm("t0") = CSR_CRMD_IE;
> +
>   	__asm__ __volatile__(
>   		"csrxchg %[val], %[mask], %[reg]\n\t"
>   		: [val] "+r" (flags)
> -		: [mask] "r" (CSR_CRMD_IE), [reg] "i" (LOONGARCH_CSR_CRMD)
> +		: [mask] "r" (mask), [reg] "i" (LOONGARCH_CSR_CRMD)
>   		: "memory");
>   }
>   
>   static inline unsigned long arch_local_irq_save(void)
>   {
>   	u32 flags = 0;
> +	register u32 mask asm("t0") = CSR_CRMD_IE;
> +
>   	__asm__ __volatile__(
>   		"csrxchg %[val], %[mask], %[reg]\n\t"
>   		: [val] "+r" (flags)
> -		: [mask] "r" (CSR_CRMD_IE), [reg] "i" (LOONGARCH_CSR_CRMD)
> +		: [mask] "r" (mask), [reg] "i" (LOONGARCH_CSR_CRMD)
>   		: "memory");
>   	return flags;
>   }
>   
>   static inline void arch_local_irq_restore(unsigned long flags)
>   {
> +	register u32 mask asm("t0") = CSR_CRMD_IE;
> +
>   	__asm__ __volatile__(
>   		"csrxchg %[val], %[mask], %[reg]\n\t"
>   		: [val] "+r" (flags)
> -		: [mask] "r" (CSR_CRMD_IE), [reg] "i" (LOONGARCH_CSR_CRMD)
> +		: [mask] "r" (mask), [reg] "i" (LOONGARCH_CSR_CRMD)
>   		: "memory");
>   }
>