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Re: [PATCH v2 2/4] xen/riscv: add csr_read_safe() helper


  • To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 2 Apr 2026 08:30:24 +0200
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  • Cc: Romain Caritey <Romain.Caritey@xxxxxxxxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 02 Apr 2026 06:30:34 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 31.03.2026 21:04, Oleksii Kurochko wrote:
> @@ -78,6 +80,38 @@
>                             : "memory" );                        \
>  })
>  
> +static always_inline bool csr_read_safe(unsigned long csr,
> +                                        unsigned long *val)
> +{
> +#ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
> +    asm_inline goto (
> +        "1: csrr %[val], %[csr]\n"
> +        ASM_EXTABLE(1b, %l[fault])
> +        : [val] "=&r" (*val)

Why the & when there's only a single insn?

> +        : [csr] "i" (csr)
> +        :
> +        : fault );
> +
> +    return true;
> +
> + fault:
> +    return false;
> +#else
> +    bool allowed = false;
> +
> +    asm_inline volatile (
> +        "1: csrr %[val], %[csr]\n"
> +        "   li %[allowed], 1\n"
> +        "2:\n"
> +        ASM_EXTABLE(1b, 2b)
> +        : [val] "=&r" (*val), [allowed] "+r" (allowed)
> +        : [csr] "i" (csr)
> +        : );

Why the excess colon?

With these adjusted (again happy to do so while committing, so long
as you agree):
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan



 


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