Re: [PATCH] Arm64: make setup_virt_paging()'s pa_range_info[] static

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 29/11/2022 15:39, Jan Beulich wrote:
> While not as inefficient as it would be on x86 (due to suitable constant
> loading and register pair storing instructions being available to fill
> some of the fields), having the compiler construct an array of constants
> on the stack still looks odd to me.
The function is only called once at boot. So this seems more a 
micro-optimization than anything else.
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

> ---
> Actual space savings could be had if further converting the field types
> to e.g. unsigned char (all of the values fit in that type).
This is a micro-optimization. If you want to send it then I will review it.

> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -2281,12 +2281,12 @@ void __init setup_virt_paging(void)
>       val |= VTCR_T0SZ(0x18); /* 40 bit IPA */
>       val |= VTCR_SL0(0x1); /* P2M starts at first level */
>   #else /* CONFIG_ARM_64 */
> -    const struct {
> +    static const struct {
>           unsigned int pabits; /* Physical Address Size */
>           unsigned int t0sz;   /* Desired T0SZ, minimum in comment */
>           unsigned int root_order; /* Page order of the root of the p2m */
>           unsigned int sl0;    /* Desired SL0, maximum in comment */
> -    } pa_range_info[] = {
> +    } pa_range_info[] __initconst = {
>           /* T0SZ minimum and SL0 maximum from ARM DDI 0487H.a Table D5-6 */
>           /*      PA size, t0sz(min), root-order, sl0(max) */
>           [0] = { 32,      32/*32*/,  0,          1 },
--
Julien Grall