Re: [Xen-devel] [PATCH v2 05/35] xen/arm64: head: Introduce print_reg

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 22 Jul 2019, Julien Grall wrote:
> At the moment, the user should save x30/lr if it cares about it.
> 
> Follow-up patches will introduce more use of putn in place where lr
> should be preserved.
> 
> Furthermore, any user of putn should also move the value to register x0
> if it was stored in a different register.
> 
> For convenience, a new macro is introduced to print a given register.
> The macro will take care for us to move the value to x0 and also
> preserve lr.
> 
> Lastly the new macro is used to replace all the callsite of putn. This
> will simplify rework/review later on.
> 
> Note that CurrentEL is now stored in x5 instead of x4 because the latter
> will be clobbered by the macro print_reg.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

and committed

> ---
>     Changes in v2:
>         - Re-order the instructions to avoid cloberring x4 early. This
>         allows to print content of x4.
> ---
>  xen/arch/arm/arm64/head.S | 29 ++++++++++++++++++++++-------
>  1 file changed, 22 insertions(+), 7 deletions(-)
> 
> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> index b684091aac..63d63bc8ec 100644
> --- a/xen/arch/arm/arm64/head.S
> +++ b/xen/arch/arm/arm64/head.S
> @@ -90,8 +90,25 @@
>          bl    puts    ;    \
>          mov   lr, x3 ;     \
>          RODATA_STR(98, _s)
> +
> +/*
> + * Macro to print the value of register \xb
> + *
> + * Clobbers x0 - x4
> + */
> +.macro print_reg xb
> +        mov   x0, \xb
> +        mov   x4, lr
> +        bl    putn
> +        mov   lr, x4
> +.endm
> +
>  #else /* CONFIG_EARLY_PRINTK */
>  #define PRINT(s)
> +
> +.macro print_reg xb
> +.endm
> +
>  #endif /* !CONFIG_EARLY_PRINTK */
>  
>  /* Load the physical address of a symbol into xb */
> @@ -304,22 +321,20 @@ GLOBAL(init_secondary)
>  #ifdef CONFIG_EARLY_PRINTK
>          ldr   x23, =EARLY_UART_BASE_ADDRESS /* x23 := UART base address */
>          PRINT("- CPU ")
> -        mov   x0, x24
> -        bl    putn
> +        print_reg x24
>          PRINT(" booting -\r\n")
>  #endif
>  
>  common_start:
>  
>          PRINT("- Current EL ")
> -        mrs   x4, CurrentEL
> -        mov   x0, x4
> -        bl    putn
> +        mrs   x5, CurrentEL
> +        print_reg x5
>          PRINT(" -\r\n")
>  
>          /* Are we in EL2 */
> -        cmp   x4, #PSR_MODE_EL2t
> -        ccmp  x4, #PSR_MODE_EL2h, #0x4, ne
> +        cmp   x5, #PSR_MODE_EL2t
> +        ccmp  x5, #PSR_MODE_EL2h, #0x4, ne
>          b.eq  el2 /* Yes */
>  
>          /* OK, we're boned. */
> -- 
> 2.11.0
> 

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