Re: [XEN RFC PATCH 02/40] xen/arm: Print a 64-bit number in hex from early uart

[Julien Grall <julien@xen.org>]

Hi Wei,

On 11/08/2021 11:23, Wei Chen wrote:
> Current putn function that is using for early print
> only can print low 32-bit of AArch64 register. This
> will lose some important messages while debugging
> with early console. For example:
> (XEN) Bringing up CPU5
> - CPU 0000000100000100 booting -
> Will be truncated to
> (XEN) Bringing up CPU5
> - CPU 00000100 booting -
> 
> In this patch, we increased the print loops and shift
> bits to make putn print 64-bit number.
> 
> Signed-off-by: Wei Chen <wei.chen@arm.com>

Acked-by: Julien Grall <jgrall@amazon.com>

> ---
>   xen/arch/arm/arm64/head.S | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> index aa1f88c764..b32639d7d6 100644
> --- a/xen/arch/arm/arm64/head.S
> +++ b/xen/arch/arm/arm64/head.S
> @@ -862,17 +862,18 @@ puts:
>           ret
>   ENDPROC(puts)
>   
> -/* Print a 32-bit number in hex.  Specific to the PL011 UART.
> +/* Print a 64-bit number in hex.  Specific to the PL011 UART.

As you modify the line, can you take the opportunity to write:

/*
  * Print a 64-bit...

And also drop the second sentence as it the code has not been PL011 
specific for quite a while now.

>    * x0: Number to print.
>    * x23: Early UART base address
>    * Clobbers x0-x3 */
> +#define PRINT_MASK 0xf000000000000000
>   putn:
>           adr   x1, hex
> -        mov   x3, #8
> +        mov   x3, #16
>   1:
>           early_uart_ready x23, 2
> -        and   x2, x0, #0xf0000000    /* Mask off the top nybble */
> -        lsr   x2, x2, #28
> +        and   x2, x0, #PRINT_MASK    /* Mask off the top nybble */
> +        lsr   x2, x2, #60
>           ldrb  w2, [x1, x2]           /* Convert to a char */
>           early_uart_transmit x23, w2
>           lsl   x0, x0, #4             /* Roll it through one nybble at a time */
> 

Cheers,

-- 
Julien Grall