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

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@xxxxxxx>

Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

  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:
-/* 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
          adr   x1, hex
-        mov   x3, #8
+        mov   x3, #16
          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 


Julien Grall



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