xen/arm64: do not clobber callee saved register in early_putch

x23 is callee saved in the ARM 64 bit calling convention. Use x15 instead
which is a temporary register which need not be preserved.

Fixes a random crash during boot.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

diff --git a/xen/arch/arm/arm64/debug.S b/xen/arch/arm/arm64/debug.S
index f0c77615bd8625c291715032e42b2961ad343de8..38b7c74ff7d69a3c2b9561bb9a9b408d228de4be 100644 (file)
--- a/xen/arch/arm/arm64/debug.S
+++ b/xen/arch/arm/arm64/debug.S
@@ -27,9 +27,9 @@
 /* Print a character on the UART - this function is called by C
  * x0: character to print */
 early_putch:
-        ldr   x23, =FIXMAP_ADDR(FIXMAP_CONSOLE)
-        early_uart_ready x23, 1
-        early_uart_transmit x23, w0
+        ldr   x15, =FIXMAP_ADDR(FIXMAP_CONSOLE)
+        early_uart_ready x15, 1
+        early_uart_transmit x15, w0
         ret
 
 /*