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

[Julien Grall <julien.grall@xxxxxxx>]

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>

---
    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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