Boot CPU and secondary CPUs will use different entry point to C code. At
the moment, the decision on which entry to use is taken within launch().
In order to avoid a branch for the decision and make the code clearer,
launch() is reworked to take in parameters the entry point and its
arguments.
Lastly, document the behavior and the main registers usage within the
function.
Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
---
Changes in v2:
- Use x3 instead of x4
- Add a clobbers section
---
xen/arch/arm/arm64/head.S | 43 +++++++++++++++++++++++++++----------------
1 file changed, 27 insertions(+), 16 deletions(-)
diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index f165dd61ca..7541635102 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -312,6 +312,11 @@ primary_switched:
/* Use a virtual address to access the UART. */
ldr x23, =EARLY_UART_VIRTUAL_ADDRESS
#endif
+ PRINT("- Ready -\r\n")
+ /* Setup the arguments for start_xen and jump to C world */
+ mov x0, x20 /* x0 := Physical offset */
+ mov x1, x21 /* x1 := paddr(FDT) */
+ ldr x2, =start_xen
b launch
ENDPROC(real_start)
@@ -374,6 +379,9 @@ secondary_switched:
/* Use a virtual address to access the UART. */
ldr x23, =EARLY_UART_VIRTUAL_ADDRESS
#endif
+ PRINT("- Ready -\r\n")
+ /* Jump to C world */
+ ldr x2, =start_secondary
b launch
ENDPROC(init_secondary)
@@ -732,23 +740,26 @@ setup_fixmap:
ret
ENDPROC(setup_fixmap)
+/*
+ * Setup the initial stack and jump to the C world
+ *
+ * Inputs:
+ * x0 : Argument 0 of the C function to call
+ * x1 : Argument 1 of the C function to call
+ * x2 : C entry point
+ *
+ * Clobbers x3
+ */
launch:
- PRINT("- Ready -\r\n")
-
- ldr x0, =init_data
- add x0, x0, #INITINFO_stack /* Find the boot-time stack */
- ldr x0, [x0]
- add x0, x0, #STACK_SIZE /* (which grows down from the top). */
- sub x0, x0, #CPUINFO_sizeof /* Make room for CPU save record */
- mov sp, x0
-
- cbnz x22, 1f
-
- mov x0, x20 /* Marshal args: - phys_offset */
- mov x1, x21 /* - FDT */
- b start_xen /* and disappear into the land of C */
-1:
- b start_secondary /* (to the appropriate entry point) */
+ ldr x3, =init_data
+ add x3, x3, #INITINFO_stack /* Find the boot-time stack */
+ ldr x3, [x3]
+ add x3, x3, #STACK_SIZE /* (which grows down from the top). */
