arm64: ftrace: always pass instrumented pc in x0

The core ftrace hooks take the instrumented PC in x0, but for some
reason arm64's prepare_ftrace_return() takes this in x1.

For consistency, let's flip the argument order and always pass the
instrumented PC in x0.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Torsten Duwe <duwe@suse.de>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/entry-ftrace.S

@@ -176,10 +176,10 @@ ENDPROC(ftrace_stub)
  * and run return_to_handler() later on its exit.
  */
 ENTRY(ftrace_graph_caller)
-	mcount_get_lr_addr	  x0	//     pointer to function's saved lr
-	mcount_get_pc		  x1	//     function's pc
+	mcount_get_pc		  x0	//     function's pc
+	mcount_get_lr_addr	  x1	//     pointer to function's saved lr
 	mcount_get_parent_fp	  x2	//     parent's fp
-	bl	prepare_ftrace_return	// prepare_ftrace_return(&lr, pc, fp)
+	bl	prepare_ftrace_return	// prepare_ftrace_return(pc, &lr, fp)
 
 	mcount_exit
 ENDPROC(ftrace_graph_caller)

arch/arm64/kernel/ftrace.c

@@ -211,7 +211,7 @@ int __init ftrace_dyn_arch_init(void)
  *
  * Note that @frame_pointer is used only for sanity check later.
  */
-void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
+void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
 			   unsigned long frame_pointer)
 {
 	unsigned long return_hooker = (unsigned long)&return_to_handler;