tracing/function-return-tracer: call prepare_ftrace_return by registers

Impact: Optimize a bit the function return tracer

This patch changes the calling convention of prepare_ftrace_return to
pass its arguments by register. This will optimize it a bit and
prepare it to support dynamic tracing.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/entry_32.S

@@ -1217,12 +1217,9 @@ trace_return:
 	pushl %eax
 	pushl %ecx
 	pushl %edx
-	movl 0xc(%esp), %eax
-	pushl %eax
+	movl 0xc(%esp), %edx
 	lea 0x4(%ebp), %eax
-	pushl %eax
 	call prepare_ftrace_return
-	addl $8, %esp
 	popl %edx
 	popl %ecx
 	popl %eax

arch/x86/kernel/ftrace.c

@@ -95,7 +95,6 @@ unsigned long ftrace_return_to_handler(void)
  * Hook the return address and push it in the stack of return addrs
  * in current thread info.
  */
-asmlinkage
 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
 {
 	unsigned long old;