[S390] ftrace: add function trace mcount test support

Add support for early test if the function tracer is enabled or
disabled. Saves some extra function calls.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/mcount.S

@@ -21,6 +21,9 @@ _mcount:
 
 	.globl ftrace_caller
 ftrace_caller:
+	larl	%r1,function_trace_stop
+	icm	%r1,0xf,0(%r1)
+	bnzr	%r14
 	stmg	%r2,%r5,32(%r15)
 	stg	%r14,112(%r15)
 	lgr	%r1,%r15
@@ -46,6 +49,9 @@ ftrace_dyn_func:
 
 	.globl _mcount
 _mcount:
+	larl	%r1,function_trace_stop
+	icm	%r1,0xf,0(%r1)
+	bnzr	%r14
 	stmg	%r2,%r5,32(%r15)
 	stg	%r14,112(%r15)
 	lgr	%r1,%r15
@@ -74,21 +80,25 @@ _mcount:
 	.globl ftrace_caller
 ftrace_caller:
 	stm	%r2,%r5,16(%r15)
+	bras	%r1,2f
+0:	.long	ftrace_trace_function
+1:	.long	function_trace_stop
+2:	l	%r2,1b-0b(%r1)
+	icm	%r2,0xf,0(%r2)
+	jnz	3f
 	st	%r14,56(%r15)
-	lr	%r1,%r15
+	lr	%r0,%r15
 	ahi	%r15,-96
 	l	%r3,100(%r15)
 	la	%r2,0(%r14)
-	st	%r1,__SF_BACKCHAIN(%r15)
+	st	%r0,__SF_BACKCHAIN(%r15)
 	la	%r3,0(%r3)
-	bras	%r14,0f
-	.long	ftrace_dyn_func
-0:	l	%r14,0(%r14)
+	l	%r14,0b-0b(%r1)
 	l	%r14,0(%r14)
 	basr	%r14,%r14
 	ahi	%r15,96
-	lm	%r2,%r5,16(%r15)
 	l	%r14,56(%r15)
+3:	lm	%r2,%r5,16(%r15)
 	br	%r14
 
 	.data
@@ -102,21 +112,25 @@ ftrace_dyn_func:
 	.globl _mcount
 _mcount:
 	stm	%r2,%r5,16(%r15)
+	bras	%r1,2f
+0:	.long	ftrace_trace_function
+1:	.long	function_trace_stop
+2:	l	%r2,1b-0b(%r1)
+	icm	%r2,0xf,0(%r2)
+	jnz	3f
 	st	%r14,56(%r15)
-	lr	%r1,%r15
+	lr	%r0,%r15
 	ahi	%r15,-96
 	l	%r3,100(%r15)
 	la	%r2,0(%r14)
-	st	%r1,__SF_BACKCHAIN(%r15)
+	st	%r0,__SF_BACKCHAIN(%r15)
 	la	%r3,0(%r3)
-	bras	%r14,0f
-	.long	ftrace_trace_function
-0:	l	%r14,0(%r14)
+	l	%r14,0b-0b(%r1)
 	l	%r14,0(%r14)
 	basr	%r14,%r14
 	ahi	%r15,96
-	lm	%r2,%r5,16(%r15)
 	l	%r14,56(%r15)
+3:	lm	%r2,%r5,16(%r15)
 	br	%r14
 
 #endif /* CONFIG_DYNAMIC_FTRACE */