s390/ftrace: add FTRACE_GEN_NOP_ASM macro

FTRACE_GEN_NOP_ASM(name) can be used to generate assembly functions with
the required information added to allow tracing via kprobes/ftrace. It
adds the nop instruction which will be patched by ftrace later. If the
compiler supports -mnop-mcount it will also add an entry to the
__mcount_loc section.
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/ftrace.h

@@ -68,4 +68,32 @@ static inline bool arch_syscall_match_sym_name(const char *sym,
 }
 
 #endif /* __ASSEMBLY__ */
+
+#ifdef CONFIG_FUNCTION_TRACER
+
+#define FTRACE_NOP_INSN .word 0xc004, 0x0000, 0x0000 /* brcl 0,0 */
+
+#ifndef CC_USING_HOTPATCH
+
+#define FTRACE_GEN_MCOUNT_RECORD(name)		\
+	.section __mcount_loc, "a", @progbits;	\
+	.quad name;				\
+	.previous;
+
+#else /* !CC_USING_HOTPATCH */
+
+#define FTRACE_GEN_MCOUNT_RECORD(name)
+
+#endif /* !CC_USING_HOTPATCH */
+
+#define FTRACE_GEN_NOP_ASM(name)		\
+	FTRACE_GEN_MCOUNT_RECORD(name)		\
+	FTRACE_NOP_INSN
+
+#else /* CONFIG_FUNCTION_TRACER */
+
+#define FTRACE_GEN_NOP_ASM(name)
+
+#endif /* CONFIG_FUNCTION_TRACER */
+
 #endif /* _ASM_S390_FTRACE_H */