s390/ftrace: enable HAVE_FUNCTION_GRAPH_RETVAL

Add support for tracing return values in the function graph tracer.
This requires return_to_handler() to record gpr2 and the frame pointer

Signed-off-by: Sven Schnelle <[e-mail]>
Reviewed-by: Heiko Carstens <[e-mail]>
Signed-off-by: Heiko Carstens <[e-mail]>

arch/s390/Kconfig

···
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_FUNCTION_ARG_ACCESS_API
 	select HAVE_FUNCTION_ERROR_INJECTION
+	select HAVE_FUNCTION_GRAPH_RETVAL
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER
 	select HAVE_GCC_PLUGINS

arch/s390/include/asm/ftrace.h

···
 	return NULL;
 }
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+struct fgraph_ret_regs {
+	unsigned long gpr2;
+	unsigned long fp;
+};
+
+static __always_inline unsigned long fgraph_ret_regs_return_value(struct fgraph_ret_regs *ret_regs)
+{
+	return ret_regs->gpr2;
+}
+
+static __always_inline unsigned long fgraph_ret_regs_frame_pointer(struct fgraph_ret_regs *ret_regs)
+{
+	return ret_regs->fp;
+}
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
 static __always_inline unsigned long
 ftrace_regs_get_instruction_pointer(const struct ftrace_regs *fregs)
 {

arch/s390/kernel/asm-offsets.c

···
 #include <linux/sched.h>
 #include <linux/purgatory.h>
 #include <linux/pgtable.h>
+#include <linux/ftrace.h>
 #include <asm/idle.h>
 #include <asm/gmap.h>
 #include <asm/stacktrace.h>
···
 	DEFINE(OLDMEM_SIZE, PARMAREA + offsetof(struct parmarea, oldmem_size));
 	DEFINE(COMMAND_LINE, PARMAREA + offsetof(struct parmarea, command_line));
 	DEFINE(MAX_COMMAND_LINE_SIZE, PARMAREA + offsetof(struct parmarea, max_command_line_size));
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	/* function graph return value tracing */
+	OFFSET(__FGRAPH_RET_GPR2, fgraph_ret_regs, gpr2);
+	OFFSET(__FGRAPH_RET_FP, fgraph_ret_regs, fp);
+	DEFINE(__FGRAPH_RET_SIZE, sizeof(struct fgraph_ret_regs));
+#endif
 	return 0;
 }

arch/s390/kernel/mcount.S

···
 SYM_FUNC_START(return_to_handler)
 	stmg	%r2,%r5,32(%r15)
 	lgr	%r1,%r15
-	aghi	%r15,-STACK_FRAME_OVERHEAD
+	aghi	%r15,-(STACK_FRAME_OVERHEAD+__FGRAPH_RET_SIZE)
 	stg	%r1,__SF_BACKCHAIN(%r15)
+	aghik	%r3,%r15,STACK_FRAME_OVERHEAD
+	stg	%r1,__FGRAPH_RET_FP(%r3)
+	stg	%r2,__FGRAPH_RET_GPR2(%r3)
+	lgr	%r2,%r3
 	brasl	%r14,ftrace_return_to_handler
-	aghi	%r15,STACK_FRAME_OVERHEAD
+	aghi	%r15,STACK_FRAME_OVERHEAD+__FGRAPH_RET_SIZE
 	lgr	%r14,%r2
 	lmg	%r2,%r5,32(%r15)
 	BR_EX	%r14