tracing: probeevent: Add $argN for accessing function args

Add $argN special fetch variable for accessing function
arguments. This allows user to trace the Nth argument easily
at the function entry.

Note that this returns most probably assignment of registers
and stacks. In some case, it may not work well. If you need
to access correct registers or stacks you should use perf-probe.

Link: http://lkml.kernel.org/r/152465888632.26224.3412465701570253696.stgit@devbox

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_probe.h

@@ -23,6 +23,7 @@
 #include <linux/stringify.h>
 #include <linux/limits.h>
 #include <linux/uaccess.h>
+#include <linux/bitops.h>
 #include <asm/bitsperlong.h>
 
 #include "trace.h"
@@ -86,6 +87,7 @@ enum fetch_op {
 	FETCH_OP_RETVAL,	/* Return value */
 	FETCH_OP_IMM,		/* Immediate : .immediate */
 	FETCH_OP_COMM,		/* Current comm */
+	FETCH_OP_ARG,		/* Function argument : .param */
 	FETCH_OP_FOFFS,		/* File offset: .immediate */
 	// Stage 2 (dereference) op
 	FETCH_OP_DEREF,		/* Dereference: .offset */
@@ -263,8 +265,13 @@ find_event_file_link(struct trace_probe *tp, struct trace_event_file *file)
 	return NULL;
 }
 
+#define TPARG_FL_RETURN BIT(0)
+#define TPARG_FL_KERNEL BIT(1)
+#define TPARG_FL_FENTRY BIT(2)
+#define TPARG_FL_MASK	GENMASK(2, 0)
+
 extern int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
-		   struct probe_arg *parg, bool is_return, bool is_kprobe);
+		   struct probe_arg *parg, unsigned int flags);
 
 extern int traceprobe_conflict_field_name(const char *name,
 			       struct probe_arg *args, int narg);