perf probe: Fix to track down unnamed union/structure members

Fix 'perf probe' to track down unnamed union/structure members.

perf probe did not track down the tree of unnamed union/structure
members, since it just failed to find given "name" in a parent
structure/union.  To solve this issue, I've introduced 2 changes.

- Fix die_find_member() to track down the type-DIE if it is
  unnamed, and if it contains the specified member, returns the
  unnamed member.
  (note that we don't return found member, since unnamed member
   has the offset in the parent structure)
- Fix convert_variable_fields() to track down the unnamed union/
  structure (one-by-one).

With this patch, perf probe can access unnamed fields:
  -----
  #./perf probe -nfx ./perf lock__delete ops 'locked_ops=ops->locked.ops'
  Added new event:
    probe_perf:lock__delete (on lock__delete in /home/mhiramat/ksrc/linux-3/tools/perf/perf with ops locked_ops=ops->locked.ops)

  You can now use it in all perf tools, such as:

          perf record -e probe_perf:lock__delete -aR sleep 1
  -----

Reported-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Report-Link: https://lkml.org/lkml/2015/3/5/431
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150402073312.14482.37942.stgit@localhost.localdomain
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/dwarf-aux.c

@@ -801,10 +801,16 @@ static int __die_find_member_cb(Dwarf_Die *die_mem, void *data)
 {
 	const char *name = data;
 
-	if ((dwarf_tag(die_mem) == DW_TAG_member) &&
-	    die_compare_name(die_mem, name))
-		return DIE_FIND_CB_END;
-
+	if (dwarf_tag(die_mem) == DW_TAG_member) {
+		if (die_compare_name(die_mem, name))
+			return DIE_FIND_CB_END;
+		else if (!dwarf_diename(die_mem)) {	/* Unnamed structure */
+			Dwarf_Die type_die, tmp_die;
+			if (die_get_type(die_mem, &type_die) &&
+			    die_find_member(&type_die, name, &tmp_die))
+				return DIE_FIND_CB_END;
+		}
+	}
 	return DIE_FIND_CB_SIBLING;
 }
 

tools/perf/util/probe-finder.c

@@ -460,7 +460,8 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
 			       " nor array.\n", varname);
 			return -EINVAL;
 		}
-		if (field->ref) {
+		/* While prcessing unnamed field, we don't care about this */
+		if (field->ref && dwarf_diename(vr_die)) {
 			pr_err("Semantic error: %s must be referred by '.'\n",
 			       field->name);
 			return -EINVAL;
@@ -491,6 +492,11 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
 	}
 	ref->offset += (long)offs;
 
+	/* If this member is unnamed, we need to reuse this field */
+	if (!dwarf_diename(die_mem))
+		return convert_variable_fields(die_mem, varname, field,
+						&ref, die_mem);
+
 next:
 	/* Converting next field */
 	if (field->next)