perf dwarf-aux: Add die_find_func_rettype()

The die_find_func_rettype() is to find a debug entry for the given
function name and sets the type information of the return value.  By
convention, it'd return the pointer to the type die (should be the
same as the given mem_die argument) if found, or NULL otherwise.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20240319055115.4063940-5-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/dwarf-aux.c

@@ -696,6 +696,49 @@ Dwarf_Die *die_find_inlinefunc(Dwarf_Die *sp_die, Dwarf_Addr addr,
 	return die_mem;
 }
 
+static int __die_find_func_rettype_cb(Dwarf_Die *die_mem, void *data)
+{
+	const char *func_name;
+
+	if (dwarf_tag(die_mem) != DW_TAG_subprogram)
+		return DIE_FIND_CB_SIBLING;
+
+	func_name = dwarf_diename(die_mem);
+	if (func_name && !strcmp(func_name, data))
+		return DIE_FIND_CB_END;
+
+	return DIE_FIND_CB_SIBLING;
+}
+
+/**
+ * die_find_func_rettype - Search a return type of function
+ * @cu_die: a CU DIE
+ * @name: target function name
+ * @die_mem: a buffer for result DIE
+ *
+ * Search a non-inlined function which matches to @name and stores the
+ * return type of the function to @die_mem and returns it if found.
+ * Returns NULL if failed.  Note that it doesn't needs to find a
+ * definition of the function, so it doesn't match with address.
+ * Most likely, it can find a declaration at the top level.  Thus the
+ * callback function continues to sibling entries only.
+ */
+Dwarf_Die *die_find_func_rettype(Dwarf_Die *cu_die, const char *name,
+				 Dwarf_Die *die_mem)
+{
+	Dwarf_Die tmp_die;
+
+	cu_die = die_find_child(cu_die, __die_find_func_rettype_cb,
+				(void *)name, &tmp_die);
+	if (!cu_die)
+		return NULL;
+
+	if (die_get_real_type(&tmp_die, die_mem) == NULL)
+		return NULL;
+
+	return die_mem;
+}
+
 struct __instance_walk_param {
 	void    *addr;
 	int	(*callback)(Dwarf_Die *, void *);

tools/perf/util/dwarf-aux.h

@@ -94,6 +94,10 @@ Dwarf_Die *die_find_top_inlinefunc(Dwarf_Die *sp_die, Dwarf_Addr addr,
 Dwarf_Die *die_find_inlinefunc(Dwarf_Die *sp_die, Dwarf_Addr addr,
 			       Dwarf_Die *die_mem);
 
+/* Search a non-inlined function by name and returns its return type */
+Dwarf_Die *die_find_func_rettype(Dwarf_Die *sp_die, const char *name,
+				 Dwarf_Die *die_mem);
+
 /* Walk on the instances of given DIE */
 int die_walk_instances(Dwarf_Die *in_die,
 		       int (*callback)(Dwarf_Die *, void *), void *data);