diff --git a/gdb/auto-load.c b/gdb/auto-load.c
index 00869fe..a3507bd 100644
--- a/gdb/auto-load.c
+++ b/gdb/auto-load.c
@@ -175,21 +175,18 @@ std::vector<gdb::unique_xmalloc_ptr<char>> auto_load_safe_path_vec;
    substitute_path_component.  */
 
 static std::vector<gdb::unique_xmalloc_ptr<char>>
-auto_load_expand_dir_vars (const char *string)
+auto_load_expand_dir_vars (const std::string &string)
 {
-  char *s = xstrdup (string);
-  substitute_path_component (&s, "$datadir", gdb_datadir);
-  substitute_path_component (&s, "$debugdir", debug_file_directory);
+  std::string s (string);
+  substitute_path_component (s, "$datadir", gdb_datadir);
+  substitute_path_component (s, "$debugdir", debug_file_directory);
 
-  if (debug_auto_load && strcmp (s, string) != 0)
+  if (debug_auto_load && s.compare (string) != 0)
     fprintf_unfiltered (gdb_stdlog,
-			_("auto-load: Expanded $-variables to \"%s\".\n"), s);
+			_("auto-load: Expanded $-variables to \"%s\".\n"),
+			s.c_str ());
 
-  std::vector<gdb::unique_xmalloc_ptr<char>> dir_vec
-    = dirnames_to_char_ptr_vec (s);
-  xfree(s);
-
-  return dir_vec;
+  return dirnames_to_char_ptr_vec (s.c_str ());
 }
 
 /* Update auto_load_safe_path_vec from current AUTO_LOAD_SAFE_PATH.  */
diff --git a/gdb/unittests/utils-selftests.c b/gdb/unittests/utils-selftests.c
index c874de3..4d87162 100644
--- a/gdb/unittests/utils-selftests.c
+++ b/gdb/unittests/utils-selftests.c
@@ -27,13 +27,11 @@ namespace utils {
 static void
 test_substitute_path_component ()
 {
-  auto test = [] (std::string s, const char *from, const char *to,
-		  const char *expected)
+  auto test = [] (std::string s, const std::string from, const std::string to,
+            const std::string expected)
     {
-      char *temp = xstrdup (s.c_str ());
-      substitute_path_component (&temp, from, to);
-      SELF_CHECK (strcmp (temp, expected) == 0);
-      xfree (temp);
+      substitute_path_component (s, from, to);
+      SELF_CHECK (s == expected);
     };
 
   test ("/abc/$def/g", "abc", "xyz", "/xyz/$def/g");
diff --git a/gdb/utils.c b/gdb/utils.c
index 6fb5736..2394443 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -3057,49 +3057,24 @@ parse_pid_to_attach (const char *args)
   return pid;
 }
 
-/* Substitute all occurences of string FROM by string TO in *STRINGP.  *STRINGP
-   must come from xrealloc-compatible allocator and it may be updated.  FROM
-   needs to be delimited by IS_DIR_SEPARATOR or DIRNAME_SEPARATOR (or be
-   located at the start or end of *STRINGP.  */
+/* See utils.h.  */
 
 void
-substitute_path_component (char **stringp, const char *from, const char *to)
+substitute_path_component (std::string &str, const std::string &from,
+			   const std::string &to)
 {
-  char *string = *stringp, *s;
-  const size_t from_len = strlen (from);
-  const size_t to_len = strlen (to);
-
-  for (s = string;;)
+  for (size_t pos = str.find (from); pos != std::string::npos;
+       pos = str.find (from, pos + to.length ()))
     {
-      s = strstr (s, from);
-      if (s == NULL)
-	break;
-
-      if ((s == string || IS_DIR_SEPARATOR (s[-1])
-	   || s[-1] == DIRNAME_SEPARATOR)
-          && (s[from_len] == '\0' || IS_DIR_SEPARATOR (s[from_len])
-	      || s[from_len] == DIRNAME_SEPARATOR))
+      char start = pos == 0 ? str[0] : str[pos - 1];
+      char end = str[pos + from.length ()];
+      if ((pos == 0 || IS_DIR_SEPARATOR (start) || start == DIRNAME_SEPARATOR)
+	  && (end == '\0' || IS_DIR_SEPARATOR (end)
+	      || end == DIRNAME_SEPARATOR))
 	{
-	  char *string_new;
-
-	  string_new
-	    = (char *) xrealloc (string, (strlen (string) + to_len + 1));
-
-	  /* Relocate the current S pointer.  */
-	  s = s - string + string_new;
-	  string = string_new;
-
-	  /* Replace from by to.  */
-	  memmove (&s[to_len], &s[from_len], strlen (&s[from_len]) + 1);
-	  memcpy (s, to, to_len);
-
-	  s += to_len;
+	  str.replace (pos, from.length (), to);
 	}
-      else
-	s++;
     }
-
-  *stringp = string;
 }
 
 #ifdef HAVE_WAITPID
diff --git a/gdb/utils.h b/gdb/utils.h
index 896feb9..bc319de 100644
--- a/gdb/utils.h
+++ b/gdb/utils.h
@@ -292,8 +292,14 @@ private:
 extern int gdb_filename_fnmatch (const char *pattern, const char *string,
 				 int flags);
 
-extern void substitute_path_component (char **stringp, const char *from,
-				       const char *to);
+/* Substitute all occurences of string FROM by string TO in STR.  STR
+   must come from xrealloc-compatible allocator and it may be updated.  FROM
+   needs to be delimited by IS_DIR_SEPARATOR or DIRNAME_SEPARATOR (or be
+   located at the start or end of STR).  */
+
+extern void substitute_path_component (std::string &str,
+				       const std::string &from,
+				       const std::string &to);
 
 std::string ldirname (const char *filename);
 
