Defining Py_GCC_ATTRIBUTE finds even some more undocumented functions.
diff --git a/Doc/tools/undoc_symbols.py b/Doc/tools/undoc_symbols.py
index d603a36..3d776fa 100644
--- a/Doc/tools/undoc_symbols.py
+++ b/Doc/tools/undoc_symbols.py
@@ -77,7 +77,7 @@
 
     incfiles = os.path.join(incdir, INCLUDEPATTERN)
 
-    fp = os.popen("ctags -IPyAPI_FUNC --c-types=%s -f - %s"
+    fp = os.popen("ctags -IPyAPI_FUNC -IPy_GCC_ATTRIBUTE --c-types=%s -f - %s"
                   % (TAG_KINDS, incfiles))
     dict = findnames(fp, prefix)
     names = dict.keys()