6.7.3.2 -aux-info filename

Output to the given file name prototype declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C/C++. Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (I, N for new or O for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (C or F, respectively, in the following character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration.