The symbol index of a BSD archive is a member named __.SYMDEF, or __.SYMDEF SORTED when the entries are sorted by symbol name. On macOS the 64-bit forms are __.SYMDEF_64 and __.SYMDEF_64 SORTED. The name is usually written the long way, with #1/ in the header.
Layout
0Table size: how many bytes of ranlib entries follow4 or 8 bytes…ranlib entries8 or 16 bytes each…Strings size: how many bytes of names follow4 or 8 bytes…Names: zero-terminatedstrings size
Each ranlib entry is a pair of values: ran_strx, a symbol’s name as an offset into the names, and ran_off, the file offset of the member header that defines it. The 64-bit forms make the sizes and the entries 8 bytes each. The numbers are in the byte order of the machine the library is for.