Copyright (C) 2021.  David Anderson.
This simple file is hereby placed in the Public Domain.
This file documents the arrangement of line table headers
across all Standard versions of DWARF and some special
experimental line tables.
Line Table Header variations.
The experimental version has a distinct version
number of 0xf006 so cannot be confused with DWARF4 or 5.
DWversion
2,3,4,5 meaning the DWARF standards
x meaning gcc's experimental two level line table.
2345x  1. unit_length (4 or 12 bytes)
2345x  2. version (2 bytes, for x is 0xF006)
5      2.1  address_size
5      2.2  segment_selector_size
2345x  3. header_length (4 or 8 bytes)
2345x  4. minimum_instruction_length (1 byte)
45  x  5. maximum_operations_per_instruction (1 byte)
2345x  6. default_is_stmt (1 byte)
2345x  7. line_base (1 byte)
2345x  8. line_range (1 byte)
2345x  9. opcode_base (1 byte)
2345x 10. standard_opcode_lengths (array of length opcode_base - 1)
234 x 11. include directories (for x just one NUL byte(empty list))
234 x 12. file_names (for x just one NUL byte(empty list))
x     13. fake_extended_op (5 bytes: 00 FF FF 7F 7F)
x     14. logicals_table_offset (4 or 8 bytes)
x     15. actuals_table_offset (4 or 8 bytes)
x5    16. directory_entry_format_count (1 byte)
x5    17. directory_entry_format (sequence of unsigned LEB128 pairs)
x5    18. directories_count (unsigned LEB128)
x5    19. directories (sequence of directory entries)
x5    20. file_name_entry_format_count (1 byte)
x5    21. file_name_entry_format (sequence of unsigned LEB128 pairs)
x5    22. file_names_count (unsigned LEB128)
x5    23. file_names (sequence of directory entries)
x     24. subprogram_entry_format_count (1 byte)
x     25. subprogram_entry_format (sequence of unsigned LEB128 pairs)
x     26. subprograms_count (unsigned LEB128)
x     27. subprograms (sequence of directory entries)