[Dwarf-discuss] Tables which have a unit_length header field must be contiguous.

[Keith Walker]

# Problem

There is no statement if tables must be contiguous or if
there can be padding between the tables.

# Background

Some sections have an implicit assumption that the tables in a section
are contiguous so the section can be processed by serially reading the
section. Sections in this category are:

  .debug_info (Unit Headers, Section 7.5.1)
  .debug_aranges (Address Lookup Tables, Section 6.1.2)
  .debug_names (Name Index Section Header, Section 6.1.1)
  .debug_frame (Section 6.4.1)

All other tables may be accessed indirectly via an offset into a section,
so in theory there is no need to ensure the tables are contiguous provided
the tables are only accessed via these offsets.

However there are use cases when this can be a problem

- The file is "stripped" to just contain line information (.debug_line /
.debug_line_str). The .debug_line_str was added for exactly this use case.
There is now the assumption that the .debug_line section can be processed
serially.

- File dump utilities which list the contents of the sections serially.

Sections with tables which have headers with a unit_length field:

  .debug_aranges (Section 6.1.2)
  .debug_addr (Section 7.27)
  .debug_info / .debug_info.dwo (Section 7.5.1)
  .debug_line / .debug_line.dwo  (Section 6.2.4)
  .debug_loclists / .debug_loclists.dwo (Section 7.29)
  .debug_names (Section 6.1.1)
  .debug_rnglists / .debug_rnglists.dwo (Section 7.28)
  .debug_str_offsets / .debug_str_offsets.dwo (Section 7.26)

Sections with tables/contributions without headers:

  .debug_abbrev / .debug_abbrev.dwo (Section 7.5.3)
  .debug_frame (Section 6.4.1)
  .debug_line_str
  .debug_macro / .debug_macro.dwo (Section 6.3.1)
  .debug_str / .debug_str.dwo

It is a point for discussion on whether to only require the tables
with a unit_length header field be contiguous, or should all tables be
made contiguous.

# Proposed Addition:

7.34 Contiguous Tables

Tables which start with a unit_length field must be contiguous with the
preceding table in the section or start of the section if there is no
preceding table.

# Alternative Proposed Addition:

7.34 Contiguous Tables

Tables must be contiguous with the preceding table in the section or
start of the section if there is no preceding table.
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