[Bug gdb/23504] New: index cache: Produce and consume DWARF5 format

[simon.marchi at ericsson dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=23504

Bug ID: 23504
Summary: index cache: Produce and consume DWARF5 format
Product: gdb
Version: HEAD
Status: NEW
Severity: normal
Priority: P2
Component: gdb
Assignee: unassigned at sourceware dot org
Reporter: simon.marchi at ericsson dot com
Target Milestone: ---

Currently, the DWARF index cache only produces and consumes files in GDB's own
index format. We should make it use the DWARF5 format too.

The main difficulty is that producing a DWARF5 format generates two files:

- The index itself (.debug_names)
- An addendum to the string section (.debug_str)

It is expected that the .debug_str addendum will be appended to the possibly
existing .debug_str section of the existing binary. There are offset values in
.debug_names that are therefore larger than the size of the original
.debug_str, if they point to strings in the addendum.

With the index cache, we don't modify the original binary. So when loading a
DWARF5 index from the index cache, we need some special treatment: if
requesting a string at an offset larger than the size of the original
.debug_str, we actually need to look it up in the .debug_str addendum (with the
offset adjusted, of course).