gdb/progspace: Add reverse safe iterator

This patch changes progspace objfile_list insertion so that separate
debug objfiles are placed into the list after the parent objfile,
instead of before.  Additionally qf_require_partial_symbols now returns
a safe_range.

These changes are intended to prepare gdb for on-demand debuginfo
downloading and the downloading of .gdb_index sections.

With on-demand downloading enabled, gdb might need to delete a
.gdb_index quick_symbol_functions from a parent objfile while looping
the objfile's list of quick_symbol_functions because the separate
debug objfile has just been downloaded.  The use of a safe_range
prevents this removal from causing iterator invalidation.

gdb might also download a debuginfo file during symtab expansion.
In this case an objfile will be added to the current progspace's
objfiles_list during iteration over the list (for example, in
iterate_over_symtabs).  We want these loops to also iterate over
newly downloaded objfiles.  So objfiles need to be inserted into
objfiles_list after their parent since it is during the search of
the parent objfile for some symbol or filename that the separate
debug objfile might be downloaded.

To facilitate the safe deletion of objfiles, this patch also adds
basic_safe_reverse_range and basic_safe_reverse_iterator.  This allows
objfiles to be removed from the objfiles_list in a loop without iterator
invalidation.

If a forward safe iterator were to be used, the deletion of an
objfile could invalidate the safe iterator's reference to the next
objfile in the objfiles_list.  This can happen when the deletion
of an objfile causes the deletion of a separate debug objfile that
happens to the be next element in the objfiles_list.

The standard reverse iterator is not suitable for safe objfile deletion.
In order to safely delete the first objfile in the objfiles_list, the
standard reverse iterator's underlying begin iterator would have to be
decremented, resulting in undefined behavior.

A small change was also made to a testcase in py-objfile.exp to
account for the new placement of separate debug objfiles in
objfiles_list.

0 files changed, 0 insertions, 0 deletions