gdb/dwarf2/parent-map.h

/* DIE indexing 

   Copyright (C) 2024 Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#ifndef GDB_DWARF2_PARENT_MAP_H
#define GDB_DWARF2_PARENT_MAP_H

#include "addrmap.h"
#include "dwarf2/types.h"
#include "gdbsupport/gdb_obstack.h"

class cooked_index_entry;

/* A class that handles mapping from a DIE range to a parent
   entry.

   The generated DWARF can sometimes have the declaration for a method
   in a class (or perhaps namespace) scope, with the definition
   appearing outside this scope... just one of the many bad things
   about DWARF.

   For example, a program like this:

   struct X { int method (); };
   int X::method () { return 23; }

   ... ends up with DWARF like:

    <1><2e>: Abbrev Number: 2 (DW_TAG_structure_type)
       <2f>   DW_AT_name        : X
    ...
    <2><39>: Abbrev Number: 3 (DW_TAG_subprogram)
       <3a>   DW_AT_external    : 1
       <3a>   DW_AT_name        : (indirect string, offset: 0xf): method
    ...
    <1><66>: Abbrev Number: 8 (DW_TAG_subprogram)
       <67>   DW_AT_specification: <0x39>

    Here, the name of DIE 0x66 can't be determined without knowing the
    parent of DIE 0x39.

    In order to handle this situation, we defer certain entries until
    the end of scanning, at which point we'll know the containing
    context of all the DIEs that we might have scanned.  */
class parent_map
{
public:

  parent_map () = default;
  ~parent_map () = default;

  /* Move only.  */
  DISABLE_COPY_AND_ASSIGN (parent_map);
  parent_map (parent_map &&) = default;
  parent_map &operator= (parent_map &&) = default;

  /* A reasonably opaque type that is used as part of a DIE range.  */
  enum addr_type : CORE_ADDR { };

  /* Turn a section offset into a value that can be used in a parent
     map.  */
  static addr_type form_addr (const gdb_byte *info_ptr)
  {
    static_assert (sizeof (addr_type) >= sizeof (uintptr_t));
    return (addr_type) (uintptr_t) info_ptr;
  }

  /* Add a new entry to this map.  DIEs from START to END, inclusive,
     are mapped to PARENT.  */
  void add_entry (addr_type start, addr_type end,
		  const cooked_index_entry *parent)
  {
    gdb_assert (parent != nullptr);
    m_map.set_empty (start, end, (void *) parent);
  }

  /* Look up an entry in this map.  */
  const cooked_index_entry *find (addr_type search) const
  {
    return static_cast<const cooked_index_entry *> (m_map.find (search));
  }

  /* Return a fixed addrmap that is equivalent to this map.  */
  addrmap_fixed *to_fixed (struct obstack *obstack) const
  {
    return new (obstack) addrmap_fixed (obstack, &m_map);
  }

  /* Dump a human-readable form of this map.  */
  void dump (dwarf2_per_bfd *per_bfd) const;

private:

  /* An addrmap that maps from section offsets to cooked_index_entry *.  */
  addrmap_mutable m_map;
};

/* Keep a collection of parent_map objects, and allow for lookups
   across all of them.  */
class parent_map_map
{
public:

  parent_map_map () = default;
  ~parent_map_map () = default;

  DISABLE_COPY_AND_ASSIGN (parent_map_map);

  /* Add a parent_map to this map.  Note that a copy of MAP is made --
     modifications to MAP after this call will have no effect.  */
  void add_map (const parent_map &map)
  {
    m_maps.push_back (map.to_fixed (&m_storage));
  }

  /* Look up an entry in this map.  */
  const cooked_index_entry *find (parent_map::addr_type search) const
  {
    for (const auto &iter : m_maps)
      {
	const cooked_index_entry *result
	  = static_cast<const cooked_index_entry *> (iter->find (search));
	if (result != nullptr)
	  return result;
      }
    return nullptr;
  }

  /* Dump a human-readable form of this collection of parent_maps.  */
  void dump (dwarf2_per_bfd *per_bfd) const;

private:

  /* Storage for the convert maps.  */
  auto_obstack m_storage;

  /* While conceptually this class is a combination of parent_maps, in
     practice it is just a number of fixed maps.  This is important
     because we want to allow concurrent lookups, but a mutable
     addrmap is based on a splay-tree, which is not thread-safe, even
     for nominally read-only lookups.  */
  std::vector<addrmap_fixed *> m_maps;
};

#endif /* GDB_DWARF2_PARENT_MAP_H */