[binutils-gdb] Remove symtab links from dwarf2_psymtab and dwarf2_per_cu_quick_data

[binutils-gdb] Remove symtab links from dwarf2_psymtab and dwarf2_per_cu_quick_data

[Simon Marchi]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=af758d117e1454daebc6135cb70529b9843c3437

commit af758d117e1454daebc6135cb70529b9843c3437
Author: Simon Marchi <simon.marchi@polymtl.ca>
Date:   Wed May 27 11:15:47 2020 -0400

    Remove symtab links from dwarf2_psymtab and dwarf2_per_cu_quick_data
    
    The dwarf2_psymtab and dwarf2_per_cu_quick_data types contain a pointer
    to a compunit_symtab, which is a pointer to the corresponding full
    symtab.  The dwarf2_psymtab and dwarf2_per_cu_quick_data objects are
    going to become objfile-independent, and possibly shared by multiple
    objfiles, whereas compunit_symtab will stay objfile-dependent.  This
    backlink to the compunit_symtab must therefore be removed.
    
    This patch replaces them with a vector in the dwarf2_per_objfile type,
    that serves as a mapping from dwarf2_per_cu_data objects to
    compunit_symtab objects, for this particular objfile.  The vector is
    indexed using the index assigned to the dwarf2_per_cu_data at its
    creation.
    
    I removed the get_compunit_symtab, as it appears to bring not much value
    over calling dwarf2_per_objfile::get_symtab directly.
    
    gdb/ChangeLog:
    
    YYYY-MM-DD  Tom Tromey  <tom@tromey.com>
    YYYY-MM-DD  Simon Marchi  <simon.marchi@efficios.com>
    
            * dwarf2/read.h (struct dwarf2_per_bfd) <num_psymtabs>: New
            method.
            (struct dwarf2_per_objfile) <resize_symtabs, symtab_set_p,
            get_symtab, set_symtab>: New methods.
            <m_symtabs>: New field.
            (struct dwarf2_psymtab): Derive from partial_symtab.
            <readin_p, get_compunit_symtab>: Declare methods.
            * dwarf2/read.c (dwarf2_per_objfile::symtab_set_p,
            dwarf2_per_objfile::get_symtab, dwarf2_per_objfile::set_symtab):
            New methods.
            (struct dwarf2_per_cu_quick_data) <compunit_symtab>: Remove.
            (dw2_do_instantiate_symtab, dw2_instantiate_symtab)
            (dw2_map_expand_apply, dw2_map_symtabs_matching_filename)
            (dw2_symtab_iter_next, dw2_print_stats)
            (dw2_expand_symtabs_with_fullname)
            (dw2_expand_symtabs_matching_one)
            (dw_expand_symtabs_matching_file_matcher)
            (dw2_find_pc_sect_compunit_symtab, dw2_map_symbol_filenames)
            (dw2_debug_names_iterator::next)
            (dw2_debug_names_map_matching_symbols)
            (fill_in_sig_entry_from_dwo_entry, dwarf2_psymtab::read_symtab)
            (process_queue, dwarf2_psymtab::expand_psymtab): Update.
            (dwarf2_psymtab::readin_p, dwarf2_psymtab::get_compunit_symtab):
            New methods.
            (get_compunit_symtab, process_full_comp_unit)
            (process_full_type_unit): Update.
            (dwarf2_build_psymtabs, dwarf2_initialize_objfile, add_type_unit): Call
    
    Change-Id: Iec53d96e0b70a57d8b68408febdac3c6c3d4854b

Diff:
---
 gdb/ChangeLog     |  31 +++++++++++
 gdb/dwarf2/read.c | 162 +++++++++++++++++++++++++++++++-----------------------
 gdb/dwarf2/read.h |  37 ++++++++++++-
 3 files changed, 160 insertions(+), 70 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index bb51c6d2f93..55ee15a98cd 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,34 @@
+2020-05-27  Tom Tromey  <tom@tromey.com>
+	    Simon Marchi  <simon.marchi@efficios.com>
+
+	* dwarf2/read.h (struct dwarf2_per_bfd) <num_psymtabs>: New
+	method.
+	(struct dwarf2_per_objfile) <resize_symtabs, symtab_set_p,
+	get_symtab, set_symtab>: New methods.
+	<m_symtabs>: New field.
+	(struct dwarf2_psymtab): Derive from partial_symtab.
+	<readin_p, get_compunit_symtab>: Declare methods.
+	* dwarf2/read.c (dwarf2_per_objfile::symtab_set_p,
+	dwarf2_per_objfile::get_symtab, dwarf2_per_objfile::set_symtab):
+	New methods.
+	(struct dwarf2_per_cu_quick_data) <compunit_symtab>: Remove.
+	(dw2_do_instantiate_symtab, dw2_instantiate_symtab)
+	(dw2_map_expand_apply, dw2_map_symtabs_matching_filename)
+	(dw2_symtab_iter_next, dw2_print_stats)
+	(dw2_expand_symtabs_with_fullname)
+	(dw2_expand_symtabs_matching_one)
+	(dw_expand_symtabs_matching_file_matcher)
+	(dw2_find_pc_sect_compunit_symtab, dw2_map_symbol_filenames)
+	(dw2_debug_names_iterator::next)
+	(dw2_debug_names_map_matching_symbols)
+	(fill_in_sig_entry_from_dwo_entry, dwarf2_psymtab::read_symtab)
+	(process_queue, dwarf2_psymtab::expand_psymtab): Update.
+	(dwarf2_psymtab::readin_p, dwarf2_psymtab::get_compunit_symtab):
+	New methods.
+	(get_compunit_symtab, process_full_comp_unit)
+	(process_full_type_unit): Update.
+	(dwarf2_build_psymtabs, dwarf2_initialize_objfile, add_type_unit): Call
+
 2020-05-27  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* dwarf2/read.h (dwarf2_per_objfile): Rename to dwarf2_per_bfd,
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index b2734dbee93..a7409b5a1ef 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -1811,6 +1811,38 @@ private:
   dwarf2_per_objfile *m_per_objfile;
 };
 
+/* See read.h.  */
+
+bool
+dwarf2_per_objfile::symtab_set_p (const dwarf2_per_cu_data *per_cu) const
+{
+  gdb_assert (per_cu->index < this->m_symtabs.size ());
+
+  return this->m_symtabs[per_cu->index] != nullptr;
+}
+
+/* See read.h.  */
+
+compunit_symtab *
+dwarf2_per_objfile::get_symtab (const dwarf2_per_cu_data *per_cu) const
+{
+  gdb_assert (per_cu->index < this->m_symtabs.size ());
+
+  return this->m_symtabs[per_cu->index];
+}
+
+/* See read.h.  */
+
+void
+dwarf2_per_objfile::set_symtab (const dwarf2_per_cu_data *per_cu,
+				compunit_symtab *symtab)
+{
+  gdb_assert (per_cu->index < this->m_symtabs.size ());
+  gdb_assert (this->m_symtabs[per_cu->index] == nullptr);
+
+  this->m_symtabs[per_cu->index] = symtab;
+}
+
 /* Try to locate the sections we need for DWARF 2 debugging
    information and return true if we have enough to do something.
    NAMES points to the dwarf2 section names, or is NULL if the standard
@@ -2198,10 +2230,6 @@ struct dwarf2_per_cu_quick_data
      NOTE: This points into dwarf2_per_objfile->per_bfd->quick_file_names_table.  */
   struct quick_file_names *file_names;
 
-  /* The corresponding symbol table.  This is NULL if symbols for this
-     CU have not yet been read.  */
-  struct compunit_symtab *compunit_symtab;
-
   /* A temporary mark bit used when iterating over all CUs in
      expand_symtabs_matching.  */
   unsigned int mark : 1;
@@ -2325,9 +2353,7 @@ dw2_do_instantiate_symtab (struct dwarf2_per_cu_data *per_cu, bool skip_partial)
      with the dwarf queue empty.  */
   dwarf2_queue_guard q_guard (dwarf2_per_objfile);
 
-  if (dwarf2_per_objfile->per_bfd->using_index
-      ? per_cu->v.quick->compunit_symtab == NULL
-      : (per_cu->v.psymtab == NULL || !per_cu->v.psymtab->readin))
+  if (!dwarf2_per_objfile->symtab_set_p (per_cu))
     {
       queue_comp_unit (per_cu, language_minimal);
       load_cu (per_cu, skip_partial);
@@ -2362,7 +2388,8 @@ dw2_instantiate_symtab (struct dwarf2_per_cu_data *per_cu, bool skip_partial)
   struct dwarf2_per_objfile *dwarf2_per_objfile = per_cu->dwarf2_per_objfile;
 
   gdb_assert (dwarf2_per_objfile->per_bfd->using_index);
-  if (!per_cu->v.quick->compunit_symtab)
+
+  if (!dwarf2_per_objfile->symtab_set_p (per_cu))
     {
       free_cached_comp_units freer (dwarf2_per_objfile);
       scoped_restore decrementer = increment_reading_symtab ();
@@ -2370,7 +2397,7 @@ dw2_instantiate_symtab (struct dwarf2_per_cu_data *per_cu, bool skip_partial)
       process_cu_includes (dwarf2_per_objfile);
     }
 
-  return per_cu->v.quick->compunit_symtab;
+  return dwarf2_per_objfile->get_symtab (per_cu);
 }
 
 /* See declaration.  */
@@ -3274,7 +3301,8 @@ dw2_map_expand_apply (struct objfile *objfile,
   struct compunit_symtab *last_made = objfile->compunit_symtabs;
 
   /* Don't visit already-expanded CUs.  */
-  if (per_cu->v.quick->compunit_symtab)
+  dwarf2_per_objfile *per_objfile = get_dwarf2_per_objfile (objfile);
+  if (per_objfile->symtab_set_p (per_cu))
     return 0;
 
   /* This may expand more than one symtab, and we want to iterate over
@@ -3302,7 +3330,7 @@ dw2_map_symtabs_matching_filename
   for (dwarf2_per_cu_data *per_cu : dwarf2_per_objfile->per_bfd->all_comp_units)
     {
       /* We only need to look at symtabs not already expanded.  */
-      if (per_cu->v.quick->compunit_symtab)
+      if (dwarf2_per_objfile->symtab_set_p (per_cu))
 	continue;
 
       quick_file_names *file_data = dw2_get_file_names (per_cu);
@@ -3444,7 +3472,7 @@ dw2_symtab_iter_next (struct dw2_symtab_iterator *iter)
       dwarf2_per_cu_data *per_cu = dwarf2_per_objfile->per_bfd->get_cutu (cu_index);
 
       /* Skip if already read in.  */
-      if (per_cu->v.quick->compunit_symtab)
+      if (dwarf2_per_objfile->symtab_set_p (per_cu))
 	continue;
 
       /* Check static vs global.  */
@@ -3559,7 +3587,7 @@ dw2_print_stats (struct objfile *objfile)
     {
       dwarf2_per_cu_data *per_cu = dwarf2_per_objfile->per_bfd->get_cutu (i);
 
-      if (!per_cu->v.quick->compunit_symtab)
+      if (!dwarf2_per_objfile->symtab_set_p (per_cu))
 	++count;
     }
   printf_filtered (_("  Number of read CUs: %d\n"), total - count);
@@ -3642,7 +3670,7 @@ dw2_expand_symtabs_with_fullname (struct objfile *objfile,
   for (dwarf2_per_cu_data *per_cu : dwarf2_per_objfile->per_bfd->all_comp_units)
     {
       /* We only need to look at symtabs not already expanded.  */
-      if (per_cu->v.quick->compunit_symtab)
+      if (dwarf2_per_objfile->symtab_set_p (per_cu))
 	continue;
 
       quick_file_names *file_data = dw2_get_file_names (per_cu);
@@ -4503,15 +4531,14 @@ dw2_expand_symtabs_matching_one
 {
   if (file_matcher == NULL || per_cu->v.quick->mark)
     {
-      bool symtab_was_null
-	= (per_cu->v.quick->compunit_symtab == NULL);
+      dwarf2_per_objfile *per_objfile = per_cu->dwarf2_per_objfile;
+      bool symtab_was_null = !per_objfile->symtab_set_p (per_cu);
 
-      dw2_instantiate_symtab (per_cu, false);
+      compunit_symtab *symtab = dw2_instantiate_symtab (per_cu, false);
+      gdb_assert (symtab != nullptr);
 
-      if (expansion_notify != NULL
-	  && symtab_was_null
-	  && per_cu->v.quick->compunit_symtab != NULL)
-	expansion_notify (per_cu->v.quick->compunit_symtab);
+      if (expansion_notify != NULL && symtab_was_null)
+	expansion_notify (symtab);
     }
 }
 
@@ -4629,7 +4656,7 @@ dw_expand_symtabs_matching_file_matcher
       per_cu->v.quick->mark = 0;
 
       /* We only need to look at symtabs not already expanded.  */
-      if (per_cu->v.quick->compunit_symtab)
+      if (dwarf2_per_objfile->symtab_set_p (per_cu))
 	continue;
 
       quick_file_names *file_data = dw2_get_file_names (per_cu);
@@ -4767,7 +4794,8 @@ dw2_find_pc_sect_compunit_symtab (struct objfile *objfile,
   if (!data)
     return NULL;
 
-  if (warn_if_readin && data->v.quick->compunit_symtab)
+  dwarf2_per_objfile *per_objfile = get_dwarf2_per_objfile (objfile);
+  if (warn_if_readin && per_objfile->symtab_set_p (data))
     warning (_("(Internal error: pc %s in read in CU, but not in symtab.)"),
 	     paddress (objfile->arch (), pc));
 
@@ -4800,7 +4828,7 @@ dw2_map_symbol_filenames (struct objfile *objfile, symbol_filename_ftype *fun,
 
       for (dwarf2_per_cu_data *per_cu : dwarf2_per_objfile->per_bfd->all_comp_units)
 	{
-	  if (per_cu->v.quick->compunit_symtab)
+	  if (dwarf2_per_objfile->symtab_set_p (per_cu))
 	    {
 	      void **slot = htab_find_slot (visited.get (),
 					    per_cu->v.quick->file_names,
@@ -4813,7 +4841,7 @@ dw2_map_symbol_filenames (struct objfile *objfile, symbol_filename_ftype *fun,
       for (dwarf2_per_cu_data *per_cu : dwarf2_per_objfile->per_bfd->all_comp_units)
 	{
 	  /* We only need to look at symtabs not already expanded.  */
-	  if (per_cu->v.quick->compunit_symtab)
+	  if (dwarf2_per_objfile->symtab_set_p (per_cu))
 	    continue;
 
 	  quick_file_names *file_data = dw2_get_file_names (per_cu);
@@ -5484,7 +5512,7 @@ dw2_debug_names_iterator::next ()
     }
 
   /* Skip if already read in.  */
-  if (per_cu->v.quick->compunit_symtab)
+  if (dwarf2_per_objfile->symtab_set_p (per_cu))
     goto again;
 
   /* Check static vs global.  */
@@ -5725,11 +5753,11 @@ dw2_debug_names_map_matching_symbols
      the psymtab code does.  */
   for (dwarf2_per_cu_data *per_cu : dwarf2_per_objfile->per_bfd->all_comp_units)
     {
-      struct compunit_symtab *cust = per_cu->v.quick->compunit_symtab;
-      if (cust != nullptr)
+      compunit_symtab *symtab = dwarf2_per_objfile->get_symtab (per_cu);
+      if (symtab != nullptr)
 	{
 	  const struct block *block
-	    = BLOCKVECTOR_BLOCK (COMPUNIT_BLOCKVECTOR (cust), block_kind);
+	    = BLOCKVECTOR_BLOCK (COMPUNIT_BLOCKVECTOR (symtab), block_kind);
 	  if (!iterate_over_symbols_terminated (block, name,
 						domain, callback))
 	    break;
@@ -5879,6 +5907,7 @@ dwarf2_initialize_objfile (struct objfile *objfile, dw_index_kind *index_kind)
       dwarf2_per_objfile->per_bfd->quick_file_names_table
 	= create_quick_file_names_table
 	    (dwarf2_per_objfile->per_bfd->all_comp_units.size ());
+      dwarf2_per_objfile->resize_symtabs ();
 
       for (int i = 0; i < (dwarf2_per_objfile->per_bfd->all_comp_units.size ()
 			   + dwarf2_per_objfile->per_bfd->all_type_units.size ()); ++i)
@@ -5899,6 +5928,7 @@ dwarf2_initialize_objfile (struct objfile *objfile, dw_index_kind *index_kind)
   if (dwarf2_read_debug_names (dwarf2_per_objfile))
     {
       *index_kind = dw_index_kind::DEBUG_NAMES;
+      dwarf2_per_objfile->resize_symtabs ();
       return true;
     }
 
@@ -5907,6 +5937,7 @@ dwarf2_initialize_objfile (struct objfile *objfile, dw_index_kind *index_kind)
 			     get_gdb_index_contents_from_section<dwz_file>))
     {
       *index_kind = dw_index_kind::GDB_INDEX;
+      dwarf2_per_objfile->resize_symtabs ();
       return true;
     }
 
@@ -5917,6 +5948,7 @@ dwarf2_initialize_objfile (struct objfile *objfile, dw_index_kind *index_kind)
     {
       global_index_cache.hit ();
       *index_kind = dw_index_kind::GDB_INDEX;
+      dwarf2_per_objfile->resize_symtabs ();
       return true;
     }
 
@@ -5945,6 +5977,8 @@ dwarf2_build_psymtabs (struct objfile *objfile)
       dwarf2_build_psymtabs_hard (dwarf2_per_objfile);
       psymtabs.keep ();
 
+      dwarf2_per_objfile->resize_symtabs ();
+
       /* (maybe) store an index in the cache.  */
       global_index_cache.store (dwarf2_per_objfile);
     }
@@ -6375,6 +6409,8 @@ add_type_unit (struct dwarf2_per_objfile *dwarf2_per_objfile, ULONGEST sig,
 
   signatured_type *sig_type = dwarf2_per_objfile->per_bfd->allocate_signatured_type ();
 
+  dwarf2_per_objfile->resize_symtabs ();
+
   dwarf2_per_objfile->per_bfd->all_type_units.push_back (sig_type);
   sig_type->signature = sig;
   sig_type->per_cu.is_debug_types = 1;
@@ -6410,7 +6446,7 @@ fill_in_sig_entry_from_dwo_entry (struct dwarf2_per_objfile *dwarf2_per_objfile,
   if (dwarf2_per_objfile->per_bfd->using_index)
     {
       gdb_assert (sig_entry->per_cu.v.quick != NULL);
-      gdb_assert (sig_entry->per_cu.v.quick->compunit_symtab == NULL);
+      gdb_assert (!dwarf2_per_objfile->symtab_set_p (&sig_entry->per_cu));
     }
   else
       gdb_assert (sig_entry->per_cu.v.psymtab == NULL);
@@ -8837,7 +8873,8 @@ dwarf2_psymtab::read_symtab (struct objfile *objfile)
   struct dwarf2_per_objfile *dwarf2_per_objfile
     = get_dwarf2_per_objfile (objfile);
 
-  gdb_assert (!readin);
+  gdb_assert (!dwarf2_per_objfile->symtab_set_p (per_cu_data));
+
   /* If this psymtab is constructed from a debug-only objfile, the
      has_section_at_zero flag will not necessarily be correct.  We
      can get the correct value for this flag by looking at the data
@@ -8933,9 +8970,7 @@ process_queue (struct dwarf2_per_objfile *dwarf2_per_objfile)
     {
       dwarf2_queue_item &item = dwarf2_per_objfile->per_bfd->queue.front ();
 
-      if ((dwarf2_per_objfile->per_bfd->using_index
-	   ? !item.per_cu->v.quick->compunit_symtab
-	   : (item.per_cu->v.psymtab && !item.per_cu->v.psymtab->readin))
+      if (!dwarf2_per_objfile->symtab_set_p (item.per_cu)
 	  /* Skip dummy CUs.  */
 	  && item.per_cu->cu != NULL)
 	{
@@ -8990,7 +9025,7 @@ process_queue (struct dwarf2_per_objfile *dwarf2_per_objfile)
 void
 dwarf2_psymtab::expand_psymtab (struct objfile *objfile)
 {
-  gdb_assert (!readin);
+  gdb_assert (!readin_p (objfile));
 
   expand_dependencies (objfile);
 
@@ -8998,6 +9033,24 @@ dwarf2_psymtab::expand_psymtab (struct objfile *objfile)
   gdb_assert (get_compunit_symtab (objfile) != nullptr);
 }
 
+/* See psympriv.h.  */
+
+bool
+dwarf2_psymtab::readin_p (struct objfile *objfile) const
+{
+  dwarf2_per_objfile *per_objfile = get_dwarf2_per_objfile (objfile);
+  return per_objfile->symtab_set_p (per_cu_data);
+}
+
+/* See psympriv.h.  */
+
+compunit_symtab *
+dwarf2_psymtab::get_compunit_symtab (struct objfile *objfile) const
+{
+  dwarf2_per_objfile *per_objfile = get_dwarf2_per_objfile (objfile);
+  return per_objfile->get_symtab (per_cu_data);
+}
+
 /* Trivial hash function for die_info: the hash value of a DIE
    is its offset in .debug_info for this objfile.  */
 
@@ -9535,17 +9588,6 @@ rust_union_quirks (struct dwarf2_cu *cu)
   cu->rust_unions.clear ();
 }
 
-/* Return the symtab for PER_CU.  This works properly regardless of
-   whether we're using the index or psymtabs.  */
-
-static struct compunit_symtab *
-get_compunit_symtab (struct dwarf2_per_cu_data *per_cu)
-{
-  return (per_cu->dwarf2_per_objfile->per_bfd->using_index
-	  ? per_cu->v.quick->compunit_symtab
-	  : per_cu->v.psymtab->compunit_symtab);
-}
-
 /* A helper function for computing the list of all symbol tables
    included by PER_CU.  */
 
@@ -9555,10 +9597,7 @@ recursively_compute_inclusions (std::vector<compunit_symtab *> *result,
 				struct dwarf2_per_cu_data *per_cu,
 				struct compunit_symtab *immediate_parent)
 {
-  void **slot;
-  struct compunit_symtab *cust;
-
-  slot = htab_find_slot (all_children, per_cu, INSERT);
+  void **slot = htab_find_slot (all_children, per_cu, INSERT);
   if (*slot != NULL)
     {
       /* This inclusion and its children have been processed.  */
@@ -9566,8 +9605,9 @@ recursively_compute_inclusions (std::vector<compunit_symtab *> *result,
     }
 
   *slot = per_cu;
+
   /* Only add a CU if it has a symbol table.  */
-  cust = get_compunit_symtab (per_cu);
+  compunit_symtab *cust = per_cu->dwarf2_per_objfile->get_symtab (per_cu);
   if (cust != NULL)
     {
       /* If this is a type unit only add its symbol table if we haven't
@@ -9612,7 +9652,7 @@ compute_compunit_symtab_includes (struct dwarf2_per_cu_data *per_cu)
       int len;
       std::vector<compunit_symtab *> result_symtabs;
       htab_t all_children, all_type_symtabs;
-      struct compunit_symtab *cust = get_compunit_symtab (per_cu);
+      compunit_symtab *cust = per_cu->dwarf2_per_objfile->get_symtab (per_cu);
 
       /* If we don't have a symtab, we can just skip this case.  */
       if (cust == NULL)
@@ -9749,14 +9789,7 @@ process_full_comp_unit (struct dwarf2_per_cu_data *per_cu,
       cust->call_site_htab = cu->call_site_htab;
     }
 
-  if (dwarf2_per_objfile->per_bfd->using_index)
-    per_cu->v.quick->compunit_symtab = cust;
-  else
-    {
-      dwarf2_psymtab *pst = per_cu->v.psymtab;
-      pst->compunit_symtab = cust;
-      pst->readin = true;
-    }
+  dwarf2_per_objfile->set_symtab (per_cu, cust);
 
   /* Push it for inclusion processing later.  */
   dwarf2_per_objfile->per_bfd->just_read_cus.push_back (per_cu);
@@ -9829,14 +9862,7 @@ process_full_type_unit (struct dwarf2_per_cu_data *per_cu,
       cust = sig_type->type_unit_group->compunit_symtab;
     }
 
-  if (dwarf2_per_objfile->per_bfd->using_index)
-    per_cu->v.quick->compunit_symtab = cust;
-  else
-    {
-      dwarf2_psymtab *pst = per_cu->v.psymtab;
-      pst->compunit_symtab = cust;
-      pst->readin = true;
-    }
+  dwarf2_per_objfile->set_symtab (per_cu, cust);
 
   /* Not needed any more.  */
   cu->reset_builder ();
diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
index 4dc9496046f..7631938edb0 100644
--- a/gdb/dwarf2/read.h
+++ b/gdb/dwarf2/read.h
@@ -123,6 +123,11 @@ struct dwarf2_per_bfd
      is allocated on the dwarf2_per_bfd obstack.  */
   signatured_type *allocate_signatured_type ();
 
+  /* Return the number of partial symtabs allocated with allocate_per_cu
+     and allocate_signatured_type so far.  */
+  int num_psymtabs () const
+  { return m_num_psymtabs; }
+
 private:
   /* This function is mapped across the sections and remembers the
      offset and size of each of the debugging sections we are
@@ -278,12 +283,38 @@ struct dwarf2_per_objfile
 				const struct comp_unit_head *cu_header,
 				unsigned int *bytes_read_ptr);
 
+  /* Resize the M_SYMTABS vector to the needed size (the number of partial
+     symtabs allocated by the per-bfd).  */
+  void resize_symtabs ()
+  {
+    /* The symtabs vector should only grow, not shrink.  */
+    gdb_assert (per_bfd->num_psymtabs () >= m_symtabs.size ());
+
+    m_symtabs.resize (per_bfd->num_psymtabs ());
+  }
+
+  /* Return true if the symtab corresponding to PER_CU has been set,
+     false otherwise.  */
+  bool symtab_set_p (const dwarf2_per_cu_data *per_cu) const;
+
+  /* Return the compunit_symtab associated to PER_CU, if it has been created.  */
+  compunit_symtab *get_symtab (const dwarf2_per_cu_data *per_cu) const;
+
+  /* Set the compunit_symtab associated to PER_CU.  */
+  void set_symtab (const dwarf2_per_cu_data *per_cu, compunit_symtab *symtab);
+
   /* Back link.  */
   struct objfile *objfile;
 
   /* Pointer to the data that is (possibly) shared between this objfile and
      other objfiles backed by the same BFD.  */
   struct dwarf2_per_bfd *per_bfd;
+
+private:
+  /* Hold the corresponding compunit_symtab for each CU or TU.  This
+     is indexed by dwarf2_per_cu_data::index.  A NULL value means
+     that the CU/TU has not been expanded yet.  */
+  std::vector<compunit_symtab *> m_symtabs;
 };
 
 /* Get the dwarf2_per_objfile associated to OBJFILE.  */
@@ -291,17 +322,19 @@ struct dwarf2_per_objfile
 dwarf2_per_objfile *get_dwarf2_per_objfile (struct objfile *objfile);
 
 /* A partial symtab specialized for DWARF.  */
-struct dwarf2_psymtab : public standard_psymtab
+struct dwarf2_psymtab : public partial_symtab
 {
   dwarf2_psymtab (const char *filename, struct objfile *objfile,
 		  dwarf2_per_cu_data *per_cu)
-    : standard_psymtab (filename, objfile, 0),
+    : partial_symtab (filename, objfile, 0),
       per_cu_data (per_cu)
   {
   }
 
   void read_symtab (struct objfile *) override;
   void expand_psymtab (struct objfile *) override;
+  bool readin_p (struct objfile *) const override;
+  compunit_symtab *get_compunit_symtab (struct objfile *) const override;
 
   struct dwarf2_per_cu_data *per_cu_data;
 };