Re: [PATCH 1/7] gdb: implement readnow_functions::find_pc_sect_compunit_symtab

["Jan Vraný" <Jan.Vrany@labware.com>]

On Thu, 2026-02-19 at 13:01 -0700, Tom Tromey wrote:
> > > > > > "Jan" == Jan Vrany <jan.vrany@labware.com> writes:
> 
> Jan> +struct compunit_symtab *
> Jan> +readnow_functions::find_pc_sect_compunit_symtab
> Jan> +     (struct objfile *objfile,
> Jan> +      bound_minimal_symbol msymbol,
> Jan> +      CORE_ADDR pc,
> Jan> +      struct obj_section *section,
> Jan> +      int warn_if_readin)
> Jan> +{
> Jan> +  dwarf2_per_objfile *per_objfile = get_dwarf2_per_objfile (objfile);
> Jan> +  dwarf2_per_bfd *per_bfd = per_objfile->per_bfd;
> Jan> +
> Jan> +  /* This invariant is documented in read.h  */
> Jan> +  gdb_assert (per_bfd->index_table == nullptr);
> Jan> +
> Jan> +  /* Since we have no index, we simply walk all units until matching CU is
> Jan> +     found (of there are no more CUs).  */
> Jan> +  for (int i = 0; i < per_bfd->all_units.size (); i++)
> Jan> +    {
> Jan> +      dwarf2_per_cu *data = per_bfd->all_units[i].get ();
> Jan> +      compunit_symtab *result = find_pc_sect_compunit_symtab_includes (
> Jan> +	dw2_instantiate_symtab (data, per_objfile, false), pc);
> 
> There shouldn't be any need to instantiate a symtab here, since for
> readnow they are all already expanded.

Not always. dwarf2_base_index_functions::expand_all_symtabs skips 
"partial symtabs", so in some cases not all symtabs are instantiated.

An example of this is dwz-symtabs.exp. If I change the code as

--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -2181,8 +2181,10 @@ readnow_functions::find_pc_sect_compunit_symtab
   for (int i = 0; i < per_bfd->all_units.size (); i++)
     {
       dwarf2_per_cu *data = per_bfd->all_units[i].get ();
-      compunit_symtab *result = find_pc_sect_compunit_symtab_includes (
-       dw2_instantiate_symtab (data, per_objfile, false), pc);
+
+      gdb_assert (per_objfile->symtab_set_p (data));
+      compunit_symtab *result = find_pc_sect_compunit_symtab_includes
+       (per_objfile->get_symtab (data), pc);
       if (result != nullptr)
        return result;
     }

I get an assertion failure. 

dw2_instantiate_symtab checks if the symtab has been instantiated and if 
yes, it's an no-op so calling it should not hurt much.

Jan

> 
> Tom