[Bug symtab/30739] New: [gdb/symtab] wrong

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30739

            Bug ID: 30739
           Summary: [gdb/symtab] wrong
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: symtab
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

I went looking for a test-case that triggers the m_deferred_entries case, and
found gdb.dwarf2/pr13961.exp, which contains:
...
 <1><25>: Abbrev Number: 8 (DW_TAG_class_type)
    <26>   DW_AT_specification: <0x2a>
 <1><2a>: Abbrev Number: 2 (DW_TAG_class_type)
    <2b>   DW_AT_name        : foo
    <2f>   DW_AT_byte_size   : 4
    <30>   DW_AT_decl_file   : 1
    <31>   DW_AT_decl_line   : 1
    <32>   DW_AT_sibling     : <0x44>
...

The DIE at 0x25 contains an intra-CU forward reference, and is deferred.

Then I looked at the resulting cooked index entries:
...
    [12] ((cooked_index_entry *) 0x3dbbd00)
    name:       foo
    canonical:  foo
    DWARF tag:  DW_TAG_class_type
    flags:      0x0 []
    DIE offset: 0x25
    parent:     ((cooked_index_entry *) 0x3dbbca0) [foo]

    [13] ((cooked_index_entry *) 0x3dbbca0)
    name:       foo
    canonical:  foo
    DWARF tag:  DW_TAG_class_type
    flags:      0x0 []
    DIE offset: 0x2a
    parent:     ((cooked_index_entry *) 0)
...
and noticed that 0x2a is the parent of 0x25.

The parent field is documented as:
...
  /* The parent entry.  This is NULL for top-level entries.                     
     Otherwise, it points to the parent entry, such as a namespace or           
     class.  */
  const cooked_index_entry *parent_entry;
...
so I'd expect no parent for 0x25.

I'd expect the current situation to match in a foo::foo name lookup.

The parent is set here:
...
  for (const auto &entry : m_deferred_entries)
    {
      void *obj = m_die_range_map.find (entry.spec_offset);
      cooked_index_entry *parent = static_cast<cooked_index_entry *> (obj);
      m_index_storage->add (entry.die_offset, entry.tag, entry.flags,
                            entry.name, parent, m_per_cu);
    }
...
and AFAICT, we store in m_die_range_map the parent of the respective DIE
(though that's not clear from the comment describing it).

But, for DIE 0x2a we have m_die_range_map.find (0x2a) == 0x2a.

AFAICT, this is an off-by-one error, fixed by:
...
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index dd4fac52ca8..d60a592669a 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -16477,7 +16477,7 @@ cooked_indexer::recurse (cutu_reader *reader,

   if (parent_entry != nullptr)
     {
-      CORE_ADDR start = form_addr (parent_entry->die_offset,
+      CORE_ADDR start = form_addr (parent_entry->die_offset + 1,
                                   reader->cu->per_cu->is_dwz);
       CORE_ADDR end = form_addr (sect_offset (info_ptr - 1 - reader->buffer),
                                 reader->cu->per_cu->is_dwz);
...
which gives us:
...
    [12] ((cooked_index_entry *) 0x41e21f0)
    name:       foo
    canonical:  foo
    DWARF tag:  DW_TAG_class_type
    flags:      0x0 []
    DIE offset: 0x25
    parent:     ((cooked_index_entry *) 0)

    [13] ((cooked_index_entry *) 0x41e2190)
    name:       foo
    canonical:  foo
    DWARF tag:  DW_TAG_class_type
    flags:      0x0 []
    DIE offset: 0x2a
    parent:     ((cooked_index_entry *) 0)
...

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