[gdb/symtab] Fix off-by-one error in cooked_indexer::recurse

Test-case gdb.dwarf2/pr13961.exp 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 during
DIE indexing in the cooked_index, by adding it to m_deferred_entries.

The resulting cooked index entries are:
...
        [25] ((cooked_index_entry *) 0x333b5d0)
        name:       foo
        canonical:  foo
        qualified:  foo
        DWARF tag:  DW_TAG_class_type
        flags:      0x0 []
        DIE offset: 0x2a
        parent:     ((cooked_index_entry *) 0)

        [26] ((cooked_index_entry *) 0x333b630)
        name:       foo
        canonical:  foo
        qualified:  foo::foo
        DWARF tag:  DW_TAG_class_type
        flags:      0x0 []
        DIE offset: 0x25
        parent:     ((cooked_index_entry *) 0x333b5d0) [foo]
...

Notice that 0x2a is the parent of 0x25, and that this is why the qualified
name of 0x25 is "foo::foo", which is incorrect, it's supposed to be "foo".

The parent is set here in cooked_indexer::make_index:
...
  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
spec_offset DIE (though that's not clear from the comment describing it).

So, the root cause of this is that when we lookup the parent for DIE 0x25, we get
m_die_range_map.find (0x2a) == 0x2a.

This is an off-by-one error, fixed in cooked_indexer::recurse by:
...
-      CORE_ADDR start = form_addr (parent_entry->die_offset,
+      CORE_ADDR start = form_addr (parent_entry->die_offset + 1,
...
which gives us:
...
    [12] ((cooked_index_entry *) 0x41e21f0)
    name:       foo
    canonical:  foo
    qualified:  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
    qualified:  foo
    DWARF tag:  DW_TAG_class_type
    flags:      0x0 []
    DIE offset: 0x2a
    parent:     ((cooked_index_entry *) 0)
...

Tested on x86_64-linux.

Approved-By: Tom Tromey <[email protected]>

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

Author: vries

gdb/dwarf2/read.c

@@ -16477,7 +16477,9 @@ cooked_indexer::recurse (cutu_reader *reader,
 
   if (parent_entry != nullptr)
     {
-      CORE_ADDR start = form_addr (parent_entry->die_offset,
+      /* Both start and end are inclusive, so use both "+ 1" and "- 1" to
+	 limit the range to the children of parent_entry.  */
+      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);

gdb/testsuite/gdb.dwarf2/pr13961.exp

@@ -34,3 +34,13 @@ gdb_test "break -q main" "Breakpoint.*at.*"
 
 # If we get this far gdb didn't crash.
 pass $testfile
+
+# Regression test for PR symtab/30739.
+gdb_test_multiple "maint print objfiles $binfile" "no foo::foo" {
+    -re -wrap "\r\n *qualified: *foo::foo\r\n.*" {
+	fail $gdb_test_name
+    }
+    -re -wrap "" {
+	pass $gdb_test_name
+    }
+}