[gdb/symtab] Fix segfault on invalid debug info

While looking at PR symtab/31478 (a problem in the cooked indexer with invalid
dwarf) it occurred to me that I could trigger a similar problem using:
...
  Compilation Unit @ offset 0xb2:
   Length:        0x1f (32-bit)
   Version:       4
   Abbrev Offset: 0x6c
   Pointer Size:  8
 <0><bd>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <be>   DW_AT_language    : 2	(non-ANSI C)
 <1><bf>: Abbrev Number: 2 (DW_TAG_subprogram)
    <c0>   DW_AT_low_pc      : 0x4004a7
    <c8>   DW_AT_high_pc     : 0x4004b2
    <d0>   DW_AT_specification: <0xd5>
 <1><d4>: Abbrev Number: 0
  Compilation Unit @ offset 0xd5:
   Length:        0x7 (32-bit)
   Version:       4
   Abbrev Offset: 0x7f
   Pointer Size:  8
...
and indeed I get:
...
$ gdb -q -batch outputs/gdb.dwarf2/dw2-inter-cu-error-2/dw2-inter-cu-error-2

Fatal signal: Segmentation fault
...

The problem is that we're calling prepare_one_comp_unit with cu == nullptr and
comp_unit_die == nullptr here in cooked_indexer::ensure_cu_exists:
...
      cutu_reader new_reader (per_cu, per_objfile, nullptr, nullptr, false,
                              m_index_storage->get_abbrev_cache ());

      prepare_one_comp_unit (new_reader.cu, new_reader.comp_unit_die,
                             language_minimal);
...

Fix this by bailing out for various types of dummy CUs:
...
      if (new_reader.dummy_p || new_reader.comp_unit_die == nullptr
	  || !new_reader.comp_unit_die->has_children)
	return nullptr;
...

Also make sure in scan_attributes that this triggers a dwarf error:
...
$ gdb -q -batch dw2-inter-cu-error-2
DWARF Error: cannot follow reference to DIE at 0xd5 \
  [in module dw2-inter-cu-error-2]
...

With target board readnow, the test-case triggers an assertion failure in
follow_die_offset, so fix this by throwing the same dwarf error.

While we're at it, make the other check for dummy CUs in
cooked_indexer::ensure_cu_exists more robust by adding an intermediate test
for comp_unit_die:
...
-  if (result->dummy_p || !result->comp_unit_die->has_children)
+  if (result->dummy_p || result->comp_unit_die == nullptr
+      || !result->comp_unit_die->has_children)
     return nullptr;
...

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>

0 files changed, 0 insertions, 0 deletions