DWARF: Fix a bug in array size computation

Summary:
r346165 introduced a bug, where we would fail to parse the size of an
array if that size happened to match an existing die offset.

The logic was:
if (DWARFDIE count = die.GetReferencedDie(DW_AT_count))
  num_elements = compute_vla_size(count);
else
  num_elements = die.GetUsigned(DW_AT_count); // a fixed-size array

The problem with this logic was that GetReferencedDie did not take the
form class of the attribute into account, and would happily return a die
reference for any form, if its value happened to match some die.

As this behavior is inconsistent with how llvm's DWARFFormValue class
operates, I chose to fix the problem by making our version of this class
match the llvm behavior. For this to work, I had to add an explicit form
class check to the .apple_XXX tables parsing code, because they do
(incorrectly?) use data forms as die references.

Reviewers: aprantl, clayborg

Subscribers: JDevlieghere, lldb-commits

Differential Revision: https://reviews.llvm.org/D55991

llvm-svn: 350086

1 files changed, 3 insertions, 1 deletions

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/HashedNameToDIE.cpp b/lldb/source/Plugins/SymbolFile/DWARF/HashedNameToDIE.cpp
index 36211a08557..f83ba6663df 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/HashedNameToDIE.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/HashedNameToDIE.cpp
@@ -279,7 +279,9 @@ bool DWARFMappedHash::Header::Read(const lldb_private::DWARFDataExtractor &data,
     switch (header_data.atoms[i].type) {
     case eAtomTypeDIEOffset: // DIE offset, check form for encoding
       hash_data.offset =
-          (dw_offset_t)form_value.Reference(header_data.die_base_offset);
+          DWARFFormValue::IsDataForm(form_value.Form())
+              ? form_value.Unsigned()
+              : form_value.Reference(header_data.die_base_offset);
       break;
 
     case eAtomTypeTag: // DW_TAG value for the DIE