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

2 files changed, 19 insertions, 13 deletions

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFFormValue.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFFormValue.cpp
index fc3cf863b30..5d2a8ffdb85 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFFormValue.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFFormValue.cpp
@@ -604,7 +604,7 @@ dw_addr_t DWARFFormValue::Address() const {
 }
 
 uint64_t DWARFFormValue::Reference() const {
-  uint64_t die_offset = m_value.value.uval;
+  uint64_t value = m_value.value.uval;
   switch (m_form) {
   case DW_FORM_ref1:
   case DW_FORM_ref2:
@@ -613,32 +613,36 @@ uint64_t DWARFFormValue::Reference() const {
   case DW_FORM_ref_udata:
     assert(m_cu); // CU must be valid for DW_FORM_ref forms that are compile
                   // unit relative or we will get this wrong
-    die_offset += m_cu->GetOffset();
-    break;
+    return value + m_cu->GetOffset();
+
+  case DW_FORM_ref_addr:
+  case DW_FORM_ref_sig8:
+  case DW_FORM_GNU_ref_alt:
+    return value;
 
   default:
-    break;
+    return DW_INVALID_OFFSET;
   }
-
-  return die_offset;
 }
 
 uint64_t DWARFFormValue::Reference(dw_offset_t base_offset) const {
-  uint64_t die_offset = m_value.value.uval;
+  uint64_t value = m_value.value.uval;
   switch (m_form) {
   case DW_FORM_ref1:
   case DW_FORM_ref2:
   case DW_FORM_ref4:
   case DW_FORM_ref8:
   case DW_FORM_ref_udata:
-    die_offset += base_offset;
-    break;
+    return value + base_offset;
+
+  case DW_FORM_ref_addr:
+  case DW_FORM_ref_sig8:
+  case DW_FORM_GNU_ref_alt:
+    return value;
 
   default:
-    break;
+    return DW_INVALID_OFFSET;
   }
-
-  return die_offset;
 }
 
 const uint8_t *DWARFFormValue::BlockData() const { return m_value.data; }
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