[LLDB] - Parse the DW_LLE_startx_length correctly for DWARF v5 case.

[grimar]

Summary

Currently, we always parse the length field of DW_LLE_startx_length entry as U32.
That is correct for pre-standard definition:

https://gcc.gnu.org/wiki/DebugFission - "A start/length entry contains one unsigned LEB128 number
and a 4-byte unsigned value (as would be represented by the form code DW_FORM_const4u). The first
number is an index into the .debug_addr section that selects the beginning offset, and the second
number is the length of the range. ")

But DWARF v5 says: "This is a form of bounded location description that has two unsigned ULEB operands.
The first value is an address index (into the .debug_addr section) that indicates the beginning of the address
range over which the location is valid. The second value is the length of the range."

Fortunately, we can easily handle the difference. No test case because it seems impossible to test
until we will be ready to use DWARF v5 in tests that need to run the executables.

include/lldb/Expression/DWARFExpression.h

 /// where the target cannot be run.  This class encapsulates a single DWARF
 /// location expression or a location list and interprets it.
 //----------------------------------------------------------------------
 class DWARFExpression {
 public:
   enum LocationListFormat : uint8_t {
     NonLocationList,     // Not a location list
     RegularLocationList, // Location list format used in non-split dwarf files
-    SplitDwarfLocationList, // Location list format used in split dwarf files
-    LocLists,               // Location list format used in DWARF v5 (.debug_loclists).
+    SplitDwarfLocationList, // Location list format used in pre-DWARF v5 split
+                            // dwarf files (.debug_loc.dwo)
+    LocLists,               // Location list format used in DWARF v5
+                            // (.debug_loclists/.debug_loclists.dwo).
   };
 
   //------------------------------------------------------------------
   /// Constructor
   //------------------------------------------------------------------
   explicit DWARFExpression(DWARFUnit *dwarf_cu);
 
   //------------------------------------------------------------------
public:
   ///
   /// @return
   ///     LLDB_INVALID_ADDRESS if the location doesn't contain a
   ///     DW_OP_addr for \a op_addr_idx, otherwise a valid file address
   //------------------------------------------------------------------
   lldb::addr_t GetLocation_DW_OP_addr(uint32_t op_addr_idx, bool &error) const;
 
   bool Update_DW_OP_addr(lldb::addr_t file_addr);
-  
   void SetModule(const lldb::ModuleSP &module) { m_module_wp = module; }
 
   bool ContainsThreadLocalStorage() const;
 
   bool LinkThreadLocalStorage(
       lldb::ModuleSP new_module_sp,
       std::function<lldb::addr_t(lldb::addr_t file_addr)> const
           &link_address_callback);

source/Expression/DWARFExpression.cpp

 }
 
 bool DWARFExpression::AddressRangeForLocationListEntry(
     const DWARFUnit *dwarf_cu, const DataExtractor &debug_loc_data,
     lldb::offset_t *offset_ptr, lldb::addr_t &low_pc, lldb::addr_t &high_pc) {
   if (!debug_loc_data.ValidOffset(*offset_ptr))
     return false;
 
-  switch (dwarf_cu->GetSymbolFileDWARF()->GetLocationListFormat()) {
+  DWARFExpression::LocationListFormat format =
+      dwarf_cu->GetSymbolFileDWARF()->GetLocationListFormat();
+  switch (format) {
   case NonLocationList:
     return false;
   case RegularLocationList:
     low_pc = debug_loc_data.GetAddress(offset_ptr);
     high_pc = debug_loc_data.GetAddress(offset_ptr);
     return true;
   case SplitDwarfLocationList:
   case LocLists:
     switch (debug_loc_data.GetU8(offset_ptr)) {
     case DW_LLE_end_of_list:
       return false;
     case DW_LLE_startx_endx: {
       uint64_t index = debug_loc_data.GetULEB128(offset_ptr);
       low_pc = ReadAddressFromDebugAddrSection(dwarf_cu, index);
       index = debug_loc_data.GetULEB128(offset_ptr);
       high_pc = ReadAddressFromDebugAddrSection(dwarf_cu, index);
       return true;
     }
     case DW_LLE_startx_length: {
       uint64_t index = debug_loc_data.GetULEB128(offset_ptr);
       low_pc = ReadAddressFromDebugAddrSection(dwarf_cu, index);
-      uint32_t length = debug_loc_data.GetU32(offset_ptr);
+      uint64_t length = (format == LocLists)
+                            ? debug_loc_data.GetULEB128(offset_ptr)
+                            : debug_loc_data.GetU32(offset_ptr);
       high_pc = low_pc + length;
       return true;
     }
     case DW_LLE_start_length: {
       low_pc = debug_loc_data.GetAddress(offset_ptr);
       high_pc = low_pc + debug_loc_data.GetULEB128(offset_ptr);
       return true;
     }