FpDebug: Fix DW_OP_reg0..31 should return the register-location, not the value in the register (except for DW_AT_frame_base). See note_732607024 in merge-request !28

components/fpdebug/fpdbgdwarf.pas

@@ -523,6 +523,9 @@ type
                                 AnInitLocParserData: PInitLocParserData = nil): Boolean; virtual;
     function ComputeDataMemberAddress(const AnInformationEntry: TDwarfInformationEntry;
                               AValueObj: TFpValueDwarf; var AnAddress: TFpDbgMemLocation): Boolean; inline;
+    (* ConstRefOrExprFromAttrData:
+       See DWARF spec "2.19 Static and Dynamic Properties of Types"
+    *)
     function ConstRefOrExprFromAttrData(const AnAttribData: TDwarfAttribData;
                               AValueObj: TFpValueDwarf; out AValue: Int64;
                               AReadState: PFpDwarfAtEntryDataReadState = nil;
@@ -3796,6 +3799,8 @@ function TFpSymbolDwarf.ConstRefOrExprFromAttrData(
   const AnAttribData: TDwarfAttribData; AValueObj: TFpValueDwarf; out
   AValue: Int64; AReadState: PFpDwarfAtEntryDataReadState;
   ADataSymbol: PFpSymbolDwarfData): Boolean;
+(* See DWARF spec "2.19 Static and Dynamic Properties of Types"
+*)
 var
   Form: Cardinal;
   FwdInfoPtr: Pointer;
@@ -3874,6 +3879,16 @@ begin
   else
   if Form in [DW_FORM_block, DW_FORM_block1, DW_FORM_block2, DW_FORM_block4]
   then begin
+    (* Dwarf Spec:
+       "For a block / For an exprloc, the value is interpreted as a DWARF
+        expression; evaluation of the expression yields the value of the
+        attribute"
+       - The examples given in the spec, show that the "location" returned, is
+         not used as address. It is treated as the integer result.
+       - Thus this not be a register-location.
+       - It may be a constant (DW_OP_lit/DW_OP_const), but those should probably
+         be DW_FORM_data.
+    *)
     // TODO: until there always will be an AValueObj
     if AValueObj = nil then begin
       if AReadState <> nil then
@@ -3893,6 +3908,7 @@ begin
     InitLocParserData.ObjectDataAddrPush := False;
     Result := LocationFromAttrData(AnAttribData, AValueObj, t, @InitLocParserData);
     if Result then begin
+      assert(t.MType in [mlfTargetMem, mlfConstant], 'TFpSymbolDwarf.ConstRefOrExprFromAttrData: t.MType in [mlfTargetMem, mlfConstant]');
       AValue := Int64(t.Address);
     end
     else begin
@@ -5903,10 +5919,13 @@ begin
 
     FFrameBaseParser := TDwarfLocationExpression.Create(@Val[0], Length(Val), CompilationUnit,
       ASender.Context);
+    FFrameBaseParser.IsDwAtFrameBase := True;
     FFrameBaseParser.Evaluate;
   end;
 
   rd := FFrameBaseParser.ResultData;
+  // TODO: should mlfConstant be allowed?
+  assert(rd.MType in [mlfTargetMem, mlfConstant], 'TFpSymbolDwarfDataProc.GetFrameBase: rd.MType in [mlfTargetMem, mlfConstant]');
   if IsValidLoc(rd) then
     Result := rd.Address;
 

components/fpdebug/fpdbgdwarfdataclasses.pas

@@ -787,6 +787,7 @@ type
     FContext: TFpDbgLocationContext;
     FCurrentObjectAddress: TFpDbgMemLocation;
     FFrameBase: TDbgPtr;
+    FIsDwAtFrameBase: Boolean;
     FLastError: TFpError;
     FOnFrameBaseNeeded: TNotifyEvent;
     FStack: TDwarfLocationStack;
@@ -807,6 +808,7 @@ type
     property Context: TFpDbgLocationContext read FContext write FContext;
     // for DW_OP_push_object_address
     property CurrentObjectAddress: TFpDbgMemLocation read FCurrentObjectAddress write FCurrentObjectAddress;
+    property IsDwAtFrameBase: Boolean read FIsDwAtFrameBase write FIsDwAtFrameBase;
     end;
 
 function ULEB128toOrdinal(var p: PByte): QWord;
@@ -2247,15 +2249,37 @@ begin
       DW_OP_consts:  FStack.PushConst(ReadSignedFromExpression(CurData, 0));
       DW_OP_lit0..DW_OP_lit31: FStack.PushConst(CurInstr^-DW_OP_lit0);
 
+      (* DW_OP_reg0..31 and DW_OP_regx
+         The DWARF spec does *not* specify that those should push the result on
+         the stack.
+         However it does not matter, since there can be no other instruction
+         after it to access the stack.
+         From the spec:
+           "A register location description must stand alone as the entire
+            description of an object or a piece of an object"
+
+         For DW_AT_frame_base the spec (dwarf 5) says:
+           "The use of one of the DW_OP_reg<n> operations in this context is
+            equivalent to using DW_OP_breg<n>(0) but more compact"
+         However, it does not say if this removes the "stand alone" restriction.
+      *)
       DW_OP_reg0..DW_OP_reg31: begin
-          if not FContext.ReadRegister(CurInstr^-DW_OP_reg0, NewValue) then begin
-            SetError;
-            exit;
+          FStack.PushTargetRegister(CurInstr^-DW_OP_reg0);
+          // Dwarf-5
+          if FIsDwAtFrameBase then begin
+            EntryP := FStack.PeekForDeref;
+            if not ReadAddressFromMemory(EntryP^, AddrSize, NewLoc) then exit;
+            EntryP^ := NewLoc; // mlfTargetMem;
           end;
-          FStack.PushConst(NewValue);
         end;
       DW_OP_regx: begin
           FStack.PushTargetRegister(ULEB128toOrdinal(CurData));
+          // Dwarf-5
+          if FIsDwAtFrameBase then begin
+            EntryP := FStack.PeekForDeref;
+            if not ReadAddressFromMemory(EntryP^, AddrSize, NewLoc) then exit;
+            EntryP^ := NewLoc; // mlfTargetMem;
+          end;
         end;
 
       DW_OP_breg0..DW_OP_breg31: begin