The magic Delphi ReturnAddress intrinsic
Posted by jpluimers on 2020/02/05
I could not find any official place where ReturnAddress is documented even though it is used at quite a few places in the RTL, VCL, FMX and 3rd party libraries like DUnitX, Spring4D, JCL, ReportBuilder, TeeChart.
I tried searching it in the contexts of Delphi 2007, Delphi 2009, but there is only a [Archive.is] different System.ObjAuto.TParameters.ReturnAddress documented in XE2 and higher.
procedure Abort; begin raise EAbort.CreateRes(@SOperationAborted) at ReturnAddress; end;
There is a (usually broken*) ReturnAddr function used in various places of the RTL/VCL/FMX and (therefore wrongfully copied) in many other peoples code.
function ReturnAddr: Pointer; // From classes.pas asm MOV EAX,[EBP+4] // sysutils.pas says [EBP-4], but this works ! end;
- See the above link; I think this was fixed in Delphi XE, but the issue is still open.
Related to the above is the documented ExceptAddr.
I’ve used this in my ExceptionHelperUnit to build a GetStackTrace function in the example gist below.
I found these posts documenting the behaviour of the above intrinsic functions and more:
- [WayBack] Undocumented Delphi routines – Chee Wee’s blog: IT solutions for Singapore and companies worldwide
- [WayBack] delphi – Undocumented intrinsic routines – Stack Overflow
- [WayBack] exception – What does `at ReturnAddress` mean in Delphi? – Stack Overflow
–jeroen
| unit ExceptionHelperUnit; | |
| interface | |
| uses | |
| System.SysUtils; | |
| type | |
| ExceptionHelper = class helper for Exception | |
| public | |
| function Describe: string; | |
| class procedure RaiseNotImplementedException(const aClass: TClass; const aMethodName: string); | |
| class function GetStackTrace: string; | |
| end; | |
| implementation | |
| uses | |
| System.RTLConsts, | |
| System.SysConst; | |
| type | |
| EStackTraceException = class(Exception); // EProgrammerNotFound to make it really clear this is only to be used in very limited places ?? | |
| { ExceptionHelper } | |
| function ExceptionHelper.Describe: string; | |
| var | |
| lStackTrace: string; | |
| begin | |
| Result := inherited ToString(); | |
| if Self is EInOutError then | |
| if Result = System.RTLConsts.SInvalidFileName then | |
| Result := System.SysConst.SInvalidFileName; | |
| if Assigned(StackInfo) then | |
| lStackTrace := StackTrace | |
| else | |
| lStackTrace := 'empty'; | |
| Result := Format('Exception'#13#10'%s at $%p: %s'#13#10'with StackTrace'#13#10'%s', [ClassName, ExceptAddr, Result, lStackTrace]); | |
| end; | |
| class function ExceptionHelper.GetStackTrace: string; | |
| begin | |
| try | |
| Result := 'Get StackTrace via Exception.'; | |
| raise EStackTraceException.Create(Result) at ReturnAddress; | |
| except | |
| on E: EStackTraceException do | |
| Result := E.StackTrace; | |
| end; | |
| end; | |
| class procedure ExceptionHelper.RaiseNotImplementedException(const aClass: TClass; const aMethodName: string); | |
| begin | |
| raise ENotImplemented.CreateFmt('Method %s.%s is not implemented.', [aClass.ClassName, aMethodName]); | |
| end; | |
| end. |
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