Hello,

I had been fighting with a stubborn problem for a few days now and the solution came from a corner I never expected it from. The program in question is a small test to drive an OLE Automation server (Corel Ventura 8 in this case), establishing the connection and calling a simple function. I get the strangest differences with various versions of my program. I tried with FPC 1.0.2, by the way.

The problem is that the enclosed program behaves differently with and without the unused variable marked by {*} added to the source. Without the variable the program does not work (it runs to the end but receives an error message back from the pdisp^.vtbl^.Invoke call) while with the variable it does work. At first I suspected some PACKRECORDS problems but the problem persists in all PACKRECORD configurations.

However, when specifying -al (to retain the assembler file) both versions work as expected. It seems to me that -al does more than simply leave the assembler file there, the resulting EXEs are drastically different.

When this will be sorted out, I'll have new problems: if this program is divided into a unit and a main program, it does not work even with -al, but let's proceed one step at a time... :-)))

Note that the original Ole2.pp in FPC is not functioning, make sure to use the one enclosed here (although I don't know how anybody could test it without Ventura installed, however, it might be modified to call another OLE server; as far as I know, MS Office programs are possible candidates).

-------------------- TEST.PP
{$APPTYPE CONSOLE}
program VPDoctor;
{$PACKRECORDS NORMAL}
uses
  Windows, Ole2;
const
  CLSCTX_INPROC_SERVER = 1;
  CLSCTX_LOCAL_SERVER = 4;
  CLSCTX_REMOTE_SERVER = 16;
  CLSCTX_SERVER = CLSCTX_INPROC_SERVER or CLSCTX_LOCAL_SERVER or
CLSCTX_REMOTE_SERVER;
  DISPATCH_METHOD = 1;
  IID_IUnknown : GUID = (Data1 : 0; Data2 : 0; Data3 : 0; Data4 : ($C0, 0, 0,
0, 0, 0, 0, $46));
  IID_IDispatch : GUID = (Data1 : $00020400; Data2 : 0; Data3 : 0; Data4 :
($C0, 0, 0, 0, 0, 0, 0, $46));
  IID_NULL : GUID = (Data1 : 0; Data2 : 0; Data3 : 0; Data4 : (0, 0, 0, 0, 0,
0, 0, 0));
  ProgID : PChar =
'C'#0'o'#0'r'#0'e'#0'l'#0'V'#0'e'#0'n'#0't'#0'u'#0'r'#0'a'#0'.'#0'A'#0'u'#0'
t'#0'o'#0'm'#0'a'#0't'#0'i'#0'o'#0'n'#0'.'#0'8'#0#0;
type
  PDispID = ^TDispID;
  TDispID = cardinal;
  PExcepInfo = pointer;
  PIUnknown = ^IUnknown;
  PDispParams = ^TDispParams;
  TDispParams = packed record
    rgvarg : PVariant;
    rgDispIDNamedArgs : PDispID;
    cArgs : word;
    cNamedArgs : word;
    end;
  PIDispatch = ^IDispatch;
  IDispatch = packed record
    vtbl : ^IDispatchVtbl;
    end;
  IDispatchVtbl = packed record
    QueryInterface : function (const pdisp : PIDispatch; const iid: TIID; var
obj): hResult; stdcall;
    AddRef : function (const pdisp : PIDispatch) : longint; stdcall;
    Release : function (const pdisp : PIDispatch) : longint; stdcall;
    GetTypeInfoCount : function (const pdisp : PIDispatch; pctinfo : PUINT) :
hResult; stdcall;
    GetTypeInfo : function (const pdisp : PIDispatch; iTInfo : word; lciid :
LCID; var ppTInfo) : hResult; stdcall;
    GetIDsOfNames : function (const pdisp : PIDispatch; const iid : TIID;
rgszNames : LPCWSTR; cNames : UINT; lciid : LCID; var DispID : TDispID) :
hResult; stdcall;
    Invoke : function (const pdisp : PIDispatch; dispIdMember : TDispID; const
iid : TIID; lciid : LCID; wFlags : WORD; pDP : PDispParams; pVarResult :
PVariant; pExceptInfo : PExcepInfo; puArgErr : PUINT) : hResult; stdcall;
    end;
var
  hr : hResult;
  CLSID_Ventura : TCLSID;
  punk : ^IUnknown;
  pdisp : ^IDispatch;
  dp : TDispParams;
  dispid : TDispID; {*}
function CLSIDFromProgID (lpszProgID : LPCWSTR; var pclsid : TCLSID) :
hResult;
external 'OLE32' name 'CLSIDFromProgID';
function CoCreateInstance (rclsid : TCLSID; pUnkOuter : PIUnknown;
dwClsContext
: longint; riid : TIID; var ppv) : hResult; external 'OLE32' name
'CoCreateInstance';
function OleInitialize (pvReserved : pointer) : hResult; external 'OLE32' name
'OleInitialize';
procedure OleUninitialize; external 'OLE32' name 'OleUninitialize';
begin
  dp.rgvarg := nil;
  dp.rgDispIDNamedArgs := nil;
  dp.cArgs := 0;
  dp.cNamedArgs := 0;
  hr := OleInitialize (nil);
  hr := CLSIDFromProgID (LPCWSTR(ProgID), CLSID_Ventura);
  hr := CoCreateInstance (CLSID_Ventura, nil, CLSCTX_SERVER, IID_IUnknown,
punk);
  hr := punk^.vtbl^.QueryInterface (punk, IID_IDispatch, pdisp);
  hr := pdisp^.vtbl^.Invoke (pdisp, $0883, IID_NULL, LOCALE_USER_DEFAULT,
DISPATCH_METHOD, @dp, nil, nil, nil);
  OleUnInitialize;
end.
--------------- OLE2.PP
unit ole2;
{$PACKRECORDS 1}
  interface
    uses
       windows;
    type
      PIUnknown = ^IUnknown;
      IUnknown = packed record
        vtbl : ^IUnknownVtbl;
        end;
      IUnknownVtbl = packed record
        QueryInterface : function (const punk : PIUnknown; const iid: TIID;
var
obj): HResult; stdcall;
        AddRef : function (const punk : PIUnknown) : longint; stdcall;
        Release : function (const punk : PIUnknown) : longint; stdcall;
        end;

  implementation

end.

Regards,

   Gabor DEAK JAHN

------------------------------------------------------------------- Gabor DEAK JAHN -- Budapest, Hungary.
WWW: <http://www.tramontana.co.hu/>www.tramontana.co.hu E-mail:

However, when specifying -al (to retain the assembler file) both

versions>

work as expected. It seems to me that -al does more than simply leave

the>

assembler file there, the resulting EXEs are drastically different.

It then uses GNU binutils as (called asw.exe for win32) assembler to create the object file instead of the internal object writer

But the code differences (except jmp labels and absolute offsets) shouldn't be that much when you compare a dissamble (objdumpw.exe --disassemble) of the 2 object files.

At 12/29/2000 06:30, you wrote:

Dear Peter,

It then uses GNU binutils as (called asw.exe for win32) assembler to create

the object

file instead of the internal object writer But the code differences (except jmp labels and absolute offsets) shouldn't

be that much

when you compare a dissamble (objdumpw.exe --disassemble) of the 2 object

files.

Good point, I forgot about OBJDUMPW. I checked the two EXEs and indeed the differences are minor (apart from the addresses, only a small but not important difference in setting up the jump tables for DLL-imported functions). Still, one program works, the other does not. This and the fact that adding and removing variables can make or break the program lead to a suspicion about variable alignment. And in my later checks, this proved true.

I tried to pad all my variables with additional ones to make sure that all of them fall on 8-byte or 16-byte boundaries and lo and behold, both versions (with and without -al) started to work all right. Now the remaining question is whether I can force FPC to align all (important) variables on such boundaries -- the real program would contain too many variables to make manual padding feasible.

Bye,
   Gábor

------------------------------------------------------------------- Gabor DEAK JAHN -- Budapest, Hungary.
E-mail: ,

Hi all,

I want to create a new class and add/remove copy the vmt of an existing class and alter the method table. But I need to know how big is the vmt of a class?
And I have to create published DoNothing procedures. Can I copy the code of an existing procedure? How big is the code of a procedure?

thx in advance,
Mattias

Hi Mattias,

of

an existing procedure? How big is the code of a procedure? thx in advance, Mattias

I don't know how you could do the thing you want to do.

I also am not sure whether you should try to do so. Copying VMT's is low level object pascal. What is it you are trying to accomplish? Why do you want to create a new class and add/remove methods at runtime? Maybe there are better ways of doing so.

Vincent Snijders

Hi all,

> I want to create a new class and add/remove methods at runtime. > I copy the vmt of an existing class and alter the method table. But I

need

there

are better ways of doing so. Vincent Snijders

I'm writing code for a wysiwyg component editor. (lazarus. Which is open source, so it should help any other IDE project too). I'm using TReader, TWriter and the whole RTTI to edit components of unknown classes. All procedures in the FCL depend on real classes, and not classes with some fake methods. And because I want to use the FCL, I need a real class. Thus I create one at runtime and add/remove the methods. Ok, it is low-lvl object pascal, but it is much easier than rewriting the FCL.
Therefore...

How big is the VMT of a class?
Can I copy the code of an existing procedure? What is the size of the code of a procedure?

thx in advance,
Mattias

For all details how a VMT is build see compiler/hcgdata.pas this is the file of the compiler that generates the VMT.

Can I copy the code of an existing procedure? What is the size of the code of a procedure?

You can't copy a procedure as it can contain relative memory addresses that aren't valid anymore if run from an other location in memory.

Peter

When do you have fake methods?

And because I want to use the FCL, I need a real class. Thus I create one at runtime and add/remove the methods.

I still don't understand what you want to do :/