[fpc-devel] Bug in passing WideString parameters to dispinterface function ?

LacaK lacak at zoznam.sk
Tue Oct 25 08:24:54 CEST 2016


look please at this. I have imported OCX type library which result in 
pascal unit with "dispinterface" defined like this:

_DSamlight_client_ctrl_ocx = dispinterface
    function ScChangeTextByName(const EntityName:WideString; const 
Text_:WideString):Integer;dispid 3;

In my program I have another method which takes AnsiString parameters:
    function TSamLightClient.ChangeTextByName(const Name, Text_: 
AnsiString): boolean;

In this method I do nothing except, that I call COM object interface:
    Result := FSamLightClientCtrl.ScChangeTextByName(Name, Text_)=1;

All seems to work, but OCX behaves like Name and Text_ params are equal!

When I look at assembler:

VyrobaLaser.pas:324               Result := 
FSamLightClientCtrl.ScChangeTextByName(Name, Text_)=1;
0042A986 bac8e15b00               mov    $0x5be1c8,%edx
0042A98B 8d45b0                   lea    -0x50(%ebp),%eax
0042A98E e82d26feff               call   0x40cfc0 <fpc_finalize>
0042A993 8d5da8                   lea    -0x58(%ebp),%ebx
0042A996 8d45a4                   lea    -0x5c(%ebp),%eax
0042A999 e8b2dafdff               call   0x408450 <fpc_widestr_decr_ref>
0042A99E c745a400000000           movl   $0x0,-0x5c(%ebp)
0042A9A5 8d55a4                   lea    -0x5c(%ebp),%edx
0042A9A8 8b45f8                   mov    -0x8(%ebp),%eax
0042A9AB e840dcfdff               call   0x4085f0 <fpc_ansistr_to_widestr>
0042A9B0 8b45a4                   mov    -0x5c(%ebp),%eax
0042A9B3 8903                     mov    %eax,(%ebx)
0042A9B5 8d5da8                   lea    -0x58(%ebp),%ebx
0042A9B8 83c304                   add    $0x4,%ebx
0042A9BB 8d45a4                   lea    -0x5c(%ebp),%eax
0042A9BE e88ddafdff               call   0x408450 <fpc_widestr_decr_ref>
0042A9C3 c745a400000000           movl   $0x0,-0x5c(%ebp)
0042A9CA 8d55a4                   lea    -0x5c(%ebp),%edx
0042A9CD 8b45fc                   mov    -0x4(%ebp),%eax
0042A9D0 e81bdcfdff               call   0x4085f0 <fpc_ansistr_to_widestr>
0042A9D5 8b45a4                   mov    -0x5c(%ebp),%eax
0042A9D8 8903                     mov    %eax,(%ebx)
0042A9DA 8d45a8                   lea    -0x58(%ebp),%eax
0042A9DD 50                       push   %eax
0042A9DE b920365c00               mov    $0x5c3620,%ecx
0042A9E3 8d45b0                   lea    -0x50(%ebp),%eax
0042A9E6 8b55f4                   mov    -0xc(%ebp),%edx
0042A9E9 8b5204                   mov    0x4(%edx),%edx
0042A9EC e8ff05feff               call   0x40aff0 <fpc_dispatch_by_id>
0042A9F1 8d45b0                   lea    -0x50(%ebp),%eax
0042A9F4 e8b71ffeff               call   0x40c9b0 
0042A9F9 83f801                   cmp    $0x1,%eax

It seems to me like there is used twice before <fpc_ansistr_to_widestr> 
is called same address:
   movl   $0x0,-0x5c(%ebp)
lea    -0x5c(%ebp),%edx

Isn't it wrong ? (I guess that it is address of any temporary local 
variable used to store result of ansistr->widestr)

I can workaround this by using intermediate local variable:
   var wText: WideString;
   wText := Text_;
   Result := FSamLightClientCtrl.ScChangeTextByName(Name, wText)=1; // 
use wText instead of Text_

It is so in FPC 2.6.4 in FPC 3.0.0 is assembler different, but result is 
still wrong.

Is it something known?


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