Monday, June 25, 2007

How can i call 16-bit dll function from win32?

Gfsr_SystemResources = 0;
Gfsr_GdiResources = 1;
Gfsr_UserResources = 2;
hInst16: THandle;
GFSR: Pointer;

{ Undocumented Kernel32 calls. }
function LoadLibrary16(LibraryName: PChar): THandle; stdcall; external kernel32 index 35;
procedure FreeLibrary16(HInstance: THandle); stdcall; external kernel32 index 36;
function GetProcAddress16(Hinstance: THandle; ProcName: PChar): Pointer; stdcall; external kernel32 index 37;
procedure QT_Thunk; cdecl; external kernel32 name 'QT_Thunk';

{ QT_Thunk needs a stack frame. }
{$StackFrames On}
{ Thunking call to 16-bit USER.EXE. The ThunkTrash argument allocates space on the stack for QT_Thunk. }

function NewGetFreeSystemResources(SysResource: Word): Word;
ThunkTrash: array[0..$20] of Word;
{ Prevent the optimizer from getting rid of ThunkTrash. }
ThunkTrash[0] := hInst16;
hInst16 := LoadLibrary16('user.exe');
if hInst16 < 32 then
raise Exception.Create('Can''t load USER.EXE!');
{ Decrement the usage count. This doesn't really free the library, since USER.EXE is always loaded. }
{ Get the function pointer for the 16-bit function in USER.EXE. }
GFSR := GetProcAddress16(hInst16, 'GetFreeSystemResources');
if GFSR = nil then
raise Exception.Create('Can''t get address of GetFreeSystemResources!');
{ Thunk down to USER.EXE. }
push SysResource { push arguments }
mov edx, GFSR { load 16-bit procedure pointer }
call QT_Thunk { call thunk }
mov Result, ax { save the result }

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