[fpc-pascal]GPF when accessing DOS memory

[Sebastian Schuberth]

Hi there!

I'm currently modifiying some of my TMT Pascal sources so they to work
with
Free Pascal, too. Unfortunately I get a GPF (runtime error 216) when
executing
to following code, which works fine under TMT:

--8<--(BEGIN vbe.pas)--

Const
  VBE2=$32454256;

Type
  PDOSMemoryBlock=^DOSMemoryBlock;
  DOSMemoryBlock=Record
    Segment,Selector:Word;
  End;
  
  PCtrlInfoBlock=^CtrlInfoBlock;
  CtrlInfoBlock=Packed Record
    Signature:Cardinal;
    Version:Word;
    OEMStringPtr:PChar;
    Capabilities:Cardinal;
    VideoModePtr:PWord;
    TotalMemory:Word;

    OEMSoftwareRev:Word;
    OEMVendorNamePtr:PChar;
    OEMProductNamePtr:PChar;
    OEMProductRevPtr:PChar;
    Reserved_222:Array[0..221] Of Byte;

    OEMData:Array[0..255] Of Byte;
  End;

Var
  CIB:PCtrlInfoBlock
  CIBMem:PDOSMemoryBlock;

{ ... }

New(CIBMem);
{ Allocate DOS memory block and save segment / selector }
If Not dpmiAllocDOSMem(SizeOf(CIB^), at CIBMem^.Segment, at CIBMem^.Selector)
Then Exit;

{ Make CIB point to DOS memory }
CIB:=Ptr(CIBMem^.Segment,0);

{ Write 'VBE2' signature into DOS memory, THIS IS WHERE FPC CRASHES }
CIB^.Signature:=VBE2;

{ ... }

--8<--(END vbe.pas)--

For some reason FPC (or better: GO32V2?) won't let me write into the
allocated DOS
memory area. But why, it works under TMT (which uses PMODE/W). Is there
any DPMI
call I need to insert for FPC? BTW: I don't want to use functions from
the GO32 unit
if possible, because the code should be fully portable. I'd rather
recode the needed
functions myself.

Thanks in advance.
-- 

Sebastian Schuberth