Acces Violation Exception raised into ExecuteTLS function [callback := FixPtr(callback);]

[hafedh-trimeche]

An exception raised into ExecuteTLS function:

function ExecuteTLS(Module: PMemoryModule): Boolean;
var
  CodeBase: Pointer;
  directory: PIMAGE_DATA_DIRECTORY;
  tls: PIMAGE_TLS_DIRECTORY;
  callback: PPointer; // =^PIMAGE_TLS_CALLBACK;

  // TLS callback pointers are VA's (ImageBase included) so if the module resides at
  // the other ImageBage they become invalid. This routine relocates them to the
  // actual ImageBase.
  // The case seem to happen with DLLs only and they rarely use TLS callbacks.
  // Moreover, they probably don't work at all when using DLL dynamically which is
  // the case in our code.
  function FixPtr(OldPtr: Pointer): Pointer;
  begin
    Result := Pointer(NativeInt(OldPtr) - Module.Headers.OptionalHeader.ImageBase + NativeInt(CodeBase));
  end;

begin
  Result := True;
  CodeBase := Module.CodeBase;

  directory := GET_HEADER_DICTIONARY(Module, IMAGE_DIRECTORY_ENTRY_TLS);
  if directory.VirtualAddress = 0 then
    Exit;

  tls := PIMAGE_TLS_DIRECTORY(PByte(CodeBase) + directory.VirtualAddress);
  // Delphi syntax is quite awkward when dealing with proc pointers so we have to
  // use casts to untyped pointers
  callback := Pointer(tls.AddressOfCallBacks);
  if callback <> nil then
  begin
    --------------------------------------------------------------------------
    callback := FixPtr(callback);
    while callback^ <> nil do
    --------------------------------------------------------------------------
    begin
      PIMAGE_TLS_CALLBACK(FixPtr(callback^))(CodeBase, DLL_PROCESS_ATTACH, nil);
      Inc(callback);
    end;
  end;
end;