The Delphi Bug List

Jordan Russell:
Here is some code to reproduce the problem.

var
  F: File;
begin
  AssignFile(F, 'BigFile');   // a file larger than 2GB
  Reset(F, 1000000);
  Seek(F, 2148);              // I/O error 131 here
  CloseFile(F);
end;

This problem should be easy for Borland to fix. The Seek procedure does use a 64-bit multiply instruction to multiply the record number and record size together, but it discards the high-order 32 bits and passes NULL for the lpDistanceToMoveHigh parameter of the SetFilePointer call. This causes the error. In addition to properly passing the high-order 32 bits, it needs to use GetLastError for error checking since a FFFFFFFF result may not mean failure when a 64-bit offset is used.

Here's how I think the middle part of Delphi 6's _Seek procedure (in System.pas) should be written:

//  SetFilePointer(f.Handle, recNum*f.RecSize, FILE_BEGIN
        MOV      EAX,[ECX].TFileRec.RecSize
        MUL      EDX
        PUSH     EDX
        MOV      EDX,ESP
        PUSH     FILE_BEGIN    // pass dwMoveMethod
        PUSH     EDX           // pass lpDistanceToMoveHigh
        PUSH     EAX           // pass lDistanceToMove
        PUSH     [ECX].TFileRec.Handle   // pass hFile
        CALL     SetFilePointer          // get current position
        POP      EDX
        INC      EAX
        JNZ      @@exit
        CALL     GetLastError
        TEST     EAX,EAX
        JZ       @@exit
        JMP      InOutError