delphi – FastMM4说“块页脚已被破坏”

我在Delphi 7应用程序中有这个功能,在我将FastMM4 v4.99包含在项目中之前一直运行良好.一旦包含,FastMM4引发了以下错误消息：“FastMM在FreeMem操作期间检测到错误.块页脚已损坏.”执行在FreeMem行中停止.

function BinaryFieldToArrayOfWord( aBinaryField   : TVarBytesField;
                                   out aArrValues : TArrWord ) : Boolean;
var
  p : Pointer;
begin
  if not aBinaryField.IsBlob then
  begin
    GetMem( p,aBinaryField.DataSize );     
    try
      if aBinaryField.GetData( p ) then         
      begin
        // do something
      end;
    finally
      FreeMem( p,aBinaryField.DataSize );
    end;
  end; // if
end;

首先我认为函数中必定存在错误,但它实际上与Delphi 7帮助中的TField.GetData方法示例相同：

{ Retrieve the "raw" data from Field1 }
with Field1 do
begin
  if not IsBlob  { this does not work for BLOB fields }
  begin
    { Allocate space }
    GetMem(MyBuffer,DataSize);
    try
      if not GetData(MyBuffer) then
         MessageDlg(DisplayName + ' is NULL',mtInformation,[mbOK],0)
      else 
         { Do something with the data };
    finally
      { Free the space }
      FreeMem(MyBuffer,DataSize);
    end;
  end;
end;

我在互联网上发现上述错误信息通常是因为没有足够的空间容纳数据.所以我增加了内存块的大小,错误消息消失了,函数按预期工作.经过一些实验,我发现需要2个字节,足够：

GetMem( p,aBinaryField.DataSize + 2 );

    FreeMem( p,aBinaryField.DataSize + 2 );

虽然它解决了我的问题,但我并不完全放松这个解决方案,因为我不知道它的背景.知道这条消息的原因会很高兴. FastMM4是否需要额外的2个字节用于自己的页脚？

更新：经过一天的调试后,我现在相信Delphi 7 TField.GetData方法中存在一个错误.它在分配的内存块之外写入2个零字节.我尝试使用和不使用FastMM4,并在两种情况下都覆盖(因此它不是FastMM4错误).我也尝试将该字段类型化为TVarBytesField,没有区别.
这是我使用的代码和详细注释,包含结果.
我唯一剩下的问题是：他们是否在以后的Delphis中纠正了这个错误？

procedure TfrmMain_PBC_TH.btnDEBUGClick(Sender: TObject);
  type
    TArrBytes = array of Byte;  
  var
    p       : Pointer;
    qryTest : TADOQuery;
  begin
    qryTest := TADOQuery.Create( Application );
    try
      // The type of the TQM_BinaryData.BinData column in the MSSQL database is a       varbinary(7900). 
      // Load the #168 binary data record. It contains exactly 7900 bytes,and the value of each byte is 255
      qryTest.Connection := MainConn;
      qryTest.SQL.Add('SELECT [BinData] FROM [TQM_BinaryData] WHERE [Id] = 168');
      qryTest.Open;

      // Allocate the memory block for this.
      GetMem( p,qryTest.FieldByName('BinData').DataSize );
      // DataSize is 7902 because all TVarBytesFields have 2 byte prefix in Delphi,containing the data length.
      // So the size of the allocated memory block is 7902 bytes - we are correct so far.
      try
        // Values of the first four bytes beyond the end of the memory block (memory thrash at this point) before GetData:
        // TArrBytes(p)[7902] = 96
        // TArrBytes(p)[7903] = 197
        // TArrBytes(p)[7904] = 219
        // TArrBytes(p)[7905] = 43

        // Critical point: get the data from the field with the Delphi GetData method
        qryTest.FieldByName('BinData').GetData( p );

        // Values after GetData:
        // TArrBytes(p)[0]    = 220    TArrBytes(p)[0] and TArrBytes(p)[1] contains the length of the binary data
        // TArrBytes(p)[1]    = 30     it is correct as 30 * 256 + 220 = 7900
        // TArrBytes(p)[2]    = 255    actual data starts
        // TArrBytes(p3[2]    = 255    
        // ...
        // TArrBytes(p)[7900] = 255
        // TArrBytes(p)[7901] = 255    actual data ends
        // TArrBytes(p)[7902] = 0      changed from 96!
        // TArrBytes(p)[7903] = 0      changed from 197!
        // TArrBytes(p)[7904] = 219    no change
        // TArrBytes(p)[7905] = 43     no change
      finally
        // Here FastMM4 throws the block footer corrupt error because GetData modified the 2 bytes after the allocated memory block 
        FreeMem( p );
      end;

      qryTest.Close;
    finally
      qryTest.Free;
    end;
  end;

添加数据断点后,调用堆栈为：

@FillChar(???,???,???)
    TDataSet.DataConvert($7D599770,$12F448,$7D51F7F0,True)
    VarToBuffer
    TCustomADODataSet.GetFieldData($7D599770,True)
    TField.GetData($7D51F7F0,True)
    TfrmMain_PBC_TH.btnDEBUGClick($7FF7A380)
    TControl.Click
    TButton.Click