2004.07.11 15:16 "[Tiff] CVS libtiff & thandle_t", by Bob Friesenhahn

CVS libtiff has a severe problem with the definition of thandle_t on 64-bit machines, and there is still a problem on 32-bit machines. For some reason this change was made though the ChangeLog notes that the change can't work for 64-bit environments. Here is the new definition:

#if defined(USE_WIN32_FILEIO)
#include <windows.h>
#ifdef __WIN32__
DECLARE_HANDLE(thandle_t);      /* Win32 file handle */
#else
typedef HFILE thandle_t;        /* client data handle */
#endif
#else
typedef int thandle_t;          /* client data handle */
#endif

Note that outside of Windows, thandle_t is is typedef 'int'. ImageMagick, GraphicsMagick, and likely other software, have been passing pointers via the thandle_t argument of TIFFClientOpen() since thandle_t used to be defined as void*.

The 'int' type is not sufficient to store a pointer on 64 bit machines. Even on 32-bit machines the 'int' type only covers 1/2 of the available address space so using 'int' (rather than 'unsigned int') is wrong.

This is the definition from tiff-v3.6.1:

#if defined(USE_WIN32_FILEIO)
#include <windows.h>
#ifdef __WIN32__
DECLARE_HANDLE(thandle_t);      /* Win32 file handle */
#else
typedef HFILE thandle_t;        /* client data handle */
#endif
#else
typedef void* thandle_t;        /* client data handle */
#endif

If thandle_t has to be an integer value now (the reason for the API change was not noted), then it should at least be an 'unsigned long' so that it can be assured to support a pointer.

Bob

======================================
Bob Friesenhahn
bfriesen@simple.dallas.tx.us
http://www.simplesystems.org/users/bfriesen