tlwidget does the assignment (ftkstripchart.c):
sigval.sival_int = GPOINTER_TO_INT(stripchart);
and then the extraction:
FtkStripchart * stripchart = GINT_TO_POINTER(sigval.sival_int);
unfortunatly, sigval_t is defined as:
/* Type for data associated with a signal. */
typedef union sigval
so, on 64-bit, that would only be a 32-bit field.
The description is from an old version of the stripchart that used kernel
timers. The current version uses glib timers and thus doesn't contain the
signal code cited.
The cited code is obsolete and is no longer in the widget.