Enum describing the various type of stack frame.
  - 
    Call: The stack frame was created on a call instruction
  
 
  - 
    Interrupt: The stack frame was created on an interrupt event
  
 
  - 
    Manual: The stack frame was created on an inactive stack (not the 
    current one). This happens on userland callback from kernelland.
  
 
  - 
    Damaged: The stack frame is artificial and used to replace others one 
    that were modify (return address) on an inactive stack (not the current
    one).
  
 
  - 
    Unknown: The stack frame is on the stack but the creation is unknown. 
    For example, the stack frame was created by a call that was executed 
    before the beginning of the trace.