A C pointer passed to LISP

[shen@dolphin.Jpl.Nasa.Gov (Sheldon Shen)]

It is mentioned in the Foreign Function Interface chapter that "Passing a pointer to LISP  
data is not safe, because such data can be relocated at any time".

In my program, I pass a C pointer to LISP.   It is a pointer to a STRUCT that maintains the  
status of a database.
 

Eval (zone-pointer my-pointer)  returns NIL.  I guess it means that this is a relocatable  
pointer.

Repeatedly updating the database (or repeatedly using this pointer) eventually crashes  
the system.

How do I make this pointer "safe'? Is there anyway to force a relocatable pointer  
non-relocatable?  


(The same update activities were tested in C first.  And it is fine.  I then assume it is LISP  
causing the program.)

Any suggestions?  Thanks.

Sheldon Shen