File: ivmspace.h

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/* Copyright (C) 2001-2006 Artifex Software, Inc.
   All Rights Reserved.
  
   This software is provided AS-IS with no warranty, either express or
   implied.

   This software is distributed under license and may not be copied, modified
   or distributed except as expressly authorized under the terms of that
   license.  Refer to licensing information at http://www.artifex.com/
   or contact Artifex Software, Inc.,  7 Mt. Lassen Drive - Suite A-134,
   San Rafael, CA  94903, U.S.A., +1(415)492-9861, for further information.
*/

/* $Id: ivmspace.h 9043 2008-08-28 22:48:19Z giles $ */
/* Local/global space management */
/* Requires iref.h */

#ifndef ivmspace_INCLUDED
#  define ivmspace_INCLUDED

#include "gsgc.h"

/*
 * r_space_bits and r_space_shift, which define the bits in a ref
 * that carry VM space information, are defined in iref.h.
 * r_space_bits must be at least 2.
 */
#define a_space (((1 << r_space_bits) - 1) << r_space_shift)
/*
 * The i_vm_xxx values are defined in gsgc.h.
 */
typedef enum {
    avm_foreign = (i_vm_foreign << r_space_shift),
    avm_system = (i_vm_system << r_space_shift),
    avm_global = (i_vm_global << r_space_shift),
    avm_local = (i_vm_local << r_space_shift),
    avm_max = avm_local
} avm_space;

#define r_space(rp) (avm_space)(r_type_attrs(rp) & a_space)
#define r_space_index(rp) ((int)r_space(rp) >> r_space_shift)
#define r_set_space(rp,space) r_store_attrs(rp, a_space, (uint)space)

/*
 * According to the PostScript language specification, attempting to store
 * a reference to a local object into a global object must produce an
 * invalidaccess error.  However, systemdict must be able to refer to
 * a number of local dictionaries such as userdict and errordict.
 * Therefore, we implement a special hack in 'def' that allows such stores
 * if the dictionary being stored into is systemdict (which is normally
 * only writable during initialization) or a dictionary that appears
 * in systemdict (such as level2dict), and the current save level is zero
 * (to guarantee that we can't get dangling pointers).
 * We could allow this for any global dictionary, except that the garbage
 * collector must treat any such dictionaries as roots when collecting
 * local VM without collecting global VM.
 * We make a similar exception for .makeglobaloperator; this requires
 * treating the operator table as a GC root as well.
 *
 * We extend the local-into-global store check because we have four VM
 * spaces (local, global, system, and foreign), and we allow PostScript
 * programs to create objects in any of the first three.  If we define
 * the "generation" of an object as foreign = 0, system = 1, global = 2,
 * and local = 3, then a store is legal iff the generation of the object
 * into which a pointer is being stored is greater than or equal to
 * the generation of the object into which the store is occurring.
 *
 * We must check for local-into-global stores in three categories of places:
 *
 *      - The scanner, when it encounters a //name inside {}.
 *
 *      - All operators that allocate ref-containing objects and also
 *      store into them:
 *              packedarray  gstate  makepattern?
 *              makefont  scalefont  definefont  filter
 *
 *      - All operators that store refs into existing objects
 *      ("operators" marked with * are actually PostScript procedures):
 *              put(array)  putinterval(array)  astore  copy(to array)
 *              def  store*  put(dict)  copy(dict)
 *              dictstack  execstack  .make(global)operator
 *              currentgstate  defineusername
 */

/* Test whether an object is in local space, */
/* which implies that we need not check when storing into it. */
#define r_is_local(rp) (r_space(rp) == avm_local)
/* Test whether an object is foreign, i.e., outside known space. */
#define r_is_foreign(rp) (r_space(rp) == avm_foreign)
/* Check whether a store is allowed. */
#define store_check_space(destspace,rpnew)\
  if ( r_space(rpnew) > (destspace) )\
    return_error(e_invalidaccess)
#define store_check_dest(rpdest,rpnew)\
  store_check_space(r_space(rpdest), rpnew)
/* BACKWARD COMPATIBILITY (not used by any Ghostscript code per se) */
#define check_store_space(rdest,rnewcont)\
  store_check_dest(&(rdest),&(rnewcont))

#endif /* ivmspace_INCLUDED */