--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/vdb.c	Fri Nov 25 01:42:08 2005 +0000
@@ -0,0 +1,157 @@
+/* Virtual diry bit implementation (platform independent) for XEmacs.
+   Copyright (C) 2005 Marcus Crestani.
+
+This file is part of XEmacs.
+
+XEmacs is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 2, or (at your option) any
+later version.
+
+XEmacs is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with XEmacs; see the file COPYING.  If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+Boston, MA 02111-1307, USA.  */
+
+/* Synched up with: Not in FSF. */
+
+#include <config.h>
+#include "lisp.h"
+#include "gc.h"
+#include "mc-alloc.h"
+#include "vdb.h"
+
+
+typedef struct
+{
+  Dynarr_declare (void *);
+} void_ptr_dynarr;
+
+void_ptr_dynarr *page_fault_table;
+
+/* Init page fault table and protect heap. */
+void
+vdb_start_dirty_bits_recording (void)
+{
+  page_fault_table = Dynarr_new2 (void_ptr_dynarr, void *);
+  protect_heap_pages ();
+}
+
+/* Remove heap protection. */
+void
+vdb_stop_dirty_bits_recording (void)
+{
+  unprotect_heap_pages ();
+}
+
+/* Read page fault table and pass page faults to garbage collector. */
+int 
+vdb_read_dirty_bits (void)
+{
+  int repushed_objects = 0;
+  Elemcount count;
+  for (count = Dynarr_length (page_fault_table); count; count--)
+    repushed_objects += 
+      repush_all_objects_on_page (Dynarr_at (page_fault_table, count - 1));
+  Dynarr_free (page_fault_table);
+  page_fault_table = 0;
+  return repushed_objects;
+}
+
+/* Called by the page fault handler: add address to page fault table. */
+void 
+vdb_designate_modified (void *addr)
+{
+  Dynarr_add (page_fault_table, addr);
+}
+
+
+/* For testing and debugging... */
+
+DEFUN ("test-vdb", Ftest_vdb, 0, 0, "", /*
+Test virtual dirty bit implementation. Prints results to stderr.
+*/
+       ())
+{
+  Rawbyte *p;
+  char c;
+  Elemcount count;
+  
+  /* Wrap up gc (if currently running). */
+  gc_full ();
+
+  /* Allocate a buffer; it will have the default
+     protection of PROT_READ|PROT_WRITE. */
+  p = (Rawbyte *) mc_alloc (mc_get_page_size());
+  set_lheader_implementation ((struct lrecord_header *) p, &lrecord_cons);
+  fprintf (stderr, "Allocate p: [%x ... %x], length %d\n", 
+	   (int) p, (int) (p + mc_get_page_size ()), 
+	   (int) mc_get_page_size ());
+
+  /* Test read. */
+  fprintf (stderr, "Attempt to read p[666]... ");
+  c = p[666];
+  fprintf (stderr, "read ok.\n");
+
+  /* Test write. */
+  fprintf (stderr, "Attempt to write 42 to p[666]... ");
+  p[666] = 42;
+  fprintf (stderr, "write ok, p[666] = %d\n", p[666]);
+
+  /* Mark the buffer read-only and set environemnt for write-barrier. */
+  fprintf (stderr, "Write-protect the page.\n");
+  MARK_BLACK (p);
+  vdb_start_dirty_bits_recording ();
+  write_barrier_enabled = 1;
+
+  /* Test write-barrier read. */
+  fprintf (stderr, "Attempt to read p[666]... ");
+  c = p[666];
+  fprintf (stderr, "read ok.\n");
+ 
+  /* Test write-barrier write, program receives SIGSEGV. */
+  fprintf (stderr, "Attempt to write 23 to p[666]... ");
+  p[666] = 23;
+  fprintf (stderr, "Written p[666] = %d\n", p[666]);
+
+  /* Stop write-barrier mode. */
+  write_barrier_enabled = 0;
+  MARK_WHITE (p);
+  vdb_unprotect (p, mc_get_page_size ());
+  for (count = Dynarr_length (page_fault_table); count; count--)
+    if (Dynarr_at (page_fault_table, count - 1) == &p[666])
+      fprintf (stderr, "VALID page fault at %x\n",
+	       (int) Dynarr_at (page_fault_table, count - 1));
+    else
+      fprintf (stderr, "WRONG page fault at %x\n",
+	       (int) Dynarr_at (page_fault_table, count - 1));
+  Dynarr_free (page_fault_table);
+  mc_free (p);
+  return Qnil;
+}
+
+DEFUN ("test-segfault", Ftest_segfault, 0, 0, "", /*
+Test virtual dirty bit implementation: provoke a segfault on purpose.
+WARNING: this function causes a SEGFAULT on purpose and thus crashes
+XEmacs!  This is only used for debbugging, e.g. for testing how the
+debugger behaves when XEmacs segfaults and the write barrier is
+enabled.
+*/
+       ())
+{
+  Rawbyte *q = 0;
+  q[0] = 23;
+  return Qnil;
+}
+
+void
+syms_of_vdb (void)
+{
+  DEFSUBR (Ftest_vdb);
+  DEFSUBR (Ftest_segfault);
+}