path: root/psi/isave.c

/* Copyright (C) 2001-2023 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 the license contained in the file LICENSE in this distribution.

   Refer to licensing information at http://www.artifex.com or contact
   Artifex Software, Inc.,  39 Mesa Street, Suite 108A, San Francisco,
   CA 94129, USA, for further information.
*/


/* Save/restore manager for Ghostscript interpreter */
#include "ghost.h"
#include "memory_.h"
#include "ierrors.h"
#include "gsexit.h"
#include "gsstruct.h"
#include "stream.h"		/* for linking for forgetsave */
#include "iastate.h"
#include "inamedef.h"
#include "iname.h"
#include "ipacked.h"
#include "isave.h"
#include "isstate.h"
#include "gsstate.h"
#include "store.h"		/* for ref_assign */
#include "ivmspace.h"
#include "igc.h"
#include "gsutil.h"		/* gs_next_ids prototype */
#include "icstate.h"

/* Structure descriptor */
private_st_alloc_save();

/* Define the maximum amount of data we are willing to scan repeatedly -- */
/* see below for details. */
static const long max_repeated_scan = 100000;

/* Define the minimum space for creating an inner clump. */
/* Must be at least sizeof(clump_head_t). */
static const long min_inner_clump_space = sizeof(clump_head_t) + 500;

/*
 * The logic for saving and restoring the state is complex.
 * Both the changes to individual objects, and the overall state
 * of the memory manager, must be saved and restored.
 */

/*
 * To save the state of the memory manager:
 *      Save the state of the current clump in which we are allocating.
 *      Shrink all clumps to their inner unallocated region.
 *      Save and reset the free block chains.
 * By doing this, we guarantee that no object older than the save
 * can be freed.
 *
 * To restore the state of the memory manager:
 *      Free all clumps newer than the save, and the descriptors for
 *        the inner clumps created by the save.
 *      Make current the clump that was current at the time of the save.
 *      Restore the state of the current clump.
 *
 * In addition to save ("start transaction") and restore ("abort transaction"),
 * we support forgetting a save ("commit transation").  To forget a save:
 *      Reassign to the next outer save all clumps newer than the save.
 *      Free the descriptors for the inners clump, updating their outer
 *        clumps to reflect additional allocations in the inner clumps.
 *      Concatenate the free block chains with those of the outer save.
 */

/*
 * For saving changes to individual objects, we add an "attribute" bit
 * (l_new) that logically belongs to the slot where the ref is stored,
 * not to the ref itself.  The bit means "the contents of this slot
 * have been changed, or the slot was allocated, since the last save."
 * To keep track of changes since the save, we associate a chain of
 * <slot, old_contents> pairs that remembers the old contents of slots.
 *
 * When creating an object, if the save level is non-zero:
 *      Set l_new in all slots.
 *
 * When storing into a slot, if the save level is non-zero:
 *      If l_new isn't set, save the address and contents of the slot
 *        on the current contents chain.
 *      Set l_new after storing the new value.
 *
 * To do a save:
 *      If the save level is non-zero:
 *              Reset l_new in all slots on the contents chain, and in all
 *                objects created since the previous save.
 *      Push the head of the contents chain, and reset the chain to empty.
 *
 * To do a restore:
 *      Check all the stacks to make sure they don't contain references
 *        to objects created since the save.
 *      Restore all the slots on the contents chain.
 *      Pop the contents chain head.
 *      If the save level is now non-zero:
 *              Scan the newly restored contents chain, and set l_new in all
 *                the slots it references.
 *              Scan all objects created since the previous save, and set
 *                l_new in all the slots of each object.
 *
 * To forget a save:
 *      If the save level is greater than 1:
 *              Set l_new as for a restore, per the next outer save.
 *              Concatenate the next outer contents chain to the end of
 *                the current one.
 *      If the save level is 1:
 *              Reset l_new as for a save.
 *              Free the contents chain.
 */

/*
 * A consequence of the foregoing algorithms is that the cost of a save is
 * proportional to the total amount of data allocated since the previous
 * save.  If a PostScript program reads in a large amount of setup code and
 * then uses save/restore heavily, each save/restore will be expensive.  To
 * mitigate this, we check to see how much data we have scanned at this save
 * level: if it is large, we do a second, invisible save.  This greatly
 * reduces the cost of inner saves, at the expense of possibly saving some
 * changes twice that otherwise would only have to be saved once.
 */

/*
 * The presence of global and local VM complicates the situation further.
 * There is a separate save chain and contents chain for each VM space.
 * When multiple contexts are fully implemented, save and restore will have
 * the following effects, according to the privacy status of the current
 * context's global and local VM:
 *      Private global, private local:
 *              The outermost save saves both global and local VM;
 *                otherwise, save only saves local VM.
 *      Shared global, private local:
 *              Save only saves local VM.
 *      Shared global, shared local:
 *              Save only saves local VM, and suspends all other contexts
 *                sharing the same local VM until the matching restore.
 * Since we do not currently implement multiple contexts, only the first
 * case is relevant.
 *
 * Note that when saving the contents of a slot, the choice of chain
 * is determined by the VM space in which the slot is allocated,
 * not by the current allocation mode.
 */

/* Tracing printout */
static void
print_save(const char *str, uint spacen, const alloc_save_t *sav)
{
  if_debug5('u', "[u]%s space %u "PRI_INTPTR": cdata = "PRI_INTPTR", id = %lu\n",\
            str, spacen, (intptr_t)sav, (intptr_t)sav->client_data, (ulong)sav->id);
}

/* A link to igcref.c . */
ptr_proc_reloc(igc_reloc_ref_ptr_nocheck, ref_packed);

static
CLEAR_MARKS_PROC(change_clear_marks)
{
    alloc_change_t *const ptr = (alloc_change_t *)vptr;

    if (r_is_packed(&ptr->contents))
        r_clear_pmark((ref_packed *) & ptr->contents);
    else
        r_clear_attrs(&ptr->contents, l_mark);
}
static
ENUM_PTRS_WITH(change_enum_ptrs, alloc_change_t *ptr) return 0;
ENUM_PTR(0, alloc_change_t, next);
case 1:
    if (ptr->offset >= 0)
        ENUM_RETURN((byte *) ptr->where - ptr->offset);
    else
        if (ptr->offset != AC_OFFSET_ALLOCATED)
            ENUM_RETURN_REF(ptr->where);
        else {
            /* Don't enumerate ptr->where, because it
               needs a special processing with
               alloc_save__filter_changes. */
            ENUM_RETURN(0);
        }
case 2:
    ENUM_RETURN_REF(&ptr->contents);
ENUM_PTRS_END
static RELOC_PTRS_WITH(change_reloc_ptrs, alloc_change_t *ptr)
{
    RELOC_VAR(ptr->next);
    switch (ptr->offset) {
        case AC_OFFSET_STATIC:
            break;
        case AC_OFFSET_REF:
            RELOC_REF_PTR_VAR(ptr->where);
            break;
        case AC_OFFSET_ALLOCATED:
            /* We know that ptr->where may point to an unmarked object
               because change_enum_ptrs skipped it,
               and we know it always points to same space
               because we took a special care when calling alloc_save_change_alloc.
               Therefore we must skip the check for the mark,
               which would happen if we call the regular relocation function
               igc_reloc_ref_ptr from RELOC_REF_PTR_VAR.
               Calling igc_reloc_ref_ptr_nocheck instead. */
            {	/* A sanity check. */
                obj_header_t *pre = (obj_header_t *)ptr->where - 1;

                if (pre->o_type != &st_refs)
                    gs_abort(gcst->heap);
            }
            if (ptr->where != 0 && !gcst->relocating_untraced)
                ptr->where = igc_reloc_ref_ptr_nocheck(ptr->where, gcst);
            break;
        default:
            {
                byte *obj = (byte *) ptr->where - ptr->offset;

                RELOC_VAR(obj);
                ptr->where = (ref_packed *) (obj + ptr->offset);
            }
            break;
    }
    if (r_is_packed(&ptr->contents))
        r_clear_pmark((ref_packed *) & ptr->contents);
    else {
        RELOC_REF_VAR(ptr->contents);
        r_clear_attrs(&ptr->contents, l_mark);
    }
}
RELOC_PTRS_END
gs_private_st_complex_only(st_alloc_change, alloc_change_t, "alloc_change",
                change_clear_marks, change_enum_ptrs, change_reloc_ptrs, 0);

/* Debugging printout */
#ifdef DEBUG
static void
alloc_save_print(const gs_memory_t *mem, alloc_change_t * cp, bool print_current)
{
    dmprintf2(mem, " "PRI_INTPTR"x: "PRI_INTPTR": ", (intptr_t) cp, (intptr_t) cp->where);
    if (r_is_packed(&cp->contents)) {
        if (print_current)
            dmprintf2(mem, "saved=%x cur=%x\n", *(ref_packed *) & cp->contents,
                      *cp->where);
        else
            dmprintf1(mem, "%x\n", *(ref_packed *) & cp->contents);
    } else {
        if (print_current)
            dmprintf6(mem, "saved=%x %x %lx cur=%x %x %lx\n",
                      r_type_attrs(&cp->contents), r_size(&cp->contents),
                      (ulong) cp->contents.value.intval,
                      r_type_attrs((ref *) cp->where),
                      r_size((ref *) cp->where),
                      (ulong) ((ref *) cp->where)->value.intval);
        else
            dmprintf3(mem, "%x %x %lx\n",
                      r_type_attrs(&cp->contents), r_size(&cp->contents),
                      (ulong) cp->contents.value.intval);
    }
}
#endif

/* Forward references */
static int  restore_resources(alloc_save_t *, gs_ref_memory_t *);
static void restore_free(gs_ref_memory_t *);
static int  save_set_new(gs_ref_memory_t * mem, bool to_new, bool set_limit, ulong *pscanned);
static int  save_set_new_changes(gs_ref_memory_t *, bool, bool);
static bool check_l_mark(void *obj);

/* Initialize the save/restore machinery. */
void
alloc_save_init(gs_dual_memory_t * dmem)
{
    alloc_set_not_in_save(dmem);
}

/* Record that we are in a save. */
static void
alloc_set_masks(gs_dual_memory_t *dmem, uint new_mask, uint test_mask)
{
    int i;
    gs_ref_memory_t *mem;

    dmem->new_mask = new_mask;
    dmem->test_mask = test_mask;
    for (i = 0; i < countof(dmem->spaces.memories.indexed); ++i)
        if ((mem = dmem->spaces.memories.indexed[i]) != 0) {
            mem->new_mask = new_mask, mem->test_mask = test_mask;
            if (mem->stable_memory != (gs_memory_t *)mem) {
                mem = (gs_ref_memory_t *)mem->stable_memory;
                mem->new_mask = new_mask, mem->test_mask = test_mask;
            }
        }
}
void
alloc_set_in_save(gs_dual_memory_t *dmem)
{
    alloc_set_masks(dmem, l_new, l_new);
}

/* Record that we are not in a save. */
void
alloc_set_not_in_save(gs_dual_memory_t *dmem)
{
    alloc_set_masks(dmem, 0, ~0);
}

/* Save the state. */
static alloc_save_t *alloc_save_space(gs_ref_memory_t *mem,
                                       gs_dual_memory_t *dmem,
                                       ulong sid);
static void
alloc_free_save(gs_ref_memory_t *mem, alloc_save_t *save, const char *scn)
{
    gs_ref_memory_t save_mem;
    save_mem = mem->saved->state;
    gs_free_object((gs_memory_t *)mem, save, scn);
    /* Free any inner clump structures.  This is the easiest way to do it. */
    restore_free(mem);
    /* Restore the 'saved' state - this pulls our object off the linked
     * list of states. Without this we hit a SEGV in the gc later. */
    *mem = save_mem;
}
int
alloc_save_state(gs_dual_memory_t * dmem, void *cdata, ulong *psid)
{
    gs_ref_memory_t *lmem = dmem->space_local;
    gs_ref_memory_t *gmem = dmem->space_global;
    ulong sid = gs_next_ids((const gs_memory_t *)lmem->stable_memory, 2);
    bool global =
        lmem->save_level == 0 && gmem != lmem &&
        gmem->num_contexts == 1;
    alloc_save_t *gsave =
        (global ? alloc_save_space(gmem, dmem, sid + 1) : (alloc_save_t *) 0);
    alloc_save_t *lsave = alloc_save_space(lmem, dmem, sid);

    if (lsave == 0 || (global && gsave == 0)) {
        /* Only 1 of lsave or gsave will have been allocated, but
         * nevertheless (in case things change in future), we free
         * lsave, then gsave, so they 'pop' correctly when restoring
         * the mem->saved states. */
        if (lsave != 0)
            alloc_free_save(lmem, lsave, "alloc_save_state(local save)");
        if (gsave != 0)
            alloc_free_save(gmem, gsave, "alloc_save_state(global save)");
        return_error(gs_error_VMerror);
    }
    if (gsave != 0) {
        gsave->client_data = 0;
        print_save("save", gmem->space, gsave);
        /* Restore names when we do the local restore. */
        lsave->restore_names = gsave->restore_names;
        gsave->restore_names = false;
    }
    lsave->id = sid;
    lsave->client_data = cdata;
    print_save("save", lmem->space, lsave);
    /* Reset the l_new attribute in all slots.  The only slots that */
    /* can have the attribute set are the ones on the changes chain, */
    /* and ones in objects allocated since the last save. */
    if (lmem->save_level > 1) {
        ulong scanned;
        int code = save_set_new(&lsave->state, false, true, &scanned);

        if (code < 0)
            return code;
#if 0 /* Disable invisible save levels. */
        if ((lsave->state.total_scanned += scanned) > max_repeated_scan) {
            /* Do a second, invisible save. */
            alloc_save_t *rsave;

            rsave = alloc_save_space(lmem, dmem, 0L);
            if (rsave != 0) {
                rsave->client_data = cdata;
#if 0 /* Bug 688153 */
                rsave->id = lsave->id;
                print_save("save", lmem->space, rsave);
                lsave->id = 0;	/* mark as invisible */
                rsave->state.save_level--; /* ditto */
                lsave->client_data = 0;
#else
                rsave->id = 0;  /* mark as invisible */
                print_save("save", lmem->space, rsave);
                rsave->state.save_level--; /* ditto */
                rsave->client_data = 0;
#endif
                /* Inherit the allocated space count -- */
                /* we need this for triggering a GC. */
                print_save("save", lmem->space, lsave);
            }
        }
#endif
    }

    alloc_set_in_save(dmem);
    *psid = sid;
    return 0;
}
/* Save the state of one space (global or local). */
static alloc_save_t *
alloc_save_space(gs_ref_memory_t * mem, gs_dual_memory_t * dmem, ulong sid)
{
    gs_ref_memory_t save_mem;
    alloc_save_t *save;
    clump_t *cp;
    clump_t *new_cc = NULL;
    clump_splay_walker sw;

    save_mem = *mem;
    alloc_close_clump(mem);
    mem->cc = NULL;
    gs_memory_status((gs_memory_t *) mem, &mem->previous_status);
    ialloc_reset(mem);

    /* Create inner clumps wherever it's worthwhile. */

    for (cp = clump_splay_walk_init(&sw, &save_mem); cp != 0; cp = clump_splay_walk_fwd(&sw)) {
        if (cp->ctop - cp->cbot > min_inner_clump_space) {
            /* Create an inner clump to cover only the unallocated part. */
            clump_t *inner =
                gs_raw_alloc_struct_immovable(mem->non_gc_memory, &st_clump,
                                              "alloc_save_space(inner)");

            if (inner == 0)
                break;		/* maybe should fail */
            alloc_init_clump(inner, cp->cbot, cp->ctop, cp->sreloc != 0, cp);
            alloc_link_clump(inner, mem);
            if_debug2m('u', (gs_memory_t *)mem, "[u]inner clump: cbot="PRI_INTPTR" ctop="PRI_INTPTR"\n",
                       (intptr_t) inner->cbot, (intptr_t) inner->ctop);
            if (cp == save_mem.cc)
                new_cc = inner;
        }
    }
    mem->cc = new_cc;
    alloc_open_clump(mem);

    save = gs_alloc_struct((gs_memory_t *) mem, alloc_save_t,
                           &st_alloc_save, "alloc_save_space(save)");
    if_debug2m('u', (gs_memory_t *)mem, "[u]save space %u at "PRI_INTPTR"\n",
               mem->space, (intptr_t) save);
    if (save == 0) {
        /* Free the inner clump structures.  This is the easiest way. */
        restore_free(mem);
        *mem = save_mem;
        return 0;
    }
    save->client_data = NULL;
    save->state = save_mem;
    save->spaces = dmem->spaces;
    save->restore_names = (name_memory(mem) == (gs_memory_t *) mem);
    save->is_current = (dmem->current == mem);
    save->id = sid;
    mem->saved = save;
    if_debug2m('u', (gs_memory_t *)mem, "[u%u]file_save "PRI_INTPTR"\n",
               mem->space, (intptr_t) mem->streams);
    mem->streams = 0;
    mem->total_scanned = 0;
    mem->total_scanned_after_compacting = 0;
    if (sid)
        mem->save_level++;
    return save;
}

/* Record a state change that must be undone for restore, */
/* and mark it as having been saved. */
int
alloc_save_change_in(gs_ref_memory_t *mem, const ref * pcont,
                  ref_packed * where, client_name_t cname)
{
    register alloc_change_t *cp;

    if (mem->new_mask == 0)
        return 0;		/* no saving */
    cp = gs_alloc_struct((gs_memory_t *)mem, alloc_change_t,
                         &st_alloc_change, "alloc_save_change");
    if (cp == 0)
        return -1;
    cp->next = mem->changes;
    cp->where = where;
    if (pcont == NULL)
        cp->offset = AC_OFFSET_STATIC;
    else if (r_is_array(pcont) || r_has_type(pcont, t_dictionary))
        cp->offset = AC_OFFSET_REF;
    else if (r_is_struct(pcont))
        cp->offset = (byte *) where - (byte *) pcont->value.pstruct;
    else {
        lprintf3("Bad type %u for save!  pcont = "PRI_INTPTR", where = "PRI_INTPTR"\n",
                 r_type(pcont), (intptr_t) pcont, (intptr_t) where);
        gs_abort((const gs_memory_t *)mem);
    }
    if (r_is_packed(where))
        *(ref_packed *)&cp->contents = *where;
    else {
        ref_assign_inline(&cp->contents, (ref *) where);
        r_set_attrs((ref *) where, l_new);
    }
    mem->changes = cp;
#ifdef DEBUG
    if (gs_debug_c('U')) {
        dmlprintf1((const gs_memory_t *)mem, "[U]save(%s)", client_name_string(cname));
        alloc_save_print((const gs_memory_t *)mem, cp, false);
    }
#endif
    return 0;
}
int
alloc_save_change(gs_dual_memory_t * dmem, const ref * pcont,
                  ref_packed * where, client_name_t cname)
{
    gs_ref_memory_t *mem =
        (pcont == NULL ? dmem->space_local :
         dmem->spaces_indexed[r_space(pcont) >> r_space_shift]);

    return alloc_save_change_in(mem, pcont, where, cname);
}

/* Allocate a structure for recording an allocation event. */
int
alloc_save_change_alloc(gs_ref_memory_t *mem, client_name_t cname, alloc_change_t **pcp)
{
    register alloc_change_t *cp;

    if (mem->new_mask == 0)
        return 0;		/* no saving */
    cp = gs_alloc_struct((gs_memory_t *)mem, alloc_change_t,
                         &st_alloc_change, "alloc_save_change");
    if (cp == 0)
        return_error(gs_error_VMerror);
    cp->next = mem->changes;
    cp->where = 0;
    cp->offset = AC_OFFSET_ALLOCATED;
    make_null(&cp->contents);
    *pcp = cp;
    return 1;
}

/* Remove an AC_OFFSET_ALLOCATED element. */
void
alloc_save_remove(gs_ref_memory_t *mem, ref_packed *obj, client_name_t cname)
{
    alloc_change_t **cpp = &mem->changes;

    for (; *cpp != NULL;) {
        alloc_change_t *cp = *cpp;

        if (cp->offset == AC_OFFSET_ALLOCATED && cp->where == obj) {
            if (mem->scan_limit == cp)
                mem->scan_limit = cp->next;
            *cpp = cp->next;
            gs_free_object((gs_memory_t *)mem, cp, "alloc_save_remove");
        } else
            cpp = &(*cpp)->next;
    }
}

/* Filter save change lists. */
static inline void
alloc_save__filter_changes_in_space(gs_ref_memory_t *mem)
{
    /* This is a special function, which is called
       from the garbager after setting marks and before collecting
       unused space. Therefore it just resets marks for
       elements being released instead releasing them really. */
    alloc_change_t **cpp = &mem->changes;

    for (; *cpp != NULL; ) {
        alloc_change_t *cp = *cpp;

        if (cp->offset == AC_OFFSET_ALLOCATED && !check_l_mark(cp->where)) {
            obj_header_t *pre = (obj_header_t *)cp - 1;

            *cpp = cp->next;
            cp->where = 0;
            if (mem->scan_limit == cp)
                mem->scan_limit = cp->next;
            o_set_unmarked(pre);
        } else
            cpp = &(*cpp)->next;
    }
}

/* Filter save change lists. */
void
alloc_save__filter_changes(gs_ref_memory_t *memory)
{
    gs_ref_memory_t *mem = memory;

    for  (; mem; mem = &mem->saved->state)
        alloc_save__filter_changes_in_space(mem);
}

/* Return (the id of) the innermost externally visible save object, */
/* i.e., the innermost save with a non-zero ID. */
ulong
alloc_save_current_id(const gs_dual_memory_t * dmem)
{
    const alloc_save_t *save = dmem->space_local->saved;

    while (save != 0 && save->id == 0)
        save = save->state.saved;
    if (save)
        return save->id;

    /* This should never happen, if it does, return a totally
     * impossible value.
     */
    return (ulong)-1;
}
alloc_save_t *
alloc_save_current(const gs_dual_memory_t * dmem)
{
    return alloc_find_save(dmem, alloc_save_current_id(dmem));
}

/* Test whether a reference would be invalidated by a restore. */
bool
alloc_is_since_save(const void *vptr, const alloc_save_t * save)
{
    /* A reference postdates a save iff it is in a clump allocated */
    /* since the save (including any carried-over inner clumps). */

    const char *const ptr = (const char *)vptr;
    register gs_ref_memory_t *mem = save->space_local;

    if_debug2m('U', (gs_memory_t *)mem, "[U]is_since_save "PRI_INTPTR", "PRI_INTPTR":\n",
               (intptr_t) ptr, (intptr_t) save);
    if (mem->saved == 0) {	/* This is a special case, the final 'restore' from */
        /* alloc_restore_all. */
        return true;
    }
    /* Check against clumps allocated since the save. */
    /* (There may have been intermediate saves as well.) */
    for (;; mem = &mem->saved->state) {
        if_debug1m('U', (gs_memory_t *)mem, "[U]checking mem="PRI_INTPTR"\n", (intptr_t) mem);
        if (ptr_is_within_mem_clumps(ptr, mem)) {
            if_debug0m('U', (gs_memory_t *)mem, "[U+]found\n");
            return true;
        }
        if_debug1m('U', (gs_memory_t *)mem, "[U-]not in any chunks belonging to "PRI_INTPTR"\n", (intptr_t) mem);
        if (mem->saved == save) {	/* We've checked all the more recent saves, */
            /* must be OK. */
            break;
        }
    }

    /*
     * If we're about to do a global restore (a restore to the level 0),
     * and there is only one context using this global VM
     * (the normal case, in which global VM is saved by the
     * outermost save), we also have to check the global save.
     * Global saves can't be nested, which makes things easy.
     */
    if (save->state.save_level == 0 /* Restoring to save level 0 - see bug 688157, 688161 */ &&
        (mem = save->space_global) != save->space_local &&
        save->space_global->num_contexts == 1
        ) {
        if_debug1m('U', (gs_memory_t *)mem, "[U]checking global mem="PRI_INTPTR"\n", (intptr_t) mem);
        if (ptr_is_within_mem_clumps(ptr, mem)) {
            if_debug0m('U', (gs_memory_t *)mem, "[U+]  found\n");
            return true;
        }
    }
    return false;

#undef ptr
}

/* Test whether a name would be invalidated by a restore. */
bool
alloc_name_is_since_save(const gs_memory_t *mem,
                         const ref * pnref, const alloc_save_t * save)
{
    const name_string_t *pnstr;

    if (!save->restore_names)
        return false;
    pnstr = names_string_inline(mem->gs_lib_ctx->gs_name_table, pnref);
    if (pnstr->foreign_string)
        return false;
    return alloc_is_since_save(pnstr->string_bytes, save);
}
bool
alloc_name_index_is_since_save(const gs_memory_t *mem,
                               uint nidx, const alloc_save_t *save)
{
    const name_string_t *pnstr;

    if (!save->restore_names)
        return false;
    pnstr = names_index_string_inline(mem->gs_lib_ctx->gs_name_table, nidx);
    if (pnstr->foreign_string)
        return false;
    return alloc_is_since_save(pnstr->string_bytes, save);
}

/* Check whether any names have been created since a given save */
/* that might be released by the restore. */
bool
alloc_any_names_since_save(const alloc_save_t * save)
{
    return save->restore_names;
}

/* Get the saved state with a given ID. */
alloc_save_t *
alloc_find_save(const gs_dual_memory_t * dmem, ulong sid)
{
    alloc_save_t *sprev = dmem->space_local->saved;

    if (sid == 0)
        return 0;		/* invalid id */
    while (sprev != 0) {
        if (sprev->id == sid)
            return sprev;
        sprev = sprev->state.saved;
    }
    return 0;
}

/* Get the client data from a saved state. */
void *
alloc_save_client_data(const alloc_save_t * save)
{
    return save->client_data;
}

/*
 * Do one step of restoring the state.  The client is responsible for
 * calling alloc_find_save to get the save object, and for ensuring that
 * there are no surviving pointers for which alloc_is_since_save is true.
 * Return true if the argument was the innermost save, in which case
 * this is the last (or only) step.
 * Note that "one step" may involve multiple internal steps,
 * if this is the outermost restore (which requires restoring both local
 * and global VM) or if we created extra save levels to reduce scanning.
 */
static void restore_finalize(gs_ref_memory_t *);
static void restore_space(gs_ref_memory_t *, gs_dual_memory_t *);

int
alloc_restore_step_in(gs_dual_memory_t *dmem, alloc_save_t * save)
{
    /* Get save->space_* now, because the save object will be freed. */
    gs_ref_memory_t *lmem = save->space_local;
    gs_ref_memory_t *gmem = save->space_global;
    gs_ref_memory_t *mem = lmem;
    alloc_save_t *sprev;
    int code;

    /* Finalize all objects before releasing resources or undoing changes. */
    do {
        ulong sid;

        sprev = mem->saved;
        sid = sprev->id;
        restore_finalize(mem);	/* finalize objects */
        mem = &sprev->state;
        if (sid != 0)
            break;
    }
    while (sprev != save);
    if (mem->save_level == 0) {
        /* This is the outermost save, which might also */
        /* need to restore global VM. */
        mem = gmem;
        if (mem != lmem && mem->saved != 0) {
            restore_finalize(mem);
        }
    }

    /* Do one (externally visible) step of restoring the state. */
    mem = lmem;
    do {
        ulong sid;

        sprev = mem->saved;
        sid = sprev->id;
        code = restore_resources(sprev, mem);	/* release other resources */
        if (code < 0)
            return code;
        restore_space(mem, dmem);	/* release memory */
        if (sid != 0)
            break;
    }
    while (sprev != save);

    if (mem->save_level == 0) {
        /* This is the outermost save, which might also */
        /* need to restore global VM. */
        mem = gmem;
        if (mem != lmem && mem->saved != 0) {
            code = restore_resources(mem->saved, mem);
            if (code < 0)
                return code;
            restore_space(mem, dmem);
        }
        alloc_set_not_in_save(dmem);
    } else {			/* Set the l_new attribute in all slots that are now new. */
        ulong scanned;

        code = save_set_new(mem, true, false, &scanned);
        if (code < 0)
            return code;
    }

    return sprev == save;
}
/* Restore the memory of one space, by undoing changes and freeing */
/* memory allocated since the save. */
static void
restore_space(gs_ref_memory_t * mem, gs_dual_memory_t *dmem)
{
    alloc_save_t *save = mem->saved;
    alloc_save_t saved;

    print_save("restore", mem->space, save);

    /* Undo changes since the save. */
    {
        register alloc_change_t *cp = mem->changes;

        while (cp) {
#ifdef DEBUG
            if (gs_debug_c('U')) {
                dmlputs((const gs_memory_t *)mem, "[U]restore");
                alloc_save_print((const gs_memory_t *)mem, cp, true);
            }
#endif
            if (cp->offset == AC_OFFSET_ALLOCATED)
                DO_NOTHING;
            else
            if (r_is_packed(&cp->contents))
                *cp->where = *(ref_packed *) & cp->contents;
            else
                ref_assign_inline((ref *) cp->where, &cp->contents);
            cp = cp->next;
        }
    }

    /* Free memory allocated since the save. */
    /* Note that this frees all clumps except the inner ones */
    /* belonging to this level. */
    saved = *save;
    restore_free(mem);

    /* Restore the allocator state. */
    {
        int num_contexts = mem->num_contexts;	/* don't restore */

        *mem = saved.state;
        mem->num_contexts = num_contexts;
    }
    alloc_open_clump(mem);

    /* Make the allocator current if it was current before the save. */
    if (saved.is_current) {
        dmem->current = mem;
        dmem->current_space = mem->space;
    }
}

/* Restore to the initial state, releasing all resources. */
/* The allocator is no longer usable after calling this routine! */
int
alloc_restore_all(i_ctx_t *i_ctx_p)
{
    /*
     * Save the memory pointers, since freeing space_local will also
     * free dmem itself.
     */
    gs_ref_memory_t *lmem = idmemory->space_local;
    gs_ref_memory_t *gmem = idmemory->space_global;
    gs_ref_memory_t *smem = idmemory->space_system;

    gs_ref_memory_t *mem;
    int code;

    /* Restore to a state outside any saves. */
    while (lmem->save_level != 0) {
        vm_save_t *vmsave = alloc_save_client_data(alloc_save_current(idmemory));
        if (vmsave->gsave) {
            gs_grestoreall_for_restore(i_ctx_p->pgs, vmsave->gsave);
        }
        vmsave->gsave = 0;
        code = alloc_restore_step_in(idmemory, lmem->saved);

        if (code < 0)
            return code;
    }

    /* Finalize memory. */
    restore_finalize(lmem);
    if ((mem = (gs_ref_memory_t *)lmem->stable_memory) != lmem)
        restore_finalize(mem);
    if (gmem != lmem && gmem->num_contexts == 1) {
        restore_finalize(gmem);
        if ((mem = (gs_ref_memory_t *)gmem->stable_memory) != gmem)
            restore_finalize(mem);
    }
    restore_finalize(smem);

    /* Release resources other than memory, using fake */
    /* save and memory objects. */
    {
        alloc_save_t empty_save;

        empty_save.spaces = idmemory->spaces;
        empty_save.restore_names = false;	/* don't bother to release */
        code = restore_resources(&empty_save, NULL);
        if (code < 0)
            return code;
    }

    /* Finally, release memory. */
    restore_free(lmem);
    if ((mem = (gs_ref_memory_t *)lmem->stable_memory) != lmem)
        restore_free(mem);
    if (gmem != lmem) {
        if (!--(gmem->num_contexts)) {
            restore_free(gmem);
            if ((mem = (gs_ref_memory_t *)gmem->stable_memory) != gmem)
                restore_free(mem);
        }
    }
    restore_free(smem);
    return 0;
}

/*
 * Finalize objects that will be freed by a restore.
 * Note that we must temporarily disable the freeing operations
 * of the allocator while doing this.
 */
static void
restore_finalize(gs_ref_memory_t * mem)
{
    clump_t *cp;
    clump_splay_walker sw;

    alloc_close_clump(mem);
    gs_enable_free((gs_memory_t *) mem, false);
    for (cp = clump_splay_walk_bwd_init(&sw, mem); cp != 0; cp = clump_splay_walk_bwd(&sw)) {
        SCAN_CLUMP_OBJECTS(cp)
            DO_ALL
            struct_proc_finalize((*finalize)) =
            pre->o_type->finalize;
        if (finalize != 0) {
            if_debug2m('u', (gs_memory_t *)mem, "[u]restore finalizing %s "PRI_INTPTR"\n",
                       struct_type_name_string(pre->o_type),
                       (intptr_t) (pre + 1));
            (*finalize) ((gs_memory_t *) mem, pre + 1);
        }
        END_OBJECTS_SCAN
    }
    gs_enable_free((gs_memory_t *) mem, true);
}

/* Release resources for a restore */
static int
restore_resources(alloc_save_t * sprev, gs_ref_memory_t * mem)
{
    int code;
#ifdef DEBUG
    if (mem) {
        /* Note restoring of the file list. */
        if_debug4m('u', (gs_memory_t *)mem, "[u%u]file_restore "PRI_INTPTR" => "PRI_INTPTR" for "PRI_INTPTR"\n",
                   mem->space, (intptr_t)mem->streams,
                   (intptr_t)sprev->state.streams, (intptr_t)sprev);
    }
#endif

    /* Remove entries from font and character caches. */
    code = font_restore(sprev);
    if (code < 0)
        return code;

    /* Adjust the name table. */
    if (sprev->restore_names)
        names_restore(mem->gs_lib_ctx->gs_name_table, sprev);
    return 0;
}

/* Release memory for a restore. */
static void
restore_free(gs_ref_memory_t * mem)
{
    /* Free clumps allocated since the save. */
    gs_free_all((gs_memory_t *) mem);
}

/* Forget a save, by merging this level with the next outer one. */
static void file_forget_save(gs_ref_memory_t *);
static void combine_space(gs_ref_memory_t *);
static void forget_changes(gs_ref_memory_t *);
int
alloc_forget_save_in(gs_dual_memory_t *dmem, alloc_save_t * save)
{
    gs_ref_memory_t *mem = save->space_local;
    alloc_save_t *sprev;
    ulong scanned;
    int code;

    print_save("forget_save", mem->space, save);

    /* Iteratively combine the current level with the previous one. */
    do {
        sprev = mem->saved;
        if (sprev->id != 0)
            mem->save_level--;
        if (mem->save_level != 0) {
            alloc_change_t *chp = mem->changes;

            code = save_set_new(&sprev->state, true, false, &scanned);
            if (code < 0)
                return code;
            /* Concatenate the changes chains. */
            if (chp == 0)
                mem->changes = sprev->state.changes;
            else {
                while (chp->next != 0)
                    chp = chp->next;
                chp->next = sprev->state.changes;
            }
            file_forget_save(mem);
            combine_space(mem);	/* combine memory */
        } else {
            forget_changes(mem);
            code = save_set_new(mem, false, false, &scanned);
            if (code < 0)
                return code;
            file_forget_save(mem);
            combine_space(mem);	/* combine memory */
            /* This is the outermost save, which might also */
            /* need to combine global VM. */
            mem = save->space_global;
            if (mem != save->space_local && mem->saved != 0) {
                forget_changes(mem);
                code = save_set_new(mem, false, false, &scanned);
                if (code < 0)
                    return code;
                file_forget_save(mem);
                combine_space(mem);
            }
            alloc_set_not_in_save(dmem);
            break;		/* must be outermost */
        }
    }
    while (sprev != save);
    return 0;
}
/* Combine the clumps of the next outer level with those of the current one, */
/* and free the bookkeeping structures. */
static void
combine_space(gs_ref_memory_t * mem)
{
    alloc_save_t *saved = mem->saved;
    gs_ref_memory_t *omem = &saved->state;
    clump_t *cp;
    clump_splay_walker sw;

    alloc_close_clump(mem);
    for (cp = clump_splay_walk_init(&sw, mem); cp != 0; cp = clump_splay_walk_fwd(&sw)) {
        if (cp->outer == 0)
            alloc_link_clump(cp, omem);
        else {
            clump_t *outer = cp->outer;

            outer->inner_count--;
            if (mem->cc == cp)
                mem->cc = outer;
            if (mem->cfreed.cp == cp)
                mem->cfreed.cp = outer;
            /* "Free" the header of the inner clump, */
            /* and any immediately preceding gap left by */
            /* the GC having compacted the outer clump. */
            {
                obj_header_t *hp = (obj_header_t *) outer->cbot;

                hp->o_pad = 0;
                hp->o_alone = 0;
                hp->o_size = (char *)(cp->chead + 1)
                    - (char *)(hp + 1);
                hp->o_type = &st_bytes;
                /* The following call is probably not safe. */
#if 0				/* **************** */
                gs_free_object((gs_memory_t *) mem,
                               hp + 1, "combine_space(header)");
#endif /* **************** */
            }
            /* Update the outer clump's allocation pointers. */
            outer->cbot = cp->cbot;
            outer->rcur = cp->rcur;
            outer->rtop = cp->rtop;
            outer->ctop = cp->ctop;
            outer->has_refs |= cp->has_refs;
            gs_free_object(mem->non_gc_memory, cp,
                           "combine_space(inner)");
        }
    }
    /* Update relevant parts of allocator state. */
    mem->root = omem->root;
    mem->allocated += omem->allocated;
    mem->gc_allocated += omem->allocated;
    mem->lost.objects += omem->lost.objects;
    mem->lost.refs += omem->lost.refs;
    mem->lost.strings += omem->lost.strings;
    mem->saved = omem->saved;
    mem->previous_status = omem->previous_status;
    {				/* Concatenate free lists. */
        int i;

        for (i = 0; i < num_freelists; i++) {
            obj_header_t *olist = omem->freelists[i];
            obj_header_t *list = mem->freelists[i];

            if (olist == 0);
            else if (list == 0)
                mem->freelists[i] = olist;
            else {
                while (*(obj_header_t **) list != 0)
                    list = *(obj_header_t **) list;
                *(obj_header_t **) list = olist;
            }
        }
        if (omem->largest_free_size > mem->largest_free_size)
            mem->largest_free_size = omem->largest_free_size;
    }
    gs_free_object((gs_memory_t *) mem, saved, "combine_space(saved)");
    alloc_open_clump(mem);
}
/* Free the changes chain for a level 0 .forgetsave, */
/* resetting the l_new flag in the changed refs. */
static void
forget_changes(gs_ref_memory_t * mem)
{
    register alloc_change_t *chp = mem->changes;
    alloc_change_t *next;

    for (; chp; chp = next) {
        ref_packed *prp = chp->where;

        if_debug1m('U', (gs_memory_t *)mem, "[U]forgetting change "PRI_INTPTR"\n", (intptr_t) chp);
        if (chp->offset == AC_OFFSET_ALLOCATED)
            DO_NOTHING;
        else
        if (!r_is_packed(prp))
            r_clear_attrs((ref *) prp, l_new);
        next = chp->next;
        gs_free_object((gs_memory_t *) mem, chp, "forget_changes");
    }
    mem->changes = 0;
}
/* Update the streams list when forgetting a save. */
static void
file_forget_save(gs_ref_memory_t * mem)
{
    const alloc_save_t *save = mem->saved;
    stream *streams = mem->streams;
    stream *saved_streams = save->state.streams;

    if_debug4m('u', (gs_memory_t *)mem, "[u%d]file_forget_save "PRI_INTPTR" + "PRI_INTPTR" for "PRI_INTPTR"\n",
               mem->space, (intptr_t) streams, (intptr_t) saved_streams,
               (intptr_t) save);
    if (streams == 0)
        mem->streams = saved_streams;
    else if (saved_streams != 0) {
        while (streams->next != 0)
            streams = streams->next;
        streams->next = saved_streams;
        saved_streams->prev = streams;
    }
}

static inline int
mark_allocated(void *obj, bool to_new, uint *psize)
{
    obj_header_t *pre = (obj_header_t *)obj - 1;
    uint size = pre_obj_contents_size(pre);
    ref_packed *prp = (ref_packed *) (pre + 1);
    ref_packed *next = (ref_packed *) ((char *)prp + size);
#ifdef ALIGNMENT_ALIASING_BUG
                ref *rpref;
# define RP_REF(rp) (rpref = (ref *)rp, rpref)
#else
# define RP_REF(rp) ((ref *)rp)
#endif

    if (pre->o_type != &st_refs) {
        /* Must not happen. */
        if_debug0('u', "Wrong object type when expected a ref.\n");
        return_error(gs_error_Fatal);
    }
    /* We know that every block of refs ends with */
    /* a full-size ref, so we only need the end check */
    /* when we encounter one of those. */
    if (to_new)
        while (1) {
            if (r_is_packed(prp))
                prp++;
            else {
                RP_REF(prp)->tas.type_attrs |= l_new;
                prp += packed_per_ref;
                if (prp >= next)
                    break;
            }
    } else
        while (1) {
            if (r_is_packed(prp))
                prp++;
            else {
                RP_REF(prp)->tas.type_attrs &= ~l_new;
                prp += packed_per_ref;
                if (prp >= next)
                    break;
            }
        }
#undef RP_REF
    *psize = size;
    return 0;
}

/* Check if a block contains refs marked by garbager. */
static bool
check_l_mark(void *obj)
{
    obj_header_t *pre = (obj_header_t *)obj - 1;
    uint size = pre_obj_contents_size(pre);
    ref_packed *prp = (ref_packed *) (pre + 1);
    ref_packed *next = (ref_packed *) ((char *)prp + size);
#ifdef ALIGNMENT_ALIASING_BUG
                ref *rpref;
# define RP_REF(rp) (rpref = (ref *)rp, rpref)
#else
# define RP_REF(rp) ((ref *)rp)
#endif

    /* We know that every block of refs ends with */
    /* a full-size ref, so we only need the end check */
    /* when we encounter one of those. */
    while (1) {
        if (r_is_packed(prp)) {
            if (r_has_pmark(prp))
                return true;
            prp++;
        } else {
            if (r_has_attr(RP_REF(prp), l_mark))
                return true;
            prp += packed_per_ref;
            if (prp >= next)
                return false;
        }
    }
#undef RP_REF
}

/* Set or reset the l_new attribute in every relevant slot. */
/* This includes every slot on the current change chain, */
/* and every (ref) slot allocated at this save level. */
/* Return the number of bytes of data scanned. */
static int
save_set_new(gs_ref_memory_t * mem, bool to_new, bool set_limit, ulong *pscanned)
{
    ulong scanned = 0;
    int code;

    /* Handle the change chain. */
    code = save_set_new_changes(mem, to_new, set_limit);
    if (code < 0)
        return code;

    /* Handle newly allocated ref objects. */
    SCAN_MEM_CLUMPS(mem, cp) {
        if (cp->has_refs) {
            bool has_refs = false;

            SCAN_CLUMP_OBJECTS(cp)
                DO_ALL
                if_debug3m('U', (gs_memory_t *)mem, "[U]set_new scan("PRI_INTPTR"(%u), %d)\n",
                           (intptr_t) pre, size, to_new);
            if (pre->o_type == &st_refs) {
                /* These are refs, scan them. */
                ref_packed *prp = (ref_packed *) (pre + 1);
                uint size;
                has_refs = true && to_new;
                code = mark_allocated(prp, to_new, &size);
                if (code < 0)
                    return code;
                scanned += size;
            } else
                scanned += sizeof(obj_header_t);
            END_OBJECTS_SCAN
                cp->has_refs = has_refs;
        }
    }
    END_CLUMPS_SCAN
    if_debug2m('u', (gs_memory_t *)mem, "[u]set_new (%s) scanned %ld\n",
               (to_new ? "restore" : "save"), scanned);
    *pscanned = scanned;
    return 0;
}

/* Drop redundant elements from the changes list and set l_new. */
static void
drop_redundant_changes(gs_ref_memory_t * mem)
{
    register alloc_change_t *chp = mem->changes, *chp_back = NULL, *chp_forth;

    /* As we are trying to throw away redundant changes in an allocator instance
       that has already been "saved", the active clump has already been "closed"
       by alloc_save_space(). Using such an allocator (for example, by calling
       gs_free_object() with it) can leave it in an unstable state, causing
       problems for the garbage collector (specifically, the clump validator code).
       So, before we might use it, open the current clump, and then close it again
       when we're done.
     */
    alloc_open_clump(mem);

    /* First reverse the list and set all. */
    for (; chp; chp = chp_forth) {
        chp_forth = chp->next;
        if (chp->offset != AC_OFFSET_ALLOCATED) {
            ref_packed *prp = chp->where;

            if (!r_is_packed(prp)) {
                ref *const rp = (ref *)prp;

                rp->tas.type_attrs |= l_new;
            }
        }
        chp->next = chp_back;
        chp_back = chp;
    }
    mem->changes = chp_back;
    chp_back = NULL;
    /* Then filter, reset and reverse again. */
    for (chp = mem->changes; chp; chp = chp_forth) {
        chp_forth = chp->next;
        if (chp->offset != AC_OFFSET_ALLOCATED) {
            ref_packed *prp = chp->where;

            if (!r_is_packed(prp)) {
                ref *const rp = (ref *)prp;

                if ((rp->tas.type_attrs & l_new) == 0) {
                    if (mem->scan_limit == chp)
                        mem->scan_limit = chp_back;
                    if (mem->changes == chp)
                        mem->changes = chp_back;
                    gs_free_object((gs_memory_t *)mem, chp, "alloc_save_remove");
                    continue;
                } else
                    rp->tas.type_attrs &= ~l_new;
            }
        }
        chp->next = chp_back;
        chp_back = chp;
    }
    mem->changes = chp_back;

    alloc_close_clump(mem);
}

/* Set or reset the l_new attribute on the changes chain. */
static int
save_set_new_changes(gs_ref_memory_t * mem, bool to_new, bool set_limit)
{
    register alloc_change_t *chp;
    register uint new = (to_new ? l_new : 0);
    ulong scanned = 0;

    if (!to_new && mem->total_scanned_after_compacting > max_repeated_scan * 16) {
        mem->total_scanned_after_compacting = 0;
        drop_redundant_changes(mem);
    }
    for (chp = mem->changes; chp; chp = chp->next) {
        if (chp->offset == AC_OFFSET_ALLOCATED) {
            if (chp->where != 0) {
                uint size;
                int code = mark_allocated((void *)chp->where, to_new, &size);

                if (code < 0)
                    return code;
                scanned += size;
            }
        } else {
            ref_packed *prp = chp->where;

            if_debug3m('U', (gs_memory_t *)mem, "[U]set_new "PRI_INTPTR": ("PRI_INTPTR", %d)\n",
                       (intptr_t)chp, (intptr_t)prp, new);
            if (!r_is_packed(prp)) {
                ref *const rp = (ref *) prp;

                rp->tas.type_attrs =
                    (rp->tas.type_attrs & ~l_new) + new;
            }
        }
        if (mem->scan_limit == chp)
            break;
    }
    if (set_limit) {
        mem->total_scanned_after_compacting += scanned;
        if (scanned  + mem->total_scanned >= max_repeated_scan) {
            mem->scan_limit = mem->changes;
            mem->total_scanned = 0;
        } else
            mem->total_scanned += scanned;
    }
    return 0;
}

gs_memory_t *
gs_save_any_memory(const alloc_save_t *save)
{
    return((gs_memory_t *)save->space_local);
}