/*
 * Copyright 2014, General Dynamics C4 Systems
 *
 * This software may be distributed and modified according to the terms of
 * the GNU General Public License version 2. Note that NO WARRANTY is provided.
 * See "LICENSE_GPLv2.txt" for details.
 *
 * @TAG(GD_GPL)
 */

#include <assert.h>
#include <kernel/boot.h>
#include <kernel/thread.h>
#include <machine/io.h>
#include <machine/registerset.h>
#include <model/statedata.h>
#include <arch/machine.h>
#include <arch/kernel/boot.h>
#include <arch/kernel/vspace.h>
#include <linker.h>
#include <plat/machine/hardware.h>
#include <util.h>

/* (node-local) state accessed only during bootstrapping */
ndks_boot_t ndks_boot BOOT_DATA;

rootserver_mem_t rootserver BOOT_DATA;
static region_t rootserver_mem BOOT_DATA;

BOOT_CODE bool_t insert_region(region_t reg)
{
    word_t i;

    assert(reg.start <= reg.end);
    if (is_reg_empty(reg)) {
        return true;
    }
    for (i = 0; i < MAX_NUM_FREEMEM_REG; i++) {
        if (is_reg_empty(ndks_boot.freemem[i])) {
            ndks_boot.freemem[i] = reg;
            return true;
        }
    }
#ifdef CONFIG_ARCH_ARM
    /* boot.h should have calculated MAX_NUM_FREEMEM_REG correctly.
     * If we've run out, then something is wrong.
     * Note that the capDL allocation toolchain does not know about
     * MAX_NUM_FREEMEM_REG, so throwing away regions may prevent
     * capDL applications from being loaded! */
    printf("Can't fit memory region 0x%lx-0x%lx, try increasing MAX_NUM_FREEMEM_REG (currently %d)\n",
           reg.start, reg.end, (int)MAX_NUM_FREEMEM_REG);
    assert(!"Ran out of freemem slots");
#else
    printf("Dropping memory region 0x%lx-0x%lx, try increasing MAX_NUM_FREEMEM_REG (currently %d)\n",
           reg.start, reg.end, (int)MAX_NUM_FREEMEM_REG);
#endif
    return false;
}

BOOT_CODE static pptr_t alloc_rootserver_obj(word_t size_bits, word_t n)
{
    pptr_t allocated = rootserver_mem.start;
    /* allocated memory must be aligned */
    assert(allocated % BIT(size_bits) == 0);
    rootserver_mem.start += (n * BIT(size_bits));
    /* we must not have run out of memory */
    assert(rootserver_mem.start <= rootserver_mem.end);
    memzero((void *) allocated, n * BIT(size_bits));
    return allocated;
}

BOOT_CODE static word_t rootserver_max_size_bits(word_t extra_bi_size_bits)
{
    word_t cnode_size_bits = CONFIG_ROOT_CNODE_SIZE_BITS + seL4_SlotBits;
    word_t max = MAX(cnode_size_bits, seL4_VSpaceBits);
    return MAX(max, extra_bi_size_bits);
}

BOOT_CODE static word_t calculate_rootserver_size(v_region_t v_reg, word_t extra_bi_size_bits)
{
    /* work out how much memory we need for root server objects */
    word_t size = BIT(CONFIG_ROOT_CNODE_SIZE_BITS + seL4_SlotBits);
    size += BIT(seL4_TCBBits); // root thread tcb
    size += 2 * BIT(seL4_PageBits); // boot info + ipc buf
    size += BIT(seL4_ASIDPoolBits);
    size += extra_bi_size_bits > 0 ? BIT(extra_bi_size_bits) : 0;
    size += BIT(seL4_VSpaceBits); // root vspace
    /* for all archs, seL4_PageTable Bits is the size of all non top-level paging structures */
    return size + arch_get_n_paging(v_reg) * BIT(seL4_PageTableBits);
}

BOOT_CODE static void maybe_alloc_extra_bi(word_t cmp_size_bits, word_t extra_bi_size_bits)
{
    if (extra_bi_size_bits >= cmp_size_bits && rootserver.extra_bi == 0) {
        rootserver.extra_bi = alloc_rootserver_obj(extra_bi_size_bits, 1);
    }
}

BOOT_CODE void create_rootserver_objects(pptr_t start, v_region_t v_reg, word_t extra_bi_size_bits)
{
    /* the largest object the PD, the root cnode, or the extra boot info */
    word_t cnode_size_bits = CONFIG_ROOT_CNODE_SIZE_BITS + seL4_SlotBits;
    word_t max = rootserver_max_size_bits(extra_bi_size_bits);

    word_t size = calculate_rootserver_size(v_reg, extra_bi_size_bits);
    rootserver_mem.start = start;
    rootserver_mem.end = start + size;

    maybe_alloc_extra_bi(max, extra_bi_size_bits);

    /* the root cnode is at least 4k, so it could be larger or smaller than a pd. */
#if (CONFIG_ROOT_CNODE_SIZE_BITS + seL4_SlotBits) > seL4_VSpaceBits
    rootserver.cnode = alloc_rootserver_obj(cnode_size_bits, 1);
    maybe_alloc_extra_bi(seL4_VSpaceBits, extra_bi_size_bits);
    rootserver.vspace = alloc_rootserver_obj(seL4_VSpaceBits, 1);
#else
    rootserver.vspace = alloc_rootserver_obj(seL4_VSpaceBits, 1);
    maybe_alloc_extra_bi(cnode_size_bits, extra_bi_size_bits);
    rootserver.cnode = alloc_rootserver_obj(cnode_size_bits, 1);
#endif

    /* at this point we are up to creating 4k objects - which is the min size of
     * extra_bi so this is the last chance to allocate it */
    maybe_alloc_extra_bi(seL4_PageBits, extra_bi_size_bits);
    rootserver.asid_pool = alloc_rootserver_obj(seL4_ASIDPoolBits, 1);
    rootserver.ipc_buf = alloc_rootserver_obj(seL4_PageBits, 1);
    rootserver.boot_info = alloc_rootserver_obj(seL4_PageBits, 1);

    /* TCBs on aarch32 can be larger than page tables in certain configs */
#if seL4_TCBBits >= seL4_PageTableBits
    rootserver.tcb = alloc_rootserver_obj(seL4_TCBBits, 1);
#endif

    /* paging structures are 4k on every arch except aarch32 (1k) */
    word_t n = arch_get_n_paging(v_reg);
    rootserver.paging.start = alloc_rootserver_obj(seL4_PageTableBits, n);
    rootserver.paging.end = rootserver.paging.start + n * BIT(seL4_PageTableBits);

    /* for most archs, TCBs are smaller than page tables */
#if seL4_TCBBits < seL4_PageTableBits
    rootserver.tcb = alloc_rootserver_obj(seL4_TCBBits, 1);
#endif
    /* we should have allocated all our memory */
    assert(rootserver_mem.start == rootserver_mem.end);
}

BOOT_CODE void write_slot(slot_ptr_t slot_ptr, cap_t cap)
{
    slot_ptr->cap = cap;

    slot_ptr->cteMDBNode = nullMDBNode;
    mdb_node_ptr_set_mdbRevocable(&slot_ptr->cteMDBNode, true);
    mdb_node_ptr_set_mdbFirstBadged(&slot_ptr->cteMDBNode, true);
}

/* Our root CNode needs to be able to fit all the initial caps and not
 * cover all of memory.
 */
compile_assert(root_cnode_size_valid,
               CONFIG_ROOT_CNODE_SIZE_BITS < 32 - seL4_SlotBits &&
               BIT(CONFIG_ROOT_CNODE_SIZE_BITS) >= seL4_NumInitialCaps &&
               BIT(CONFIG_ROOT_CNODE_SIZE_BITS) >= (seL4_PageBits - seL4_SlotBits))

BOOT_CODE cap_t
create_root_cnode(void)
{
    /* write the number of root CNode slots to global state */
    ndks_boot.slot_pos_max = BIT(CONFIG_ROOT_CNODE_SIZE_BITS);

    cap_t cap =
        cap_cnode_cap_new(
            CONFIG_ROOT_CNODE_SIZE_BITS,      /* radix      */
            wordBits - CONFIG_ROOT_CNODE_SIZE_BITS, /* guard size */
            0,                                /* guard      */
            rootserver.cnode              /* pptr       */
        );

    /* write the root CNode cap into the root CNode */
    write_slot(SLOT_PTR(rootserver.cnode, seL4_CapInitThreadCNode), cap);

    return cap;
}

/* Check domain scheduler assumptions. */
compile_assert(num_domains_valid,
               CONFIG_NUM_DOMAINS >= 1 && CONFIG_NUM_DOMAINS <= 256)
compile_assert(num_priorities_valid,
               CONFIG_NUM_PRIORITIES >= 1 && CONFIG_NUM_PRIORITIES <= 256)

BOOT_CODE void
create_domain_cap(cap_t root_cnode_cap)
{
    /* Check domain scheduler assumptions. */
    assert(ksDomScheduleLength > 0);
    for (word_t i = 0; i < ksDomScheduleLength; i++) {
        assert(ksDomSchedule[i].domain < CONFIG_NUM_DOMAINS);
        assert(ksDomSchedule[i].length > 0);
    }

    cap_t cap = cap_domain_cap_new();
    write_slot(SLOT_PTR(pptr_of_cap(root_cnode_cap), seL4_CapDomain), cap);
}


BOOT_CODE cap_t create_ipcbuf_frame_cap(cap_t root_cnode_cap, cap_t pd_cap, vptr_t vptr)
{
    clearMemory((void *)rootserver.ipc_buf, PAGE_BITS);

    /* create a cap of it and write it into the root CNode */
    cap_t cap = create_mapped_it_frame_cap(pd_cap, rootserver.ipc_buf, vptr, IT_ASID, false, false);
    write_slot(SLOT_PTR(pptr_of_cap(root_cnode_cap), seL4_CapInitThreadIPCBuffer), cap);

    return cap;
}

BOOT_CODE void create_bi_frame_cap(cap_t root_cnode_cap, cap_t pd_cap, vptr_t vptr)
{
    /* create a cap of it and write it into the root CNode */
    cap_t cap = create_mapped_it_frame_cap(pd_cap, rootserver.boot_info, vptr, IT_ASID, false, false);
    write_slot(SLOT_PTR(pptr_of_cap(root_cnode_cap), seL4_CapBootInfoFrame), cap);
}

BOOT_CODE word_t calculate_extra_bi_size_bits(word_t extra_size)
{
    if (extra_size == 0) {
        return 0;
    }

    word_t clzl_ret = clzl(ROUND_UP(extra_size, seL4_PageBits));
    /* If region is bigger than a page, make sure we overallocate rather than underallocate */
    if (extra_size & ((1 << clzl_ret) - 1)) {
        clzl_ret--;
    }
    return seL4_WordBits - 1 - clzl_ret;
}

BOOT_CODE void populate_bi_frame(node_id_t node_id, word_t num_nodes, vptr_t ipcbuf_vptr,
                                 word_t extra_bi_size)
{
    clearMemory((void *) rootserver.boot_info, BI_FRAME_SIZE_BITS);
    if (extra_bi_size) {
        clearMemory((void *) rootserver.extra_bi, calculate_extra_bi_size_bits(extra_bi_size));
    }

    /* initialise bootinfo-related global state */
    ndks_boot.bi_frame = BI_PTR(rootserver.boot_info);
    ndks_boot.slot_pos_cur = seL4_NumInitialCaps;
    BI_PTR(rootserver.boot_info)->nodeID = node_id;
    BI_PTR(rootserver.boot_info)->numNodes = num_nodes;
    BI_PTR(rootserver.boot_info)->numIOPTLevels = 0;
    BI_PTR(rootserver.boot_info)->ipcBuffer = (seL4_IPCBuffer *) ipcbuf_vptr;
    BI_PTR(rootserver.boot_info)->initThreadCNodeSizeBits = CONFIG_ROOT_CNODE_SIZE_BITS;
    BI_PTR(rootserver.boot_info)->initThreadDomain = ksDomSchedule[ksDomScheduleIdx].domain;
    BI_PTR(rootserver.boot_info)->extraLen = extra_bi_size;
}

BOOT_CODE bool_t provide_cap(cap_t root_cnode_cap, cap_t cap)
{
    if (ndks_boot.slot_pos_cur >= ndks_boot.slot_pos_max) {
        printf("Kernel init failed: ran out of cap slots\n");
        return false;
    }
    write_slot(SLOT_PTR(pptr_of_cap(root_cnode_cap), ndks_boot.slot_pos_cur), cap);
    ndks_boot.slot_pos_cur++;
    return true;
}

BOOT_CODE create_frames_of_region_ret_t create_frames_of_region(
    cap_t    root_cnode_cap,
    cap_t    pd_cap,
    region_t reg,
    bool_t   do_map,
    sword_t  pv_offset
)
{
    pptr_t     f;
    cap_t      frame_cap;
    seL4_SlotPos slot_pos_before;
    seL4_SlotPos slot_pos_after;

    slot_pos_before = ndks_boot.slot_pos_cur;

    for (f = reg.start; f < reg.end; f += BIT(PAGE_BITS)) {
        if (do_map) {
            frame_cap = create_mapped_it_frame_cap(pd_cap, f, pptr_to_paddr((void *)(f - pv_offset)), IT_ASID, false, true);
        } else {
            frame_cap = create_unmapped_it_frame_cap(f, false);
        }
        if (!provide_cap(root_cnode_cap, frame_cap))
            return (create_frames_of_region_ret_t) {
            S_REG_EMPTY, false
        };
    }

    slot_pos_after = ndks_boot.slot_pos_cur;

    return (create_frames_of_region_ret_t) {
        (seL4_SlotRegion) { slot_pos_before, slot_pos_after }, true
    };
}

BOOT_CODE cap_t create_it_asid_pool(cap_t root_cnode_cap)
{
    cap_t ap_cap = cap_asid_pool_cap_new(IT_ASID >> asidLowBits, rootserver.asid_pool);
    write_slot(SLOT_PTR(pptr_of_cap(root_cnode_cap), seL4_CapInitThreadASIDPool), ap_cap);

    /* create ASID control cap */
    write_slot(
        SLOT_PTR(pptr_of_cap(root_cnode_cap), seL4_CapASIDControl),
        cap_asid_control_cap_new()
    );

    return ap_cap;
}

BOOT_CODE bool_t create_idle_thread(void)
{
    pptr_t pptr;

#ifdef ENABLE_SMP_SUPPORT
    for (int i = 0; i < CONFIG_MAX_NUM_NODES; i++) {
#endif /* ENABLE_SMP_SUPPORT */
        pptr = (pptr_t) &ksIdleThreadTCB[SMP_TERNARY(i, 0)];
        NODE_STATE_ON_CORE(ksIdleThread, i) = TCB_PTR(pptr + TCB_OFFSET);
        configureIdleThread(NODE_STATE_ON_CORE(ksIdleThread, i));
#ifdef CONFIG_DEBUG_BUILD
        setThreadName(NODE_STATE_ON_CORE(ksIdleThread, i), "idle_thread");
#endif
        SMP_COND_STATEMENT(NODE_STATE_ON_CORE(ksIdleThread, i)->tcbAffinity = i);
#ifdef ENABLE_SMP_SUPPORT
    }
#endif /* ENABLE_SMP_SUPPORT */
    return true;
}

BOOT_CODE tcb_t *create_initial_thread(cap_t root_cnode_cap, cap_t it_pd_cap, vptr_t ui_v_entry, vptr_t bi_frame_vptr,
                                       vptr_t ipcbuf_vptr, cap_t ipcbuf_cap)
{
    tcb_t *tcb = TCB_PTR(rootserver.tcb + TCB_OFFSET);
    tcb->tcbTimeSlice = CONFIG_TIME_SLICE;
    Arch_initContext(&tcb->tcbArch.tcbContext);

    /* derive a copy of the IPC buffer cap for inserting */
    deriveCap_ret_t dc_ret = deriveCap(SLOT_PTR(pptr_of_cap(root_cnode_cap), seL4_CapInitThreadIPCBuffer), ipcbuf_cap);
    if (dc_ret.status != EXCEPTION_NONE) {
        printf("Failed to derive copy of IPC Buffer\n");
        return NULL;
    }

    /* initialise TCB (corresponds directly to abstract specification) */
    cteInsert(
        root_cnode_cap,
        SLOT_PTR(pptr_of_cap(root_cnode_cap), seL4_CapInitThreadCNode),
        SLOT_PTR(rootserver.tcb, tcbCTable)
    );
    cteInsert(
        it_pd_cap,
        SLOT_PTR(pptr_of_cap(root_cnode_cap), seL4_CapInitThreadVSpace),
        SLOT_PTR(rootserver.tcb, tcbVTable)
    );
    cteInsert(
        dc_ret.cap,
        SLOT_PTR(pptr_of_cap(root_cnode_cap), seL4_CapInitThreadIPCBuffer),
        SLOT_PTR(rootserver.tcb, tcbBuffer)
    );
    tcb->tcbIPCBuffer = ipcbuf_vptr;

    /* Set the root thread's IPC buffer */
    Arch_setTCBIPCBuffer(tcb, ipcbuf_vptr);

    setRegister(tcb, capRegister, bi_frame_vptr);
    setNextPC(tcb, ui_v_entry);

    /* initialise TCB */
    tcb->tcbPriority = seL4_MaxPrio;
    tcb->tcbMCP = seL4_MaxPrio;
    setupReplyMaster(tcb);
    setThreadState(tcb, ThreadState_Running);

    ksCurDomain = ksDomSchedule[ksDomScheduleIdx].domain;
    ksDomainTime = ksDomSchedule[ksDomScheduleIdx].length;
    assert(ksCurDomain < CONFIG_NUM_DOMAINS && ksDomainTime > 0);

    SMP_COND_STATEMENT(tcb->tcbAffinity = 0);

    /* create initial thread's TCB cap */
    cap_t cap = cap_thread_cap_new(TCB_REF(tcb));
    write_slot(SLOT_PTR(pptr_of_cap(root_cnode_cap), seL4_CapInitThreadTCB), cap);

#ifdef CONFIG_DEBUG_BUILD
    setThreadName(tcb, "rootserver");
#endif

    return tcb;
}

BOOT_CODE void init_core_state(tcb_t *scheduler_action)
{
#ifdef CONFIG_HAVE_FPU
    NODE_STATE(ksActiveFPUState) = NULL;
#endif
#ifdef CONFIG_DEBUG_BUILD
    /* add initial threads to the debug queue */
    NODE_STATE(ksDebugTCBs) = NULL;
    if (scheduler_action != SchedulerAction_ResumeCurrentThread &&
        scheduler_action != SchedulerAction_ChooseNewThread) {
        tcbDebugAppend(scheduler_action);
    }
    tcbDebugAppend(NODE_STATE(ksIdleThread));
#endif
    NODE_STATE(ksSchedulerAction) = scheduler_action;
    NODE_STATE(ksCurThread) = NODE_STATE(ksIdleThread);
}

BOOT_CODE static bool_t provide_untyped_cap(
    cap_t      root_cnode_cap,
    bool_t     device_memory,
    pptr_t     pptr,
    word_t     size_bits,
    seL4_SlotPos first_untyped_slot
)
{
    bool_t ret;
    cap_t ut_cap;
    word_t i = ndks_boot.slot_pos_cur - first_untyped_slot;
    if (i < CONFIG_MAX_NUM_BOOTINFO_UNTYPED_CAPS) {
        ndks_boot.bi_frame->untypedList[i] = (seL4_UntypedDesc) {
            pptr_to_paddr((void *)pptr), 0, 0, size_bits, device_memory
        };
        ut_cap = cap_untyped_cap_new(MAX_FREE_INDEX(size_bits),
                                     device_memory, size_bits, pptr);
        ret = provide_cap(root_cnode_cap, ut_cap);
    } else {
        printf("Kernel init: Too many untyped regions for boot info\n");
        ret = true;
    }
    return ret;
}

BOOT_CODE bool_t create_untypeds_for_region(
    cap_t      root_cnode_cap,
    bool_t     device_memory,
    region_t   reg,
    seL4_SlotPos first_untyped_slot
)
{
    word_t align_bits;
    word_t size_bits;

    while (!is_reg_empty(reg)) {
        /* Determine the maximum size of the region */
        size_bits = seL4_WordBits - 1 - clzl(reg.end - reg.start);

        /* Determine the alignment of the region */
        if (reg.start != 0) {
            align_bits = ctzl(reg.start);
        } else {
            align_bits = size_bits;
        }
        /* Reduce size bits to align if needed */
        if (align_bits < size_bits) {
            size_bits = align_bits;
        }
        if (size_bits > seL4_MaxUntypedBits) {
            size_bits = seL4_MaxUntypedBits;
        }

        if (size_bits >= seL4_MinUntypedBits) {
            if (!provide_untyped_cap(root_cnode_cap, device_memory, reg.start, size_bits, first_untyped_slot)) {
                return false;
            }
        }
        reg.start += BIT(size_bits);
    }
    return true;
}

BOOT_CODE bool_t create_kernel_untypeds(cap_t root_cnode_cap, region_t boot_mem_reuse_reg,
                                        seL4_SlotPos first_untyped_slot)
{
    word_t     i;
    region_t   reg;

    /* if boot_mem_reuse_reg is not empty, we can create UT objs from boot code/data frames */
    if (!create_untypeds_for_region(root_cnode_cap, false, boot_mem_reuse_reg, first_untyped_slot)) {
        return false;
    }

    /* convert remaining freemem into UT objects and provide the caps */
    for (i = 0; i < MAX_NUM_FREEMEM_REG; i++) {
        reg = ndks_boot.freemem[i];
        ndks_boot.freemem[i] = REG_EMPTY;
        if (!create_untypeds_for_region(root_cnode_cap, false, reg, first_untyped_slot)) {
            return false;
        }
    }

    return true;
}

BOOT_CODE void bi_finalise(void)
{
    seL4_SlotPos slot_pos_start = ndks_boot.slot_pos_cur;
    seL4_SlotPos slot_pos_end = ndks_boot.slot_pos_max;
    ndks_boot.bi_frame->empty = (seL4_SlotRegion) {
        slot_pos_start, slot_pos_end
    };
}

static inline pptr_t ceiling_kernel_window(pptr_t p)
{
    /* Adjust address if it exceeds the kernel window
     * Note that we compare physical address in case of overflow.
     */
    if (pptr_to_paddr((void *)p) > PADDR_TOP) {
        p = PPTR_TOP;
    }
    return p;
}

/* we can't delcare arrays on the stack, so this is space for
 * the below function to use. */
static BOOT_DATA region_t avail_reg[MAX_NUM_FREEMEM_REG];
/**
 * Dynamically initialise the available memory on the platform.
 * A region represents an area of memory.
 */
BOOT_CODE void init_freemem(word_t n_available, const p_region_t *available,
                            word_t n_reserved, region_t *reserved,
                            v_region_t it_v_reg, word_t extra_bi_size_bits)
{
    /* Force ordering and exclusivity of reserved regions */
    for (word_t i = 0; n_reserved > 0 && i < n_reserved - 1; i++) {
        assert(reserved[i].start <= reserved[i].end);
        assert(reserved[i].end <= reserved[i + 1].start);
    }

    /* Force ordering and exclusivity of available regions */
    assert(n_available > 0);
    for (word_t i = 0; i < n_available - 1; i++) {
        assert(available[i].start < available[i].end);
        assert(available[i].end <= available[i + 1].start);
    }

    for (word_t i = 0; i < MAX_NUM_FREEMEM_REG; i++) {
        ndks_boot.freemem[i] = REG_EMPTY;
    }

    /* convert the available regions to pptrs */
    for (word_t i = 0; i < n_available; i++) {
        avail_reg[i] = paddr_to_pptr_reg(available[i]);
        avail_reg[i].end = ceiling_kernel_window(avail_reg[i].end);
        avail_reg[i].start = ceiling_kernel_window(avail_reg[i].start);
    }

    word_t a = 0;
    word_t r = 0;
    /* Now iterate through the available regions, removing any reserved regions. */
    while (a < n_available && r < n_reserved) {
        if (reserved[r].start == reserved[r].end) {
            /* reserved region is empty - skip it */
            r++;
        } else if (avail_reg[a].start >= avail_reg[a].end) {
            /* skip the entire region - it's empty now after trimming */
            a++;
        } else if (reserved[r].end <= avail_reg[a].start) {
            /* the reserved region is below the available region - skip it*/
            r++;
        } else if (reserved[r].start >= avail_reg[a].end) {
            /* the reserved region is above the available region - take the whole thing */
            insert_region(avail_reg[a]);
            a++;
        } else {
            /* the reserved region overlaps with the available region */
            if (reserved[r].start <= avail_reg[a].start) {
                /* the region overlaps with the start of the available region.
                 * trim start of the available region */
                avail_reg[a].start = MIN(avail_reg[a].end, reserved[r].end);
                r++;
            } else {
                assert(reserved[r].start < avail_reg[a].end);
                /* take the first chunk of the available region and move
                 * the start to the end of the reserved region */
                region_t m = avail_reg[a];
                m.end = reserved[r].start;
                insert_region(m);
                if (avail_reg[a].end > reserved[r].end) {
                    avail_reg[a].start = reserved[r].end;
                    r++;
                } else {
                    a++;
                }
            }
        }
    }

    /* no more reserved regions - add the rest */
    for (; a < n_available; a++) {
        if (avail_reg[a].start < avail_reg[a].end) {
            insert_region(avail_reg[a]);
        }
    }

    /* now try to fit the root server objects into a region */
    word_t i = MAX_NUM_FREEMEM_REG - 1;
    if (!is_reg_empty(ndks_boot.freemem[i])) {
        printf("Insufficient MAX_NUM_FREEMEM_REG");
        halt();
    }
    /* skip any empty regions */
    for (; is_reg_empty(ndks_boot.freemem[i]) && i >= 0; i--);

    /* try to grab the last available p region to create the root server objects
     * from. If possible, retain any left over memory as an extra p region */
    word_t size = calculate_rootserver_size(it_v_reg, extra_bi_size_bits);
    word_t max = rootserver_max_size_bits(extra_bi_size_bits);
    for (; i >= 0; i--) {
        word_t next = i + 1;
        pptr_t start = ROUND_DOWN(ndks_boot.freemem[i].end - size, max);
        if (start >= ndks_boot.freemem[i].start) {
            create_rootserver_objects(start, it_v_reg, extra_bi_size_bits);
            if (i < MAX_NUM_FREEMEM_REG) {
                ndks_boot.freemem[next].end = ndks_boot.freemem[i].end;
                ndks_boot.freemem[next].start = start + size;
            }
            ndks_boot.freemem[i].end = start;
            break;
        } else if (i < MAX_NUM_FREEMEM_REG) {
            ndks_boot.freemem[next] = ndks_boot.freemem[i];
        }
    }
}