address_space_init源码分析（GPA的生成）

参考博客https://www.cnblogs.com/ccxikka/p/9477530.html

目的原本AS是树状结构通过该方式将其展开成平面结构，最终得到的FlatView相当于一个内存条

 最终生成的结构体间关系如下图所示

 具体实现步骤分析：

//exec.c中memory_map_init函数
static void memory_map_init(void)
{
    system_memory = g_malloc(sizeof(*system_memory));//动态分配system_memory这memory_region
    memory_region_init(system_memory, NULL, "system", UINT64_MAX);//创建system_memory的qom
    address_space_init(&address_space_memory, system_memory, "memory");//地址空间初始化
    system_io = g_malloc(sizeof(*system_io));
    memory_region_init_io(system_io, NULL, &unassigned_io_ops, NULL, "io",
                          65536);
    address_space_init(&address_space_io, system_io, "I/O");
}

 地址空间即CPU所能看到的空间，包括Io空间和memory空间，IO空间使用in、out指令访问，有回掉函数。Memory空间使用mov等指令访问。

void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
{
    memory_region_ref(root);
    as->root = root;                      //指向system_meomory这个memory region
    as->current_map = NULL;
    as->ioeventfd_nb = 0;
    as->ioeventfds = NULL;
    QTAILQ_INIT(&as->listeners);
    QTAILQ_INSERT_TAIL(&address_spaces, as, address_spaces_link);
    as->name = g_strdup(name ? name : "anonymous");
    address_space_update_topology(as);    //完成内存空间的渲染使映射到GPA
    address_space_update_ioeventfds(as);
}

static void address_space_update_topology(AddressSpace *as)
{
    MemoryRegion *physmr = memory_region_get_flatview_root(as->root);//获取as指向的mr

    flatviews_init();
    if (!g_hash_table_lookup(flat_views, physmr)) {
        generate_memory_topology(physmr);//主要解析这个
    }
    address_space_set_flatview(as);
}

 

static FlatView *generate_memory_topology(MemoryRegion *mr)
{
    int i;
    FlatView *view;

    view = flatview_new(mr);

    if (mr) {
        render_memory_region(view, mr, int128_zero(),
                             addrrange_make(int128_zero(), int128_2_64()), false);
    }
    flatview_simplify(view);

    view->dispatch = address_space_dispatch_new(view);
    for (i = 0; i < view->nr; i++) {
        MemoryRegionSection mrs =
            section_from_flat_range(&view->ranges[i], view);
        flatview_add_to_dispatch(view, &mrs);
    }
    address_space_dispatch_compact(view->dispatch);
    g_hash_table_replace(flat_views, mr, view);

    return view;
}

static void render_memory_region(FlatView *view,
                                 MemoryRegion *mr,
                                 Int128 base,
                                 AddrRange clip,
                                 bool readonly)
{
    MemoryRegion *subregion;
    unsigned i;
    hwaddr offset_in_region;
    Int128 remain;
    Int128 now;
    FlatRange fr;
    AddrRange tmp;

    if (!mr->enabled) {
        return;
    }

    int128_addto(&base, int128_make64(mr->addr));//base=base+mr->addr
    readonly |= mr->readonly;                    //它的读写模式就是mr的读写模式
    //找出当前的mr落在父mr的地址区间
    tmp = addrrange_make(base, mr->size);        //返回base以及大小即start&size
    if (!addrrange_intersects(tmp, clip)) {      //计算结果true因此不执行这里。继续向下执行
        return;
    }

    clip = addrrange_intersection(tmp, clip);//结果为start=0，size=0xffffffffffffffffui64
    //对别名空间进行渲染
    if (mr->alias) {
        int128_subfrom(&base, int128_make64(mr->alias->addr));
        int128_subfrom(&base, int128_make64(mr->alias_offset));//以上两行的计算得出别名空间的大小
        render_memory_region(view, mr->alias, base, clip, readonly);//渲染别名空间
        return;
    }
    //渲染子region
    /* Render subregions in priority order. */
    QTAILQ_FOREACH(subregion, &mr->subregions, subregions_link) {
        render_memory_region(view, subregion, base, clip, readonly);
    }
    //teminates为false表示该容器为纯容器只需要渲染不需要生成flatrange
    if (!mr->terminates) {
        return;
    }
    //计算Mr在线性空间的大小和偏移
    offset_in_region = int128_get64(int128_sub(clip.start, base));//返回结果为0
    base = clip.start;//为0
    remain = clip.size;//为0xffffffffffffffffui64
    //Flatrange成员的初始化
    fr.mr = mr;
    fr.dirty_log_mask = memory_region_get_dirty_log_mask(mr);
    fr.romd_mode = mr->romd_mode;
    fr.readonly = readonly;
    //flatview的nr什么时候初始化？
    /* Render the region itself into any gaps left by the current view. */
    for (i = 0; i < view->nr && int128_nz(remain); ++i) {
        if (int128_ge(base, addrrange_end(view->ranges[i].addr))) {
            continue;
        }
        if (int128_lt(base, view->ranges[i].addr.start)) {
            now = int128_min(remain,   //找出两个中小的赋值给now
                             int128_sub(view->ranges[i].addr.start, base));
            fr.offset_in_region = offset_in_region;
            fr.addr = addrrange_make(base, now);  //完成fr的addrfange的赋值
            flatview_insert(view, i, &fr);
            ++i;
            int128_addto(&base, now);
            offset_in_region += int128_get64(now);
            int128_subfrom(&remain, now);
        }
        now = int128_sub(int128_min(int128_add(base, remain),
                                    addrrange_end(view->ranges[i].addr)),
                         base);
        int128_addto(&base, now);
        offset_in_region += int128_get64(now);
        int128_subfrom(&remain, now);
    }
    if (int128_nz(remain)) {
        fr.offset_in_region = offset_in_region;
        fr.addr = addrrange_make(base, remain);
        flatview_insert(view, i, &fr);
    }
}