浅析armlinux-setup_arch()->setup_arch()函数-最终

文章来源:http://gliethttp.cublog.cn

建议首先参考《浅析armlinux2_4_19启动程序[head-armv.s文件]》与[http://gliethttp.cublog.cn]

《浅析setup_arch()函数tag_list的uboot[u-boot]由来》
《浅析armlinux-setup_arch()->setup_processor()函数1》
《浅析armlinux-setup_arch()->setup_machine()函数2 》
《浅析armlinux-setup_arch()->convert_to_tag_list()函数3 》
《浅析armlinux-setup_arch()->bootmem_init()函数4》
《浅析armlinux-setup_arch()->paging_init()函数5》
《浅析armlinux-seup_arch-alloc_bootmem_low_pages函数5-1》
《浅析armlinux-setup_arch()-memtable_init()函数5-2》
《浅析armlinux-setup_arch()-clear_mapping()函数5-2-1》
《浅析armlinux-setup_arch()-create_mapping()函数5-2-2》
《我看Buddy(伙伴)算法－为什么要有除2操作》
《浅析armlinux-paging_init()->at91rm9200_map_io()函数5-3》
《浅析armlinux-paging_init()->free_area_init_core()函数5-4》
《浅析armlinux-setup_arch()->request_standard_resources()函数6》
《浅析armlinux-setup_arch()->init_arch_irq()函数7》

//1.arch/arm/kernel/Setup.c->setup_arch()
void __init setup_arch(char **cmdline_p)
{
    struct tag *tags = (struct tag *)&init_tags;
    struct machine_desc *mdesc;
    char *from = default_command_line;

    ROOT_DEV = MKDEV(0, 255);//ROOT_DEV = 0xff;
//见《浅析armlinux-setup_arch()->setup_processor()函数1》[http://gliethttp.cublog.cn]
    setup_processor();
//见《浅析armlinux-setup_arch()->setup_machine(machine_arch_type)函数2》[http://gliethttp.cublog.cn]
    mdesc = setup_machine(machine_arch_type);//mdesc指向机器描述空间单元
//++++++++++++++
//arch/arm/mach-at91rm9200/Core.c
//位于.arch.info段
//MACHINE_START(AT91RM9200, "ATMEL AT91RM9200")//.nr = MACH_TYPE_##_type=MACH_TYPE_AT91RM9200=251
//与上面从u-boot传到r1中的一样[gliethttp]
//MAINTAINER("SAN People / ATMEL")
//BOOT_MEM(AT91_SDRAM_BASE, AT91C_BASE_SYS, AT91C_VA_BASE_SYS)
//BOOT_PARAMS(AT91_SDRAM_BASE + 0x100)//tag list存放的物理地址0x20000100[gliethttp]
//FIXUP(at91rm9200_fixup)
//MAPIO(at91rm9200_map_io)
//INITIRQ(at91rm9200_init_irq)
//MACHINE_END[gliethttp]
//--------------
    machine_name = mdesc->name;//machine_name="ATMEL AT91RM9200"

    if (mdesc->soft_reboot)//mdesc->soft_reboot初值为1
        reboot_setup("s");//分析见后

    if (mdesc->param_offset)//mdesc->param_offset=AT91_SDRAM_BASE + 0x100=物理地址0x20000100
        tags = phys_to_virt(mdesc->param_offset);//将tag list物理地址转换成虚拟地址,以便访问

    if (mdesc->fixup)//调用at91rm9200_fixup()修正函数,分析见后
        mdesc->fixup(mdesc, (struct param_struct *)tags,
             &from, &meminfo);
//很明显由bootloader[u-boot-1.1.5]传递到物理地址0x20000100处的参数是tag list结构[gliethttp]
    if (tags->hdr.tag != ATAG_CORE)
        convert_to_tag_list(tags);
//对于tag list的生成,请参考《浅析setup_arch()函数tag_list的uboot[u-boot]由来》[http://gliethttp.cublog.cn]

    if (tags->hdr.tag == ATAG_CORE) {
        if (meminfo.nr_banks != 0)//如果是tag list,那么如果系统已经创建了默认的meminfo.nr_banks
            squash_mem_tags(tags);//那么使用squash_mem_tags失效所有ATAG_MEM初始化的东东为ATAG_NONE,tag->hdr.size不变
        parse_tags(tags);
    }

    if (meminfo.nr_banks == 0) {//如果tag list中没有传递ATAG_MEM参数,那么采用编译时的默认配置值
        meminfo.nr_banks = 1;
        meminfo.bank[0].start = PHYS_OFFSET;//0x20000000
        meminfo.bank[0].size = MEM_SIZE;//32M
    }
//_text,_etext,_edata,_end参见arch/arm/vmlinux-armv.lds.in链接脚本
    init_mm.start_code = (unsigned long) &_text;
    init_mm.end_code = (unsigned long) &_etext;
    init_mm.end_data = (unsigned long) &_edata;
    init_mm.brk     = (unsigned long) &_end;

    memcpy(saved_command_line, from, COMMAND_LINE_SIZE);
    saved_command_line[COMMAND_LINE_SIZE-1] = '\0';//追0,防止非法字符串越界
//parse_cmdline,主要完成phys_initrd_start,phys_initrd_size和mem的解析,并将*cmdline_p=command_line全局量
    parse_cmdline(&meminfo, cmdline_p, from);
//将kernel自身和位图管理页占用的页对应的页位图置1,标识相应页已被占用
//将initrd占用的页对应的页位图置1,标识相应页已被占用[gliethttp]
    bootmem_init(&meminfo);
//清空页目录项,建立at91rm9200中断向量表空间和io寄存器空间从虚拟地址到物理地址的映射表
//建立map位图和page页管理空间,以及free_area.map位图管理空间等
    paging_init(&meminfo, mdesc);
    request_standard_resources(&meminfo, mdesc);//登记注册所有需要登记注册的cpu总线上的设备实体
    init_arch_irq = mdesc->init_irq;//中断初始化函数指针

#ifdef CONFIG_VT
#if defined(CONFIG_VGA_CONSOLE)
    conswitchp = &vga_con;//显示设备指针conswitchp指向vga_con设备
#elif defined(CONFIG_DUMMY_CONSOLE)//frambuffer选中后,就会使用dummy_con设备
    conswitchp = &dummy_con;//显示设备指针conswitchp指向dummy_con设备
#endif
#endif
}
//2.arch/arm/kernel/Process.c->reboot_setup()
static char reboot_mode = 'h';
int __init reboot_setup(char *str)
{
//reboot_mode将在machine_restart()系统重启时arch_reset()使用
    reboot_mode = str[0];//reboot_mode='s';
    return 1;
}
//3.arch/arm/mach-at91rm9200/Core.c->at91rm9200_fixup
static void __init at91rm9200_fixup(struct machine_desc *desc, struct param_struct *unused,
         char **cmdline, struct meminfo *mi)
{
#ifdef CONFIG_BLK_DEV_INITRD//CONFIG_BLK_DEV_INITRD = 1

//设置根目录为ramdisk
    ROOT_DEV = MKDEV(RAMDISK_MAJOR, 0);//0x100
//由make menuconfig产生CONFIG_BLK_DEV_RAM_SIZE = 15360k = 15M
    setup_ramdisk(1, 0, 0, CONFIG_BLK_DEV_RAM_SIZE);
//    setup_initrd(0xc0100000, 3*1024*1024);
#endif
}
void __init setup_ramdisk(int doload, int prompt, int image_start, unsigned int rd_sz)
{
#ifdef CONFIG_BLK_DEV_RAM
    extern int rd_size, rd_image_start, rd_prompt, rd_doload;
    rd_image_start = image_start;
    rd_prompt = prompt;
    rd_doload = doload;
    if (rd_sz)
        rd_size = rd_sz;//15M
#endif
}
//4.解析tag list中各个元素,进而改变内核全局量,来影响内核
//arch/arm/kernel/Setup.c->parse_tags()
static void __init parse_tags(const struct tag *t)
{
    for (; t->hdr.size; t = tag_next(t))
        if (!parse_tag(t))//解析该t
            printk(KERN_WARNING
                "Ignoring unrecognised tag 0x%08x\n",
                t->hdr.tag);
}
//5.arch/arm/kernel/Setup.c->parse_tag()
static int __init parse_tag(const struct tag *tag)
{
    extern struct tagtable __tagtable_begin, __tagtable_end;
    struct tagtable *t;
    for (t = &__tagtable_begin; t < &__tagtable_end; t++)
        if (tag->hdr.tag == t->tag) {
            t->parse(tag);
            break;
        }
    return t < &__tagtable_end;//找到匹配项,1;否则0
}
//arch/arm/vmlinux-armv.lds.in链接脚本中有如下定以
//...
//__tagtable_begin = .;
//*(.taglist)
//__tagtable_end = .;
//...
//在include/asm-arm/Setup.h中有如下定义
#define __tag __attribute__((unused, __section__(".taglist")))
#define __tagtable(tag, fn) \
static struct tagtable __tagtable_##fn __tag = { tag, fn }
__tagtable(ATAG_CORE, parse_tag_core);//ATAG_CORE解析函数parse_tag_core
__tagtable(ATAG_MEM, parse_tag_mem32);//ATAG_MEM解析函数parse_tag_mem32
__tagtable(ATAG_RAMDISK, parse_tag_ramdisk);//ATAG_RAMDISK解析函数parse_tag_ramdisk
__tagtable(ATAG_INITRD, parse_tag_initrd);//ATAG_INITRD解析函数parse_tag_initrd
__tagtable(ATAG_SERIAL, parse_tag_serialnr);//ATAG_SERIAL解析函数parse_tag_serialnr
__tagtable(ATAG_CMDLINE, parse_tag_cmdline);//ATAG_CMDLINE解析函数parse_tag_cmdline
......等

浅析armlinux-setup_arch()->bootmem_init()函数4

文章来源:http://gliethttp.cublog.cn

建议首先参考《浅析armlinux2_4_19启动程序[head-armv.s文件]》[http://gliethttp.cublog.cn]


//----------------------------------------
//1.arch/arm/mm/Init.c->bootmem_init()
void __init bootmem_init(struct meminfo *mi)
{
    struct node_info node_info[NR_NODES], *np = node_info;
    unsigned int bootmap_pages, bootmap_pfn, map_pg;
    int node, initrd_node;
    //计算为了管理所有mem内存,需管理位图占据页数目bootmap_pages,np中存储mem对应的页帧号
    bootmap_pages = find_memend_and_nodes(mi, np);
    //查找存放位图管理页的物理页帧号,实际是存放到_end后的后续页中
    bootmap_pfn = find_bootmap_pfn(0, mi, bootmap_pages);
    //检查initrd的合法性,同时将initrd所在内存bank的node返回给initrd_node
    initrd_node = check_initrd(mi);
    map_pg = bootmap_pfn;//位图页帧号
    np += numnodes - 1;
    for (node = numnodes - 1; node >= 0; node--, np--) {
        /*
         * If there are no pages in this node, ignore it.
         * Note that node 0 must always have some pages.
         */
        if (np->end == 0) {
            if (node == 0)
                BUG();
            continue;
        }
        //将map_pg开始的位图管理空间全部置0xff
        init_bootmem_node(NODE_DATA(node), map_pg, np->start, np->end);
        //释放虚拟地址node_bootmem_map开始的位图管理的所有页,使相应页可用[gliethttp]
        free_bootmem_node_bank(node, mi);
        map_pg += np->bootmap_pages;
        /*
         * If this is node 0, we need to reserve some areas ASAP -
         * we may use bootmem on node 0 to setup the other nodes.
         */
        if (node == 0)//我的at91rm9200开发板仅仅有一个node=0
//将kernel自身和位图管理页占用的页对应的页位图置1,标识相应页已被占用
            reserve_node_zero(bootmap_pfn, bootmap_pages);
    }
#ifdef CONFIG_BLK_DEV_INITRD//在我的at91rm9200开发板中,initrd是开启的
//并且phys_initrd_start=0x21100000
//phys_initrd_size=6000000=0x5B8D80=5.73M
//initrd_node=0;
    if (phys_initrd_size && initrd_node >= 0) {
//将initrd占用的页对应的页位图置1,标识相应页已被占用
        reserve_bootmem_node(NODE_DATA(initrd_node), phys_initrd_start,
                 phys_initrd_size);
        initrd_start = __phys_to_virt(phys_initrd_start);//转成虚拟地址
        initrd_end = initrd_start + phys_initrd_size;
    }
#endif
    if (map_pg != bootmap_pfn + bootmap_pages)//保证所有bootmap都已经被遍历
        BUG();
}
//----------------------------------------
//2.arch/arm/mm/Init.c->find_memend_and_nodes()
static unsigned int __init find_memend_and_nodes(struct meminfo *mi, struct node_info *np)
{unsigned int i, bootmem_pages = 0, memend_pfn = 0;
    for (i = 0; i < NR_NODES; i++) {//默认失效
        np[i].start = -1U;
        np[i].end = 0;
        np[i].bootmap_pages = 0;
    }
    for (i = 0; i < mi->nr_banks; i++) {
        unsigned long start, end;
        int node;
        if (mi->bank[i].size == 0) {
            mi->bank[i].node = -1;//该bank的node无效-1
            continue;
        }
        node = mi->bank[i].node;//at91rm9200dk中mem连续node=0
        if (node >= numnodes) {
            numnodes = node + 1;
            if (numnodes > NR_NODES)
                BUG();
        }
//获取当前bank的pfns
//#define PAGE_ALIGN(addr) (((addr)+PAGE_SIZE-1)&PAGE_MASK)//页边界对齐
//define O_PFN_UP(x) (PAGE_ALIGN(x) >> PAGE_SHIFT)
        start = O_PFN_UP(mi->bank[i].start);//获取该bank.start对应物理页帧号
//同理,//获取该bank.end对应物理页帧号
        end = O_PFN_DOWN(mi->bank[i].start + mi->bank[i].size);
        if (np[node].start > start)
            np[node].start = start;//存储
        if (np[node].end < end)
            np[node].end = end;//存储
        if (memend_pfn < end)
            memend_pfn = end;
    }
    for (i = 0; i < numnodes; i++) {
        if (np[i].end == 0)
            continue;
//bootmem_bootmap_pages计算pages个页需要多少个页来存储其位图管理信息
        np[i].bootmap_pages = bootmem_bootmap_pages(np[i].end - np[i].start);
        bootmem_pages += np[i].bootmap_pages;//累计位图管理信息页总数
    }
    /*
     * This doesn't seem to be used by the Linux memory
     * manager any more. If we can get rid of it, we
     * also get rid of some of the stuff above as well.
     */
    max_low_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
// max_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
    mi->end = memend_pfn << PAGE_SHIFT;//所管理的物理内存结束地址
    return bootmem_pages;
}
//----------------------------------------
//3.mm/Bootmem.c->bootmem_bootmap_pages()
//计算pages个页需要多少个页来存储其位图管理信息
unsigned long __init bootmem_bootmap_pages (unsigned long pages)
{unsigned long mapsize;
    mapsize = (pages+7)/8;//所需8bits个数
    mapsize = (mapsize + ~PAGE_MASK) & PAGE_MASK;//mapsize个字节页对齐
    mapsize >>= PAGE_SHIFT;//mapsize个字节对应页数目
    return mapsize;
}
//----------------------------------------
//4.arch/arm/mm/Init.c->find_bootmap_pfn()
//查找存放位图管理页的物理页帧号-init_mm.brk
static unsigned int __init
find_bootmap_pfn(int node, struct meminfo *mi, unsigned int bootmap_pages)
{unsigned int start_pfn, bank, bootmap_pfn;
    start_pfn = V_PFN_UP(&_end);//将_end虚拟内存转换为对应的物理页帧号
    bootmap_pfn = 0;
    for (bank = 0; bank < mi->nr_banks; bank ++) {
        unsigned int start, end;
        if (mi->bank[bank].node != node)
            continue;
        start = O_PFN_UP(mi->bank[bank].start);
        end = O_PFN_DOWN(mi->bank[bank].size +
                 mi->bank[bank].start);
        if (end < start_pfn)
            continue;
        if (start < start_pfn)
            start = start_pfn;//_end对应init_mm.brk临界点

        if (end <= start)
            continue;
        if (end - start >= bootmap_pages) {
            bootmap_pfn = start;//从init_mm.brk开始存放位图管理页
            break;
        }
    }
    if (bootmap_pfn == 0)
        BUG();
    return bootmap_pfn;//ok[gliethttp]
}
//----------------------------------------
//5.arch/arm/mm/Init.c->check_initrd()
//检查initrd的合法性
static int __init check_initrd(struct meminfo *mi)
{
    int initrd_node = -2;
    unsigned long end = phys_initrd_start + phys_initrd_size;
#ifdef CONFIG_BLK_DEV_INITRD
    /*
     * Make sure that the initrd is within a valid area of
     * memory.
     */
    if (phys_initrd_size) {
        unsigned int i;
        initrd_node = -1;
        for (i = 0; i < mi->nr_banks; i++) {
            unsigned long bank_end;
            bank_end = mi->bank[i].start + mi->bank[i].size;
            if (mi->bank[i].start <= phys_initrd_start &&
             end <= bank_end)
                initrd_node = mi->bank[i].node;
        }
    }
    if (initrd_node == -1) {
        printk(KERN_ERR "initrd (0x%08lx - 0x%08lx) extends beyond "
         "physical memory - disabling initrd\n",
         phys_initrd_start, end);
        phys_initrd_start = phys_initrd_size = 0;
    }
#endif
    return initrd_node;//将initrd所在内存bank对应的node返回
}
//----------------------------------------
//6.mm/Bootmem.c->init_bootmem_node()
unsigned long __init init_bootmem_node (pg_data_t *pgdat, unsigned long freepfn, unsigned long startpfn, unsigned long endpfn)
{
    return(init_bootmem_core(pgdat, freepfn, startpfn, endpfn));
}
//mm/Bootmem.c->init_bootmem_core()
static unsigned long __init init_bootmem_core (pg_data_t *pgdat,
    unsigned long mapstart, unsigned long start, unsigned long end)
{
    bootmem_data_t *bdata = pgdat->bdata;//读取&node_bootmem_data[0]
    unsigned long mapsize = ((end - start)+7)/8;
    pgdat->node_next = pgdat_list;
    pgdat_list = pgdat;
    mapsize = (mapsize + (sizeof(long) - 1UL)) & ~(sizeof(long) - 1UL);//4字节对齐
    bdata->node_bootmem_map = phys_to_virt(mapstart << PAGE_SHIFT);//位图页帧号转为系统用的虚拟地址
    bdata->node_boot_start = (start << PAGE_SHIFT);//本map所处物理内存起始地址
    bdata->node_low_pfn = end;//本map所处物理内存结束地址
    //用0xff填充map位图页帧后,mapsize个字节数据
    //arch/arm/lib/memset.S->memset(),对虚拟地址bdata->node_bootmem_map进行赋值
    memset(bdata->node_bootmem_map, 0xff, mapsize);
    return mapsize;
}
//----------------------------------------
//7.mm/Bootmem.c->free_bootmem_node_bank()
static inline void free_bootmem_node_bank(int node, struct meminfo *mi)
{
    pg_data_t *pgdat = NODE_DATA(node);//读取&node_bootmem_data[0]
    int bank;
    for (bank = 0; bank < mi->nr_banks; bank++)
        if (mi->bank[bank].node == node)
            free_bootmem_node(pgdat, mi->bank[bank].start,
                     mi->bank[bank].size);
}
void __init free_bootmem_node (pg_data_t *pgdat, unsigned long physaddr, unsigned long size)
{
    return(free_bootmem_core(pgdat->bdata, physaddr, size));
}
static void __init free_bootmem_core(bootmem_data_t *bdata, unsigned long addr, unsigned long size)
{
    unsigned long i;
    unsigned long start;
    /*
     * round down end of usable mem, partially free pages are
     * considered reserved.
     */
    unsigned long sidx;
    unsigned long eidx = (addr + size - bdata->node_boot_start)/PAGE_SIZE;
    unsigned long end = (addr + size)/PAGE_SIZE;
    if (!size) BUG();
    if (end > bdata->node_low_pfn)//一般相等
        BUG();
    start = (addr + PAGE_SIZE-1) / PAGE_SIZE;//mem起始物理地址对应的页帧号
    sidx = start - (bdata->node_boot_start/PAGE_SIZE);//起始大小
    for (i = sidx; i < eidx; i++) {///sidx=0,eidx=size/PAGE_SIZE[gliethttp]
//清0各位图管理位,使相应页可用
//如i=4,那么第4物理页可用,清0bdata->node_bootmem_map[0]的第4位
        if (!test_and_clear_bit(i, bdata->node_bootmem_map))//node_bootmem_map位图管理起始虚拟地址
            BUG();
    }
}
///arch/arm/lib/testclearbit.S->test_and_clear_bit()
ENTRY(test_and_clear_bit)
        add r1, r1, r0, lsr #3//获取第r0位,对应字节对应的地址
        and r3, r0, #7//获取字节中偏移
        mov r0, #1
//include/asm-arm/proc-armv/Assembler.h->save_and_disable_irqs[gliethttp]
//.macro save_and_disable_irqs, oldcpsr, temp
//mrs \oldcpsr, cpsr//
//mov \temp, #I_BIT | MODE_SVC
//msr cpsr_c, \temp
//.endm
        save_and_disable_irqs ip, r2//将cpsr保存到ip
        ldrb r2, [r1]//取出字节数据
        tst r2, r0, lsl r3//先测一次,我感觉没用
        bic r2, r2, r0, lsl r3//将r2的第r3位清0,成功清0后Z=0,因为硬件故障未能成功那么Z=1,返回后会halt系统
        strb r2, [r1]//存储清0后的结果
        restore_irqs ip//恢复cpsr
        moveq r0, #0//如果因为硬件故障导致不能清0,那么r0=0;清0失败
        RETINSTR(mov,pc,lr)
//----------------------------------------
//8.arch/arm/mm/Init.c->reserve_node_zero()
//将kernel自身和位图管理页占用的页对应的页位图置1,标识相应页已被占用
static __init void reserve_node_zero(unsigned int bootmap_pfn, unsigned int bootmap_pages)
{
    pg_data_t *pgdat = NODE_DATA(0);//获取node0的所有物理内存管理单元pgdat
//对于_end和_stext,参考arch/arm/vmlinux-armv.lds.in链接脚本
//_end为init_mm.brk,是kernel最末端地址
//__pa(&_stext)物理地址开始的&_end - &_stext个数据,对应页位图置1标识相应页已被占用
    reserve_bootmem_node(pgdat, __pa(&_stext), &_end - &_stext);
#ifdef CONFIG_CPU_32
//将arch/arm/kernel/head-armv.s中4M保留页swapper_pg_dir,我的at91rm9200板子对应的物理地址为0x20004000~0x20008000
//swapper_pg_dir~swapper_pg_dir+4k*4的页对应的页位图置1标识相应页已被占用
//#define PTRS_PER_PGD 4096
    reserve_bootmem_node(pgdat, __pa(swapper_pg_dir),
             PTRS_PER_PGD * sizeof(pgd_t));
#endif
//将_end即init_mm.brk之后存放node物理页位图的位图管理空间也保护起来
//bootmap_pfn << PAGE_SHIFT~(bootmap_pfn << PAGE_SHIFT)+(bootmap_pages << PAGE_SHIFT)的页对应的页位图置1标识相应页已被占用
    reserve_bootmem_node(pgdat, bootmap_pfn << PAGE_SHIFT,
             bootmap_pages << PAGE_SHIFT);
//以下代码在at91rm9200dk下均不被编译进vmlinuz
    if (machine_is_integrator())//if(0),否则会因为reserve_bootmem_node回环,halt系统
        reserve_bootmem_node(pgdat, 0, __pa(swapper_pg_dir));
    if (machine_is_archimedes() || machine_is_a5k())
        reserve_bootmem_node(pgdat, 0x02000000, 0x00080000);
    if (machine_is_edb7211() || machine_is_fortunet())
        reserve_bootmem_node(pgdat, 0xc0000000, 0x00020000);
    if (machine_is_p720t())
        reserve_bootmem_node(pgdat, PHYS_OFFSET, 0x00014000);
#ifdef CONFIG_SA1111//非SA1111
    reserve_bootmem_node(pgdat, PHYS_OFFSET, __pa(swapper_pg_dir)-PHYS_OFFSET);
#endif
}
void __init reserve_bootmem_node (pg_data_t *pgdat, unsigned long physaddr, unsigned long size)
{//使pgdat管理的物理内存,physaddr~(physaddr+size)之间的物理内存不可使用--占用保留
 //physaddr~(physaddr+size)对应页位图置1标识相应页已被占用
    reserve_bootmem_core(pgdat->bdata, physaddr, size);
}
static void __init reserve_bootmem_core(bootmem_data_t *bdata, unsigned long addr, unsigned long size)
{
    unsigned long i;
    /*
     * round up, partially reserved pages are considered
     * fully reserved.
     */
//bdata->node_boot_start该bdata对应node物理内存的起始地址
    unsigned long sidx = (addr - bdata->node_boot_start)/PAGE_SIZE;//计算addr所处页帧号
    unsigned long eidx = (addr + size - bdata->node_boot_start +
                         PAGE_SIZE-1)/PAGE_SIZE;//计算addr+size对应的页帧号
    unsigned long end = (addr + size + PAGE_SIZE-1)/PAGE_SIZE;
    if (!size) BUG();
    if (sidx < 0)
        BUG();
    if (eidx < 0)
        BUG();
    if (sidx >= eidx)//数据回环
        BUG();
//bdata->node_low_pfn为本node物理内存的地址上限
    if ((addr >> PAGE_SHIFT) >= bdata->node_low_pfn)
        BUG();
    if (end > bdata->node_low_pfn)
        BUG();
//条件符合,那么实行保护措施
//将sidx页到eidx页对应的位图置1,位图置1标识相应页已被占用(保护起来,不被kernel使用)
    for (i = sidx; i < eidx; i++)
        if (test_and_set_bit(i, bdata->node_bootmem_map))
            printk("hm, page %08lx reserved twice.\n", i*PAGE_SIZE);
}
///arch/arm/lib/testclearbit.S->test_and_set_bit()
//ENTRY(test_and_set_bit)
// add r1, r1, r0, lsr #3//获取第r0位对应的字节地址
// and r3, r0, #7//计算处于字节的第几位
// mov r0, #1
// save_and_disable_irqs ip, r2//ip=cpsr
// ldrb r2, [r1]
// tst r2, r0, lsl r3
//orr操作,成功操作后Z=0,因为硬件故障未能成功那么Z=1,返回后会halt系统
// orr r2, r2, r0, lsl r3//将r2中的第r3位置1
// strb r2, [r1]//回写
// restore_irqs ip
// moveq r0, #0
// RETINSTR(mov,pc,lr)
//include/asm-arm/proc-armv/Assembler.h->save_and_disable_irqs[gliethttp]
//.macro save_and_disable_irqs, oldcpsr, temp
//mrs \oldcpsr, cpsr//
//mov \temp, #I_BIT | MODE_SVC