uboot启动linux的过程

 

 

一、概述

  linux内核镜像常见到的有两种形式,zImage和uImage。这两种文件的格式稍有差别,所以启动这两种格式的内核镜像也会有所不同。目前,uboot只支持启动uImage类型的镜像,对zImage还不支持(但是可以移植,TQ2440就是这样做的)。

二、uImage和zImage

1、zImage

       zImage是用命令“#make zImage”生成的,我截取了生成信息最后部分的内容如下:

uboot启动linux的过程
  OBJCOPY arch/arm/boot/Image
  Kernel: arch/arm/boot/Image is ready
  GZIP    arch/arm/boot/compressed/piggy.gz
  AS      arch/arm/boot/compressed/piggy.o
  LD      arch/arm/boot/compressed/vmlinux
  OBJCOPY arch/arm/boot/zImage
  Kernel: arch/arm/boot/zImage is ready
uboot启动linux的过程

  从中可以看到,zImage是经过gzip压缩过的,所以在内核启动过程(不属于u-boot控制范围,在内核镜像的头部嵌有解压函数)中必然会对应一个解压过程。

2、uImage

(1) 生成方法

  uImage是u-boot专用的内核镜像,可用命令“#make uImage”生成。生成信息最后部分的内容如下:

uboot启动linux的过程
  Kernel: arch/arm/boot/Image is ready
  Kernel: arch/arm/boot/zImage is ready
  UIMAGE  arch/arm/boot/uImage
Image Name:   Linux-2.6.30.4-EmbedSky
Created:      Thu Mar 20 19:53:32 2014
Image Type:   ARM Linux Kernel Image (uncompressed)
Data Size:    2314736 Bytes = 2260.48 kB = 2.21 MB
Load Address: 0x30008000
Entry Point:  0x30008000
  Image arch/arm/boot/uImage is ready
uboot启动linux的过程

  事实上,uImage是调用mkimage(uboot制作的工具)这个工具生成的。

uboot启动linux的过程
root@daneiqi:/opt/EmbedSky#  mkimage -n linux-2.6.30 -A arm -O linux -T kernel -C none -a 0x30008000 -e 0x30008000 -d zImage uImage
Image Name:   linux-2.6.30
Created:      Thu Mar 20 19:59:36 2014
Image Type:   ARM Linux Kernel Image (uncompressed)
Data Size:    2314736 Bytes = 2260.48 kB = 2.21 MB
Load Address: 0x30008000
Entry Point:  0x30008000
uboot启动linux的过程

(2)特点

  在原来的可执行映象文件zImage的前面加上一个0x40字节的头, 记录参数所指定的信息,这样uboot才能识别这个映象是针对哪个CPU体系结构的,哪个OS的, 哪种类型,加载内存中的哪个位置,入口点在内存的那个位置以及映象名是什么。

(3)image_header

  头部的结构是在include/image.h中定义的,如下所示:

uboot启动linux的过程
typedef struct image_header {
       uint32_t  ih_magic;       /* Image Header Magic Number   */
       uint32_t  ih_hcrc;   /* Image Header CRC Checksum  */
       uint32_t  ih_time;  /* Image Creation Timestamp       */
       uint32_t  ih_size;   /* Image Data Size        */
       uint32_t  ih_load;   /* Data    Load  Address            */
       uint32_t  ih_ep;            /* Entry Point Address          */
       uint32_t  ih_dcrc;   /* Image Data CRC Checksum      */
       uint8_t           ih_os;             /* Operating System             */
       uint8_t           ih_arch;   /* CPU architecture              */
       uint8_t           ih_type;   /* Image Type               */
       uint8_t           ih_comp; /* Compression Type            */
       uint8_t           ih_name[IH_NMLEN];  /* Image Name             */
} image_header_t;
uboot启动linux的过程

  打开上边生成的uImage文件,可以看到对应的数据。

uboot启动linux的过程

(1)ih_magic    0x27051956  magic值,我觉得是uImage的头部开始值,根据这个值,判断是否是uImage

(2)ih_crc    0x19dbf9c6    头部校验

(3)ih_time   0x74295319   创建时间

(4)ih_size   0x002351f0     镜像大小为2260.48KB

(5)ih_load  0x30008000 内核加载地址

(6)ih_ep        0x30008000 内核运行地址,“theKernel”指向该地址,说明这里藏着进入第一个函数--解压

(7)ih_dcrc      0x38fc654e    内核校验

(8)ih_os        0x05       #define IH_OS_LINUX  5 /* Linux */

(9)ih_arch     0x02     #define IH_CPU_ARM  2 /* ARM  */

(10)ih_type   0x02         #define IH_TYPE_KERNEL  2 /* OS Kernel Image  */

(11)ih_comp  0x00        #define IH_COMP_NONE  0 /*  No  Compression Used */

(12)ih_name         Linux_2.6.30.4-EmbedSky

三、u-boot内核启动流程概述

  前文已经说明u-boot只支持uImage,步骤三、四都是针对uImage的。

  另外声明一点,步骤三四的测试uboot代码是韦东山视频提供的。

1、从NandFlash中读取内核到RAM中

2、在RAM中,给内核进行重定位

3、给内核传递参数

4、启动内核

四、u-boot启动内核细节分析

1、启动命令

从环境变量中查看启动命令:

uboot启动linux的过程

2、从NandFlash中读取内核到RAM中

  nand read.jffs2 0x30007FC0 kernel

  此命令会激活(common/cmd_nand.c)中的do_nand函数,从而将nandflash上的kernel分区加载到0x30007fc0位置处。

uboot启动linux的过程
OpenJTAG> mtd

device nand0 <nandflash0>, # parts = 4
 #: name                        size            offset          mask_flags
 0: bootloader          0x00040000      0x00000000      0
 1: params              0x00020000      0x00040000      0
 2: kernel              0x00200000      0x00060000      0
 3: root                0x0fda0000      0x00260000      0

active partition: nand0,0 - (bootloader) 0x00040000 @ 0x00000000

defaults:
mtdids  : nand0=nandflash0
mtdparts: mtdparts=nandflash0:256k@0(bootloader),128k(params),2m(kernel),-(root)
uboot启动linux的过程

  从分区表中,可以看出kernel分区的起始地址是0x60000,大小是0x200000(2M),这条命令实际上等效于

uboot启动linux的过程
nand read.jffs2 0x30007FC0 0x60000 0x200000
uboot启动linux的过程

  也可以使用命令

nand read 0x30007FC0 0x60000 0x200000

  nand read.jffs2可以自动页对齐,所以大小可以是非页整的;如果使用nand read的大小必须是页对齐的。

3、读取uImage头部

  bootm 0x30007fc0

  此命令会激活(common/cmd_bootm.c)中的do_bootm函数,从而开始执行

uboot启动linux的过程
2、在RAM中,给内核进行重定位
3、给内核传递参数
4、启动内核
uboot启动linux的过程

image_header_t header;  定义一个全局变量header,是读取头部的缓冲区

addr = simple_strtoul(argv[1], NULL, 16);  定位头部地址,将字符串“0x30007fc0”转化为整型

printf ("## Booting image at %08lx ...\n", addr); 显示从哪儿启动

memmove (&header, (char *)addr, sizeof(image_header_t)); 读取头部到header变量中

4、判断当前的内存区是否是uImage的开始位置

uboot启动linux的过程
 if (ntohl(hdr->ih_magic) != IH_MAGIC) {
      {
  puts ("Bad Magic Number\n");
  SHOW_BOOT_PROGRESS (-1);
  return 1;
     }
 }
uboot启动linux的过程

注意到:

uboot启动linux的过程
#define IH_MAGIC 0x27051956 /* Image Magic Number  */(include/image.h)
uboot启动linux的过程

5、校验头部

uboot启动linux的过程
    data = (ulong)&header;
    len  = sizeof(image_header_t);

    checksum = ntohl(hdr->ih_hcrc);
    hdr->ih_hcrc = 0;

    if (crc32 (0, (uchar *)data, len) != checksum) {
        puts ("Bad Header Checksum\n");
        SHOW_BOOT_PROGRESS (-2);
        return 1;
    }
uboot启动linux的过程

6、打印头部信息

uboot启动linux的过程
    /* for multi-file images we need the data part, too */
    print_image_hdr ((image_header_t *)addr);
uboot启动linux的过程

7、核查内核数据

uboot启动linux的过程
    if (verify) {
        puts ("   Verifying Checksum ... ");
        if (crc32 (0, (uchar *)data, len) != ntohl(hdr->ih_dcrc)) {
            printf ("Bad Data CRC\n");
            SHOW_BOOT_PROGRESS (-3);
            return 1;
        }
        puts ("OK\n");
    }
uboot启动linux的过程

8、核查架构、内核类型、压缩类型等信息

uboot启动linux的过程
    len_ptr = (ulong *)data;

#if defined(__PPC__)
    if (hdr->ih_arch != IH_CPU_PPC)
#elif defined(__ARM__)
    if (hdr->ih_arch != IH_CPU_ARM)
#elif defined(__I386__)
    if (hdr->ih_arch != IH_CPU_I386)
#elif defined(__mips__)
    if (hdr->ih_arch != IH_CPU_MIPS)
#elif defined(__nios__)
    if (hdr->ih_arch != IH_CPU_NIOS)
#elif defined(__M68K__)
    if (hdr->ih_arch != IH_CPU_M68K)
#elif defined(__microblaze__)
    if (hdr->ih_arch != IH_CPU_MICROBLAZE)
#elif defined(__nios2__)
    if (hdr->ih_arch != IH_CPU_NIOS2)
#elif defined(__blackfin__)
    if (hdr->ih_arch != IH_CPU_BLACKFIN)
#elif defined(__avr32__)
    if (hdr->ih_arch != IH_CPU_AVR32)
#else
# error Unknown CPU type
#endif
    {
        printf ("Unsupported Architecture 0x%x\n", hdr->ih_arch);
        SHOW_BOOT_PROGRESS (-4);
        return 1;
    }
    SHOW_BOOT_PROGRESS (5);

    switch (hdr->ih_type) {
    case IH_TYPE_STANDALONE:
        name = "Standalone Application";
        /* A second argument overwrites the load address */
        if (argc > 2) {
            hdr->ih_load = htonl(simple_strtoul(argv[2], NULL, 16));
        }
        break;
    case IH_TYPE_KERNEL:
        name = "Kernel Image";
        break;
    case IH_TYPE_MULTI:
        name = "Multi-File Image";
        len  = ntohl(len_ptr[0]);
        /* OS kernel is always the first image */
        data += 8; /* kernel_len + terminator */
        for (i=1; len_ptr[i]; ++i)
            data += 4;
        break;
    default: printf ("Wrong Image Type for %s command\n", cmdtp->name);
        SHOW_BOOT_PROGRESS (-5);
        return 1;
    }
    SHOW_BOOT_PROGRESS (6);

    /*
     * We have reached the point of no return: we are going to
     * overwrite all exception vector code, so we cannot easily
     * recover from any failures any more...
     */

    iflag = disable_interrupts();

#ifdef CONFIG_AMIGAONEG3SE 
    /*
     * We‘ve possible left the caches enabled during
     * bios emulation, so turn them off again
     */
    icache_disable();  
    invalidate_l1_instruction_cache();
    flush_data_cache();
    dcache_disable();
#endif

    switch (hdr->ih_comp) {
    case IH_COMP_NONE:
        if(ntohl(hdr->ih_load) == data) {
            printf ("   XIP %s ... ", name);
        } else {
#if defined(CONFIG_HW_WATCHDOG) || defined(CONFIG_WATCHDOG)
            size_t l = len;
            void *to = (void *)ntohl(hdr->ih_load);
            void *from = (void *)data;

            printf ("   Loading %s ... ", name);

            while (l > 0) {
                size_t tail = (l > CHUNKSZ) ? CHUNKSZ : l;
                WATCHDOG_RESET();
                memmove (to, from, tail);
                to += tail;
                from += tail;
                l -= tail;
            }
#else    /* !(CONFIG_HW_WATCHDOG || CONFIG_WATCHDOG) */
            memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);
#endif    /* CONFIG_HW_WATCHDOG || CONFIG_WATCHDOG */
        }
        break;
    case IH_COMP_GZIP:
        printf ("   Uncompressing %s ... ", name);
        if (gunzip ((void *)ntohl(hdr->ih_load), unc_len,
                (uchar *)data, &len) != 0) {
            puts ("GUNZIP ERROR - must RESET board to recover\n");
            SHOW_BOOT_PROGRESS (-6);
            do_reset (cmdtp, flag, argc, argv);
        }
        break;
#ifdef CONFIG_BZIP2
    case IH_COMP_BZIP2:
        printf ("   Uncompressing %s ... ", name);
        /*
         * If we‘ve got less than 4 MB of malloc() space,
         * use slower decompression algorithm which requires
         * at most 2300 KB of memory.
         */
        i = BZ2_bzBuffToBuffDecompress ((char*)ntohl(hdr->ih_load),
                        &unc_len, (char *)data, len,
                        CFG_MALLOC_LEN < (4096 * 1024), 0);
        if (i != BZ_OK) {
            printf ("BUNZIP2 ERROR %d - must RESET board to recover\n", i);
            SHOW_BOOT_PROGRESS (-6);
            udelay(100000);
            do_reset (cmdtp, flag, argc, argv);
        }
        break;
#endif /* CONFIG_BZIP2 */
    default:
        if (iflag)
            enable_interrupts();
        printf ("Unimplemented compression type %d\n", hdr->ih_comp);
        SHOW_BOOT_PROGRESS (-7);
        return 1;
    }
    puts ("OK\n");
    SHOW_BOOT_PROGRESS (7);

    switch (hdr->ih_type) {
    case IH_TYPE_STANDALONE:
        if (iflag)
            enable_interrupts();

        /* load (and uncompress), but don‘t start if "autostart"
         * is set to "no"
         */
        if (((s = getenv("autostart")) != NULL) && (strcmp(s,"no") == 0)) {
            char buf[32];
            sprintf(buf, "%lX", len);
            setenv("filesize", buf);
            return 0;
        }
        appl = (int (*)(int, char *[]))ntohl(hdr->ih_ep);
        (*appl)(argc-1, &argv[1]);
        return 0;
    case IH_TYPE_KERNEL:
    case IH_TYPE_MULTI:
        /* handled below */
        break;
    default:
        if (iflag)
            enable_interrupts();
        printf ("Can‘t boot image type %d\n", hdr->ih_type);
        SHOW_BOOT_PROGRESS (-8);
        return 1;
    }
    SHOW_BOOT_PROGRESS (8);
View Code

9、更具操作系统类型,启动对应的操作系统

uboot启动linux的过程
    switch (hdr->ih_os) {
    default:            /* handled by (original) Linux case */
    case IH_OS_LINUX:
#ifdef CONFIG_SILENT_CONSOLE
        fixup_silent_linux();
#endif
        do_bootm_linux  (cmdtp, flag, argc, argv,
                 addr, len_ptr, verify);
        break;
    case IH_OS_NETBSD:   
uboot启动linux的过程

10、执行do_bootm_linux,继续启动linux系统

  此函数在lib_arm/armlinux.c中

uboot启动linux的过程
    void (*theKernel)(int zero, int arch, uint params);
    image_header_t *hdr = &header;
    bd_t *bd = gd->bd;

#ifdef CONFIG_CMDLINE_TAG
    char *commandline = getenv ("bootargs");
#endif

    theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);
uboot启动linux的过程

  可见,已经将内核运行的首地址赋给了theKernel函数指针变量,将来可以利用这个变量调用进入内核的函数。

  另外,在进入内核之前,要给内核传递参数。方法是将参数以一定的结构放在内存指定的位置上,将来内核从该地址读取数据即可。

  命令行的启动参数存储在以bootargs命名的对象里,值为

uboot启动linux的过程
bootargs=noinitrd root=/dev/mtdblock3 init=/linuxrc console=ttySAC0
uboot启动linux的过程

  告诉内核,启动后的根文件系统位于mtd的哪个区,初始进程,以及控制台

11、判断是否是一个ramdisk或者multi镜像

uboot启动linux的过程
    /*
     * Check if there is an initrd image
     */
    if (argc >= 3) {
        SHOW_BOOT_PROGRESS (9);

        addr = simple_strtoul (argv[2], NULL, 16);

        printf ("## Loading Ramdisk Image at %08lx ...\n", addr);

        /* Copy header so we can blank CRC field for re-calculation */
#ifdef CONFIG_HAS_DATAFLASH
        if (addr_dataflash (addr)) {
            read_dataflash (addr, sizeof (image_header_t),
                    (char *) &header);
        } else
#endif
            memcpy (&header, (char *) addr,
                sizeof (image_header_t));

        if (ntohl (hdr->ih_magic) != IH_MAGIC) {
            printf ("Bad Magic Number\n");
            SHOW_BOOT_PROGRESS (-10);
            do_reset (cmdtp, flag, argc, argv);
        }

        data = (ulong) & header;
        len = sizeof (image_header_t);

        checksum = ntohl (hdr->ih_hcrc);
        hdr->ih_hcrc = 0;

        if (crc32 (0, (unsigned char *) data, len) != checksum) {
            printf ("Bad Header Checksum\n");
            SHOW_BOOT_PROGRESS (-11);
            do_reset (cmdtp, flag, argc, argv);
        }

        SHOW_BOOT_PROGRESS (10);

        print_image_hdr (hdr);

        data = addr + sizeof (image_header_t);
        len = ntohl (hdr->ih_size);

#ifdef CONFIG_HAS_DATAFLASH
        if (addr_dataflash (addr)) {
            read_dataflash (data, len, (char *) CFG_LOAD_ADDR);
            data = CFG_LOAD_ADDR;
        }
#endif

        if (verify) {
            ulong csum = 0;

            printf ("   Verifying Checksum ... ");
            csum = crc32 (0, (unsigned char *) data, len);
            if (csum != ntohl (hdr->ih_dcrc)) {
                printf ("Bad Data CRC\n");
                SHOW_BOOT_PROGRESS (-12);
                do_reset (cmdtp, flag, argc, argv);
            }
            printf ("OK\n");
        }

        SHOW_BOOT_PROGRESS (11);

        if ((hdr->ih_os != IH_OS_LINUX) ||
            (hdr->ih_arch != IH_CPU_ARM) ||
            (hdr->ih_type != IH_TYPE_RAMDISK)) {
            printf ("No Linux ARM Ramdisk Image\n");
            SHOW_BOOT_PROGRESS (-13);
            do_reset (cmdtp, flag, argc, argv);
        }

#if defined(CONFIG_B2) || defined(CONFIG_EVB4510) || defined(CONFIG_ARMADILLO)
        /*
         *we need to copy the ramdisk to SRAM to let Linux boot
         */
        memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);
        data = ntohl(hdr->ih_load);
#endif /* CONFIG_B2 || CONFIG_EVB4510 */

        /*
         * Now check if we have a multifile image
         */
    } else if ((hdr->ih_type == IH_TYPE_MULTI) && (len_ptr[1])) {
        ulong tail = ntohl (len_ptr[0]) % 4;
        int i;

        SHOW_BOOT_PROGRESS (13);

        /* skip kernel length and terminator */
        data = (ulong) (&len_ptr[2]);
        /* skip any additional image length fields */
        for (i = 1; len_ptr[i]; ++i)
            data += 4;
        /* add kernel length, and align */
        data += ntohl (len_ptr[0]);
        if (tail) {
            data += 4 - tail;
        }

        len = ntohl (len_ptr[1]);

    } else {
        /*
         * no initrd image
         */
        SHOW_BOOT_PROGRESS (14);

        len = data = 0;
    }

#ifdef    DEBUG
    if (!data) {
        printf ("No initrd\n");
    }
#endif
View Code

12、给内核传递参数

uboot启动linux的过程
#if defined (CONFIG_SETUP_MEMORY_TAGS) || \
    defined (CONFIG_CMDLINE_TAG) ||     defined (CONFIG_INITRD_TAG) ||     defined (CONFIG_SERIAL_TAG) ||     defined (CONFIG_REVISION_TAG) ||     defined (CONFIG_LCD) ||     defined (CONFIG_VFD)
    setup_start_tag (bd);
#ifdef CONFIG_SERIAL_TAG
    setup_serial_tag (&params);
#endif
#ifdef CONFIG_REVISION_TAG
    setup_revision_tag (&params);
#endif
#ifdef CONFIG_SETUP_MEMORY_TAGS
    setup_memory_tags (bd);
#endif
#ifdef CONFIG_CMDLINE_TAG
    setup_commandline_tag (bd, commandline);
#endif
#ifdef CONFIG_INITRD_TAG
    if (initrd_start && initrd_end)
        setup_initrd_tag (bd, initrd_start, initrd_end);
#endif
#if defined (CONFIG_VFD) || defined (CONFIG_LCD)
    setup_videolfb_tag ((gd_t *) gd);
#endif
    setup_end_tag (bd);
#endif
uboot启动linux的过程

  比较重要的函数有:

   setup_start_tag (bd);

  setup_memory_tags (bd);

  setup_commandline_tag (bd, commandline);

  setup_end_tag (bd);

  其中 bd->bi_boot_params(参考uboot全局变量),bi_boot_params=>>0x30000100,启动参数存放的位置。

13、启动内核

uboot启动linux的过程
    printf ("\nStarting kernel ...\n\n");
  theKernel (0, bd->bi_arch_number, bd->bi_boot_params);
uboot启动linux的过程

  把机器码以及启动参数存放的位置都告诉给内核。

五、u-boot启动zImage

uboot启动linux的过程,布布扣,bubuko.com

uboot启动linux的过程

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