Mini440之uboot移植流程之linux内核启动分析(六)

在前面的章节关于u-boot的源码,以及u-boot的移植这一块我们介绍完了。接下来,我们开始进入第二个阶段,linux内核移植,以及驱动开发。

在这之前,我们遗漏了u-boot中的一个重要环节没有介绍,就是u-boot如何执行bootm命令,如何实现linux内核启动。

一、linux内核启动入口之do_bootm

我们在Mini440之uboot移植之源码分析命令解析(五) 介绍过如果配置了CONFIG_BOOTCOMMAND宏:

#define CONFIG_BOOTCOMMAND "nand read 0x30000000 kernel; bootm 0x30000000" //bootcmd  

那么在执行autoboot_command函数的时候,将会执行该命令。

bootm这个命令用于启动一个操作系统映射,它会从映射文件的头部取得一些信息,这些信息包括:映射文件的基于的cpu架构、其操作系统类型、映射的类型、压缩方式、映射文件在内存中的加载地址、映射文件运行的入口地址、映射文件名等。

nand read 0x30000000命令:这里将NAND kernel分区的代码加载到地址0x30000000;

bootm 0x3000000:启动linux内核;

1.1 autoboot_command(common/autoboot.c)

void autoboot_command(const char *s)
{
    debug("### main_loop: bootcmd=\"%s\"\n", s ? s : "<UNDEFINED>");

    if (stored_bootdelay != -1 && s && !abortboot(stored_bootdelay)) {
        run_command_list(s, -1, 0);
    }
}

如果在u-boot启动倒计时结束之前,没有按下任何键,将会执行那么将执行run_command_list,此函数会执行参数s指定的一系列命令,也就是bootcmd中配置中的命令,bootcmd中保存着默认的启动命令。

在默认环境变量default_environment中定义有:

#ifdef    CONFIG_BOOTCOMMAND
    "bootcmd="    CONFIG_BOOTCOMMAND        "\0"
#endif

1.2 do_bootm(cmd/bootm.c)

由于要执行bootm命令,所以我们需要打开与bootm命令相关的文件进行分析,bootm命令定义在cmc/bootm.c文件中:

U_BOOT_CMD(
    bootm,    CONFIG_SYS_MAXARGS,    1,    do_bootm,
    "boot application image from memory", bootm_help_text
);

找到对应的do_bootm函数,去除无用的代码:

/*******************************************************************/
/* bootm - boot application image from image in memory */
/*******************************************************************/

int do_bootm(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
    /* determine if we have a sub command */
    argc--; argv++;
    if (argc > 0) {
        char *endp;

        simple_strtoul(argv[0], &endp, 16);
        /* endp pointing to NULL means that argv[0] was just a
         * valid number, pass it along to the normal bootm processing
         *
         * If endp is ':' or '#' assume a FIT identifier so pass
         * along for normal processing.
         *
         * Right now we assume the first arg should never be '-'
         */
        if ((*endp != 0) && (*endp != ':') && (*endp != '#'))
            return do_bootm_subcommand(cmdtp, flag, argc, argv);
    }

// 到这里参数中的bootm参数会被去掉 return do_bootm_states(cmdtp, flag, argc, argv, BOOTM_STATE_START | BOOTM_STATE_FINDOS | BOOTM_STATE_FINDOTHER | BOOTM_STATE_LOADOS | BOOTM_STATE_OS_PREP | BOOTM_STATE_OS_FAKE_GO | BOOTM_STATE_OS_GO, &images, 1); }

当执行bootm 0x30000000,函数入参:第一个参数是bootm命令结构体,flag是命令标志位,argv[0]='"bootm"、argv[1]="0x3000000",argc=2。

这里进入函数之后argc=1,argv[0]=0x30000000.

bootm的核心是do_bootm_states,以全局变量bootm_headers_t images作为do_bootm_states的参数,改变量在cmd/bootm.c文件中声明。

bootm_headers_t images;        /* pointers to os/initrd/fdt images */

 bootm会根据参数以及参数指向的镜像来填充这个结构体里面的成员。 最终再使用这个结构体里面的信息来填充kernel启动信息并且到跳转到kernel中。 

下面详细说明这个函数。

二、do_bootm_states(cmd/bootm.c)

我们先来看一下这个函数的声明:

int do_bootm_states(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[],
            int states, bootm_headers_t *images, int boot_progress);

2.1 bootm_headers_t(include/image.h)

bootm_headers_t是一个复杂的数据结构,官网是这样描述的:

/*
 * Legacy and FIT format headers used by do_bootm() and do_bootm_<os>()
 * routines.
 */
typedef struct bootm_headers {
    /*
     * Legacy os image header, if it is a multi component image
     * then boot_get_ramdisk() and get_fdt() will attempt to get
     * data from second and third component accordingly.
     */
    image_header_t    *legacy_hdr_os;        /* image header pointer */
    image_header_t    legacy_hdr_os_copy;    /* header copy */
    ulong        legacy_hdr_valid;

#if IMAGE_ENABLE_FIT
    const char    *fit_uname_cfg;    /* configuration node unit name */

    void        *fit_hdr_os;    /* os FIT image header */
    const char    *fit_uname_os;    /* os subimage node unit name */
    int        fit_noffset_os;    /* os subimage node offset */

    void        *fit_hdr_rd;    /* init ramdisk FIT image header */
    const char    *fit_uname_rd;    /* init ramdisk subimage node unit name */
    int        fit_noffset_rd;    /* init ramdisk subimage node offset */

    void        *fit_hdr_fdt;    /* FDT blob FIT image header */
    const char    *fit_uname_fdt;    /* FDT blob subimage node unit name */
    int        fit_noffset_fdt;/* FDT blob subimage node offset */

    void        *fit_hdr_setup;    /* x86 setup FIT image header */
    const char    *fit_uname_setup; /* x86 setup subimage node name */
    int        fit_noffset_setup;/* x86 setup subimage node offset */
#endif

#ifndef USE_HOSTCC
    image_info_t    os;        /* os image info */
    ulong        ep;        /* entry point of OS */

    ulong        rd_start, rd_end;/* ramdisk start/end */

    char        *ft_addr;    /* flat dev tree address */
    ulong        ft_len;        /* length of flat device tree */

    ulong        initrd_start;
    ulong        initrd_end;
    ulong        cmdline_start;
    ulong        cmdline_end;
    bd_t        *kbd;
#endif

    int        verify;        /* getenv("verify")[0] != 'n' */

#define    BOOTM_STATE_START    (0x00000001)
#define    BOOTM_STATE_FINDOS    (0x00000002)
#define    BOOTM_STATE_FINDOTHER    (0x00000004)
#define    BOOTM_STATE_LOADOS    (0x00000008)
#define    BOOTM_STATE_RAMDISK    (0x00000010)
#define    BOOTM_STATE_FDT        (0x00000020)
#define    BOOTM_STATE_OS_CMDLINE    (0x00000040)
#define    BOOTM_STATE_OS_BD_T    (0x00000080)
#define    BOOTM_STATE_OS_PREP    (0x00000100)
#define    BOOTM_STATE_OS_FAKE_GO    (0x00000200)    /* 'Almost' run the OS */
#define    BOOTM_STATE_OS_GO    (0x00000400)
    int        state;

#ifdef CONFIG_LMB
    struct lmb    lmb;        /* for memory mgmt */
#endif
} bootm_headers_t;

bootm_headers_t用于Legacy或设备树(FDT)方式镜像的启动,其中包括了os/initrd/fdt images的信息。我们这里大概介绍一下和这个结构体的成员变量:

  • legacy_hdr_os:Legacy-uImage的镜像头;
  • legacy_hdr_os_copy:Legacy-uImage的镜像头备份;
  • fit_uname_cfg:配置节点名;
  • fit_hdr_os:FIT-uImage中kernel镜像头;
  • fit_uname_os:FIT-uImag中kernel的节点名;
  • fit_noffset_os:FIT-uImage中kernel的节点偏移;
  • fit_hdr_rd:FIT-uImage中ramdisk的镜像头;
  • fit_uname_rd:FIT-uImage中ramdisk的节点名;
  • fit_noffset_rd:FIT-uImage中ramdisk的节点偏移;
  • fit_hdr_fdt:FIT-uImage中FDT的镜像头;
  • fit_uname_fdt:FIT-uImage中FDT的节点名;
  • fit_noffset_fdt:FIT-uImage中FDT的节点偏移;
  • os:操作系统信息的结构体,比如内核镜像在内存的起始地址、以及大小;
  • ep:操作系统的入口地址;
  • rd_start:ramdisk在内存上的起始地址;
  • rd_end:ramdisk在内存上的结束地址
  • ft_addr:fdt在内存上的地址;
  • ft_len:fdt在内存上的长度;
  • verify:是否需要验证;
  • state:状态标识,用于标识对应的bootm需要做什么操作;

其中 legacy_hdr_os是image_header_t类型。这个结构尤为重要,下面来介绍。

2.2 (include/image.h)

/*
 * Legacy format image header,
 * all data in network byte order (aka natural aka bigendian).
 */
typedef struct image_header {
    __be32        ih_magic;    /* Image Header Magic Number    */
    __be32        ih_hcrc;    /* Image Header CRC Checksum    */
    __be32        ih_time;    /* Image Creation Timestamp    */
    __be32        ih_size;    /* Image Data Size        */
    __be32        ih_load;    /* Data     Load  Address        */
    __be32        ih_ep;        /* Entry Point Address        */
    __be32        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;

比较重要的成员有:

  • ih_magic:镜像的魔数,用来给uboot判断是什么格式的镜像(zImage、uImage等);
  • ih_ep:镜像的入口;
  • inj_os:镜像的系统;

2.3 状态说明

do_bootm_states的state参数是一大堆的标志宏,这些标志宏就是u-boot启动时需要的阶段,每个阶段都有一个宏来表示。

#define    BOOTM_STATE_START    (0x00000001)
#define    BOOTM_STATE_FINDOS    (0x00000002)
#define    BOOTM_STATE_FINDOTHER    (0x00000004)
#define    BOOTM_STATE_LOADOS    (0x00000008)
#define    BOOTM_STATE_RAMDISK    (0x00000010)
#define    BOOTM_STATE_FDT        (0x00000020)
#define    BOOTM_STATE_OS_CMDLINE    (0x00000040)
#define    BOOTM_STATE_OS_BD_T    (0x00000080)
#define    BOOTM_STATE_OS_PREP    (0x00000100)
#define    BOOTM_STATE_OS_FAKE_GO    (0x00000200)    /* 'Almost' run the OS */
#define    BOOTM_STATE_OS_GO    (0x00000400)
  • BOOTM_STATE_START :开始执行bootm的一些准备动作;
  • BOOTM_STATE_FINDOS :查找操作系统镜像;
  • BOOTM_STATE_FINDOTHER :查找操作系统镜像外的其它镜像,比如FDT、ramdisk等;
  • BOOTM_STATE_LOADOS :加载操作系统;
  • BOOTM_STATE_RAMDISK :操作ramdisk;
  • BOOTM_STATE_FDT :操作FDT;
  • BOOTM_STATE_OS_CMDLINE :操作commandline;
  • BOOTM_STATE_OS_BD_T :跳转到操作系统的前的准备动作;
  • BOOTM_STATE_OS_PREP :执行跳转前的准备动作 ;
  • BOOTM_STATE_OS_FAKE_GO :伪跳转,一般都能直接跳转到kernel中去
  • BOOTM_STATE_OS_GO :设置启动参数,跳转到kernel所在的地址上 ;

do_bootm_states根据states来判断要执行的操作。在这些流程中,起传递作用的是bootm_headers_t images这个数据结构,有些流程是解析镜像,往这个结构体里写数据。 而跳转的时候,则需要使用到这个结构体里面的数据。

2.4 do_bootm_states函数执行流程

/**
 * Execute selected states of the bootm command.
 *
 * Note the arguments to this state must be the first argument, Any 'bootm'
 * or sub-command arguments must have already been taken.
 *
 * Note that if states contains more than one flag it MUST contain
 * BOOTM_STATE_START, since this handles and consumes the command line args.
 *
 * Also note that aside from boot_os_fn functions and bootm_load_os no other
 * functions we store the return value of in 'ret' may use a negative return
 * value, without special handling.
 *
 * @param cmdtp        Pointer to bootm command table entry
 * @param flag        Command flags (CMD_FLAG_...)
 * @param argc        Number of subcommand arguments (0 = no arguments)
 * @param argv        Arguments
 * @param states    Mask containing states to run (BOOTM_STATE_...)
 * @param images    Image header information
 * @param boot_progress 1 to show boot progress, 0 to not do this
 * @return 0 if ok, something else on error. Some errors will cause this
 *    function to perform a reboot! If states contains BOOTM_STATE_OS_GO
 *    then the intent is to boot an OS, so this function will not return
 *    unless the image type is standalone.
 */
int do_bootm_states(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[],
            int states, bootm_headers_t *images, int boot_progress)
{
    boot_os_fn *boot_fn;
    ulong iflag = 0;
    int ret = 0, need_boot_fn;

    images->state |= states;

    /*
     * Work through the states and see how far we get. We stop on
     * any error.
     */
    if (states & BOOTM_STATE_START)
        ret = bootm_start(cmdtp, flag, argc, argv);

    if (!ret && (states & BOOTM_STATE_FINDOS))
        ret = bootm_find_os(cmdtp, flag, argc, argv);

    if (!ret && (states & BOOTM_STATE_FINDOTHER)) {
        ret = bootm_find_other(cmdtp, flag, argc, argv);
        argc = 0;    /* consume the args */
    }

    /* Load the OS */
    if (!ret && (states & BOOTM_STATE_LOADOS)) {
        ulong load_end;

        iflag = bootm_disable_interrupts();
        ret = bootm_load_os(images, &load_end, 0);
        if (ret == 0)
            lmb_reserve(&images->lmb, images->os.load,
                    (load_end - images->os.load));
        else if (ret && ret != BOOTM_ERR_OVERLAP)
            goto err;
        else if (ret == BOOTM_ERR_OVERLAP)
            ret = 0;
#if defined(CONFIG_SILENT_CONSOLE) && !defined(CONFIG_SILENT_U_BOOT_ONLY)
        if (images->os.os == IH_OS_LINUX)
            fixup_silent_linux();
#endif
    }

    /* Relocate the ramdisk */
#ifdef CONFIG_SYS_BOOT_RAMDISK_HIGH
    if (!ret && (states & BOOTM_STATE_RAMDISK)) {
        ulong rd_len = images->rd_end - images->rd_start;

        ret = boot_ramdisk_high(&images->lmb, images->rd_start,
            rd_len, &images->initrd_start, &images->initrd_end);
        if (!ret) {
            setenv_hex("initrd_start", images->initrd_start);
            setenv_hex("initrd_end", images->initrd_end);
        }
    }
#endif
#if IMAGE_ENABLE_OF_LIBFDT && defined(CONFIG_LMB)
    if (!ret && (states & BOOTM_STATE_FDT)) {
        boot_fdt_add_mem_rsv_regions(&images->lmb, images->ft_addr);
        ret = boot_relocate_fdt(&images->lmb, &images->ft_addr,
                    &images->ft_len);
    }
#endif

    /* From now on, we need the OS boot function */
    if (ret)
        return ret;
    boot_fn = bootm_os_get_boot_func(images->os.os);
    need_boot_fn = states & (BOOTM_STATE_OS_CMDLINE |
            BOOTM_STATE_OS_BD_T | BOOTM_STATE_OS_PREP |
            BOOTM_STATE_OS_FAKE_GO | BOOTM_STATE_OS_GO);
    if (boot_fn == NULL && need_boot_fn) {
        if (iflag)
            enable_interrupts();
        printf("ERROR: booting os '%s' (%d) is not supported\n",
               genimg_get_os_name(images->os.os), images->os.os);
        bootstage_error(BOOTSTAGE_ID_CHECK_BOOT_OS);
        return 1;
    }

    /* Call various other states that are not generally used */
    if (!ret && (states & BOOTM_STATE_OS_CMDLINE))
        ret = boot_fn(BOOTM_STATE_OS_CMDLINE, argc, argv, images);
    if (!ret && (states & BOOTM_STATE_OS_BD_T))
        ret = boot_fn(BOOTM_STATE_OS_BD_T, argc, argv, images);
    if (!ret && (states & BOOTM_STATE_OS_PREP))
        ret = boot_fn(BOOTM_STATE_OS_PREP, argc, argv, images);

#ifdef CONFIG_TRACE
    /* Pretend to run the OS, then run a user command */
    if (!ret && (states & BOOTM_STATE_OS_FAKE_GO)) {
        char *cmd_list = getenv("fakegocmd");

        ret = boot_selected_os(argc, argv, BOOTM_STATE_OS_FAKE_GO,
                images, boot_fn);
        if (!ret && cmd_list)
            ret = run_command_list(cmd_list, -1, flag);
    }
#endif

    /* Check for unsupported subcommand. */
    if (ret) {
        puts("subcommand not supported\n");
        return ret;
    }

    /* Now run the OS! We hope this doesn't return */
    if (!ret && (states & BOOTM_STATE_OS_GO))
        ret = boot_selected_os(argc, argv, BOOTM_STATE_OS_GO,
                images, boot_fn);

    /* Deal with any fallout */
err:
    if (iflag)
        enable_interrupts();

    if (ret == BOOTM_ERR_UNIMPLEMENTED)
        bootstage_error(BOOTSTAGE_ID_DECOMP_UNIMPL);
    else if (ret == BOOTM_ERR_RESET)
        do_reset(cmdtp, flag, argc, argv);

    return ret;
}

代码具体执行流程:

  • 初始化images->state|=states;
  • states跟宏BOOTM_STATE_START进行与操作,通过执行bootm_start;
  • states跟宏BOOTM_STATE_FINDOS进行与操作,通过执行bootm_find_os;
  • states跟宏BOOTM_STATE_FINDOTHER进行与操作,通过执行bootm_find_other;
  • states跟宏BOOTM_STATE_LOADOS进行与操作,通过关闭中断,执行bootm_load_os;
  • states跟宏BOOTM_STATE_OS_PREP进行与操作,通过执行boot_fn;
  • states跟宏BOOTM_STATE_OS_GO进行与操作,通过执行boot_selected_os;

boot_selected_os,这函数里面就执行do_bootm_linux跳转到我们的内核去运行了,如无意外,到了这里一般情况下就不返回了。

我们根据状态参数,绘制出这个函数的执行流程:

Mini440之uboot移植流程之linux内核启动分析(六)

2.5 bootm_start(common/bootm.c)

static int bootm_start(cmd_tbl_t *cmdtp, int flag, int argc,
               char * const argv[])
{
    memset((void *)&images, 0, sizeof(images));
    images.verify = getenv_yesno("verify");

    boot_start_lmb(&images);

    bootstage_mark_name(BOOTSTAGE_ID_BOOTM_START, "bootm_start");
    images.state = BOOTM_STATE_START;

    return 0;
}

代码具体执行流程:

  • 清空images结构体;
  • 获取环境遍历verify,并赋值给images.verify;
  • 执行boot_start_lmb()初始化images.lmb;
  • 执行bootstage_mark_name,记录启动阶段的名字;
  • 设置images.state = BOOTM_STATE_START;

2.6 bootm_find_os(common/bootm.c)

 

 

static int bootm_find_os(cmd_tbl_t *cmdtp, int flag, int argc,
             char * const argv[])
{
    const void *os_hdr;
    bool ep_found = false;
    int ret;

    /* get kernel image header, start address and length */
    os_hdr = boot_get_kernel(cmdtp, flag, argc, argv,
            &images, &images.os.image_start, &images.os.image_len);
    if (images.os.image_len == 0) {
        puts("ERROR: can't get kernel image!\n");
        return 1;
    }

    /* get image parameters */
    switch (genimg_get_format(os_hdr)) {
#if defined(CONFIG_IMAGE_FORMAT_LEGACY)
    case IMAGE_FORMAT_LEGACY:
        images.os.type = image_get_type(os_hdr);
        images.os.comp = image_get_comp(os_hdr);
        images.os.os = image_get_os(os_hdr);

        images.os.end = image_get_image_end(os_hdr);
        images.os.load = image_get_load(os_hdr);
        images.os.arch = image_get_arch(os_hdr);
        break;
#endif
#if IMAGE_ENABLE_FIT
    case IMAGE_FORMAT_FIT:
        if (fit_image_get_type(images.fit_hdr_os,
                       images.fit_noffset_os,
                       &images.os.type)) {
            puts("Can't get image type!\n");
            bootstage_error(BOOTSTAGE_ID_FIT_TYPE);
            return 1;
        }

        if (fit_image_get_comp(images.fit_hdr_os,
                       images.fit_noffset_os,
                       &images.os.comp)) {
            puts("Can't get image compression!\n");
            bootstage_error(BOOTSTAGE_ID_FIT_COMPRESSION);
            return 1;
        }

        if (fit_image_get_os(images.fit_hdr_os, images.fit_noffset_os,
                     &images.os.os)) {
            puts("Can't get image OS!\n");
            bootstage_error(BOOTSTAGE_ID_FIT_OS);
            return 1;
        }

        if (fit_image_get_arch(images.fit_hdr_os,
                       images.fit_noffset_os,
                       &images.os.arch)) {
            puts("Can't get image ARCH!\n");
            return 1;
        }

        images.os.end = fit_get_end(images.fit_hdr_os);

        if (fit_image_get_load(images.fit_hdr_os, images.fit_noffset_os,
                       &images.os.load)) {
            puts("Can't get image load address!\n");
            bootstage_error(BOOTSTAGE_ID_FIT_LOADADDR);
            return 1;
        }
        break;
#endif
#ifdef CONFIG_ANDROID_BOOT_IMAGE
    case IMAGE_FORMAT_ANDROID:
        images.os.type = IH_TYPE_KERNEL;
        images.os.comp = IH_COMP_NONE;
        images.os.os = IH_OS_LINUX;

        images.os.end = android_image_get_end(os_hdr);
        images.os.load = android_image_get_kload(os_hdr);
        images.ep = images.os.load;
        ep_found = true;
        break;
#endif
    default:
        puts("ERROR: unknown image format type!\n");
        return 1;
    }

    /* If we have a valid setup.bin, we will use that for entry (x86) */
    if (images.os.arch == IH_ARCH_I386 ||
        images.os.arch == IH_ARCH_X86_64) {
        ulong len;

        ret = boot_get_setup(&images, IH_ARCH_I386, &images.ep, &len);
        if (ret < 0 && ret != -ENOENT) {
            puts("Could not find a valid setup.bin for x86\n");
            return 1;
        }
        /* Kernel entry point is the setup.bin */
    } else if (images.legacy_hdr_valid) {
        images.ep = image_get_ep(&images.legacy_hdr_os_copy);
#if IMAGE_ENABLE_FIT
    } else if (images.fit_uname_os) {
        int ret;

        ret = fit_image_get_entry(images.fit_hdr_os,
                      images.fit_noffset_os, &images.ep);
        if (ret) {
            puts("Can't get entry point property!\n");
            return 1;
        }
#endif
    } else if (!ep_found) {
        puts("Could not find kernel entry point!\n");
        return 1;
    }

    if (images.os.type == IH_TYPE_KERNEL_NOLOAD) {
        images.os.load = images.os.image_start;
        images.ep += images.os.load;
    }

    images.os.start = map_to_sysmem(os_hdr);

    return 0;
}

 

代码具体执行流程:

  • boot_get_kernel函数获取内核镜像在内存地址和大小:
    • genimg_get_kernel_addr_fit获取内核真是地址,也就是我们传入的0x30000000参数;
    • genimg_get_image解析0x30000000这个地址,如果这个地址位于dataflash storage,将会将内核镜像加载到RAM中;
    • genimg_get_format获取内核镜像头信息,它是在 zImage 之前加上一个长度为0x40的头信息(tag)(也就是说uImage 是一个二进制文件),在头信息内说明了该镜像文件的类型、加载 位置、生成时间、大小等信息;镜像文件的类型有多种:传统格式,FIT格式和安卓格式等;

    • 然后初始化images.os.image_start和images.os.image_len,如果是FIT格式,还会初始化images中部分与fit相关的字段;
  • 根据返回的头部信息指针,我们去获取到内核想信息并复制给images.os的各个成员,包括内核类型type,内核压缩方式comp,内核是什么操作系统os,内核要装载到内存的哪个位置load,内核是什么体系架构arch,为以后的工作做准备,这里要说明一下,现在内核所在的内存地址是uboot所指定,而内核启动的内存地址不一定在这里,是在laod成员所执行的地址,后面需要把整个镜像拷贝到这里;

  • 最后将images.os.load赋值给images.ep,其实就是内核的启动地址了;

 

2.7 bootm_find_other

2.8 bootm_load_os

2.9 boot_fn

2.10 boot_selected_os

参考文章

[1]七,移植linux-3.19内核

[2][uboot] uboot启动kernel篇(二)——bootm跳转到kernel的流程

[3]linux驱动之uboot启动过程及参数传递

[4]S5PV210-uboot解析(五)-do_bootm函数分析

[5]Linux内核镜像格式

 

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