U-Boot启动引导内核分析(三)

最新推荐文章于 2023-11-26 15:25:28 发布

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#linux #代码分析 #tags #image #os #struct

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本文详细解析了U-Boot中do_bootm_linux()函数的工作流程，包括如何寻找内核入口点、初始化TAG结构体以及传递控制权给Linux内核。

标签：ARM bootloader U-Boot 代码分析抵岸科技

do_bootm_linux()函数位于lib_arm/Bootm.c文件中，主要流程分析如下：

void do_bootm_linux (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],
             bootm_headers_t *images)
{
    ulong    initrd_start, initrd_end;
    ulong    ep = 0;
    bd_t    *bd = gd->bd;
    char    *s;
    int    machid = bd->bi_arch_number;
    void    (*theKernel)(int zero, int arch, uint params);
    int    ret;

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

    /* find kernel entry point */
    if (images->legacy_hdr_valid) {
        ep = image_get_ep (&images->legacy_hdr_os_copy);
#if defined(CONFIG_FIT)
    } else if (images->fit_uname_os) {
        ret = fit_image_get_entry (images->fit_hdr_os,
                    images->fit_noffset_os, &ep);
        if (ret) {
            puts ("Can't get entry point property!/n");
            goto error;
        }
#endif
    } else {
        puts ("Could not find kernel entry point!/n");
        goto error;
    }
    theKernel = (void (*)(int, int, uint))ep;

    s = getenv ("machid");
    if (s) {
        machid = simple_strtoul (s, NULL, 16);
        printf ("Using machid 0x%x from environment/n", machid);
    }

    ret = boot_get_ramdisk (argc, argv, images, IH_ARCH_ARM,
            &initrd_start, &initrd_end);
    if (ret)
        goto error;

    show_boot_progress (15);

    debug ("## Transferring control to Linux (at address %08lx) .../n",
           (ulong) theKernel);

#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)
    /* 初始化TAG结构体开始 */
    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
    /* 设置RAM参数 */
    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
    /* 初始化TAG结构体结束 */
    setup_end_tag (bd);
#endif

    /* we assume that the kernel is in place */
    printf ("/nStarting kernel .../n/n");

#ifdef CONFIG_USB_DEVICE
    {
        extern void udc_disconnect (void);
        udc_disconnect ();
    }
#endif

    cleanup_before_linux ();

    /* 将控制权交给内核，让内核自解压启动 */
    /* 传给KERNEL的参数：（struct tag *）bd->bi_boot_params */
    /* 在board/atmel/at91sam9g20ek/At91sam9g20ek.c文件中有如下定义：
    gd->bd->bi_boot_params = PHYS_SDRAM + 0x100;(PHYS_SDRAM = 0x20000000)
    */
    theKernel (0, machid, bd->bi_boot_params);
    /* does not return */
    return;

error:
    do_reset (cmdtp, flag, argc, argv);
    return;
}

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