Kernel获取bootargs

/*
 * arch/arm64/kernel/setup.c
 * By: start_kernel()
 */
void __init setup_arch(char **cmdline_p)
{
    setup_processor();

    setup_machine_fdt(__fdt_pointer);
    ......
}

//arch/arm64/kernel/setup.c
static void __init setup_machine_fdt(phys_addr_t dt_phys)
{
    if (!dt_phys || !early_init_dt_scan(phys_to_virt(dt_phys))) {
        early_print("\n"
            "Error: invalid device tree blob at physical address 0x%p (virtual address 0x%p)\n"
            "The dtb must be 8-byte aligned and passed in the first 512MB of memory\n"
            "\nPlease check your bootloader.\n",
            dt_phys, phys_to_virt(dt_phys));

        while (true)
            cpu_relax();
    }

    machine_name = of_flat_dt_get_machine_name();
    if (machine_name) {
        dump_stack_set_arch_desc("%s (DT)", machine_name);
        pr_info("Machine: %s\n", machine_name);
    }
}

//drivers/of/fdt.c
bool __init early_init_dt_scan(void *params)
{
    bool status;

    status = early_init_dt_verify(params);
    if (!status)
        return false;

    early_init_dt_scan_nodes();
    return true;
}

//drivers/of/fdt.c
void __init early_init_dt_scan_nodes(void)
{
    /* Retrieve various information from the /chosen node */
    of_scan_flat_dt(early_init_dt_scan_chosen, boot_command_line); //获得command line，保存在全局变量boot_command_line中

    /* Initialize {size,address}-cells info */
    of_scan_flat_dt(early_init_dt_scan_root, NULL);

    /* Setup memory, calling early_init_dt_add_memory_arch */
    of_scan_flat_dt(early_init_dt_scan_memory, NULL);