Analyze the role of the Linux kernel main function in system startup

Title: Analysis of the role of the Linux kernel main function in system startup

In the Linux operating system, the kernel main function is the core part of the entire system startup process. It is responsible for initializing various functions of the system, loading necessary modules and drivers, and finally booting the system to user mode. This article will analyze in detail the specific role of the Linux kernel main function in the system startup process, and give some code examples to illustrate its functions.

1. The role of the kernel main function

The kernel main function, generally located in the start_kernel() function in the file init/main.c, is the entry point for the entire kernel startup. When the system starts, the main functions of the kernel main function include:

• Initialize the kernel data structure and system variables
• Set the processor environment
• Initialize the kernel subsystem
• Load the necessary modules and drivers
• Start the system scheduler
• Load the user mode program

Through these steps, the kernel main function will The system boots from hardware to software, ultimately allowing users to run various applications on the system.

2. Specific code examples of the kernel main function

The following are some simple code examples to show some key operations of the kernel main function during the system startup process:

(1) Initializing the kernel data structure and system variables

void start_kernel(void)
{
    setup_arch();
    setup_log();
    MMU_init();
    init_IRQ();
    init_timers();
    calibrate_delay();
    setup_timer();
    init_task();
    cpus_timer_all();
    smp_prepare_cpus();
    boot_cpu_init();
    time_init();
    softirq_init();
    build_all_zonelists();
    page_alloc_init();
    enable_sysrq();
    migrate_init();
    printk("Linux version %s
", UTS_RELEASE);
    printk("System is %s on %s
", system_name, machine_name);
    printk("CPU revision is %d
", cpu_data.revision);
    printk("machine is %s
", machine_id);
}

The above code example shows the process of initializing the kernel data structure and system variables in the kernel main function.

(2) Set the processor environment

void setup_arch(void)
{
    switch (system_type)
    {
        case SYSTEM_32BIT:
            setup_32bit();
            break;
        case SYSTEM_64BIT:
            setup_64bit();
            break;
        default:
            panic("Unsupported system type");
    }
}

When setting the processor environment, call the corresponding initialization function according to the system bit number to set the processor.

(3) Initialize the kernel subsystem

void init_task(void)
{
    struct task_struct *p;
    p = (struct task_struct *) kmalloc(sizeof(struct task_struct));
    if (!p)
        panic("Cannot allocate memory for init task");
    memset(p, 0, sizeof(struct task_struct));
    p->pid = 1;
    p->state = TASK_RUNNING;
    p->mm = &init_mm;
    current = p;

    sprintf(p->comm, "%s", "init");
}

When initializing the kernel subsystem, create the init process as the first process of the system.

(4) Start the system scheduler

void cpu_idle(void)
{
    while (1)
    {
        schedule();
        sti();
    }
}

The system scheduler is responsible for switching between processes and allocating resources. The cpu_idle function is the processing function when the system is idle.

3. Summary

In the Linux operating system, the kernel main function plays a very important role in the system startup process. It is responsible for the initialization and configuration of the entire system and provides user-mode programs. provides the basis for its operation. By gradually analyzing the various functions and code examples of the kernel main function, we can better understand the entire process of kernel startup and delve into the working principle of the Linux kernel.

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