Three parts of the Linux process and their functions

Linux operating system is a widely used open source operating system that uses multitasking to manage processes. Process is one of the most important concepts in the operating system. When a program is running, it will be assigned by the operating system as one or more processes. The Linux process can be divided into three parts: process control block (PCB), kernel stack and user stack. This article will introduce the functions of these three parts in detail and give corresponding code examples to illustrate their practical application.

1. Process Control Block (PCB)

The process control block is a data structure used in the operating system to manage process information. In the Linux system, each process has a corresponding process control block, which is used to save the status, identifier, priority and other information of the process. When a process is created, the operating system allocates a new process control block to it to track and manage the running of the process.

The following is a simple C language program that shows how to create a new process in a Linux system and access its process control block information:

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main() {
    pid_t pid = fork();

    if (pid == 0) {
        printf("Child process PID: %d
", getpid());
    } else {
        printf("Parent process PID: %d
", getpid());
    }

    return 0;
}

In this sample program, a new child process is created by calling the fork() function. The fork() function will return a new process ID. The parent and child processes can be distinguished by judging the size of the return value, and the PID of the current process can be obtained through the getpid() function.

2. Kernel stack

The kernel stack is a data structure used by each process to save temporary data and status information in the kernel state. When a process is executed in kernel mode, the kernel stack is used to save information such as parameters, local variables, return addresses, etc. of function calls. The kernel stack plays an important role during process switching or system calls to ensure that data confusion does not occur when the process is running in the kernel state.

The following is a simple assembly code snippet showing the use of the kernel stack:

section .data
    message db 'Hello, World!', 0

section.text
    global_start

_start:
    mov eax, 4; sys_write
    mov ebx, 1 ; file descriptor stdout
    mov ecx, message; message address
    mov edx, 13; message length
    int 0x80; trigger system call

In this assembly code, the kernel mode system call sys_write is used to output a string to the console. By saving parameters in registers, data conflicts caused by using the user-mode stack in kernel mode can be avoided.

3. User stack

The user stack is a data structure used to save parameters, local variables and other data for function calls in user mode. Each process uses its own user stack when running to maintain the context of program execution. When a process switches from user mode to kernel mode, the data in the user stack will be saved in the kernel stack for later recovery.

The following is a simple C language program showing the use of the user stack:

#include <stdio.h>

void func(int n) {
    int result = n * n;
    printf("Result: %d
", result);
}

int main() {
    int num = 5;
    func(num);
    return 0;
}

In this sample program, a simple function func is defined to calculate the square of the input parameter, and the function is called in the main function. During the function call, the parameter n and the local variable result will be saved in the user stack, ensuring the correct execution of the function call.

To sum up, the process in the Linux operating system can be divided into three parts: process control block, kernel stack and user stack. Each part has different roles and functions. Understanding the principles and practical applications of these parts will help us better understand the mechanism of process management and write more efficient and stable programs.

The above is the detailed content of Three parts of the Linux process and their functions. For more information, please follow other related articles on the PHP Chinese website!