Detailed explanation of how to switch between Linux user mode and kernel mode

User mode switching to kernel mode

The article "Detailed Explanation of How to Switch between User Mode and Kernel Mode in Linux" brought by php editor Zimo provides an in-depth analysis of the switching method between user mode and kernel mode in the Linux operating system. It discusses several ways to switch from user mode to kernel mode, including system calls, interrupts, exceptions, etc., to help readers more fully understand the operating mechanism of the Linux operating system. Through the detailed elaboration of this article, readers can deeply understand the interaction process between user mode and kernel mode, laying a solid foundation for further in-depth study of Linux system programming.

The user program encounters Applying for external resources during operation. For example, during program execution, it needs to access: Disk, Memory allocation, Network card, sound card, or evenmotherboard LED indicator, the switch from user mode to kernel mode will occur.

For example, reading and writing files: open/read/write will switch from user mode to kernel mode;

For example, when applying for memory: C language: malloc/java language new object needs to apply for memory space;

Including select/poll/epoll are all system calls;

Switching method

There are generally three ways to switch from user mode to kernel mode: System call, Exception, Interrupt; System call and There are calls to process, file, device, information, communication, etc.;

To view the available system calls provided by the kernel, you can use: man syscallsYou can export syscalls and take a look:
man syscalls|col -b >syscalls .txt

System calls are generally classified as follows:

Process call: Terminal commandexit fork;

File call: chmod chown;

Device call: read write;

Information reading: such as cpu information getcpu;

Communication: pipe mmap(file memory mapping)

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