Tips for implementing system-level programming using C++

With the continuous development of computer technology, more and more software and systems require system-level programming. System-level programming requires direct interaction with the operating system and requires efficiency, stability, and security, so it requires mastering some professional skills. This article will focus on the techniques of implementing system-level programming using C.

1. Understand the operating system
Before performing system-level programming, you must have an in-depth understanding of the operating system used. The operating system is the basis for system-level programming. For example, Windows operating systems and Linux operating systems have different file systems, process management, memory management and other mechanisms. It requires a deep understanding of these mechanisms to perform system-level programming. It is recommended to read more related operating system books, including operating system principles, process management, file systems, drivers, etc.

2. Use system calls
System calls are the basis of system-level programming. The operating system provides a set of APIs, which we call system calls. System calls are the only interface provided by the operating system kernel to applications. System calls can provide a series of services within the operating system, such as file I/O, process management, network communication, etc. Therefore, we must learn how to call system calls.

C provides some built-in functions to make system calls, such as open, read, write, close, etc. There are some details that need to be paid attention to when using these functions. For example, for the open function:

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int open(const char* path, int flags);

Among them, path is the path of the file, flags is the opening method of the file, and the return value is the file descriptor of the file. When performing file I/O operations, you must handle file descriptor error conditions, such as file opening failure, read and write failure, etc.

In addition to using C built-in functions to make system calls, you can also use the system call library to make system calls. In Linux, you can use the libc library, which provides a large number of system call functions. For example, the above open function can be called through the libc library:

#include <unistd.h>

int fd = open(path, O_RDWR);

Among them, O_RDWR represents the read and write mode, and fd is the file descriptor. The libc library also provides other system call functions, such as fork, execve, kill, etc.

3. Memory management
When performing system-level programming, memory management issues must be considered. Normally, the operating system allocates a memory address space to each process and provides some mechanisms to manage memory. C also provides some memory management tools, such as new, delete, etc. But when doing system-level programming, you need to understand more complex memory management mechanisms.

In C, you can use malloc and free functions to allocate and release memory. It should be noted that the pointer type returned by malloc is void* and needs to be converted to the type that requires memory allocation. At the same time, when using malloc to allocate memory, you need to pay attention to memory alignment issues. Memory alignment can improve program performance, but it also wastes some memory space.

In addition to using malloc and free for memory allocation and release, you can also use the mmap function. The mmap function can map a file and a memory area together to facilitate file I/O operations. The pointer returned by the mmap function can directly read and write the contents of the file. Of course, when using the mmap function, you also need to pay attention to memory alignment issues.

4. Process management
When performing system-level programming, process management is often required. The operating system provides some process management system calls for applications, such as fork, execve, wait, etc. These system calls make it easy to create, execute, and manage processes.

The fork system call can create a child process that shares the code of the parent process, but is independent in the data space, and the stack space of the child process is also independent. The return value of fork is the ID of the child process, which can be used to distinguish the parent process and the child process. The execve system call can execute a new program that will replace the current process's image. The wait system call can wait for a child process to finish and return its termination status.

When performing process management, you also need to pay attention to the issue of data communication between multiple processes. Communication between multiple processes can use mechanisms such as pipes, shared memory, and message queues.

5. Driver development
Drivers are an important part of system-level programming. Drivers can provide hardware services to the upper layer, manage hardware devices, and interact with the hardware to the lower layer. Drivers usually run in kernel mode and are efficient and real-time.

Special caution is required when developing drivers. Because the driver interacts directly with the hardware, it is easy to affect the system and may even cause the system to crash. When developing drivers, special attention needs to be paid to memory allocation and release, interrupt handling, lock usage, etc.

C provides some special syntax for driver development, such as virtual functions, overloaded operators, etc. However, when developing drivers, we need to follow the kernel's regulations and coding style. Drivers need to be written in kernel code and compiled and linked through makefiles. Therefore, when developing drivers, you need to master the relevant knowledge of kernel programming.

Summary
This article introduces some techniques for using C to implement system-level programming, including understanding the operating system, using system calls, memory management, process management, driver development, etc. System-level programming requires a deep understanding of the operating system and some professional skills. It also requires rigorous coding style and attention to program security and other issues. I hope this article can be helpful to readers when doing system-level programming.

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