Links to the 3.13.0 kernel source tree on GitHub are provided. Other kernel versions will be similar, but the exact line numbers, organization of code, and file paths will vary. You are interested in the Linux kernel, version 3.13.0.The discussion about the methods may be useful for people using other systems, but the code samples below contain CPU-specific code. You are using a 32-bit or 64-bit Intel or AMD CPU.This blog post makes the following assumptions that: Prerequisite information Hardware and software Glibc provides wrapper code which abstracts you away from the underlying code which arranges the arguments you’ve passed and enters the kernel.īefore we can dive into the details of how system calls are made, we’ll need to define some terms and examine some core ideas that will appear later. You simply include the appropriate header file and make the call as if it were a normal function. There are several different ways for user programs to make system calls and the low-level instructions for making a system call vary among CPU architectures.Īs an application developer, you don’t typically need to think about how exactly a system call is made. You can find a list of system calls by checking the man page for syscalls(2). Programs use system calls to perform a variety of operations such as: creating processes, doing network and file IO, and much more. System calls are how a program enters the kernel to perform some task. When you run a program which calls open, fork, read, write (and many others) you are making a system call.
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