SYSCALLS(2) Linux Programmer's Manual SYSCALLS(2) NAME syscalls - Linux system calls SYNOPSIS Linux system calls. DESCRIPTION The system call is the fundamental interface between an application and the Linux kernel. System calls and library wrapper functions System calls are generally not invoked directly, but rather via wrapper functions in glibc (or perhaps some other library). For details of direct invocation of a system call, see intro(2). Often, but not always, the name of the wrapper function is the same as the name of the system call that it invokes. For example, glibc contains a function truncate() which invokes the underlying "truncate" system call. Often the glibc wrapper function is quite thin, doing little work other than copying arguments to the right registers before invoking the system call, and then setting errno appropriately after the system call has returned. (These are the same steps that are performed by syscall(2), which can be used to invoke system calls for which no wrapper function is provided.) Note: system calls indicate a failure by returning a negative error number to the caller; when this happens, the wrapper function negates the returned error number (to make it positive), copies it to errno, and returns -1 to the caller of the wrapper. Sometimes, however, the wrapper function does some extra work before invoking the system call. For example, nowadays there are (for reasons described below) two related system calls, truncate(2) and truncate64(2), and the glibc truncate() wrapper function checks which of those system calls are provided by the kernel and determines which should be employed. System call list Below is a list of the Linux system calls. In the list, the Kernel column indicates the kernel version for those system calls that were new in Linux 2.2, or have appeared since that kernel version. Note the following points: * Where no kernel version is indicated, the system call appeared in kernel 1.0 or earlier. * Where a system call is marked "1.2" this means the system call probably appeared in a 1.1.x kernel version, and first appeared in a stable kernel with 1.2. (Development of the 1.2 kernel was initiated from a branch of kernel 1.0.6 via the 1.1.x unsta‐ ble kernel series.) * Where a system call is marked "2.0" this means the system call probably appeared in a 1.3.x kernel version, and first appeared in a stable kernel with 2.0. (Development of the 2.0 kernel was initiated from a branch of kernel 1.2.x, somewhere around 1.2.10, via the 1.3.x unstable kernel series.) * Where a system call is marked "2.2" this means the system call probably appeared in a 2.1.x kernel version, and first appeared in a stable kernel with 2.2.0. (Development of the 2.2 kernel was initiated from a branch of kernel 2.0.21 via the 2.1.x
中断:
异常:
用户态与内核态切换,与cpu上下文切换的关系
上下文切换 指的是内核（操作系统的核心）在CPU上对进程或者线程进行切换。上下文切换过程中的信息被保存在进程控制块（PCB-Process Control Block）中。PCB又被称作切换桢（SwitchFrame）。上下文切换的信息会一直被保存在CPU的内存中，直到被再次使用。
