ARM Architecture Reference Manual
Arm 指令框架手册
1. 处理器7种工作模式
Processor mode | Mode number | Description |
User usr | 0b10000 | Normal program execution mode |
FIQ fiq | 0b10001 | Supports a high-speed data transfer or channel process |
Supervisor svc | 0b10011 | A protected mode for the operating system |
Abort abt | 0b10111 | Implements virtual memory and/or memory protection |
Undefined und | 0b11011 | Supports software emulation of hardware coprocessors |
System sys | 0b11111 | Runs privileged operating system tasks (ARMv4 and above) |
Linux 应用程序运行在usr模式
Linux 内核运行在svc模式
原文：http://www.cnblogs.com/chengfangming/p/4805504.html