x86的hlt指令不可用

heixia108

搜了一下为什么编译出来的可执行文件有hlt，却要在_exit里退出了

http://stackoverflow.com/questions/5213466/why-does-gcc-place-a-halt-instruction-in-programs-after-the-call-to-main

After main returns, exit will be called. The hlt is there in case the system's version of exit doesn't stop execution of the process immediately. In user mode, it will cause a protection fault, which will kill the process. If the process is for some reason running in ring 0, it will just stop the processor until the next interrupt, which will hopefully trigger the OS to remove the process. In processes designed to run in ring 0, there is often a jmp instruction after the hlt which will cause the hlt to be performed over and over until the process is terminated.