从用户模式切换到内核模式 [英] Switching from user mode to kernel mode

问题描述

在我的操作系统类中，我被问到是否有特权从用户模式切换到内核模式.这不是特定于操作系统的.起初我以为是，但是好像是22个大问题.我提到了我的教科书:

In my operating systems class, I'm asked whether switching from user to kernel mode is privileged. This is not OS-specific. At first I thought yes, but it seems like a big Catch 22. I referred to my textbook:

硬件允许仅在以下位置执行特权指令 内核模式. ...

The hardware allows privileged instructions to be executed only in kernel mode. ...

切换到内核模式的指令是特权的示例 指示.

The instruction to switch to kernel mode is an example of a privileged instruction.

加涅，格雷格；亚伯拉罕·西尔伯斯查兹(Abraham Silberschatz)彼得·B·加尔文(2010年1月26日). 操作系统概念(第22页).威利高等教育Kindle版.

Gagne, Greg; Abraham Silberschatz; Peter B. Galvin (2010-01-26). Operating System Concepts (p. 22). Wiley Higher Ed. Kindle Edition.

所以我们从用户模式开始.要切换到内核模式，需要特权指令.特权指令必须在内核模式下完成，因此我们必须切换到内核模式才能启用切换到内核模式.

So we start in user mode. To switch to kernel mode requires a privileged instruction. A privileged instruction must be done in kernel mode, therefore we must switch to kernel mode to enable switching to kernel mode.

我认为系统不允许用户直接切换到内核模式，但是当用户试图执行另一条特权指令时，它是由内核完成的.正确吗?

I'm thinking the system does not allow a user to switch itself to kernel mode directly, but that it is done by the kernel when the user seeks to execute another privileged instruction. Is that correct?

推荐答案

这是第8版中引入的错字，并保留在第9版中.在第七版的第19页中，改为:

That is a typo introduced in the 8th edition and kept in the 9th. In the seventh edition, page 19, it says instead:

切换到用户模式的指令是特权的示例 指令."

"The instruction to switch to user mode is an example of a privileged instruction."

显然更有意义.

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