CS-3013 Operating Systems Hugh C. Lauer System Calls CS-3013 Operating Systems Hugh C. Lauer (Slides include materials from Slides include materials from Modern Operating Systems, 3rd ed., by Andrew Tanenbaum and from Operating System Concepts, 7th ed., by Silbershatz, Galvin, & Gagne) CS-3013, A-Term 2011 System Calls

Definition – System Call A structured function call across a protection boundary between less privileged applications and more privileged operating system functions Also, across privilege layers of the operating system itself CS-3013, A-Term 2011 System Calls

Structure of an Operating System XYZ Office Media Player Business Appl. UI/Shell/GUI Prog. Tools Services Practical OS OS Kernel Traditional OS Hardware Interfaces – Registers, etc. Processor(s) I/O Controllers CS-3013, A-Term 2011 System Calls 3

System Organization (continued) CS-3013, A-Term 2011 System Calls 4

Operating System Organization (continued) Kernel System Libraries (user space) Utilities, tools, Window packages, program management, other stuff Drivers & modules File Systems Protection Boundary CS-3013, A-Term 2011 System Calls 5

Protection Boundary Application programs are not allowed to Read or write data structures in the kernel Call functions in the kernel directly Change settings of the machine Control arbitrary devices directly Interfere with the operation of the kernel in any way Enforced by hardware CS-3013, A-Term 2011 System Calls

System Call A trap caused by executing a special machine language instruction Causes a synchronous interrupt to a specific interrupt/trap handler in the OS Allows the OS to control access, check arguments, manage behavior, etc. Causes machine to switch modes from “user” to “system” As indicated by bits in the PSW I.e., specifying protection levels CS-3013, A-Term 2011 System Calls

Operating System Organization (continued) Kernel System Libraries (user space) Utilities, tools, Window packages, program management, other stuff Drivers & modules File Systems Also part of Protection Boundary CS-3013, A-Term 2011 System Calls 8

Figure 10-1. The layers in a Linux system. Interfaces to Linux Figure 10-1. The layers in a Linux system. CS-3013, A-Term 2011 System Calls Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639

Windows Vista Operating System Structure Protection Boundaries Figure 11-13. Windows kernel-mode organization. CS-3013, A-Term 2011 System Calls Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639

We will work with System Calls in Project #2 Questions? We will work with System Calls in Project #2 CS-3013, A-Term 2011 System Calls