1. 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

2. 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

3. 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
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4. System Organization (continued)
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System Calls 4

5. Operating System Organization (continued)
Kernel
System Libraries (user space)
Utilities, tools, Window packages, program management, other stuff
Drivers & modules
File Systems
Protection Boundary
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6. 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

7. 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

8. 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
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9. Figure 10-1. The layers in a Linux system.
Interfaces to Linux
Figure 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

10. Windows Vista Operating System Structure
Protection Boundaries
Figure 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

11. 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