1. Chapter 2: OS Structures CSS503 Systems Programming
Prof. Munehiro Fukuda
Computing & Software Systems University of Washington Bothell
CSS503
Chapter 2: OS Structures

2. Chapter 2: OS Structures
A View of OS Services
CSS503
Chapter 2: OS Structures

3. Chapter 2: OS Structures
System Calls
Software interface to OS
A System function is compiled into “trap args”
“Trap” changes CPU mode from user to kernel.
CPU checks the OS branch table.
Jumps to the code pointed to by the table entry.
Work on the requested call.
IRET.
user application
open( )
INT or TRAP argument
user
mode
system call interface
kernel
mode
branch
table
trusted code
open( ) {
IRET; }
CSS503
Chapter 2: OS Structures

4. System Calls - Questions
In the previous chart,
Why can’t a user program technically execute the OS-trusted code?
Which process executes the OS-trusted code? The same process? If so, can’t the same stack mix up the user and the kernel-local variables?
CSS503
Chapter 2: OS Structures

5. Chapter 2: OS Structures
System Call Examples
Windows
Unix
Process Control
CreateProcess( )
fork( )
ExitProcess( )
exit( )
WaitForSingleObject( )
wait( )
File Manipulation
CreateFile( )
open( )
ReadFile( )
read( )
WriteFile( )
write( )
CloseHandle( )
close( )
Device Manipulation
SetCosoleMode( )
ioctl( )
ReadConsole( )
WriteConsole( )
Information Maintenance
GetCurrentProcessID( )
getpid( )
SetTimer( )
aAlarm( )
Sleep( )
sSleep( )
Communication
CreatePipe( )
pipe( )
CreateFileMapping( )
shmget( )
MapViewOfFile( )
mmap( )
Protection
SetFileSecurity( )
cChmod( )
InitializeSecurityDescriptor( )
umask( )
SetSecurityDescriptorGroup( )
chown( )
CSS503
Chapter 2: OS Structures

6. Chapter 2: OS Structures
Standard C Library
C program invoking fopen(), fgets(), and printf(), which call open(), read() and write() system calls
#include <stdio.h>
Int main( ) {
FILE *f = fopen( “myFile”, “r” );
char buf[10];
fgets( buf, sizeof( buf ), f );
printf( “%s\n”, buf );
return 0; }
user
mode
Standard C Library
System Call Interface: sd = open( “myFile”, O_RDONLY ), read( fd, buf, sizeof( buf ), write( 1, buf, sizeof( buf ) )
kernel
mode
CSS503
Chapter 2: OS Structures

7. Chapter 2: OS Structures
Command Interpreter
The program that reads and interprets control statements
command-line interpreter (in DOS)
shell (in UNIX)
Mouse-based window and menu system (in Macintosh, Windows, and Linux)
What control statements can you pass the command interpreter?
Program execution: a.out, g++, emacs
Process management: ps, kill, sleep, top, nice, pstack
I/O operations: lpr, clear, lprm, mt
File-system manipulation: ls, mkdir, mv, rm, chmod, [u]mount
Communication: write, ping, mesg
CSS503
Chapter 2: OS Structures

8. Command Interpreter (Cont’d)
MS-DOS
(a) At system startup (b) running a program
Unix
Shell (interpreter) as one of user processes
CSS503
Chapter 2: OS Structures

9. Command Interpreter (Cont’d)
Bourne shell command interpreter
Mac OS X GUI
CSS503
Chapter 2: OS Structures

10. Chapter 2: OS Structures
Unix Shell
fork, exec, and dup are
System calls
telnetd
goodall login: mfukuda
fork, exec and wait
login
Shell
goodall[1]% (you got to type)
(1)fork & wait
(5)exit
Shell wc
Shell
who
(3)fork
goodall[1]% who | wc -l
(4)exec
(4)exec
cin
(2)pipe
cout
CSS503
Chapter 2: OS Structures

11. Virtual Machine Conventional OS Binary Translation Para Virtualization
Intel VM Extension
Ring 3
Ring 3
Process
Process
Process
Process
Process
Process
Process
Process
Process
Process
Process
Process
Process
Process
Process
Process
Ring 1
System calls
System calls
System calls
System calls
Ring 1
Guest OS
Guest OS
Guest OS
Guest OS
Priveleged
instr.
Interrupts
Function
calls
Ring 0
Interrupts
Ring 0 OS
Virtual Machine Monitor
(e.g. VMWare)
Hypervisor
(e.g. Xen)
Guest OS
Guest OS
Priveleged instr.
VM Exit
VM Return
VMX
Root
Priveleged instr.
Interrupts
VMM
Priveleged instr.
Interrupts
Priveleged instr.
Interrupts
Priveleged instr.
Interrupts
Physical
Layer
Hardware
Hardware
Hardware
Hardware
Physical
Layer
CSS503
Chapter 2: OS Structures

12. Chapter 2: OS Structures
Discussion
Solve Text Exercises:
2.7 (System Programs)
2.16 (System Calls)
Discuss about:
In what particular situation have your program received a segmentation fault?
To read data from a file, why do we need to call open and close the file? In other words, why doesn’t OS allow read( filename, data, size )?
If your C++ program terminates upon an exception, it may not print out a cout statement that must have been executed before the exception. Why?
CSS503
Chapter 2: OS Structures