lab4 slide operator system

Faculty of Computer Science and Engineering
Ho Chi Minh City University of Technology

CO2018
Operating Systems

Process (cont’d)
Autumn, 2016

Nguyen Duc Hai


Objective
• Know how data are layout inside a process
• Understand dynamic memory allocation mechanism

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

2


Reading materials
• Randal E. Bryant, David R. O’Hallaron, Computer Systems: A Programmer's
Perspective, Chapter 9.

• Avi Silberschatz, Peter Baer Galvin, Greg Gagne, Operating System Concepts,
Chapter 4.

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

3


Inside a process
• Each process has its own address space which
is a set of memory addresses that a process
can access.

0xffffffff

• Address space is a large array of bytes starting
at 0 and going up to some large number (232-1
or 264-1).

• The address space is split into multiple parts,
each part holds different parts of the process
•
•
•
•

Text
Data
Heap
Stack

0x00000000

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

4


Inside a process
• Exercise: Given following
program, identify the
memory segments which
variables (or function)
belongs to.
• global_f
• local_f
• func
• dynamic_f

Autumn 2016

#include <stdio.h>
#include <stdlib.h>
int global_f = 10;
int func() {
return 0;
}
int main() {

int local_f = 100;
int *dynamic_f = (int*)malloc(sizeof(int));
printf(“global_f: %p\n”, &global_f);
printf(“local_f:
%p\n”, &local_f);
printf(“func:
%p\n”, &func);
printf(“dynamic_f: %p\n”, dynamic_f);
}

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

5


Inside a process
• Exercise: Compile and run
this program multiple
times then identify the
location of those variables
and functions on address
space.

Autumn 2016

#include <stdio.h>
#include <stdlib.h>
int global_f = 10;
int func() {

return 0;
}
int main() {
int local_f = 100;
int *dynamic_f = (int*)malloc(sizeof(int));
printf(“global_f: %p\n”, &global_f);
printf(“local_f:
%p\n”, &local_f);
printf(“func:
%p\n”, &func);
printf(“dynamic_f: %p\n”, dynamic_f);
}

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

6


Inside a process
• Sample output:

0xffffffffffffffff

global_f:

0x600984

local_f:

0x7fffd2939774

func:

0x400504

dynamic_f: 0x2499010

0x0000000000000000

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

7


Inside a process
• Sample output:

0xffffffffffffffff

global_f:

0x600984

local_f:

0x7fffd2939774

func:

0x400504

dynamic_f: 0x2499010

global_f

0x0000000000000000

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

8


Inside a process
• Sample output:

0xffffffffffffffff

global_f:

0x600984

local_f:

0x7fffd2939774

func:

0x400504

local_f

dynamic_f: 0x2499010

global_f

0x0000000000000000

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

9


Inside a process
• Sample output:

0xffffffffffffffff

global_f:

0x600984

local_f:

0x7fffd2939774

func:

0x400504

local_f

dynamic_f: 0x2499010

global_f
func
0x0000000000000000

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

10


Inside a process
• Sample output:

0xffffffffffffffff

global_f:

0x600984

local_f:

0x7fffd2939774

func:

0x400504

dynamic_f: 0x2499010

local_f

dynamic_f

global_f
func
0x0000000000000000

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

11

Inside a process
• Sample output:

0xffffffffffffffff

global_f:

0x600984

local_f:

0x7fffd2939774

func:

0x400504

dynamic_f: 0x2499010

Stack
local_f

dynamic_f

global_f
func
0x0000000000000000

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

12


Inside a process
• Sample output:

0xffffffffffffffff

global_f:

0x600984

local_f:

0x7fffd2939774

func:

0x400504

dynamic_f: 0x2499010

Stack
local_f

dynamic_f
Heap

global_f
func
0x0000000000000000

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

13


Inside a process
• Sample output:

0xffffffffffffffff

global_f:

0x600984

local_f:

0x7fffd2939774

func:

0x400504

dynamic_f: 0x2499010

Stack
local_f

dynamic_f
Heap
Data
global_f
func
0x0000000000000000

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

14


Inside a process
• Sample output:

0xffffffffffffffff

global_f:

0x600984

local_f:

0x7fffd2939774

func:

0x400504

dynamic_f: 0x2499010

Stack
local_f

dynamic_f
Heap
Data
global_f
func
Text
0x0000000000000000

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

15


Inside a process
• Check again: Open file /proc//maps to see the actual memory segments
used by the process. (Hint: Add sleep at the end of main function to make it run

longer and add an “&” at the end of execution command to see the PID of the
process).

• Wait!!!!  File?

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

16


Inside a process
• Process address space in Linux

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

17


Heap region
• The heap is placed right after data region in address space.
•

break (program break) separates used regions and unused regions.

•

Heap increases upward but the break cannot go through rlimit

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

18


Heap region
• We could increase or decrease the size of heap region by using two system
calls:
• brk  changes the value of break pointer.
• sbrk  increases the value of break by a given number of bytes.

• We could use those system calls to implement malloc and free.

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

19


Heap region
• A simple implementation of malloc

void *simple_malloc(size_t size) {

void *p = sbrk(0);
if (sbrk(size) == (void*)-1) {
return NULL;
}
return p;
}
• Is there any problem with this implementation?

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

20


Heap region
• Exercise: How to implement malloc so that given the pointer returned from
this function, we could easily identify the size of memory regions pointed by
this pointer to write free function?

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

21

Dynamic allocation
• Actually, malloc does not allocate a new memory region whose size exactly
equals to the size given by user. It allocates a few extra bytes to hold needed
information (including the size of allocated region) so that free function
could easily clean this region.

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

22


Dynamic allocation
• How to allocate and clean memory region on heap?

void *p;
p = malloc(100);

Used

Unused

// do something

free(p);

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

23


Dynamic allocation
• How to allocate and clean memory region on heap?

void *p;
p = malloc(100);

Used

100 bytes

Unused

// do something

free(p);

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

24

Dynamic allocation
• How to allocate and clean memory region on heap?

void *p;
p = malloc(100);

Used

100 bytes

Unused

// do something

free(p);

Autumn 2016

FACULTY OF COMPUTER SCIENCE AND ENGINEERING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

25