1. Lecture 4: Process Memory Layout

2. Review: Unix File Access Control
Subject
Users(owner, group, others)
Object
Directory/File
Actions
read
write
execute
Each file has associated with it a set of access permissions indicating, for each of three classes of principals, what sorts of operations on the file are allowed. The three classes are the owner of the file, known as user, the group owner of the file, known simply as group, and everyone else, known as others. The operations are grouped into the classes read, write, and execute, with their obvious meanings. The access permissions apply to directories as well as to ordinary files, though the meaning of execute for directories is not quite so obvious: one must have execute permission for a directory file in order to follow a path through it.
The system, when checking permissions, first determines the smallest class of principals the requester belongs to: user (smallest), group, or others (largest). It then, within the chosen class, checks for appropriate permissions.
Copyright © 2002 Thomas W. Doeppner. All rights reserved.

3. System Calls For File Management

4. System Calls For Directory Management

5. System Calls For Miscellaneous Tasks

6. In this lecture
Process memory layout

7. Linux process memory layout
Stack
Heap
Static data
Text (program)
Address space
or core image

8. Linux process memory layout
Stack:
Automatically allocated and deallocated
Local variables, parameters
Heap:
Manually allocated (malloc) and deallocated (free)
Dynamic sized data structures
Static data
Global variables
Text
Program

9. An example int g; int main() { int a;
int*b = (int*)malloc(sizeof(int) *2);
return 0; }

10. An example Stack, a Stack, b Heap, b_content Static data, g
Text (program)

11. Multiple processes in memory
Unused
Stack
Heap
Static data
Text (program)
Process 1
Stack
Heap
Static data
Text (program)
Unused
Process 2

12. Function Call int main() { int a; a=f(); } int f() { int a,b;
return (a*b); }

13. Stack Frame arguments return address stack frame pointer
Heap
Static data
Text (program)
arguments
return address
stack frame pointer
local variables
To previous stack
frame pointer
To the point at which
this function was called

14. Function Call Hierarchy
int f() {
int a;
a=10;
return (a*g()); }
int g() {
int a;
a=100;
return (a); }
int main() {
int a;
a=f(); }

15. Fibonacci Numbers int fib (int n) { if (n < 0) return 0;
return (fib(n-1)+fib(n-2)); }
fib (3): how many
stack frames?

16. Memory leakage Stack, a Stack, b (pointer) Heap, b_content
Static data, g
Text (program)

17. Garbage Collection
No need to explicitly deallocate memory i.e. no need for free() or equivalent
No memory leaks
Automatic Garbage Collection
A key feature of Java is its garbage-collected heap

18. Summarizing Process memory layout Stack frame for function calls Stack
Heap
Static data
Text
Stack frame for function calls