Lecture 4 Process Memory Layout 1 Review Unix

Review: Unix File Access Control • Subject – Users(owner, group, others) • Object –

In this lecture • Process memory layout 6

Linux process memory layout Stack Address space or core image Heap Static data Text

Linux process memory layout • Stack: – Automatically allocated and deallocated – Local variables,

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

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

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

Function Call int main() { int a; int f() { int a, b; a=f();

Stack Frame To previous stack frame pointer Stack arguments return address stack frame pointer

Function Call Hierarchy int main() { int a; int f() { int a; int

Fibonacci Numbers int fib (int n) { fib (3): how many if (n <

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

Garbage Collection • No need to explicitly deallocate memory i. e. no need for

Summarizing • Process memory layout – Stack – Heap – Static data – Text

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Lecture 4: Process Memory Layout 1

System Calls For File Management 3

System Calls For Directory Management 4

System Calls For Miscellaneous Tasks 5

In this lecture • Process memory layout 6

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

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 8

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

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

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

Function Call int main() { int a; int f() { int a, b; a=f(); a=10; b=10; return (a*b); } } 12

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

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

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

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

Garbage Collection • No need to explicitly deallocate memory i. e. no need for free() or equivalent • No memory leaks • Automatic Garbage Collection http: //sleibowitz. home. att. net/CPP_Java/AGC. html • A key feature of Java is its garbagecollected heap http: //www. javaworld. com/javaworld/jw-08 -1996/jw-08 gc. html 17

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