part3 - CS354 Operating Systems Spring 2012 Part 3 Program...

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1 CS354: Operating Systems Spring 2012 Part 3: Program Structure Dongyan Xu Department of Computer Science Purdue University
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Virtual Address Space of a Program A program sees (virtual) memory as an array of bytes that goes from address 0 to 232-1 (0 to 4GB-1) That is assuming a 32-bit architecture. 0 (4GB-1) 232-1
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Memory Sections The virtual address space is organized into sections: Stack Text Data Bss Heap Shared Libs 0 232-1
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Memory Sections Each section has different permissions: read/write/execute or a combination of them. Text - Instructions that the program runs Data – Initialized global variables. Bss – Uninitialized global variables. They are initialized to zeroes (saving object file size). Heap – Memory returned when calling malloc/new. It grows upwards (from low to high addr). Stack – It stores local variables and return addresses. It grows downwards (from high to low
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Memory Sections Dynamic libraries – They are libraries shared with other processes. Each dynamic library has its own text, data, and bss. Each run of the program (a.k.a. process) has its own view of the memory that is independent of each other. This view is called the “Virtual Address Space” of the process. If a process modifies a byte in its own address space, it will not modify the address space of
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Example Program hello.c int a = 5; // Stored in data section int b[20]; // Stored in bss int main() { // Stored in text int x; // Stored in stack int *p =(int*) malloc(sizeof(int)); //In heap }
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This note was uploaded on 02/05/2012 for the course CS 354 taught by Professor Staff during the Spring '08 term at Purdue.

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part3 - CS354 Operating Systems Spring 2012 Part 3 Program...

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