1-Program-Structure

1-Program-Structure - PROGRAM STRUCTURE CS252 SYSTEMS...

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PROGRAM STRUCTURE CS252: SYSTEMS PROGRAMMING Charles Killian Computer Science Department Purdue University With slide credits to Gustavo Rodriguez-Rivera and others.
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Memory of a Program A program sees memory as an array of bytes that goes from address 0 to 2 32 -1 (0 to 4GB-1) [32-bit architecture] A program sees memory as an array of bytes that goes from address 0 to 2 64 -1 (0 to 16EiB-1) [64-bit architecture] 0 (16EiB-1) 2 64 -1
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Memory Sections The memory is organized into sections called memory mappings . Stack Text Data Bss Heap Shared Libs 0 2 64 -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. Heap – Memory returned when calling malloc/new. It grows upwards. Stack – It stores local variables and return addresses. It grows downwards.
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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 program has its own view of the memory that is independent of each other. This view is called the Address Space of the program. If a process modifies a byte in its own address space, it will not modify the address space of another process.
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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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Memory Gaps Between each memory section there may be gaps that do not have any memory mapping.
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This note was uploaded on 02/21/2012 for the course CS 252 taught by Professor Gustavorodriguez during the Spring '11 term at Purdue.

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1-Program-Structure - PROGRAM STRUCTURE CS252 SYSTEMS...

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