1 program layout in memory –code –data global variables –stack local variables & function...
TRANSCRIPT
1
• Program Layout in memory– Code– Data
• Global variables
– Stack• Local variables & function Invocation Frames
– Heap• Dynamically allocated memory
Today’s Material
2
A Program’s Address Space
Stack
0
N
Text
Data
Code
Global variables & string constants
(consists of 3separate sections)
Dynamically allocateddata
Variables with automatic storage durationi.e., local variables and function parameters
Variables (data) allocated with mallocHeap
PC
SP
Address of the next instruction to be executed
Variables (data) with permanent storage duration, i.e., global and static variables
3
A Program’s Address Space (cont)
Stack
0
N
Text
Data
Code
.rodata section
initialized data
uninitialized data (bss)
Readonly string literals would be hereE.g., printf format strings
Initializes global & static variables
Uninitialized global & static variables
Dynamically allocateddata
Variables with automatic storage durationi.e., local variables and function parameters
Variables (data) allocated with mallocHeap
PC
SP
Address of the next instruction to be executed
Program Layout – Code Section/* Read-only String */char *str1 = "String1";
/* Initialized global vars */char str2[] = "String2int g1 = 10;
/* Uninitialized global vars */int A[2]; char str3[13]; int g2;
/* Main function */int main(){ int x = 2; /* Local var */
….} /* end-main */
0x8048448main
Code Section
Incr
easi
ng A
ddre
sses Memory Address
Program Layout – Data Section/* Read-only String */char *str1 = "String1";
/* Initialized global vars */char str2[] = "String2int g1 = 10;
/* Uninitialized global vars */int A[2]; char str3[13]; int g2;
/* Main function */int main(){ int x = 2; /* Local var */
….} /* end-main */
0x80487b4
Readonly Data section
Memory Address
str1
8 bytes
0x8049ba0
Memory Address
str2
8 bytes
Strin
g2
0x8049ba8g1 10
Program Layout – Data Section (cont)
/* Read-only String */char *str1 = "String1";
/* Initialized global vars */char str2[] = "String2int g1 = 10;
/* Uninitialized global vars */int A[2]; char str3[13]; int g2;
/* Main function */int main(){ int x = 2; /* Local var */
….} /* end-main */
0x8049bb0Memory Address
str2(13)
0x8049bb8
Unused(3)
A[0]
A[1]0x8049bb4
g20x8049bc8
7
Stack: Function Call Frame for “main”
Code
str1, str2, g1A[2], str3, g2
x: 2p: 0x804a008
Text
Data
main
TOS
/* Read-only String */char *str1 = "String1";
/* Initialized global vars */char str2[] = "String2int g1 = 10;
/* Uninitialized global vars */int A[2]; char str3[13]; int g2;
/* Main function */int main(){ int x = 2; /* Local var */ char *p = (char *)malloc(16);
….} /* end-main */
Heap
0xbf9dd5640xbf9dd560
0x804a008
0x8049bb0
0x8048448
8
Function Call Frames:When main starts executing
#include <stdio.h>
int factorial(int n);
int main(void){ int fact = 0;
fact = factorial(5);
printf("n! = %d\n", fact);} /* end-main */
int factorial(int n){ int prod = 1;
for( ; n > 1; n--) prod *= n;
return prod;} /* end-factorial */
Code
Data
fact: 0
Text
Data
mainTOS
HeapHeap
9
Function Call Frames:Right after main calls factorial
#include <stdio.h>
int factorial(int n);
int main(void){ int fact = 0;
fact = factorial(5);
printf("n! = %d\n", fact);} /* end-main */
int factorial(int n){ int prod = 1;
for( ; n > 1; n--) prod *= n;
return prod;} /* end-factorial */
Code
Data
fact: 0
Text
Data
main
n: 5prod: 1
factorial
TOS
ToS
HeapHeap
10
Function Call Frames:After returning from factorial
#include <stdio.h>
int factorial(int n);
int main(void){ int fact = 0;
fact = factorial(5);
printf("n! = %d\n", fact);} /* end-main */
int factorial(int n){ int prod = 1;
for( ; n > 1; n--) prod *= n;
return prod;} /* end-factorial */
Code
Data
fact: 120
Text
Data
mainTOS
HeapHeap
11
Recursive Functions: Example
/* Computes 1+2+3+…+n */int Sum(int n){ int s = 0;
/* Base case */ if (n == 1) return 1;
/* Divide and conquer */ s = Sum(n-1);
/* Merge */ return s + n; } /* end-Sum */
#include <stdio.h>
main(){ int x = 0;
x = Sum(3); printf(“x: %d\n”, x);
return 0;} /* end-main */
12
Recursive Functions(1)
Code
x: 0 mainToS
Code
x: 0 main
ToS
n: 3s: 0 Sum(3)
When the program starts
When Sum(3)is called
Code
x: 0 mainn: 3s: 0 Sum(3)
When Sum(2)is called
ToS
n: 2s: 0 Sum(2)
13
Recursive Functions(2)
Code
x: 0 mainn: 3s: 0 Sum(3)
When Sum(1)is called
n: 2s: 0
Sum(2)
ToS
n: 1s: 0
Sum(1)
Code
x: 0 mainn: 3s: 0 Sum(3)
After Sum(1)returns
n: 2s: 1 Sum(2)
ToS
14
Recursive Functions(3)
Code
x: 0 mainn: 3s: 3 Sum(3)
After Sum(2)returns
ToS
Code
x: 6 main
After Sum(3)returns
15
Function Call - Details
int Add(int a, int b){ int s = 0; s = a + b; return s;} /* end-Add */
main(){ int x = 0;
x = Add(2, 3);
return 0;} /* end-main */
Code
x: 0 main
ToS
When the program starts
Code
x: 0 main
ToS
b: 3a: 2
Add(2, 3)
When Add(2, 3)is called
Return Address
Base Pointer
s: 0