RELOCATING LOADER

AIM:

To write a C program for implementing relocating loader.

ALGORITHM:

Step 1: Start the program

Step 2: Read the header record with address.

Step 3: Read the text record.

Step 4: Assemble object code by half byte per address.

Step 5: Read the record address and modify the address length.

Step 6: Assemble object code with existing object code.

Step 7: Add the relocation address with the output address.

Step 8: Print the address and object code in half byte.

Step 9: Stop the program.

SOURCE CODE:

#include<stdio.h>

#include<conio.h>

#include<string.h>

struct objectcode

{

char text[5];

char ocode[10];

}obj[10];

struct modify

{

int length;

char address[5];

char saddress[5];

}m[10];

struct output

{

int address;

char o1,o2;

}op[30];

void main()

{

int start=0,i1,i,k,x,j,n,z,flag,l,y,len;

clrscr();

printf("\nEnter the relocating address\n");

scanf("%d",&i1);

printf("\nEnter the Object program");

i=0;

do

{

i++;

printf("\nEnter the object code\n");

scanf("%s",obj[i].text);

scanf("%s",obj[i].ocode);

}

while(strcmp(obj[i].text,"E")!=0);

printf("\nEnter the number of modification records:");

scanf("%d",&n);

printf("\nEnter the modification record\n");

for(j=1;j<=n;j++)

{

printf("\nStarting address\tlength\tAddress to be changed\n");

scanf("%s%d%s",m[j].saddress,&m[j].length,m[j].address);

}

i1=atoi(m[j-1].address);

z=1;

for(k=1;k<i;k++)

{

if(strcmp(obj[k].text,"H")==0)

continue;

for(x=0;x<6;x+=2)

{

op[z].address=start;

op[z].o1=obj[k].ocode[x];

op[z].o2=obj[k].ocode[x+1];

start++;

z++;

}

}

printf("\nBefore Relocation\n");

printf("\nAddress\tObject code\n");

for(k=1;k<z;k++)

{

printf("%d\t%c%c\n",op[k].address,op[k].o1,op[k].o2);

}

for(k=1;k<=n;k++)

{

flag=0;

for(x=1;x<z;x++)

{

if(atoi(m[k].saddress)==op[x].address)

{

flag=1;

break;

}

}

if(flag==1)

{

l=0;

len=m[k].length;

while(len>0)

{

if(len!=1)

{

op[x].o1=m[k].address[l];

op[x].o2=m[k].address[l+1];

l+=2;

len-=2;

}

else

{

op[x].o1=m[k].address[l];

l++;

len--;

}

x++;

}

}

}

printf("\nAfter Relocation\n");

printf("\nAddress\tObject code\n");

for(k=1;k<z;k++)

{

printf("%d\t%c%c\n",i1,op[k].o1,op[k].o2);

i1++;

}

getch();

}

OUTPUT:

Enter the relocating address

1000

Enter the Object program

Enter the object code

T       102030

Enter the object code

T       102030

Enter the object code

E       -

Enter the number of modification records:2

Enter the modification record

Starting address        length  Address to be changed

0       2       40

Starting address        length  Address to be changed

3       4       1000

Before Relocation

Address Object code

0       10

1       20

2       30

3       10

4       20

5       30

After Relocation

Address Object code

1000    40

1001    20

1002    30

1003    10

1004    00

1005    30

Result

Thus above program executed and output verified.