PASS ONE OF A DIRECT-LINKING LOADER     

AIM:

 To write a C program to implement pass one of direct linking loader.

ALGORITHM:

Step 1: Start the program.

Step 2: Get the program address and set the control section address.

Step 3: Read the header record of control section and set the cslth to control section length.

Step 4: Search the control section name and insert if it is not found.

Step 5: If the record is define insert each symbol in the record.

Step 6: Then add cslth to control section address.

Step 7: Stop the program.

SOURCE CODE:

#include<stdio.h>

#include<conio.h>

#include<string.h>

struct header

{

char text[3];

char cname[8];

int clength;

};

struct define

{

char label[10];

char address[8];

};

struct refer

{

char label[10];

};

struct object

{

char ocode[8];

};

struct csection

{

char text[3];

struct header h;

struct define d[10];

struct refer r[10];

struct object obj[10];

}csec[5];

struct exttable

{

 char label[15];

char address[10];

}et[10];

void main()

{

int n,i;

char paddr[10],csaddr[10];

int cslth;

int e=1,j,flag=0,x,y,p,w,q,o,flag1=0,f;

char temp[15];

clrscr();

printf("enter the program starting address:\n");

scanf("%s",paddr);

strcpy(csaddr,paddr);

printf("enter the number of control section");

scanf("%d",&n);

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

{

printf("\nEnter the Header record of the Control section:\n");

printf("\nEnter text name and length");

scanf("%s%s%d",csec[i].h.text,csec[i].h.cname,&csec[i].h.clength);

strcpy(temp,csec[i].h.cname);

cslth=csec[i].h.clength;

flag=0;

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

{

if(strcmp(et[j].label,temp)==0)

{

flag=1;

break;

}

}

if(flag==1)

{

printf("\nControl section name already exist\n");

continue;

}

else

{

strcpy(et[e].label,temp);

strcpy(et[e].address,csaddr);

e++;

o=1;

p=1;

q=1;

do

{

printf("\nEnter the text field of the record:\n");

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

if(strcmp(csec[i].text,"D")==0)

{

printf("\nEnter the Define Record(Label,Address):\n");

scanf("%s%s",csec[i].d[p].label,csec[i].d[p].address);

strcpy(temp,csec[i].d[p].label);

flag1=0;

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

{

if(strcmp(et[j].label,temp)==0)

{

flag1=1;

break;

}

}

if(flag1==1)

{

printf("\nLabel alresdy exists\n");

continue;

}

else

{

strcpy(et[e].label,temp);

f=atoi(csaddr)+atoi(csec[i].d[p].address);

itoa(f,et[e].address,10);

e++;

}

p++;

}

if(strcmp(csec[i].text,"T")==0)

{

printf("\nEnter the Text record (Object code):\n");

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

o++;

}

}

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

}

w=atoi(csaddr);

w=w+cslth;

itoa(w,csaddr,10);

}

printf("\nExternal Symbol Table\n");

printf("\nLabel\t\tAddress\n");

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

{

printf("%s\t\t%s\n",et[i].label,et[i].address);

}

getch();

}

OUTPUT:

enter the program starting address:

1000

enter the number of control section2

Enter the Header record of the Control section:

Enter text name and lengthH

PROGA

100

Enter the text field of the record:

D

Enter the Define Record(Label,Address):

LISTB

0060

Enter the text field of the record:

D

Enter the Define Record(Label,Address):

ENDB

0070

Enter the text field of the record:

R

Enter the text field of the record:

ENDA

Enter the text field of the record:

T

Enter the Text record (Object code):

102030

Enter the text field of the record:

E

Enter the Header record of the Control section:

Enter text name and lengthH

PROGB

100

Enter the text field of the record:

D

Enter the Define Record(Label,Address):

LISTC

0030

Enter the text field of the record:

D

Enter the Define Record(Label,Address):

ENDC

0042

Enter the text field of the record:

E

External Symbol Table

Label           Address

PROGA           1000

LISTB           1060

ENDB            1070

PROGB           1100

LISTC           1130

ENDC            1142

Result

Thus above program executed and output verified.