Lecture 7

Stack Operations and Introduction to Procedure

Modified and Presented ByDr. Rajesh Palit

Asst. Professor, EECS, NSUOriginally Prepared By

Dr. Shazzad Hosain, EECS, NSU

Stack vs. Queue

• Stack– LIFO : Last In First Out

• Queue– FIFO : First In First Out

StackQueue

PUSH vs. POP in Stack

Stack Operations

PUSH Instructions

POP Instructions

Stack example

Introduction to Procedures• Way to implement top-down programming approach• Procedure declaration name PROC type

RETname ENDP

• Some other place the procedure is called bycall name

• Type can be FAR or NEAR, and it is optional, in absence of type NEAR is assumed

• NEAR indicates that the calling statement is in the same segment, FAR implies different segment

Procedure contd.

• The RET instruction causes control to transfer back to the calling procedure.

• Every procedure, except the MAIN procedure should have a RET someplace, and usually it’s the last statement in the procedure

• A procedure must have a way to receive values from the caller, and a way to return results

• In assembly language, there is no parameter lists, so it’s up to the programmer to devise way to communicate

• In case of a few parameters, registers are fine to pass values

Procedure Example

Product = 0REPEAT IF lsb of B is 1 THEN product = product + A END_IF Shift left A Shift right BUNTIL B = 0

Passing Data Between Procedures

• Using Global Variables• Through Register (call by values)• Passing the address of the data• Using the stack– Suitable for recursive procedure– Used by high-level programming languages

• Procedure calling starts by pushing the return address on the stack

Using BP for Accessing Stack

(original BP)return addressdata 1data 2

data n

SP, BPMOV AL, aPUSH AX…MOV AL, bPUSH AX

CALL addnos

addnos PROC NEARPUSH BPMOV BP, SPMOV AX, [BP+6]ADD AX, [BP+4]POP BPRET 4

addnos ENDP

74 75 BP

76 77 Return Address

78 79 b

80 81 a

SP, BP

References

• Chapter 8 and Chapter 14 – Assembly Language Programming by Charles Marut