The document discusses stacks and parameter passing through the stack. It describes stack operations like push and pop, where push adds an element to the top of the stack and pop removes the top element. Parameters are passed through the stack instead of registers due to the limited number of registers. When a function is called, its return address is pushed to the stack followed by its parameters. Within a function, the base pointer (BP) is set to the stack pointer (SP) to access the parameters from the stack. An example of bubble sort is provided to illustrate parameter passing and accessing parameters in the stack.

1. Stack & parameters passing through
stack
Presented by:
Ashfaq Hussain (fa16-bcs-064)
MURAD ALI (Fa16-bcs-046)
saqlain raza (fa16-bcs-068)

2. Content:
 Stack
 Operations of stack
 Parameter passing through stack
 Accessing Parameter In Stack
 Example of Bubble Sort

3. Stack

4. Operations of stack are:
Push & Pop
The last element pushed is pop
out first
Push and pop operation is only
work at the top of the stack
The top of the stack is
contained in a SP register

5. The PUSH Instruction

6. The POP Instruction

7. Contd…
Physical address of the stack is obtained by the
SS:SP combination
Stack is use to save things and recover from it when
needed
A decrementing stack moves from higher addresses
to lower addresses as elements are added in it
while an incrementing stack moves from lower
addresses to higher addresses as elements are
Added
The processor 8051 has an incrementing stack and
8088 processor has decrementing stack

8. Parameter passing through stack
Why we using Stack instead of Registers?
 Due to the limited number of registers.
 Due to this, parameter passing by registers is not
expandable and generalizable.
 However this is the fastest mechanism available for passing
parameters and is used where speed is important.

9. Parameter passing through stack
Considering stack as an alternate way:
 whatever data is placed there, it stays there, and across
function calls as well.
 In bubble sort subroutine example we place both of these
array address and the count of elements
on the stack.
 The subroutine is invoked with its return address on top of
the stack and its parameters bellow it.

10. Accessing Parameter In Stack:
 When the bubble sort subroutine is called, the stack pointer is
pointing to the return address .
 SP(Stack pointer) also point to the top of stack, So we cannot
access parameter using SP.
 Mov bp,sp
 Now we can access all parameter,
 The Second parameter is at [bp+2]
 The first parameter is at [bp+4].

11. Example of Bubble Sort

12. Cont…..

13. Cont….

14. Main Point of Stack..