What is pop and push instruction?

What is pop and push instruction?

The easiest and most common way to use the stack is with the dedicated “push” and “pop” instructions. “push” stores a constant or 64-bit register out onto the stack. (“push eax” gives an error “instruction not supported in 64-bit mode”; use “push rax” instead.) “pop” retrieves the last value pushed from the stack.

What is pop instruction used for?

The POP instruction reads a byte from the address indirectly referenced by the SP register. The value read is stored at the specified address and the stack pointer is decremented. No flags are affected by this instruction.

What happens to the stack pointer when you use the pop instruction?

pop location. The data item on the top of the stack is moved to location and the stack pointer is moved to point to the next item left on the stack. So the stack is a “last in, first out” (LIFO) data structure. To illustrate the stack concept let us use our dinner plate example.

What is the concept of XY and Z register in AVR?

XYZ is a pointer register, either X or Y or Z. YZ is a pointer register, either Y or Z. s is a bit number in the status register (0 = C, 1 = Z, etc., see the list above) b is a bit number in a general-purpose or I/O register (0 = least significant, 7 = most significant)

When pushing register values onto the stack and then popping them back into the appropriate registers in what order are the values returned in Why?

16-bit programs use the PUSHF instruction to push the 16-bit FLAGS register on the stack and POPF to pop the stack into FLAGS. Pushes all of the 32-bit general-purpose registers on the stack in the following order: EAX, ECX, EDX, EBX, ESP (value before executing PUSHAD), EBP, ESI, and EDI.

What does it mean to push a register?

5 Answers. 5. 171. pushing a value (not necessarily stored in a register) means writing it to the stack. popping means restoring whatever is on top of the stack into a register.

What does push ESP do?

The PUSH ESP instruction pushes the value of the ESP register as it existed before the instruction was executed.

How the push instruction affect the stack pointer?

The PUSH instruction increments the stack pointer and stores the value of the specified byte operand at the internal RAM address indirectly referenced by the stack pointer. No flags are affected by this instruction.

How the push and pop instruction are executed?

Whenever you push data onto the stack, the 80×86 decrements the stack pointer by the size of the data you are pushing, and then it copies the data to memory where ESP is then pointing. Therefore, the stack grows and shrinks as you push data onto the stack and pop data from the stack.

Which flags get affected by LDS instruction?

This instruction loads new values into the specified register and into the DS register from four successive memory locations. The word from two memory locations is copied into the specified register and the word from the next two memory locations is copied into the DS registers. LDS does not affect any flag.

What is Z register in AVR?

X Y and Z registers are actually pairs of r27:r26, r29:r28 and r31:r30 registers. Each of them can be used as indirect pointers to SRAM: ld r16, X. with post-increment, or pre-decrement: ld r16, -Y st Z+, r16. But only Y and Z can be used with displacment ldd r16, Y + 10 std Z + 5, r16.

What are the functions of push and pop in microprocessor?

“push” stores a constant or 64-bit register out onto the stack. The 64-bit registers are the ones like “rax” or “r8”, not the 32-bit registers like “eax” or “r8d”. “pop” retrieves the last value pushed from the stack.

What is the difference between ‘pushing’ and ‘Poping’ an AVR?

Pushing pushes the contents of a CPU register onto the stack, which is a bunch of data at the end of the AVR’s RAM. Poping is the reverse, it pops data off the stack and back into a CPU register.

What is the difference between PUSH instruction and POP instruction?

Like the push instruction, the pop instruction only supports 16-bit and 32-bit operands; you cannot pop an 8-bit value from the stack. Also like the push instruction, you should avoid popping 16-bit values (unless you do two 16-bit pops in a row) because 16-bit pops may leave the ESP register containing a value that is not an even multiple of four.

What is the purpose of push and pop in a register?

The general reason for using register pushes and pops is to be able to temporarily store a register value, use the register for something else, then get that value back.

What is the difference between push and pop in C++?

Poping is the reverse, it pops data off the stack and back into a CPU register. You PUSH and POP registers to save their contents into SRAM while you re-use them for other tasks – for example, before calling a subroutine you push the contents of a few registers you’ve reserved for general use.