Implement Simple Stack with PUSH and POP Instructions

Stack in Memory

A stack is a LIFO region of RAM accessed via a dedicated stack pointer (SP). PUSH decrements SP (on descending stacks) and stores a value; POP loads the value and increments SP. x86, ARM, and RISC-V all rely on stacks for function calls and local variables.

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Stack Discipline

• Alignment: many ABIs require 16-byte SP alignment before CALL
• Overflow: writing below allocated stack corrupts other data
• Underflow: popping an empty stack reads garbage

For example, pushing 0x42 then popping should return 0x42 and restore SP to its pre-push value.

For this exercise, you will add PUSH and POP opcodes that manipulate SP and memory. This task asks you to prepare the call stack that CALL/RET and subroutine local variables depend on in the next exercise.

Working Through the Exercise

Keep the relevant datasheet, ISA manual, or architecture textbook chapter open while you implement. When your output disagrees with the reference trace on the same program, the bug is usually a mis-decoded opcode, a stale register read, or a flag bit left unchanged after arithmetic.

• Trace first: walk one failing input by hand before changing random lines
• Read the manual: skim the official doc for the mechanism named in this task
• Compare baselines: save measurements from the prior step so speedups are honest

For this exercise, you will use those habits while implementing the requirement in the starter code. Microarchitectural product names change across CPU generations, but the control ideas (fetch, bypass, cache lines, vector lanes) stay stable enough to debug from first principles.