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This is a video about the Stack and Stack Frame. I tried to go the most simple way possible trying to teach the topic. A note section is present as follows.
Level : Beginner - Intermediate

Foot Notes:

BP - Base Pointer: Always points to the base of a stack frame that acts as an anchor which in turn helps us reference itself when traversing up and down the stack.

SP - Stack Pointer: A special purpose register which always points to the top of the stack. Anything pushed onto the stack decrements the pointer by 1 and anything popped of from the stack increments it by one. We change stack pointer manually when making space for local variables on the stack frame.

IP - Instruction Pointer: Always holds the memory address to the next to execute instruction. Which means if the program is at memory, which means each instruction is also on each section of a memory. The IP holds these memory addresses and helps the CPU execute those instructions one by one and the IP increments itself on each CPU cycle completions.

A, B, C or AX, BX, CX or EAX, EBX, ECX - They are all general purpose registers that simply holds sometimes addresses and sometimes values depending on the programs for the CPU to use efficiently.

Sample instructions:

MOV AX, BX - Move whatever is in BX to AX or Copy value from second operand to first operand.

MOV AX, [BX] - Move Whatever it is in the Memory Address contained in BX to AX. [] specifies, that the operand is holding a value which is a memory address.

MOV AX, [BP-4] - Calculate what BP - 4 is, and then treat it as a memory address. Pull up the value from that memory address and copy to AX

MOV [BP-4], AX - Do the same calculation, but this time copy value from AX Register to destined memory address

PUSH AX - Save whatever it is in the AX Register to the Stack.

POP AX - Remove whatever it is that was pushed last on the stack and copy it to AX

CALL 0x0011234 / CALL add - Jump to the given memory address, where the function add resides on. In the mean time, also push current IP to the stack for the function to return to.

LEAVE - Reverts all changes made to current stack frame and pops off the last pushed value, which was the Base Pointer address, and updates the current base pointer with that address

RET - Generally comes after LEAVE, where when LEAVE pops off the BP, the only remaining value on the stack becomes the old IP value. That IP value is popped off and given to the current IP to resume the previous processes.


I wanted to write those, so the very new comers and that not only in ASM but in computer sciences all-together, could remember these instructions and the way they are used, and then go on with the video so they don't have to stumble repeteadly to new terms and look up on what they mean.


I really hope this tutorial has helped you in one way or the other. If it did, stay tuned with me and my channel for future videos. Go and look on my previous SQLi videos as-well as they are custom made and very detailed.

*Pardon me for and if the mistakes that I might have done, as I am also very new to the concept, and tried to clear them the best I could. I myself worked hard to understand these and thus wanted to share the experience.*


Thank You ...
V3IL


#Assembly #Stack #StackFrame #ComputerSciences