mini asm

My asm docs and mini programs

Using nasm assembler

Run a project

nasm -felf64 filename.asm -o outfilename.asm
ld -o filename filename.o
chmod u+x filename

Notes

Assembly language consists of commands, which are directly mapped into machine code

Registers

8 - General purpose register

name => alias

1. r0 => rax
2. r1 => rcx
3. r2 => rdx
4. r3 => rbx
5. r4 => rsp
6. r5 => rpb
7. r6 => rsi
8. r7 -> rdi

Other registers

rip => stores address of next instruction to be executed

Addressing modes

1. Immediate Addressing:

   The operand is a constant value embedded in the instruction. Example: mov rax, 42

2. Register Addressing:

   The operand is stored in a register.

   Example: mov rbx, rax

3. Direct Memory Addressing:

   The instruction contains the memory address of the operand. Example: mov rax, [0x1000]

4. Register Indirect Addressing:

   A register contains the memory address of the operand. Example: mov rax, [rbx]

5. Base + Displacement Addressing:

   Combines a base register with a constant offset. Example: mov rax, [rbx + 8]

6. Base + Index + Displacement Addressing:

   Uses a base register, an index register, and a constant offset. Example: mov rax, [rbx + rcx*4 + 8]

7. RIP-Relative Addressing:

   Address is specified relative to the current instruction pointer. Example: mov rax, [rip + label]

8. Scale-Index-Base (SIB) Addressing:

   A complex form that can include scaling of an index register. Example: mov rax, [rsi + rdi*8]

9. Stack Addressing:

   Implicit addressing using stack pointer (RSP) for push/pop operations. Example: push rax or pop rbx

Instructions

1. lea reg, [address] => allows you to calclulate an address of a memory cell and store it somewhere
2. call => used to perform function calls