hackin-breakin-risc-v

This repository is a hacking playground for my RISC-V exploration.

We will learn about the many elements in an assembly language program. Among these elements, we have directives, labels, mnemonics, operands, immediates, instructions, and pseudo instructions. Major focus on:

Describe the RISC-V assembly language syntax and features.
Identify the many elements of a RISC-V assembly program, like directives, labels, mnemonics, and operands.
Identify the pseudoinstructions in a RISC-V assembly program.
Explain how Control and Status Registers are managed in the RISC-V assembly code.
Use immediate values properly in a RISC-V assembly program.

ARCHITECTURE

32 bit

64 bit

128 bit

REGISTERS

33 registers including $pc, 32 general use

x0-x32 + pc

• 6 special purpose( stack pointer, frame pointer, program counter, etc)

• 7 temporary(t0-t6) (non-persistent)

• 12 saved(s0-s11) (non-volatile)

• 8 arguments(a0-a7)

RISC V instruction set

Three register instruction structure

<operation> <dst>,<src1>,<src2>

• addi a2,x0,64

$a2= $zero +64

$a2= 64

• la a1, helloworld

a1= <address of helloworld label>

https://riscv.org/wp-content/uploads/2017/05/riscv-spec-v2.2.pdf

RISC-V SYSCALL table

• Linux syscall defines how to interact with the kernel - specifies functions we can call, syscall numbers, arguments required, etc

Unix implementation syscall table: https://github.com/westerndigitalcorporation/RISC-V-Linux/blob/13cb16d5e8e11ebca490cad50cc5abbd222839a1/linux/include/uapi/asm-generic/unistd.h

• exit syscall is 93, write syscall is 64

• to implement a syscall:

  - set a7 to the syscall number
  
  - set a0 to the arguments for that syscall
  
  - invoke the ecall instruction to call the kernel
  

• No risc chips ? use qemu riscv for testing