Commit f258c837 authored by DevDoggo's avatar DevDoggo

Finished Lab4

parent a9e8f007
# Decryptor for the Cortex-M
## Requirements
STM32F401 Nucleo-64
## Description
This implementation of code is made to be run ontop of a microcontroller.
Specifically a STM32F401 Nucleo-64 microcontroller.
The program is able to, given a seed-number, determine the decoded values
of an array of integers, which are in its original state an encoded string of text.
That is, given a string encoded in a specific way, this program can decode it.
## How to use
There exist three .sh scripts ready to be used for quick and simple compilation/debugging/running.
- Builds using cargo onto the target thumbv7em-none-eabihf (the specific microcontroller) in --release mode
cargo build --target thumbv7em-none-eabihf --release
- Runs the code on the target
openocd -f interface/stlink-v2-1.cfg -f target/stm32f4x.cfg
- Runs gdb and connects to the target's code
arm-none-eabi-gdb target/$TARGET/release/app_a4
# Memory Safety Discussion
First of all, we do use unsafe Rust code. This means that the safety of our static global variables is at risk!
......@@ -8,4 +45,25 @@ Because the compiler won't check unsafe code,
this could potentially in a worst case lead to information leakage or perhaps physical damage to infrastructure or people,
all depending on what the code is able to affect.
# Cycle Count
We can see the comparisons of clock cycles required to perform various tasks in various modes,
Debug and Released.
After enabling the ```clock_cycle_count()``` in the Rust code,
we can find the DWT_CYCCNT register (clock cycle count) at memory address 0xe0001004,
which we read from to get the following values.
A breakpoint is set just as decoding is complete to prevent additional clock cycles affecting the result.
### ABC
#### DEBUG
Cycles: 4730
Cycles: 350
#### DEBUG
Cycles: 176506
Cycles: 11614
cargo build --target thumbv7em-none-eabihf --release
#cargo build --target thumbv7em-none-eabihf --release
cargo build --target thumbv7em-none-eabihf
arm-none-eabi-gdb target/$TARGET/release/app_a4
#arm-none-eabi-gdb target/$TARGET/release/app_a4
arm-none-eabi-gdb target/$TARGET/debug/app_a4
extern crate cortex_m;
extern crate cortex_m_semihosting;
extern crate stm32f40x;
use core::fmt::Write;
use cortex_m::asm;
use cortex_m_semihosting::hio;
use stm32f40x::DWT;
//u8 plain[132];
static mut PLAIN: [u8; 132] = [0; 132];
//static ABC: [u32; 4] = [0x9fdd9158, 0x85715808, 0xac73323a, 0];
static ABC: [u32; 4] = [0x9fdd9158, 0x85715808, 0xac73323a, 0];
static CODED: [u32; 132] = [0x015e7a47, 0x2ef84ebb, 0x177a8db4, 0x1b722ff9, 0x5dc7cff0,
0x5dc9dea6, 0x1da0c15a, 0xe4c236a2, 0x3d16b0d0, 0x1f397842, 0xaae0d2ba, 0x11246674,
0x0845317f, 0xd5512dad, 0xb6184977, 0xd293a53e, 0x7d9c2716, 0xd917eae6, 0xd8852384,
......@@ -38,7 +42,6 @@ static mut SEED: u32 = 0x0e0657c1;
fn codgen(seed: &mut u32) -> u32{
let n: u32 = seed.count_zeros(); // built-in count zeroes in n
let x: u32 = seed.rotate_left(30); // rorate left by 30 bits
......@@ -72,28 +75,33 @@ fn decode(wordarr: &[u32], bytearr: &mut [u8], mut seed: &mut u32) -> u32{
fn main() {
let mut stdout = hio::hstdout().unwrap();
unsafe {
let a: u32 = codgen(&mut TEST_SEED);
let b: u32 = codgen(&mut TEST_SEED);
let c: u32 = codgen(&mut TEST_SEED);
//println!("\nOutput Codgen:");
//println!("{:x}", a);
//println!("{:x}", b);
//println!("{:x}", c);
//writeln!(stdout, "0x{:x}", a).unwrap();
//writeln!(stdout, "{:x}", b).unwrap();
//writeln!(stdout, "{:x}", c).unwrap();
unsafe {
let mut stdout = hio::hstdout().unwrap();
unsafe {
decode(&CODED[..], &mut PLAIN[..], &mut SEED);
//println!("\nComplete Output: {}", std::str::from_utf8(&PLAIN[..]).unwrap());
//decode(&ABC[..], &mut PLAIN[..], &mut SEED);
// We check cycles at this point
writeln!(stdout, "\nComplete Output: {}", core::str::from_utf8(&PLAIN[..]).unwrap());
// How am I supposed to use this?
//let y: u32 = DWT.get().get_cycle_count();
//let x: u32 = DWT::get_cycle_count();
//writeln!(stdout, "This is it: {:?}", x);
//DWT_CYCCNT @ 0xE0001004 is the Cycle Count Register, type: RW
//writeln!(stdout, "This is it: {}", n);
loop {}
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