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Kevin Thomas 67b4312cff WEEK07-BN: add Binary Ninja lesson for Week 7 (constants + I2C LCD)

WEEK07-BN.md/.pdf mirroring the -BN series: build/flash/symbol map, load the raw
.bin, dynamic (break at the FAV_NUM printf, live r1=43) then static (resolve
functions incl. lcd_1602.c, patch FAV_NUM 2a->2b, OTHER_FAV_NUM movw 39->40, LCD
'Reverse'->'Exploit'). README links it.

2026-10-03 19:48:55 -04:00

84 KiB

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Week 7-BN: Binary Ninja Personal — Read, Hack, and Patch Constants and a 1602 LCD String (Raw `.bin`)

LEGAL DISCLAIMER: The information, tools, and code provided in this repository and course are strictly for educational, research, and defensive purposes only.

You are explicitly prohibited from using any materials contained herein to access, test, modify, or exploit any device, network, or system that you do not own 100% or for which you do not have explicit, documented, and legally binding authorization to interact with.

By using this repository and course, you acknowledge and agree that:

Any illegal, unauthorized, or malicious use of this information is solely your responsibility.
The author(s) and contributor(s) of this repository and course shall not be held liable for any damages, legal repercussions, criminal charges, or unauthorized actions resulting from the use, misuse, or abuse of the contents herein.
You will comply with all applicable local, state, national, and international laws regarding cybersecurity and computer fraud.

IF YOU DO NOT AGREE WITH THESE TERMS, DO NOT USE THIS REPOSITORY AND COURSE.

What You'll Learn This Week

Build the lesson project with Release and get both an .elf and a raw .bin
Dump the ELF symbol map with arm-none-eabi-nm and use it as ground truth
Load the raw .bin into Binary Ninja at 0x10000000
Read how a #define macro and a const variable both fold to bare instruction immediates
Tell a 16-bit movs r1, #42 from a 32-bit movw r1, #1337 in the disassembly
Follow the I2C path through the i2c_inst_t struct: I2C_PORT -> i2c1 -> &i2c1_inst -> hw -> 0x40098000
Break at the printf call on live silicon and hack the printed constant live
Optionally hack the LCD string live by pointing r0 at a RAM replacement
Resolve the functions in the Binary Ninja GUI using the ELF symbol map, including the lcd_1602.c driver symbols
Patch both constants (42 -> 43, 1337 -> 1344) and the LCD string ("Reverse" -> "Exploit")
Export the patched image, convert it to UF2, and flash it

How This Guide Works

The build produces two files for the project:

File	What it is	How we use it
`.elf`	The linked image with a full symbol table	Ground truth for every function address and name
`.bin`	The raw flash image, no headers, no symbols	The image we load into Binary Ninja and reverse

The .bin is built from the .elf, so the ELF tells you exactly what is at every address. We use the ELF symbol map to resolve functions in Binary Ninja, and we reverse-engineer the raw .bin the way a real extracted firmware image is reversed.

Build Release, not Debug. Every address in this guide matches the Week 7 lesson, and the Week 7 lesson is a Release build. Release optimizes the code the same way the original lesson was built: it inlines the static helpers init_i2c_and_lcd and write_lcd_greeting (and the whole lcd_1602.c static helper chain) straight into main or into the public lcd_* functions, and it folds both FAV_NUM and OTHER_FAV_NUM down to immediate values. If you build Debug, the SDK function addresses move and the helpers stay separate calls, so nothing lines up. Always build Release for this lesson.

The order is dynamic first, static second:

Break on the live target and prove what the code does.
Hack it live in the debugger and watch the output change.
Resolve the functions in Binary Ninja using the ELF symbol map.
Patch the bytes, export, convert, and flash.

Project	Serial output	Also does	The hacks
`0x0017_constants`	`FAV_NUM: 42`, `OTHER_FAV_NUM: 1337`	I2C1 (SDA GP2, SCL GP3) drives a 1602 LCD, writing `Reverse` / `Engineering`	`42 -> 43`, `1337 -> 1344`, and `"Reverse" -> "Exploit"`

Addresses come from your build. Every address here is from the Release build produced in Step 3. Confirm against your own .elf with the command in Step 4.

The surprise of this week is that const is not in memory. #define FAV_NUM 42 becomes the 16-bit movs r1, #42; const int OTHER_FAV_NUM = 1337 also becomes an immediate, the 32-bit movw r1, #1337. The compiler only keeps a const in .rodata if the program takes its address (&OTHER_FAV_NUM); this program never does, so the const is inlined exactly like the macro. You patch an instruction operand, not a data word.

Part 1: Build, Flash, and Get the Symbol Map

Step 1: Install the toolchain

Windows x64

Install the Raspberry Pi Pico extension in VS Code. It installs the ARM GNU toolchain, CMake, Ninja, and the Pico SDK.
Install Binary Ninja Personal and complete its license activation.
Install PuTTY for the serial monitor.

macOS Apple Silicon

brew install cmake ninja

Install Binary Ninja Personal and complete its license activation.
Install the Arm GNU Toolchain, or let the VS Code Pico extension manage it.

Linux x64

sudo apt install cmake ninja-build gcc-arm-none-eabi libnewlib-arm-none-eabi git python3 openocd minicom

Install Binary Ninja Personal and complete its license activation.

Step 2: Verify your tools are the right architecture (do not skip this)

On macOS Apple Silicon, the most common failure is an Intel x86_64 tool on your PATH:

zsh: bad CPU type in executable: cmake

You may have two Homebrews: the arm64 one at /opt/homebrew and the Intel one at /usr/local. If /usr/local/bin wins, every brew tool is x86_64. Check:

file "$(which cmake)"
file "$(which ninja)"
file "$(which arm-none-eabi-gdb)"
file "$(which arm-none-eabi-nm)"
file "$(which openocd)"
file "$(which telnet)"

All must report arm64. If any is x86_64, put the Apple Silicon prefix first for the session and check again:

export PATH="/opt/homebrew/bin:$PATH"
hash -r
file "$(which cmake)"

To make it permanent, add that export to ~/.zshrc. Do not use Rosetta as a fix; OpenOCD and GDB are exactly the kind of programs where a translation layer produces failures that look like debugger bugs.

telnet is special — and optional. The GDB MI workflow does not need it; it is only used by the command-port fallback. macOS no longer ships telnet, and the Homebrew build is often the Intel one, so telnet 127.0.0.1 4444 fails with bad CPU type in executable. Call the Apple Silicon Homebrew explicitly:

/opt/homebrew/bin/brew install telnet

If you would rather not install anything, macOS ships an arm64 nc, which can connect to the same OpenOCD port:

nc 127.0.0.1 4444

Windows x64 and Linux x64 do not have this problem. Skip to Step 3.

Step 3: Build the project with `Release`

Run this inside 0x0017_constants/:

cmake -B build -G Ninja -DPICO_BOARD=pico2 -DPICO_PLATFORM=rp2350 -DCMAKE_BUILD_TYPE=Release
cmake --build build

Point Binary Ninja at this repository (once). Every console snippet below reads the repo root from ~/.embedded-hacking-repo, so Binary Ninja never needs a database open and nothing is hardcoded. From the repo root, run once:

macOS / Linux:

pwd > ~/.embedded-hacking-repo

Windows (PowerShell):

(Get-Location).Path | Set-Content "$env:USERPROFILE\.embedded-hacking-repo"

Then build from the Binary Ninja console, so the whole build -> patch -> flash loop stays inside Binary Ninja. The console inherits a minimal PATH — on macOS just /usr/bin:/bin:/usr/sbin:/sbin — so it does not see Homebrew; add your package manager's bin first, then run plain cmake.

macOS Apple Silicon:

import os, subprocess
root = open(os.path.expanduser("~/.embedded-hacking-repo")).read().strip()
os.environ["PATH"] = "/opt/homebrew/bin:" + os.environ["PATH"]  # the console's PATH omits Homebrew
proj = os.path.join(root, "0x0017_constants")
subprocess.run(["cmake", "-B", "build", "-G", "Ninja", "-DPICO_BOARD=pico2",
                "-DPICO_PLATFORM=rp2350", "-DCMAKE_BUILD_TYPE=Release"], cwd=proj)
subprocess.run(["cmake", "--build", "build"], cwd=proj)

Linux x64:

import os, subprocess
root = open(os.path.expanduser("~/.embedded-hacking-repo")).read().strip()
proj = os.path.join(root, "0x0017_constants")
subprocess.run(["cmake", "-B", "build", "-G", "Ninja", "-DPICO_BOARD=pico2",
                "-DPICO_PLATFORM=rp2350", "-DCMAKE_BUILD_TYPE=Release"], cwd=proj)
subprocess.run(["cmake", "--build", "build"], cwd=proj)

Windows x64:

import os, subprocess
root = open(os.path.expanduser("~/.embedded-hacking-repo")).read().strip()
proj = os.path.join(root, "0x0017_constants")
subprocess.run(["cmake", "-B", "build", "-G", "Ninja", "-DPICO_BOARD=pico2",
                "-DPICO_PLATFORM=rp2350", "-DCMAKE_BUILD_TYPE=Release"], cwd=proj)
subprocess.run(["cmake", "--build", "build"], cwd=proj)

The build directory now contains the pair we need:

0x0017_constants/build/0x0017_constants.elf and .bin — the .bin is 17980 bytes (0x463c)

If the ARM toolchain is not on your PATH, add -DPICO_TOOLCHAIN_PATH=...:

OS	Typical toolchain path
Windows x64	`C:/Program Files/Arm GNU Toolchain arm-none-eabi/14.2 rel1/bin`
macOS Apple Silicon	`~/.pico-sdk/toolchain/14_2_Rel1/bin`
Linux x64	`/usr`

This guide's toolchain lives at ~/.pico-sdk/toolchain/14_2_Rel1/bin. All of arm-none-eabi-nm, arm-none-eabi-objdump, and arm-none-eabi-gdb resolved in this document come from there. If your install is elsewhere, which arm-none-eabi-nm tells you where to point.

Step 4: Dump the ELF symbol map

This is the ground truth for the whole lesson. Run arm-none-eabi-nm on the ELF and keep the output in a terminal or a text file:

macOS Apple Silicon / Linux x64:

arm-none-eabi-nm -n --defined-only build/0x0017_constants.elf | grep -E ' [Tt] '

Windows x64:

arm-none-eabi-nm -n --defined-only build\0x0017_constants.elf | Select-String ' [Tt] '

Each line is address type name. The T/t type is a function. Here are the functions this lesson uses. The signatures come from the ELF's DWARF debug info queried with arm-none-eabi-gdb -batch -ex "ptype <name>", so they are exact.

Our code and the startup chain:

Address	ELF symbol	Signature	Role
`0x1000015c`	`_reset_handler`	`void _reset_handler(void)`	reset entry
`0x10000186`	`platform_entry`	`void platform_entry(void)`	calls `runtime_init`, `main`, `exit`
`0x1000019a`	`data_cpy`	`void data_cpy(void, void, void*)`	copies `.data` from flash to SRAM
`0x100001e4`	`_init`	`void _init(void)`	runs `.init_array`
`0x10000210`	`frame_dummy`	`void frame_dummy(void)`	C runtime boilerplate
`0x10000234`	`main`	`int main(void)`	the lesson function (`init_i2c_and_lcd` and `write_lcd_greeting` inlined)

Our I2C/LCD driver (lcd_1602.c) and the SDK I2C functions main reaches:

Address	ELF symbol	Signature	Role
`0x100002bc`	`lcd_i2c_init`	`void lcd_i2c_init(i2c_inst_t*, uint8_t, int, uint8_t)`	store config + HD44780 reset/configure
`0x100006f4`	`lcd_set_cursor`	`void lcd_set_cursor(int, int)`	move the HD44780 cursor
`0x100007f0`	`lcd_puts`	`void lcd_puts(const char*)`	write a string to the LCD
`0x10003cdc`	`i2c_init`	`uint i2c_init(i2c_inst_t*, uint)`	SDK I2C init (100 kHz)
`0x10003d28`	`i2c_write_blocking`	`int i2c_write_blocking(i2c_inst_t, uint8_t, const uint8_t, size_t, bool)`	one blocking I2C transfer
`0x100008f0`	`gpio_set_function`	`void gpio_set_function(uint, gpio_function_t)`	SDK GPIO function select (I2C pins)
`0x1000092c`	`gpio_set_pulls`	`void gpio_set_pulls(uint, bool, bool)`	SDK pull config (`gpio_pull_up` inlined)

The lcd_1602.c static helpers — pcf_write_byte, pcf_pulse_enable, lcd_write4, lcd_send, lcd_store_config, lcd_hd44780_reset, lcd_hd44780_configure — have no symbol of their own in the Release build. They are inlined into lcd_i2c_init, lcd_set_cursor, and lcd_puts, which is why those three functions are large and call i2c_write_blocking and the sleep_* helpers directly.

The stdio/UART and printf chain main reaches:

Address	ELF symbol	Signature	Role
`0x10001368`	`sleep_us`	`void sleep_us(uint64_t)`	SDK microsecond delay
`0x10001440`	`sleep_ms`	`void sleep_ms(uint32_t)`	SDK millisecond delay
`0x10001624`	`time_us_64`	`uint64_t time_us_64(void)`	SDK microsecond clock
`0x10001638`	`busy_wait_us`	`void busy_wait_us(uint64_t)`	UART timing loop
`0x100016b8`	`uart_init`	`uint uart_init(uart_inst_t*, uint)`	SDK UART init
`0x1000188c`	`clock_get_hz`	`unsigned long clock_get_hz(clock_handle_t)`	UART clock lookup
`0x100035a4`	`exit`	`void exit(int)`	C runtime exit
`0x100035ac`	`runtime_init`	`void runtime_init(void)`	SDK runtime init
`0x100035d8`	`stdio_out_chars_crlf`	`void stdio_out_chars_crlf(stdio_driver_t, const char, int)`	CRLF output driver
`0x100036e8`	`stdio_put_string`	`int stdio_put_string(const char*, int, bool, bool)`	buffered string output
`0x100037d4`	`stdio_set_driver_enabled`	`void stdio_set_driver_enabled(stdio_driver_t*, bool)`	enable the UART driver
`0x100037fc`	`stdio_init_all`	`bool stdio_init_all(void)`	SDK serial init
`0x100038c8`	`__wrap_vprintf`	`int __wrap_vprintf(const char*, va_list)`	printf core
`0x1000398c`	`__wrap_printf`	`int __wrap_printf(const char*, ...)`	the `printf` wrapper
`0x10003b48`	`stdio_uart_init`	`void stdio_uart_init(void)`	SDK UART stdio init
`0x10003e24`	`strlen`	`size_t strlen(const char*)`	C runtime string length

SDK helpers the printf path reaches:

Address	ELF symbol	Signature	Role
`0x10003548`	`vfctprintf`	`int vfctprintf(void ()(char, void), void, const char, va_list)`	printf format engine
`0x10002b64`	`_vsnprintf`	`int _vsnprintf(out_fct_type, char, size_t, const char, va_list)`	the format dispatcher
`0x10001f48`	`_ntoa_format`	`unsigned _ntoa_format(out_fct_type, char, size_t, size_t, char, size_t, bool, unsigned, unsigned, unsigned, unsigned)`	number formatter
`0x10001eac`	`_out_rev`	`unsigned _out_rev(out_fct_type, char, size_t, size_t, const char, size_t, unsigned, unsigned)`	reversed-digit output
`0x1000211c`	`_out_char`	`void _out_char(char, void*, size_t, size_t)`	single-char sink

Two things in this project have no symbol of their own, because the compiler inlined them into main:

init_i2c_and_lcd and write_lcd_greeting — the two static helpers in our own source are inlined, so there is no address to rename. You see their bodies directly inside main.
gpio_pull_up — static inline in the SDK, so gpio_pull_up(2) and gpio_pull_up(3) compile to direct calls to gpio_set_pulls at 0x10000258 and 0x10000262.

Step 5: Flash and confirm the output

A .bin has no headers, so OpenOCD must be told the base address 0x10000000. From the repository root:

macOS Apple Silicon / Linux x64:

./flash.sh 0x0017_constants/build/0x0017_constants.bin

Windows x64 (PowerShell):

.\flash.ps1 -Bin 0x0017_constants\build\0x0017_constants.bin

Or flash from the Binary Ninja console (the console reads the repo root from the marker file, so it works with no database open):

macOS Apple Silicon / Linux x64:

import os, subprocess
root = open(os.path.expanduser("~/.embedded-hacking-repo")).read().strip()  # set once (Step 3)
bin_path = os.path.join(root, "0x0017_constants", "build", "0x0017_constants.bin")
log = os.path.join(os.path.dirname(bin_path), "flash.log")
subprocess.run(["pkill", "-TERM", "-f", "openocd"])  # free the probe first
subprocess.Popen([os.path.join(root, "flash.sh"), bin_path],
                 stdout=open(log, "w"), stderr=subprocess.STDOUT, start_new_session=True)
print("flashing in the background; log:", log)

Windows x64:

import os, subprocess
root = open(os.path.expanduser("~/.embedded-hacking-repo")).read().strip()  # set once (Step 3)
bin_path = os.path.join(root, "0x0017_constants", "build", "0x0017_constants.bin")
log = os.path.join(os.path.dirname(bin_path), "flash.log")
subprocess.run(["taskkill", "/F", "/IM", "openocd.exe"])  # free the probe first
subprocess.Popen(["powershell", "-ExecutionPolicy", "Bypass", "-File",
                  os.path.join(root, "flash.ps1"), "-Bin", bin_path],
                 stdout=open(log, "w"), stderr=subprocess.STDOUT)
print("flashing in the background; log:", log)

Wait for wrote 17980 bytes ... and ** Verified OK **. Open a serial monitor at 115200 baud:

Windows x64: PuTTY -> Connection type Serial, the Pico's COM port, speed 115200.
macOS Apple Silicon: screen /dev/tty.usbmodem* 115200 (quit with Ctrl-A then K).
Linux x64: minicom -D /dev/ttyACM0 -b 115200.

FAV_NUM: 42
OTHER_FAV_NUM: 1337
FAV_NUM: 42
OTHER_FAV_NUM: 1337
...

The 1602 LCD shows Reverse on line 1 and Engineering on line 2. Both numbers print forever, because both constants are baked into the loop as immediates. That is the behavior we will change.

Part 2: Load the Raw `.bin` into Binary Ninja

Start from a fresh Binary Ninja state. If you already have a .bndb for this lesson, close it and start over; a stale database keeps old names and patches.

Step 6: Bring the raw `.bin` into Binary Ninja

A raw .bin has no headers, so Binary Ninja cannot know where it belongs or what architecture it is. You must supply both. If you just double-click the .bin, Binary Ninja may load it at address 0x0 with a guessed architecture, and every address in this lesson will be wrong.

Choose File -> Open with Options... (do not use plain File -> Open).
Select 0x0017_constants/build/0x0017_constants.bin.
In the loader options, set:
- Architecture: thumb2 (the ARMv7-M / ARMv8-M Thumb-2 architecture, which covers the Cortex-M33)
- Platform: thumb2
- Base Address: 0x10000000 (the XIP flash base)
Click Open.

Binary Ninja analyzes the image and opens the linear view.

Verify the load before going further. Press G, type 0x10000000, and read the first two words:

0x10000000   0x20082000   initial stack pointer
0x10000004   0x1000015d   reset vector (bit 0 = Thumb)

If you instead see data at 0x00000000, or a vector word without bit 0 set, close the tab and repeat with Open with Options. The Cortex-M33 only executes Thumb-2, so thumb2 is the only correct architecture.

Console equivalent:

import os
root = open(os.path.expanduser("~/.embedded-hacking-repo")).read().strip()  # set once (Step 3)
load(os.path.join(root, "0x0017_constants", "build", "0x0017_constants.bin"),
     options={"loader.imageBase": 0x10000000, "loader.platform": "thumb2"})

Step 7: Save it as a Binary Ninja database (`.bndb`)

Binary Ninja never writes back into the .bin. Your names, comments, types, and patches live in a separate .bndb database. Save one now, before you make any changes:

Choose File -> Save As....
Save it next to the image as 0x0017_constants.bndb.
From now on, save with File -> Save (Cmd+S on macOS, Ctrl+S on Windows/Linux) whenever you rename or patch.

The two files have different roles:

File	Role
`0x0017_constants.bin`	the raw firmware image; Binary Ninja never modifies it
`0x0017_constants.bndb`	your analysis database: names, types, comments, and patches

When you come back later, open the .bndb, not the .bin; that restores all your work. If a database gets messy, delete the .bndb and re-import the .bin from Step 6 — the firmware is never at risk. You export the patched image out of this view later, in Step 19.

Step 8: The views you will use

Linear view: the disassembly listing. You navigate, read, and patch here.
Graph view: the control-flow graph of the current function.
Decompiler (HLIL): the pseudo-C decompilation.
Hex view: raw bytes, used for patching.
Function list: the sidebar list of every detected function.

Navigation: G go to address, N rename, Y set type or signature, ; add a comment. Breakpoints are set from the GUI through the GDB MI adapter — see Step 12.

macOS function keys: the top-row F keys are usually mapped to system functions. Every step here uses menu paths that work without them.

Part 3: Dynamic — Break at the `printf` Call and Hack Live

Step 9: Start OpenOCD as a live debug server

Make sure no other OpenOCD is running; a forgotten server holds port 3333.

macOS / Linux:

ps aux | grep -i openocd

Windows (PowerShell):

Get-Process | Where-Object { $_.ProcessName -like '*openocd*' }

Stop any leftover server gracefully:

macOS / Linux:

pkill -TERM -f openocd

Windows (PowerShell):

Get-Process openocd -ErrorAction SilentlyContinue | Stop-Process

Start the server parked at main:

macOS Apple Silicon / Linux x64:

BP_ADDR=0x10000234 ./debug-server.sh

Windows x64 (PowerShell):

$env:BP_ADDR="0x10000234"; .\debug-server.ps1

Or start it from the Binary Ninja console, freeing the probe first and launching the server in the background so the console returns immediately:

macOS Apple Silicon / Linux x64:

import os, subprocess
root = open(os.path.expanduser("~/.embedded-hacking-repo")).read().strip()  # set once (Step 3)
subprocess.run(["pkill", "-TERM", "-f", "openocd"])  # stop any running server first
log = os.path.join(root, "openocd.log")
p = subprocess.Popen([os.path.join(root, "debug-server.sh")], cwd=root,
                     env=dict(os.environ, BP_ADDR="0x10000234"),
                     stdout=open(log, "w"), stderr=subprocess.STDOUT, start_new_session=True)
print("OpenOCD started (pid", p.pid, "); log:", log)

Windows x64:

import os, subprocess
root = open(os.path.expanduser("~/.embedded-hacking-repo")).read().strip()  # set once (Step 3)
subprocess.run(["taskkill", "/F", "/IM", "openocd.exe"])  # stop any running server first
log = os.path.join(root, "openocd.log")
p = subprocess.Popen(["powershell", "-ExecutionPolicy", "Bypass", "-File",
                      os.path.join(root, "debug-server.ps1")], cwd=root,
                     env=dict(os.environ, BP_ADDR="0x10000234"),
                     stdout=open(log, "w"), stderr=subprocess.STDOUT)
print("OpenOCD started (pid", p.pid, "); log:", log)

Popen returns in a few milliseconds; the server keeps running in the background. Check openocd.log for Listening on port 3333, then connect in Step 10.

Wait for:

Info : [rp2350.dap.core0] Examination succeed
Startup breakpoint at 0x10000234 (2-byte hardware execute, one-shot).
Info : starting gdb server for rp2350.dap.core0 on 3333
Info : Listening on port 3333 for gdb connections

BP_ADDR parks the core at main before any client connects. The script arms a 2-byte hardware breakpoint and then does the startup reset run, so the core runs from the vector table and stops at your address with no debugger attached yet. When Binary Ninja connects a moment later, the first thing it reads is already the truth: Stopped at 0x10000234. This is the whole reason the lab works cleanly — you never have to drive a reset from outside the GUI.

Use the address you actually want to stop at:

What you want to stop at Address Command

main (once per reset) 0x10000234 BP_ADDR=0x10000234 ./debug-server.sh

The loop — the FAV_NUM printf call, hit every iteration 0x10000292 BP_ADDR=0x10000292 ./debug-server.sh
BP_ADDR=0x10000234 ./debug-server.sh   # park at main
BP_ADDR=0x10000292 ./debug-server.sh   # park in the loop instead
$env:BP_ADDR="0x10000234"; .\debug-server.ps1   # park at main
$env:BP_ADDR="0x10000292"; .\debug-server.ps1   # park in the loop
This startup stop is single-use. OpenOCD flushes breakpoints when a client connects, so this one is gone once Binary Ninja attaches — fine for main, which only runs once per reset. Every breakpoint after that is set from the Binary Ninja GUI (Step 12) and is repeatable. To stop at main again, restart the server with BP_ADDR and reconnect.

What you want to stop at	Address	Command
`main` (once per reset)	`0x10000234`	`BP_ADDR=0x10000234 ./debug-server.sh`
The loop — the `FAV_NUM` `printf` call, hit every iteration	`0x10000292`	`BP_ADDR=0x10000292 ./debug-server.sh`

Exactly one core. The line must say core0 and must not mention core1. Core1 is never started by this firmware; exposing it makes Binary Ninja read core1's reset-state registers, which are not real addresses, and OpenOCD floods the log with Failed to read memory at 0xf0000000. The scripts already use USE_CORE=0; do not change it.

Windows driver note: the Debug Probe must use the WinUSB driver. If OpenOCD reports unable to open CMSIS-DAP device, install it with Zadig (select Debug Probe (CMSIS-DAP) -> WinUSB).

Step 10: Connect Binary Ninja to the GDB server

Make sure the image is open and analyzed (Part 2) and the server from Step 9 is running (parked at main).
Choose Debugger -> Connect to Remote Process.
In the adapter dropdown, select GDB MI.
In the connect settings group, set IP Address to 127.0.0.1 and Port to 3333.
Set Full GDB Executable Path to your arm-none-eabi-gdb. On macOS the build that works is the 14.2.rel1 toolchain:
```
~/.pico-sdk/toolchain/14_2_Rel1/bin/arm-none-eabi-gdb
```
Click Accept.

Use the GDB MI adapter. It launches a real arm-none-eabi-gdb --interpreter=mi2 and lets Binary Ninja drive it, so breakpoints and stepping go through real GDB — which sends the correct 2-byte breakpoint length and handles step-over itself. Verified working end to end: connect, GUI breakpoints (Add Hardware Breakpoint..., hardware execute), Step Into / Step Over, and register edits. Stops are reported as Breakpoint (not SingleStep).

Do NOT have any breakpoints set in Binary Ninja before you connect. With the GDB MI adapter, attaching while Binary Ninja already has a breakpoint hangs the session. Start the server parked with BP_ADDR (Step 9), connect, and only add hardware breakpoints after the connection is up. This is a Binary Ninja bug; it is the single most common GDB MI failure.

The GDB executable path matters. Use the 14.2.rel1 build above. The 13.3.rel1 build did not connect in testing.

Do not pick Corellium. Binary Ninja's adapter dropdown also lists Corellium, which is for Corellium's virtual devices and expects an API token, not a local OpenOCD server. It is not the adapter for this lab. The dropdown is a combo box, so an accidental arrow-key press can land on it — always read the label back and confirm it says GDB MI before clicking Accept.

The adapter and port are not saved in the .bndb. Every time you relaunch Binary Ninja you must re-select GDB MI, re-enter port 3333, and re-set the GDB path.

Watch for an off-screen error dialog. When a connection fails, Binary Ninja pops a Binary Ninja critical alert window that can be positioned mostly outside the main window, which makes it look like nothing happened. If the connect seems to do nothing, check your other display.

The target keeps running. Open the Registers tab (bug icon) and confirm you see live values. pc inside 0x10003xxx and sp just below 0x20082000 are healthy.

If pc is 0x00000088, 0x000000ec, or sp is 0xf0000000, the session is bad. Restart the server, then restart Binary Ninja (a server restart while attached leaves Binary Ninja in a stale session), and connect again.

Step 11: Find `main` without relying on its address

main can move between programs, so we do not guess it. We follow the one fixed path to it. Press G and go to 0x10000000:

0x10000000   0x20082000   initial stack pointer (top of SRAM)
0x10000004   0x1000015d   reset vector

Bit 0 of a vector is the Thumb bit, so 0x1000015d means "start at 0x1000015c". That is _reset_handler. Follow the reset path to 0x10000186, platform_entry:

10000186: ldr  r1, [pc, #80]  @ (100001d8 <data_cpy_table+0x38>)
10000188: blx  r1
1000018a: ldr  r1, [pc, #80]  @ (100001dc <data_cpy_table+0x3c>)
1000018c: blx  r1
1000018e: ldr  r1, [pc, #80]  @ (100001e0 <data_cpy_table+0x40>)
10000190: blx  r1
10000192: bkpt 0x0000
10000194: b.n  10000192  @ <platform_entry+0xc>

The middle blx at 0x1000018c is the call to main. platform_entry is byte-identical in every project, so 0x1000018c catches main no matter where the linker placed it. The literal pool at 0x100001dc holds main | 1; clearing bit 0 gives 0x10000234.

Step 12: Set a hardware breakpoint in the GUI

With the GDB MI adapter, Binary Ninja sets breakpoints through real GDB, which sends the correct 2-byte length, so you set them in the UI. There is no command port here.

Why older drafts used the command port. Binary Ninja's GDB RSP adapter is its own minimal RSP client and sends a 1-byte breakpoint (Z0,<addr>,1); the Cortex-M33 FPB comparators need 2 bytes, so OpenOCD rejected it with only breakpoints of two bytes length supported. The old workaround was to arm breakpoints by hand over telnet. The GDB MI adapter does not have this problem — it drives real arm-none-eabi-gdb, which sends the right length. So everything below is done in the GUI. The command port still exists as a fallback (see the end of this step), but you do not need it.

Where you can stop

You want to stop at	Address	How	Repeatable?
`main`	`0x10000234`	The server starts parked there with `BP_ADDR=0x10000234` (Step 9), so Binary Ninja is already stopped at `main` when it connects.	No — `main` runs once per reset.
The `FAV_NUM` `printf` call	`0x10000292`	Set a hardware breakpoint in the GUI, then click Resume.	Yes — fires on every iteration.
The `OTHER_FAV_NUM` `printf` call	`0x1000029c`	Set a hardware breakpoint in the GUI, then click Resume.	Yes — fires on every iteration.
The `lcd_puts("Reverse")` call	`0x1000027c`	Set a hardware breakpoint while stopped at `main`, then click Resume.	No — the LCD is written once at init.

Set the loop breakpoint in the GUI

Press G, type the loop address (0x10000292), and press Enter.
Set a hardware execution breakpoint at that address, either way:
- Debugger -> Add Hardware Breakpoint... — a hardware execute (HE) breakpoint. Use this one.
- click the line and press F2 (Debugger -> Toggle Breakpoint) — a software breakpoint. It will not work here: the code is in read-only flash, so GDB cannot install it and the core just keeps running.
Click Resume. The core is already running the loop, so the breakpoint fires on the next iteration. Binary Ninja stops with the PC at the loop address and reports it as a Breakpoint — verified: Stopped (Breakpoint) at 0x10000292.

No breakpoints before you connect. With GDB MI, a breakpoint set before the connection hangs the session (Step 10). Start parked with BP_ADDR, connect, then add breakpoints.

Stepping

With the target halted at the breakpoint, Step Into (F7) and Step Over (F8) run through real GDB and move the PC. Verified: 0x10000292 -> 0x1000398c -> 0x1000398e -> ....

Step Over on the raw .bin steps into calls. The raw image has no symbol for __wrap_printf, so Step Over at the printf call behaves like Step Into. When the lab needs to execute the call and then stop, it moves the breakpoint to the return site and clicks Resume instead (Step 13 shows this).

Never use Binary Ninja's Restart button. On RP2350 it resets and halts inside the boot ROM (pc=0x88, sp=0xf0000000). To reset cleanly, restart the server with BP_ADDR and reconnect.

If you ever need the command port. It is still there — nc 127.0.0.1 4444, and bp <addr> 2 hw still arms a breakpoint, rbp <addr> / rbp all still remove them. It is the fallback if you switch back to the GDB RSP adapter, whose 1-byte breakpoints the GUI cannot set. With GDB MI you do not need it for this lab.

Step 13: HACK IT LIVE — change the printed `FAV_NUM`

main loads the #define 0x2a (42) into r1 and calls printf on every iteration. We break on that call and change it live:

1000028e: movs  r1, #42      @ 0x2a
10000290: ldr   r0, [pc, #32] @ (100002b4 <main+0x80>)
10000292: bl    1000398c     @ <__wrap_printf>
10000296: movw  r1, #1337    @ 0x539
1000029a: ldr   r0, [pc, #28] @ (100002b8 <main+0x84>)
1000029c: bl    1000398c     @ <__wrap_printf>
100002a0: b.n   1000028e     @ <main+0x5a>

Press G, go to 0x10000292 (the bl __wrap_printf for FAV_NUM).
Set a hardware execute breakpoint there: Debugger -> Add Hardware Breakpoint.... (Do not use F2 — that is a software breakpoint and will not work on read-only flash.)
Click Resume in Binary Ninja. The target is already running the loop, so the breakpoint fires on the next iteration. Binary Ninja stops with the program counter at 0x10000292 and r1 = 0x2a.
Open the Registers widget (bug icon -> Registers).
Find r1. Its value is 0x2a (42), loaded by the movs r1, #42 at 0x1000028e.
Set r1 to 0x2b (43). From Binary Ninja's Python console (Plugins -> Python Console):
```
dbg.set_reg_value("r1", 0x2b)
```
dbg.set_reg_value(name, value) writes one register (returns True on success). You can also right-click r1 in the Registers widget, press E (edit), type 2b, and press Enter. The widget may not repaint the value, but the write reaches the target — you confirm it by the printed output in the next steps.
Move the breakpoint past the call. You want printf to run once and then stop, so move the breakpoint from 0x10000292 to the instruction after the call, 0x10000296 (the movw r1, #1337 that begins the OTHER_FAV_NUM half of the loop): remove the breakpoint at 0x10000292 and set a hardware breakpoint at 0x10000296. Two reasons not to just click Step Over here: a breakpoint left on the current PC re-traps the step, and Binary Ninja's Step Over steps into __wrap_printf on this raw .bin because the image carries no symbol for the call. Moving the breakpoint to the return site is deterministic.
Click Resume in Binary Ninja. The core executes bl __wrap_printf with r1 = 0x2b, so this iteration prints FAV_NUM: 43, then stops at 0x10000296.
Look at your serial monitor — the screen session on the Pico's USB serial port — and at the Target tab in Binary Ninja:
```
FAV_NUM: 43
```

You changed a running program's output without touching the binary.

Step 13b: HACK THE LCD STRING LIVE — change `"Reverse"` to `"Exploit"` (optional)

The LCD text "Reverse" lives in flash (.rodata) at 0x10003ee8, and flash is read-only at runtime — a debugger write there does not stick. So instead of overwriting the text in place, redirect the pointer: at the lcd_puts call for "Reverse", r0 holds the string address, so point r0 at a replacement string you place in RAM.

Do this one while stopped at main, before Resume. The LCD is written once during init, at 0x1000027c. If you have already resumed into the loop, restart the server parked at 0x10000234 (Step 9) and reconnect, or the breakpoint at 0x1000027c never fires again.

With Binary Ninja stopped at main (0x10000234), press G and go to 0x1000027c (the bl lcd_puts that writes "Reverse", loaded from the literal pool word at 0x100002ac).
Set a hardware execute breakpoint at 0x1000027c and click Resume. It fires once, with r0 = 0x10003ee8.
Put the replacement string into free RAM at 0x20080000 from Binary Ninja's Python console (Plugins -> Python Console) — no command port needed:
```
dbg.write_memory(0x20080000, b"Exploit\x00")
```
dbg.write_memory(address, bytes) is Binary Ninja's debugger memory-write API; it returns True on success. That writes Exploit\0.
Point r0 at that string:
```
dbg.set_reg_value("r0", 0x20080000)
```
(Or right-click r0 in the Registers widget, press E, type 0x20080000, and press Enter.)
Move the breakpoint off the current PC (remove it at 0x1000027c, set one at 0x10000280, the movs r0, #1 after the call) and click Resume. lcd_puts walks your RAM string and pushes E x p l o i t to the PCF8574 over I2C, so line 1 of the LCD now reads:
```
Exploit
```

Like the value hack, this is one boot only: the next lcd_puts for "Engineering" is unaffected, but a reset reloads r0 from flash. The permanent version is the static patch in Step 18c.

Step 14: Why the hack reverts (and why we patch next)

Press Resume. The loop branches back to 0x1000028e, which reloads movs r1, #42, so the next line is FAV_NUM: 42. The live edit changed one iteration only. There is no memory variable to change; the value is baked into the instruction. To make FAV_NUM: 43 permanent we must patch the instruction. That is the static pass.

Press Pause to stop the output flood.

Step 15: Kill the debugger and OpenOCD

The live hack is done. Do this before the static pass.

In the Debugger sidebar, click the X (Kill) (or Debugger -> Kill) to disconnect Binary Ninja.

Kill does not stop the OpenOCD process — debug-server.sh started it separately, and it keeps running and holding the probe. Stop it from the Binary Ninja console:

macOS / Linux:

import subprocess
subprocess.run(["pkill", "-TERM", "-f", "openocd"])  # stop the debug server, free the probe

Windows:

import subprocess
subprocess.run(["taskkill", "/F", "/IM", "openocd.exe"])  # stop the debug server, free the probe

Confirm nothing is left: pgrep -fl openocd (macOS/Linux) prints nothing.

From a terminal it is the same: pkill -TERM -f openocd, or Get-Process openocd | Stop-Process on Windows.

Part 4: Static — Resolve the Functions in Binary Ninja and Patch

Step 16: Resolve the functions in the Binary Ninja GUI

We now name the functions in Binary Ninja using the ELF symbol map from Step 4. Binary Ninja loaded the raw .bin with no symbols, so every function shows as sub_<addr> — resolving means giving each one its real name and signature.

Three keys do all the work:

Key	Binary Ninja action	Use it for
`G`	Go to address	Jump to a function's address
`Y`	Change Type	Set the function's signature. The dialog shows the full prototype, so this sets the name and the type in one step.
`N`	Rename	Rename only, when you just want the name and not the type

For each function below: G to its address, then Y (Change Type) and type the prototype from the table.

How to resolve a function in Binary Ninja (`Y`)

Y is the Change Type key, and it is what actually resolves the function — it turns void sub_100037fc() into bool stdio_init_all(void). The Change Type dialog shows the full declaration (name and type), so typing the prototype sets both:

G to the function's address. The cursor lands on the function.
Press Y. In the Change Type dialog, type the prototype from the table exactly — for example bool stdio_init_all(void) — and press Enter.

The decompiler header then shows the real prototype, and calls to the function read cleanly instead of sub_<addr>(). N is only for renaming without touching the type; Y alone sets both the name and the type.

If Y seems to do nothing, confirm the cursor is on the function, or right-click it and pick Change Type.... Binary Ninja parses what you type and silently keeps the old type if it does not parse, so glance at the header after each Y.

Worked example: `main`

Press G, type 0x10000234, press Enter. The view jumps there; the cursor lands on sub_10000234.
Press Y (Change Type), type int main(void), press Enter. That sets the name to main and the type to int(void).

Binary Ninja shows int32_t where Ghidra shows int. After you set int main(void), the decompiler header may read int32_t main(void). That is the same type — on this platform int is 32 bits and Binary Ninja's parser normalises it to int32_t. Do not fight it; it is not an error.

Worked example: `i2c_init`

G -> 0x10003cdc.
Y -> uint i2c_init(i2c_inst_t* i2c, uint baudrate).

i2c_init returns uint, not void. The SDK's i2c_init returns the actual configured baud rate; the ELF says unsigned int (i2c_inst_t *, uint). Keep the return type.

Worked example: `lcd_i2c_init`

G -> 0x100002bc.
Y -> void lcd_i2c_init(i2c_inst_t* i2c, uint8_t pcf_addr, int nibble_shift, uint8_t backlight_mask).

This is our own lcd_1602.c code. In this build it is one big function: the compiler inlined lcd_store_config, lcd_hd44780_reset, and lcd_hd44780_configure into it.

Worked example: `lcd_set_cursor`

G -> 0x100006f4.
Y -> void lcd_set_cursor(int line, int position).

Worked example: `lcd_puts`

G -> 0x100007f0.
Y -> void lcd_puts(const char* s).

Worked example: `gpio_set_function`

G -> 0x100008f0.
Y -> void gpio_set_function(uint gpio, gpio_function_t fn).

Worked example: `gpio_set_pulls`

G -> 0x1000092c.
Y -> void gpio_set_pulls(uint gpio, bool up, bool down).

This is what gpio_pull_up(2) in our source compiles to: the SDK's static inline gpio_pull_up disappears, and main calls gpio_set_pulls(2, true, false) directly at 0x10000258.

Worked example: `__wrap_printf`

G -> 0x1000398c.
Y -> int __wrap_printf(const char *fmt, ...). Keep the ... — printf is variadic.

Worked example: `stdio_init_all`

G -> 0x100037fc.
Y -> bool stdio_init_all(void).

printf in our source is __wrap_printf in the binary. The SDK links our printf calls to its __wrap_printf wrapper, which forwards to __wrap_vprintf. Rename it printf if you prefer the lesson's shorthand, but __wrap_printf is what the ELF says.

The rest of the chain is the same two keystrokes per function (G, then Y). This is our code plus the library functions it actually calls — not the whole SDK. main calls stdio_init_all, i2c_init, gpio_set_function, gpio_set_pulls, lcd_i2c_init, lcd_set_cursor, lcd_puts, and printf, so we follow that chain down.

The call chain for this project:

main
├── stdio_init_all ── stdio_uart_init ── gpio_set_function, uart_init, stdio_set_driver_enabled
│                                        └── uart_init ── clock_get_hz, busy_wait_us
├── i2c_init
├── gpio_set_function
├── gpio_set_pulls                 (gpio_pull_up inlined)
├── lcd_i2c_init ── i2c_write_blocking, sleep_us, sleep_ms
│   └── pcf_write_byte / pcf_pulse_enable / lcd_write4 / lcd_send / lcd_store_config /
│       lcd_hd44780_reset / lcd_hd44780_configure   (all inlined; no calls)
├── lcd_set_cursor ── i2c_write_blocking, sleep_us
├── lcd_puts ── i2c_write_blocking, sleep_us
└── __wrap_printf ── __wrap_vprintf ── vfctprintf ── _vsnprintf
    │                                              └── _ntoa_format / _out_rev / _out_char
    ├── time_us_64
    └── stdio_out_chars_crlf

Resolve every function in that chain:

Address	Rename to (`N`)	Signature (`Y`)
`0x1000015c`	`_reset_handler`	`void _reset_handler(void)`
`0x10000186`	`platform_entry`	`void platform_entry(void)`
`0x1000019a`	`data_cpy`	`void data_cpy(void, void, void*)`
`0x100001e4`	`_init`	`void _init(void)`
`0x10000210`	`frame_dummy`	`void frame_dummy(void)`
`0x10000234`	`main`	`int main(void)`
`0x100002bc`	`lcd_i2c_init`	`void lcd_i2c_init(i2c_inst_t*, uint8_t, int, uint8_t)`
`0x100006f4`	`lcd_set_cursor`	`void lcd_set_cursor(int, int)`
`0x100007f0`	`lcd_puts`	`void lcd_puts(const char*)`
`0x100008f0`	`gpio_set_function`	`void gpio_set_function(uint, gpio_function_t)`
`0x1000092c`	`gpio_set_pulls`	`void gpio_set_pulls(uint, bool, bool)`
`0x10001368`	`sleep_us`	`void sleep_us(uint64_t)`
`0x10001440`	`sleep_ms`	`void sleep_ms(uint32_t)`
`0x10001624`	`time_us_64`	`uint64_t time_us_64(void)`
`0x10001638`	`busy_wait_us`	`void busy_wait_us(uint64_t)`
`0x100016b8`	`uart_init`	`uint uart_init(uart_inst_t*, uint)`
`0x1000188c`	`clock_get_hz`	`unsigned long clock_get_hz(clock_handle_t)`
`0x100035a4`	`exit`	`void exit(int)`
`0x100035ac`	`runtime_init`	`void runtime_init(void)`
`0x100035d8`	`stdio_out_chars_crlf`	`void stdio_out_chars_crlf(stdio_driver_t, const char, int)`
`0x100036e8`	`stdio_put_string`	`int stdio_put_string(const char*, int, bool, bool)`
`0x100037d4`	`stdio_set_driver_enabled`	`void stdio_set_driver_enabled(stdio_driver_t*, bool)`
`0x100037fc`	`stdio_init_all`	`bool stdio_init_all(void)`
`0x100038c8`	`__wrap_vprintf`	`int __wrap_vprintf(const char*, va_list)`
`0x1000398c`	`__wrap_printf`	`int __wrap_printf(const char*, ...)`
`0x10003b48`	`stdio_uart_init`	`void stdio_uart_init(void)`
`0x10003cdc`	`i2c_init`	`uint i2c_init(i2c_inst_t*, uint)`
`0x10003d28`	`i2c_write_blocking`	`int i2c_write_blocking(i2c_inst_t, uint8_t, const uint8_t, size_t, bool)`
`0x10003e24`	`strlen`	`size_t strlen(const char*)`

Resolve the SDK helpers the printf path reaches:

Address	Rename to (`N`)	Signature (`Y`)
`0x10003548`	`vfctprintf`	`int vfctprintf(void ()(char, void), void, const char, va_list)`
`0x10002b64`	`_vsnprintf`	`int _vsnprintf(out_fct_type, char, size_t, const char, va_list)`
`0x10001f48`	`_ntoa_format`	`unsigned _ntoa_format(out_fct_type, char, size_t, size_t, char, size_t, bool, unsigned, unsigned, unsigned, unsigned)`
`0x10001eac`	`_out_rev`	`unsigned _out_rev(out_fct_type, char, size_t, size_t, const char, size_t, unsigned, unsigned)`
`0x1000211c`	`_out_char`	`void _out_char(char, void*, size_t, size_t)`

A void return type may not stick — here is the fix. Binary Ninja treats void as low-confidence, and its analysis can override it with an inferred type — most often int32_t on this 32-bit target. It is most visible on _reset_handler (a hand-written assembly entry that never returns normally), but it can happen to any function whose return type Binary Ninja thinks it can infer.

Setting the full signature with Y reproduces the unwanted int32_t, and fn.return_type = ... fails too. What works is the return-value setter:
from binaryninja import ReturnValue, Type
fn = bv.get_function_at(0x1000015c)
if fn is not None:
    fn.return_value = ReturnValue(Type.void())
That holds _reset_handler at void even after reanalysis. If it still will not stick, leave it — it does not affect the rest of the lesson.

i2c1_inst is data, not a function. arm-none-eabi-nm -n lists 2000062c T i2c1_inst. The T is a global data symbol: the linker parks the i2c1_inst struct at RAM address 0x2000062c. Its first word is the hardware pointer 0x40098000, the I2C1 register base. There is no function there; do not Y it with a prototype.

Shortcut — resolves name and type for every function. Instead of doing N + Y by hand, paste this into Binary Ninja's Python console (Plugins -> Python Console). It sets each function's name and signature programmatically:

from binaryninja import Symbol, SymbolType
# The raw .bin has no headers, so these SDK types don't exist. set_user_type()
# re-parses each signature as C, so an undefined name raises
# "SyntaxError: unknown type name '...'". Define them first.
sdk = bv.parse_types_from_string("""
typedef unsigned int uint;
typedef char* va_list;
typedef unsigned long clock_handle_t;
typedef void (*out_fct_type)(char, void*, size_t, size_t);
struct stdio_driver;
typedef struct stdio_driver stdio_driver_t;
struct uart_inst;
typedef struct uart_inst uart_inst_t;
struct i2c_inst;
typedef struct i2c_inst i2c_inst_t;
enum gpio_function {
    GPIO_FUNC_XIP = 0, GPIO_FUNC_SPI = 1, GPIO_FUNC_UART = 2, GPIO_FUNC_I2C = 3,
    GPIO_FUNC_PWM = 4, GPIO_FUNC_SIO = 5, GPIO_FUNC_PIO0 = 6, GPIO_FUNC_PIO1 = 7,
    GPIO_FUNC_GPCK = 8, GPIO_FUNC_USB = 9, GPIO_FUNC_NULL = 0x1f,
};
typedef enum gpio_function gpio_function_t;
""")
for name, ty in sdk.types.items():
    bv.define_user_type(name, ty)

# address: (name, signature)
funcs = {
    0x1000015c: ("_reset_handler",            "void _reset_handler(void)"),
    0x10000186: ("platform_entry",            "void platform_entry(void)"),
    0x1000019a: ("data_cpy",                  "void data_cpy(void*, void*, void*)"),
    0x100001e4: ("_init",                     "void _init(void)"),
    0x10000210: ("frame_dummy",               "void frame_dummy(void)"),
    0x10000234: ("main",                      "int main(void)"),
    0x100002bc: ("lcd_i2c_init",              "void lcd_i2c_init(i2c_inst_t*, uint8_t, int, uint8_t)"),
    0x100006f4: ("lcd_set_cursor",            "void lcd_set_cursor(int, int)"),
    0x100007f0: ("lcd_puts",                  "void lcd_puts(const char*)"),
    0x100008f0: ("gpio_set_function",         "void gpio_set_function(uint, gpio_function_t)"),
    0x1000092c: ("gpio_set_pulls",            "void gpio_set_pulls(uint, bool, bool)"),
    0x10001368: ("sleep_us",                  "void sleep_us(uint64_t)"),
    0x10001440: ("sleep_ms",                  "void sleep_ms(uint32_t)"),
    0x10001624: ("time_us_64",                "uint64_t time_us_64(void)"),
    0x10001638: ("busy_wait_us",              "void busy_wait_us(uint64_t)"),
    0x100016b8: ("uart_init",                 "uint uart_init(uart_inst_t*, uint)"),
    0x1000188c: ("clock_get_hz",              "unsigned long clock_get_hz(clock_handle_t)"),
    0x100035a4: ("exit",                      "void exit(int)"),
    0x100035ac: ("runtime_init",              "void runtime_init(void)"),
    0x100035d8: ("stdio_out_chars_crlf",      "void stdio_out_chars_crlf(stdio_driver_t*, const char*, int)"),
    0x100036e8: ("stdio_put_string",          "int stdio_put_string(const char*, int, bool, bool)"),
    0x100037d4: ("stdio_set_driver_enabled",  "void stdio_set_driver_enabled(stdio_driver_t*, bool)"),
    0x100037fc: ("stdio_init_all",            "bool stdio_init_all(void)"),
    0x100038c8: ("__wrap_vprintf",            "int __wrap_vprintf(const char*, va_list)"),
    0x1000398c: ("__wrap_printf",             "int __wrap_printf(const char*, ...)"),
    0x10003b48: ("stdio_uart_init",           "void stdio_uart_init(void)"),
    0x10003cdc: ("i2c_init",                  "uint i2c_init(i2c_inst_t*, uint)"),
    0x10003d28: ("i2c_write_blocking",        "int i2c_write_blocking(i2c_inst_t*, uint8_t, const uint8_t*, size_t, bool)"),
    0x10003e24: ("strlen",                    "size_t strlen(const char*)"),
    0x10003548: ("vfctprintf",                "int vfctprintf(void (*)(char, void*), void*, const char*, va_list)"),
    0x10002b64: ("_vsnprintf",                "int _vsnprintf(out_fct_type, char*, size_t, const char*, va_list)"),
    0x10001f48: ("_ntoa_format",              "unsigned _ntoa_format(out_fct_type, char*, size_t, size_t, char*, size_t, bool, unsigned, unsigned, unsigned, unsigned)"),
    0x10001eac: ("_out_rev",                  "unsigned _out_rev(out_fct_type, char*, size_t, size_t, const char*, size_t, unsigned, unsigned)"),
    0x1000211c: ("_out_char",                 "void _out_char(char, void*, size_t, size_t)"),
}
for addr, (name, sig) in funcs.items():
    bv.define_user_symbol(Symbol(SymbolType.FunctionSymbol, addr, name))
    f = bv.get_function_at(addr)
    if f is not None:
        f.set_user_type(sig)

SDK type names (i2c_inst_t, uart_inst_t, stdio_driver_t, gpio_function_t, plus uint, va_list, clock_handle_t, and out_fct_type) are not in the raw .bin. set_user_type re-parses each signature as C, so an undefined name raises SyntaxError: unknown type name '...' and stops the loop — it is not harmless. The sdk block above defines them first (an opaque struct/enum/typedef is enough to parse). If you add a function that uses another SDK type, add a definition for it to that block too.

Step 17: Read `main` in the decompiler

Open the Decompiler view on main. Once the functions above are typed, it reads roughly:

int32_t main(void)
{
    stdio_init_all();
    i2c_init(&i2c1_inst, 0x186a0);              // i2c_init(i2c1, 100000)
    gpio_set_function(2, GPIO_FUNC_I2C);
    gpio_set_function(3, GPIO_FUNC_I2C);
    gpio_set_pulls(2, true, false);             // gpio_pull_up(2)
    gpio_set_pulls(3, true, false);             // gpio_pull_up(3)
    lcd_i2c_init(&i2c1_inst, 0x27, 4, 8);       // lcd_i2c_init(i2c1, 0x27, 4, 0x08)
    lcd_set_cursor(0, 0);
    lcd_puts("Reverse");
    lcd_set_cursor(1, 0);
    lcd_puts("Engineering");
    while (true) {
        __wrap_printf("FAV_NUM: %d\r\n", 0x2a);         // FAV_NUM  = 42
        __wrap_printf("OTHER_FAV_NUM: %d\r\n", 0x539);  // OTHER_FAV_NUM = 1337
    }
}

The 0x2a and 0x539 are the constants we will patch. Both are immediates in the instruction stream — there is no .rodata word to change, which is why the patch edits the instruction operand. Now make the hacks permanent.

Step 18: Patch 1 — change `FAV_NUM` from 42 to 43

Go to 0x1000028e:

1000028e: 2a 21   movs  r1, #42   @ 0x2a

The halfword is 0x212a, stored little-endian as 2a 21. The immediate is the low byte, so the byte at the instruction's own address is 0x2a. Change it to 0x2b (43).

Project	Address	Before	After	Effect
`0x0017`	`0x1000028e`	`2a`	`2b`	`movs r1, #42` -> `#43`, prints `FAV_NUM: 43`

Option A — Hex view:

Switch to the Hex view (View -> Hex).
Toggle the lock off so editing is enabled.
Go to 0x1000028e and change the byte 2A to 2B.
Return to the linear view, right-click the function -> Reanalyze.

Option B — Python console:

bv.write(0x1000028e, b"\x2b")
print(hex(bv.read(0x1000028e, 1)[0]))  # -> 0x2b

After reanalysis the instruction reads movs r1, #43.

Step 18b: Patch 2 — change `OTHER_FAV_NUM` from 1337 to 1344

Go to 0x10000296:

10000296: 40 f2 39 51   movw  r1, #1337   @ 0x539

This is the 32-bit Thumb-2 encoding of movw r1, #0x539. The four bytes and their roles:

+-----------------------------------------------------------------+
|  movw r1, #0x539  ->  bytes: 40 F2 39 51                        |
|                                                                 |
|  Byte 0: 0x40  -+                                               |
|  Byte 1: 0xF2  -+   First halfword (opcode + upper imm bits)    |
|  Byte 2: 0x39  ---- Lower 8 bits of immediate (imm8) <- CHANGE  |
|  Byte 3: 0x51  ---- Destination register (r1) + upper imm bits  |
|                                                                 |
|  imm16 = 0x0539 = 1337 decimal                                  |
|  imm8 field = 0x39 (lower 8 bits of the value)                  |
|                                                                 |
+-----------------------------------------------------------------+

The imm8 byte is the third byte of the 4-byte instruction: the instruction starts at 0x10000296, so the byte to change is 0x10000296 + 2 = 0x10000298. Change 0x39 to 0x40, which changes the value from 0x539 (1337) to 0x540 (1344).

Project	Address	Before	After	Effect
`0x0017`	`0x10000298`	`39`	`40`	`movw r1, #1337` -> `#1344`, prints `OTHER_FAV_NUM: 1344`

Option A — Hex view:

Switch to the Hex view (View -> Hex).
Go to 0x10000298 and change the byte 39 to 40.
Return to the linear view and reanalyze.

Option B — Python console:

bv.write(0x10000298, b"\x40")
print(bv.read(0x10000296, 4).hex())  # -> 40f24051

Do not patch 0x10000296 itself. That is the instruction's first byte (the opcode), not the immediate. The immediate's low 8 bits are at 0x10000298; patching the opcode corrupts the instruction.

Step 18c: Patch 3 — change the LCD text from `"Reverse"` to `"Exploit"`

The string "Reverse" starts at 0x10003ee8. Its eight bytes are 52 65 76 65 72 73 65 00 (Reverse\0). Change them to 45 78 70 6c 6f 69 74 00 (Exploit\0). Both strings are exactly seven characters, so the replacement fits without touching "Engineering" at 0x10003ef0.

Project	Address	Before	After	Effect
`0x0017`	`0x10003ee8`	`52 65 76 65 72 73 65 00`	`45 78 70 6c 6f 69 74 00`	LCD line 1 prints `Exploit` instead of `Reverse`

ASCII reference:

Character	Hex
E	`0x45`
x	`0x78`
p	`0x70`
l	`0x6c`
o	`0x6f`
i	`0x69`
t	`0x74`

Option A — Hex view:

Switch to the Hex view (View -> Hex).
Go to 0x10003ee8 and change the eight bytes 52 65 76 65 72 73 65 00 to 45 78 70 6c 6f 69 74 00.
Return to the linear view and reanalyze.

Option B — Python console:

bv.write(0x10003ee8, b"Exploit\x00")
print(bv.read(0x10003ee8, 8))  # -> b'Exploit\x00'

Keep the replacement exactly eight bytes. If you use a shorter string you must pad it and keep the terminating \0, or lcd_puts will run into the "Engineering" string that follows at 0x10003ef0.

Step 19: Export the patched `.bin`

import os
seg = next(s for s in bv.segments if s.data_length)  # the loadable image segment
data = bv.read(seg.start, seg.data_length)  # base + size come from the view itself
out = os.path.join(os.path.join(root, "0x0017_constants", "build"), "0x0017_constants-h.bin")
open(out, "wb").write(data)
print(len(data), out)  # -> 17980 /.../build/0x0017_constants-h.bin

Where the two numbers come from — nothing is hardcoded:

seg.start is the image base Binary Ninja loaded the .bin at (0x10000000), the same value you pass to uf2conv --base.
seg.data_length is the segment's size in the file (0x463c = 17980). Exactly one segment carries data (the image); every peripheral and synthetic segment has data_length == 0, so next(...) picks the image.
Reading seg.start for seg.data_length bytes therefore grabs exactly the image.

Two gotchas this avoids:

No relative path. Binary Ninja's Python console runs with a read-only working directory (inside the app bundle), so open("0x0017_constants-h.bin", "wb") fails with OSError: [Errno 30] Read-only file system. root (from ~/.embedded-hacking-repo, Step 3) is the repo, so the file is written into the project's build/ — no machine-specific path and no database needed.
Read the image, not the whole view. bv.read(bv.start, bv.length) spans the entire mapped range, which is not the image. The segment's data_length is the image size.

A different size means you exported a partial view.

Step 20: Convert to UF2

Run from the project directory:

macOS Apple Silicon / Linux x64:

python3 ../uf2conv.py 0x0017_constants-h.bin \
  --base 0x10000000 --family 0xe48bff59 --output hacked.uf2

Windows x64:

python ..\uf2conv.py 0x0017_constants-h.bin ^
  --base 0x10000000 --family 0xe48bff59 --output hacked.uf2

Or convert from the Binary Ninja console — it is a normal Python interpreter, so you never have to leave the app. chdir to a writable directory first (the default one is read-only), then run the script:
import os, sys, runpy
os.chdir(os.path.join(root, "0x0017_constants", "build"))   # the project build dir (writable)
sys.argv = ["uf2conv.py", "0x0017_constants-h.bin",
            "--base", "0x10000000", "--family", "0xe48bff59", "--output", "hacked.uf2"]
runpy.run_path("../../uf2conv.py", run_name="__main__")   # path to your uf2conv.py
This writes hacked.uf2 next to the .bin, ready to drag onto the Pico.

Step 21: Flash and verify

Hold BOOTSEL, plug in the Pico 2, and drag hacked.uf2 onto the RP2350 drive. Open the serial monitor:

FAV_NUM: 43
OTHER_FAV_NUM: 1344
FAV_NUM: 43
OTHER_FAV_NUM: 1344
...

and the LCD line 1 reads Exploit while line 2 still reads Engineering.

Both constants changed and the LCD string changed — with nine operand bytes patched and no source code. (0x2a -> 0x2b, 0x39 -> 0x40, and the eight-byte string.)

Faster: flash over the Debug Probe (no BOOTSEL). The repo's flash.sh writes the raw .bin straight into XIP flash over SWD (program <bin> 0x10000000 verify reset exit), so you never touch BOOTSEL or a UF2. Run it from a terminal (./flash.sh <bin>), or from the Binary Ninja console without freezing it — use subprocess.Popen, which returns immediately, and send OpenOCD's output to a log file. (subprocess.run blocks the console until the flash finishes; do not use it here.)
import os, subprocess
root = open(os.path.expanduser("~/.embedded-hacking-repo")).read().strip()
bin_path = os.path.join(os.path.join(root, "0x0017_constants", "build"), "0x0017_constants-h.bin")
log = os.path.join(os.path.join(root, "0x0017_constants", "build"), "flash.log")
subprocess.run(["pkill", "-TERM", "-f", "openocd"])  # free the probe first
p = subprocess.Popen([os.path.join(root, "flash.sh"), bin_path],
                     stdout=open(log, "w"), stderr=subprocess.STDOUT, start_new_session=True)
print("flashing in the background; log:", log)
The pkill frees the probe first; on Windows use subprocess.run(["taskkill", "/F", "/IM", "openocd.exe"]).

The console is free the moment this returns. Check it with print(p.poll()) (None = still running, 0 = done) or read flash.log — success ends with ** Verified OK **.

The same non-blocking form without the script:
import os, subprocess
ocd = os.path.expanduser("~/.pico-sdk/openocd/0.12.0+dev")
bin_path = os.path.join(os.path.join(root, "0x0017_constants", "build"), "0x0017_constants-h.bin")
log = os.path.join(os.path.join(root, "0x0017_constants", "build"), "flash.log")
subprocess.run(["pkill", "-TERM", "-f", "openocd"])  # free the probe first
p = subprocess.Popen([f"{ocd}/openocd", "-s", f"{ocd}/scripts",
    "-f", "interface/cmsis-dap.cfg", "-f", "target/rp2350.cfg",
    "-c", "adapter speed 5000",
    "-c", f"program {bin_path} 0x10000000 verify reset exit"],
    stdout=open(log, "w"), stderr=subprocess.STDOUT, start_new_session=True)
print("flashing in the background; log:", log)
The Debug Probe is single-owner. If Binary Ninja is still attached (the debug-server.sh OpenOCD is running), the flash cannot grab the probe. Detach in Binary Ninja and stop that OpenOCD first:
# macOS / Linux
pkill -TERM -f openocd
# Windows
Get-Process openocd -ErrorAction SilentlyContinue | Stop-Process
Success looks like Programming Finished -> Verified OK -> Resetting Target. On Windows use flash.ps1 (.\flash.ps1 -Bin <path>) the same way.

Cheatsheet

Binary Ninja GUI actions

Action	How
Go to address	`G`
Rename function/symbol	`N`
Set type or signature	`Y`
Add comment	`;`
Open Hex view	`View -> Hex`
Enable hex editing	Toggle the lock in the status bar
Reanalyze after a patch	Right-click function -> `Reanalyze`
Edit a register live	`dbg.set_reg_value("r1", 0x2b)` in the Python console (or right-click the register, press `E`, type hex, Enter)
Write a RAM string live	`dbg.write_memory(0x20080000, b"Exploit\x00")`
Set a breakpoint	`Debugger -> Add Hardware Breakpoint...` (hardware execute). Do not use `F2` — software breakpoints cannot be written to read-only flash.
Move a breakpoint	Remove it and set it at the new address in the GUI (command-port fallback: `rbp <old addr>` then `bp <new addr> 2 hw`)
Confirm what is armed	The Breakpoints widget lists it (command-port fallback: `mdw 0xE0002000 8`, each armed breakpoint shows as `<addr \| 1>`)
Apply the ELF symbol map	Paste the Python snippet from Step 16 into the Python Console

OpenOCD server and reset

The server runs with gdb_breakpoint_override hard so that flash-writes are never attempted. Breakpoints in this lab are set in the Binary Ninja GUI through the GDB MI adapter (Step 12). The command-port rows below are the fallback if you use the GDB RSP adapter instead.

Action	Command
Connect to the OpenOCD prompt (fallback)	`nc 127.0.0.1 4444` (or `telnet 127.0.0.1 4444`)
Reset and run (command port)	`reset run`
Check core state (command port)	`targets`
Set a breakpoint in the GUI	`Debugger -> Add Hardware Breakpoint...` (hardware execute; `F2` software breakpoints do not work on flash)
(fallback) Add a breakpoint without the GUI	`bp <addr> 2 hw`
Remove one breakpoint	`rbp <addr>` — address only, no length, no `hw`
Remove every breakpoint	`rbp all`
Start the server parked at `main`	macOS/Linux: `BP_ADDR=0x10000234 ./debug-server.sh` — Windows: `$env:BP_ADDR="0x10000234"; .\debug-server.ps1` (one-shot)
Start the server parked in the loop	macOS/Linux: `BP_ADDR=0x10000292 ./debug-server.sh` — Windows: `$env:BP_ADDR="0x10000292"; .\debug-server.ps1`
Break on the loop in a running target	set a hardware breakpoint in the GUI at the loop address, then Resume — repeatable
Make Binary Ninja stepping work	`rp2350.dap.core0 configure -rtos none` (already in the scripts)
Step without re-trapping	move the breakpoint off the current PC first, then Step Into/Step Over
Reset without desyncing Binary Ninja	Detach, `reset run` on the port, reconnect — never `reset run` while attached

Every address and byte we changed

Project	Address	Before	After	Effect
`0x0017`	`0x1000028e`	`2a`	`2b`	`movs r1, #42` -> `#43`, prints `FAV_NUM: 43`
`0x0017`	`0x10000298`	`39`	`40`	`movw r1, #1337` -> `#1344`, prints `OTHER_FAV_NUM: 1344`
`0x0017`	`0x10003ee8`	`52 65 76 65 72 73 65 00`	`45 78 70 6c 6f 69 74 00`	LCD line 1 prints `Exploit` instead of `Reverse`

The I2C/LCD memory map

Item	Address	Notes
`i2c1_inst`	`0x2000062c`	RAM `.data`, fixed for the life of the program
`i2c1_inst.hw`	`0x40098000`	I2C1 hardware register base (first word of the struct)
`i2c1_inst.restart_on_next`	`0x20000630`	second word of the struct, `0` (false)
Literal-pool word 1	`0x100002a4`	`0x000186a0` — I2C baud rate, 100000
Literal-pool word 2	`0x100002a8`	`0x2000062c` — `&i2c1_inst`
Literal-pool word 3	`0x100002ac`	`0x10003ee8` — pointer to `"Reverse"`
Literal-pool word 4	`0x100002b0`	`0x10003ef0` — pointer to `"Engineering"`
Literal-pool word 5	`0x100002b4`	`0x10003efc` — pointer to `"FAV_NUM: %d\r\n"`
Literal-pool word 6	`0x100002b8`	`0x10003f0c` — pointer to `"OTHER_FAV_NUM: %d\r\n"`

Raw image facts

Item	Value
Build type	`Release`
Load base address	`0x10000000`
Project size	`17980` bytes (`0x463c`)
Fixed `main` anchor	`0x1000018c` (reset handler middle `blx`)
`main`	`0x10000234`
`printf` call / return, `FAV_NUM`	`0x10000292` / `0x10000296`
`printf` call, `OTHER_FAV_NUM`	`0x1000029c`
`i2c1_inst` RAM address	`0x2000062c`
I2C1 hardware registers	`0x40098000`
`FAV_NUM` format string	`0x10003efc`
`OTHER_FAV_NUM` format string	`0x10003f0c`
`"Reverse"` string	`0x10003ee8`
`"Engineering"` string	`0x10003ef0`
RP2350 UF2 family ID	`0xe48bff59`

Troubleshooting

Binary Ninja hangs or crashes when you connect (macOS 27)

Three different causes have been seen on this setup; check them in this order.

A breakpoint set before connecting. With the GDB MI adapter, if the binary view already has a breakpoint, the session hangs. Start parked with BP_ADDR, connect, then add breakpoints (see the next entry).
The wrong GDB executable. Point Full GDB Executable Path at the 14.2.rel1 toolchain (Step 10). The 13.3.rel1 build did not connect in testing.
The LLDB adapter. A crash report with libdebuggercore.dylib -> std::terminate() -> abort() and liblldb in the stack is the LLDB adapter, not GDB MI. Avoid LLDB on this setup.

Use GDB MI, with the 14.2.rel1 path above. If it still fails, fall back to plain arm-none-eabi-gdb against the same server — the addresses and register values are identical to the GUI steps.

If Binary Ninja hangs, force-quit it; the connect dialog has no working Cancel. The static steps (resolve, patch, export, flash) never touch the debugger and always work.

The GUI refuses to set a breakpoint (GDB RSP adapter only)

If you are on the GDB RSP adapter, the GUI cannot set breakpoints on this target. That adapter is Binary Ninja's own minimal RSP client and sends a 1-byte breakpoint (Z0,<addr>,1); the Cortex-M33 comparators need 2 bytes, so OpenOCD answers only breakpoints of two bytes length supported. It affects every address, both Toggle Breakpoint and Add Hardware Breakpoint, and the dialog's Size field is disabled. gdb_breakpoint_override makes no difference.

Fix: use the GDB MI adapter (Step 10). It drives real GDB, which sends the correct length, so GUI breakpoints just work. If you must stay on GDB RSP, arm breakpoints from the command port after connecting (bp <addr> 2 hw) — but the lab uses GDB MI and does not need that.

GDB MI hangs when you connect (a breakpoint already existed)

With the GDB MI adapter, if Binary Ninja already has a breakpoint set when you connect, the session hangs. This is a Binary Ninja bug. The working order is:

Start the server parked, e.g. BP_ADDR=0x10000234 ./debug-server.sh (Windows: $env:BP_ADDR="0x10000234"; .\debug-server.ps1).
Connect with the GDB MI adapter.
Only then set hardware breakpoints in the UI.

Never have a breakpoint in the binary view before the GDB MI connection. If it hangs, quit Binary Ninja, restart the server with BP_ADDR, and connect again before adding any breakpoints.

Step Into / Step Over does nothing (PC never moves)

Two causes have been seen on this target.

A breakpoint on the current PC re-traps the step. OpenOCD's step-over-breakpoint logic fails with Duplicate Breakpoint address and the PC stays put. Fix: move the breakpoint off the current PC (in the GUI), then step.
The hwthread RTOS (GDB RSP adapter only). With the GDB RSP adapter, OpenOCD can log fake step thread 0 and reply without stepping, because the RP2350 config's -rtos hwthread makes the current thread id 1 while Binary Ninja sends thread id 0. Fix: rp2350.dap.core0 configure -rtos none (the launcher scripts already pass this). GDB MI does not hit this.

To tell them apart, turn on OpenOCD logging (log_output /tmp/ocd.log, then debug_level 3 on the command port) and look for fake step versus Duplicate Breakpoint.

`zsh: bad CPU type in executable: cmake`

An Intel x86_64 tool is on your PATH on Apple Silicon. Run Step 2: export PATH="/opt/homebrew/bin:$PATH", then hash -r. Add it to ~/.zshrc to make it permanent.

My addresses do not match this guide

You probably built Debug. This lesson is a Release build. Re-run Step 3 with -DCMAKE_BUILD_TYPE=Release. A Debug build moves the SDK functions and keeps init_i2c_and_lcd / write_lcd_greeting as separate calls, so main is not at 0x10000234.

A breakpoint never fires

First, confirm you actually set one, and that it is a hardware breakpoint. With the GDB MI adapter, Debugger -> Add Hardware Breakpoint... (hardware execute) should land in the Breakpoints widget. If nothing lands, or the core keeps running, you probably used F2 (Toggle Breakpoint) — that is a software breakpoint and cannot be written to read-only flash, so it never installs. Also check you are on GDB MI, not GDB RSP (the GDB RSP adapter cannot set breakpoints on this target at all).

Then check the order and the state:

Arm it only after Binary Ninja is connected. OpenOCD flushes every breakpoint when a client attaches, so anything armed earlier is gone. This also applies to BP_ADDR on the startup command line.
Verify it is armed: mdw 0xE0002000 8. You should see your address with the low bit set (0x10000292 -> 0x10000293). All zeros means nothing is armed — re-read this first, because it distinguishes "not armed" from "armed but never reached".
Is the core running? poll on the command port should not report a halt. If it is stopped, click Resume.
Does the address get reached again? main runs once per reset, so use BP_ADDR at startup (Step 9) rather than reset run while attached. Loop addresses such as 0x10000292 fire on the next pass with no reset — arm them and click Resume in Binary Ninja.
With GDB MI the stop is reported as Breakpoint and appears in the Breakpoints widget, because GDB really did set it.

I edit `r1` (or another register) and it reverts

main reloads the value at the top of every loop iteration — movs r1, #42 at 0x1000028e runs right before the printf at 0x10000292. So r1 is only 0x2b for the instant between your edit and the next pass; then it is 0x2a again. The edit sticks only if the core is genuinely stopped at the breakpoint and stays stopped.

If it keeps reverting, the core is running, which almost always means the breakpoint is not installed — usually because it is a software breakpoint (F2) that cannot be written to read-only flash. Use Debugger -> Add Hardware Breakpoint... (hardware execute).

The Registers widget is a snapshot, not a live view. Binary Ninja reads the registers at each stop and shows that snapshot; it does not poll the target, and there is no "refresh registers" command. So a value changed outside Binary Ninja will not appear until the next stop.

The LCD string hack does nothing

The LCD is written once, during lcd_i2c_init / write_lcd_greeting, before the loop starts. You must break at 0x1000027c and redirect r0 before that call runs. If you already let the target run into the loop, the LCD already shows the old strings. Restart the server parked at main (BP_ADDR=0x10000234) and reconnect, then set the breakpoint at 0x1000027c while stopped.

Also confirm you wrote a NUL-terminated string. lcd_puts walks bytes until *s == 0; without the trailing \x00, it keeps sending RAM garbage to the PCF8574.

The compiler did not keep `const` in `.rodata`

It is not supposed to in this build. const int OTHER_FAV_NUM = 1337 becomes movw r1, #1337 because the program never takes its address (&OTHER_FAV_NUM) and the value fits in a 16-bit immediate. A const only stays in .rodata when something forces it there — an address-taken const, an array, a pointer, or volatile. When you reverse a real binary, never assume a const is a memory load; check the instruction.

The `movw` patch did not take

You patched the wrong byte. movw is a 32-bit instruction and its low immediate byte (imm8) is the third byte. The instruction starts at 0x10000296, so the byte to change is 0x10000298 (0x39 -> 0x40). Patching 0x10000296 (the opcode) corrupts the instruction and the core will fault.

The LCD shows garbage after patching

The replacement string is the wrong length or is missing its NUL. "Reverse" and "Exploit" are both seven characters, and the original eight-byte block is 52 65 76 65 72 73 65 00. Write exactly 45 78 70 6c 6f 69 74 00. A shorter string without padding runs into "Engineering" at 0x10003ef0; a longer one overwrites it.

The serial capture is garbage on macOS

Reading /dev/cu.usbmodem* with a bare read() returns garbage. Set raw termios at 115200 first: clear canonical/echo flags, set CLOCAL|CREAD, and B115200 on input and output. screen /dev/cu.usbmodem* 115200 does all of this for you; a script must call tcsetattr itself. Once set, the capture reads clean FAV_NUM: 42 lines.

It worked for a second, then stopped (Binary Ninja's view desyncs)

This is the most common failure, and it has one main cause: driving the core from the OpenOCD command port while Binary Ninja is connected.

If you send reset run from the port while attached, the core resets, runs, and halts at your breakpoint — but Binary Ninja never receives the stop event. Its sidebar keeps showing the previous location, so Step and Resume act on a stale PC and appear to do nothing.
If the OpenOCD process dies (or you restart it) while attached, Binary Ninja keeps believing it is connected: the sidebar stays, but the menu shows Pause enabled and Resume/Step disabled because Binary Ninja last saw the target running.

Recovery: Detach, then reconnect. If Detach does nothing (the connection is already dead), restart Binary Ninja — its menu still shows a session that no longer exists.

Prevention:

Stop at main with BP_ADDR on a fresh server start, not with reset run while attached.
For loop addresses, set the breakpoint in the GUI and click Resume. Let Binary Ninja be the thing that starts the core.
If you must reset, Detach first, reset run, then reconnect.
Never leave a breakpoint on the PC you are about to step or resume from.

The target "blows past" `main` and stops at `0x10003ab4` instead

0x10003ab4 is inside stdio_uart_out_flush:

10003ab0: 4b02       ldr  r3, [pc, #8]  @ (10003abc <stdio_uart_out_flush+0xc>)
10003ab2: 681a       ldr  r2, [r3]
10003ab4: 6993       ldr  r3, [r2, #24] @ the core sits here while the UART drains
10003ab6: 071b       lsls  r3, r3, #28
10003ab8: d4fc       bmi.n 10003ab4 <stdio_uart_out_flush+0x4>
10003aba: 4770       bx lr
10003abc: 2000086c  .word 0x2000086c

That is the UART transmit-FIFO drain loop inside printf, so the core is running main's loop and simply spends nearly all its time there. The breakpoint at main did not fire because main's entry runs exactly once per reset. If you arm the breakpoint after the reset, or set it while the target is already running and just resume, the core is already past main and will never re-execute it. Either arm the breakpoint before resetting, or break inside the loop at 0x10000292, which fires every iteration.

0x10003ab4 is not a function. It is one instruction inside stdio_uart_out_flush, which starts at 0x10003ab0. If Binary Ninja has created a function at 0x10003ab4 (for example because the debugger stopped at that PC), the decompiler shows garbage. Delete that bogus function (right-click it -> Delete Function, or put the cursor on it and press U to undefine) and reanalyze. The real function is stdio_uart_out_flush at 0x10003ab0.

The console floods with `Failed to read memory at 0xf0000000`

Core1 is exposed. The scripts must run with USE_CORE=0. Stop the server, confirm only core0 is reported, restart, then restart Binary Ninja.

`Connect to Remote Process` is greyed out and Pause does nothing

Binary Ninja is in a stale session, usually because the debug server restarted while attached. Quit and reopen Binary Ninja (or the .bndb) and connect again.

The decompiler still shows the old value after patching

Right-click the function and choose Reanalyze.

Fallback: do the dynamic steps with GDB (macOS 27)

If Binary Ninja's debugger crashes on attach on macOS 27 (see Troubleshooting), you can still do the live hack with the ARM GDB from the toolchain, against the same OpenOCD server. The addresses and register values are identical to the GUI steps.

Start the debug server (Step 9), then in a new terminal:

arm-none-eabi-gdb

At the (gdb) prompt:

set architecture armv8-m.main
target extended-remote :3333
hbreak *0x10000292
continue

Do not run monitor reset run before hbreak. 0x10000292 is inside main's loop, so the breakpoint fires on the next iteration with no reset. If you reset first, the core runs main and you will not catch it.

GDB stops at the printf call. Confirm the value, change it, and let it run:

info registers pc r1  # pc = 0x10000292, r1 = 0x2a
set $r1 = 0x2b
stepi
continue

The serial monitor prints FAV_NUM: 43 for the iteration you changed — the same temporary live hack as editing r1 in the Binary Ninja Registers widget. When you are done, press Ctrl-C, then detach and quit.

If you specifically want to stop at main (0x10000234), remember its entry runs only once per reset, so the breakpoint must be armed before the reset:

monitor reset halt
hbreak *0x10000234
continue

If you instead set it while the target is running and just continue, you will "blow past" main and catch the core inside printf — in this build at 0x10003ab4, the stdio_uart_out_flush UART-drain loop.

hbreak sets a hardware breakpoint, which is required for read-only flash. It works from plain GDB because GDB sends the 2-byte length the Cortex-M33 comparators need. Binary Ninja's GDB MI adapter goes through the same GDB, so its GUI breakpoints work too; the old GDB RSP adapter was the one that sent a 1-byte length and could not set breakpoints here.

Glossary

Term	Definition
AAPCS	ARM Architecture Procedure Call Standard — `r0`-`r3` for the first four arguments, `r0` for the return value
`.bss`	Section for uninitialized (or zero-initialized) static/global variables; zeroed by startup code
`const`	A source-level "read-only" qualifier; the compiler may still inline it as an immediate
`.data`	Section for initialized static/global variables; copied from flash to SRAM at boot
`#define`	Preprocessor text replacement performed before compilation; consumed by the compiler as a literal
`.elf`	Linked image with the symbol table; the ground truth for addresses and names
`imm8`	The low 8 bits of a `movw` immediate, stored in the third byte of the 32-bit instruction
Immediate value	A constant embedded directly in an instruction, not fetched from memory
I2C	Inter-Integrated Circuit — a two-wire (SDA/SCL) serial bus; open-drain, needs pull-ups
Literal pool	A block of 32-bit constants that Thumb-2 code reaches with PC-relative `ldr`
`movs`	16-bit Thumb move that loads an 8-bit immediate (0-255)
`movw`	32-bit Thumb-2 "move wide" that loads any 16-bit immediate (0-65535)
Open-drain	An output that can only pull a line LOW, not drive it HIGH; pull-ups restore HIGH
PCF8574	The I2C I/O expander on a typical 1602 LCD backpack; commonly at `0x27`
`.rodata`	Read-only section for constants and string literals; stays in flash
SCL / SDA	I2C Serial Clock and Serial Data lines
Struct	A user-defined type that groups related variables; the SDK uses one per I2C controller
Thumb bit	Bit 0 of a Cortex-M function pointer; selects Thumb instruction mode
`typedef`	Creates an alias for a type (for example `typedef struct i2c_inst i2c_inst_t`)
UF2	USB Flashing Format — the file format the Pico 2 bootloader accepts
Vector table	The first words of flash: initial stack pointer and exception vectors

Remember: the ELF tells you what every address is, and the .bin is what you actually patch. Prove the behavior dynamically, read r1 at the printf call, resolve the names from the ELF (including the lcd_1602.c symbols), then patch the bytes — 0x2a -> 0x2b, 0x39 -> 0x40, and the eight-byte LCD string — and flash.

84 KiB Raw Blame History

Week 7-BN: Binary Ninja Personal — Read, Hack, and Patch Constants and a 1602 LCD String (Raw .bin)

What You'll Learn This Week

How This Guide Works

Part 1: Build, Flash, and Get the Symbol Map

Step 1: Install the toolchain

Step 2: Verify your tools are the right architecture (do not skip this)

Step 3: Build the project with Release

Step 4: Dump the ELF symbol map

Step 5: Flash and confirm the output

Part 2: Load the Raw .bin into Binary Ninja

Step 6: Bring the raw .bin into Binary Ninja

Step 7: Save it as a Binary Ninja database (.bndb)

Step 8: The views you will use

Part 3: Dynamic — Break at the printf Call and Hack Live

Step 9: Start OpenOCD as a live debug server

Step 10: Connect Binary Ninja to the GDB server

Step 11: Find main without relying on its address

Step 12: Set a hardware breakpoint in the GUI

Where you can stop

Set the loop breakpoint in the GUI

Stepping

Step 13: HACK IT LIVE — change the printed FAV_NUM

Step 13b: HACK THE LCD STRING LIVE — change "Reverse" to "Exploit" (optional)

Step 14: Why the hack reverts (and why we patch next)

Step 15: Kill the debugger and OpenOCD

Part 4: Static — Resolve the Functions in Binary Ninja and Patch

Step 16: Resolve the functions in the Binary Ninja GUI

How to resolve a function in Binary Ninja (Y)

Worked example: main

Worked example: i2c_init

Worked example: lcd_i2c_init

Worked example: lcd_set_cursor

Worked example: lcd_puts

Worked example: gpio_set_function

Worked example: gpio_set_pulls

Worked example: __wrap_printf

Worked example: stdio_init_all

Step 17: Read main in the decompiler

Step 18: Patch 1 — change FAV_NUM from 42 to 43

Step 18b: Patch 2 — change OTHER_FAV_NUM from 1337 to 1344

Step 18c: Patch 3 — change the LCD text from "Reverse" to "Exploit"

Step 19: Export the patched .bin

Step 20: Convert to UF2

Step 21: Flash and verify

Cheatsheet

Binary Ninja GUI actions

OpenOCD server and reset

Every address and byte we changed

The I2C/LCD memory map

Raw image facts

Troubleshooting

Binary Ninja hangs or crashes when you connect (macOS 27)

The GUI refuses to set a breakpoint (GDB RSP adapter only)

GDB MI hangs when you connect (a breakpoint already existed)

Step Into / Step Over does nothing (PC never moves)

zsh: bad CPU type in executable: cmake

My addresses do not match this guide

A breakpoint never fires

I edit r1 (or another register) and it reverts

The LCD string hack does nothing

The compiler did not keep const in .rodata

The movw patch did not take

The LCD shows garbage after patching

The serial capture is garbage on macOS

It worked for a second, then stopped (Binary Ninja's view desyncs)

The target "blows past" main and stops at 0x10003ab4 instead

The console floods with Failed to read memory at 0xf0000000

Connect to Remote Process is greyed out and Pause does nothing

The decompiler still shows the old value after patching

Fallback: do the dynamic steps with GDB (macOS 27)

Glossary

84 KiB

Raw Blame History

Week 7-BN: Binary Ninja Personal — Read, Hack, and Patch Constants and a 1602 LCD String (Raw `.bin`)

Step 3: Build the project with `Release`

Part 2: Load the Raw `.bin` into Binary Ninja

Step 6: Bring the raw `.bin` into Binary Ninja

Step 7: Save it as a Binary Ninja database (`.bndb`)

Part 3: Dynamic — Break at the `printf` Call and Hack Live

Step 11: Find `main` without relying on its address

Step 13: HACK IT LIVE — change the printed `FAV_NUM`

Step 13b: HACK THE LCD STRING LIVE — change `"Reverse"` to `"Exploit"` (optional)

How to resolve a function in Binary Ninja (`Y`)

Worked example: `main`

Worked example: `i2c_init`

Worked example: `lcd_i2c_init`

Worked example: `lcd_set_cursor`

Worked example: `lcd_puts`

Worked example: `gpio_set_function`

Worked example: `gpio_set_pulls`

Worked example: `__wrap_printf`

Worked example: `stdio_init_all`

Step 17: Read `main` in the decompiler

Step 18: Patch 1 — change `FAV_NUM` from 42 to 43

Step 18b: Patch 2 — change `OTHER_FAV_NUM` from 1337 to 1344

Step 18c: Patch 3 — change the LCD text from `"Reverse"` to `"Exploit"`

Step 19: Export the patched `.bin`

`zsh: bad CPU type in executable: cmake`

I edit `r1` (or another register) and it reverts

The compiler did not keep `const` in `.rodata`

The `movw` patch did not take

The target "blows past" `main` and stops at `0x10003ab4` instead

The console floods with `Failed to read memory at 0xf0000000`

`Connect to Remote Process` is greyed out and Pause does nothing