This is the deep part. UF2 is designed for open hardware. Adafruit, SparkFun, and Raspberry Pi publish their UF2 files openly. Decompiling them is an act of learning.
However, if someone ships a proprietary binary in a UF2 file, the format doesn't magically grant IP protection. It is merely a container. Building a decompiler democratizes the inspection of what is running on your hardware.
If you bought a device, you own the silicon. A UF2 decompiler is just a flashlight in a dark room.
Below is a minimal but complete UF2 decompiler.
#!/usr/bin/env python3 # uf2_decompile.pyimport struct import sys import os
UF2_MAGIC_START0 = 0x0A324655 UF2_MAGIC_START1 = 0x9E5D5157 UF2_MAGIC_END = 0x0AB16F30 uf2 decompiler
def parse_uf2(uf2_path): blocks = [] with open(uf2_path, 'rb') as f: while True: block = f.read(512) if len(block) < 512: break magic0, magic1 = struct.unpack('<II', block[0:8]) if magic0 != UF2_MAGIC_START0 or magic1 != UF2_MAGIC_START1: continue # skip invalid padding flags, addr, psize, block_no, num_blocks, family = struct.unpack('<IIIIII', block[8:32]) magic_end = struct.unpack('<I', block[508:512])[0] if magic_end != UF2_MAGIC_END: continue data = block[32:32+psize] blocks.append( 'addr': addr, 'data': data, 'block_no': block_no, 'num_blocks': num_blocks, 'family': family ) return blocks
def reassemble_binary(blocks): if not blocks: return b'' blocks.sort(key=lambda b: b['block_no']) # Determine min and max address min_addr = min(b['addr'] for b in blocks) max_addr = max(b['addr'] + len(b['data']) for b in blocks) bin_size = max_addr - min_addr firmware = bytearray(b'\xFF' * bin_size) for b in blocks: offset = b['addr'] - min_addr firmware[offset:offset+len(b['data'])] = b['data'] return firmware, min_addr
def main(): if len(sys.argv) < 2: print(f"Usage: sys.argv[0] firmware.uf2 [output.bin]") sys.exit(1) uf2_file = sys.argv[1] out_file = sys.argv[2] if len(sys.argv) > 2 else uf2_file.replace('.uf2', '.bin') blocks = parse_uf2(uf2_file) if not blocks: print("No valid UF2 blocks found.") sys.exit(1) print(f"Found len(blocks) blocks, family ID = 0xblocks[0]['family']:08X") firmware, base_addr = reassemble_binary(blocks) with open(out_file, 'wb') as f: f.write(firmware) print(f"Reassembled len(firmware) bytes -> out_file (base 0xbase_addr:08X)")
if name == 'main': main()
Compilation discards information:
| Tool | Purpose |
|------|---------|
| uf2conv.py | Convert UF2 ↔ bin / hex |
| arm-none-eabi-objdump | Disassemble ARM binary |
| Ghidra | Decompiler to C‑like pseudocode |
| radare2 / Cutter | Interactive disassembly + decompilation |
| picotool | Inspect UF2 on RP2040 hardware |
If you’ve worked with microcontroller boards like the Raspberry Pi Pico, Adafruit Feather, or Arduino Nano RP2040 Connect, you’ve likely encountered UF2 files. These are the .uf2 files you drag‑and‑drop onto a USB drive that appears when the board is in bootloader mode.
A common question from curious developers and reverse engineers is:
“Is there a UF2 decompiler to get back my original source code?” This is the deep part
The short answer is no, not in the way you’re hoping. Let’s break down why – and what you can actually do with a UF2 file.
The biggest loss in the UF2 "compilation" process is symbol stripping. The source code had void i2c_init(uint32_t baud). The UF2 file has 0x08001234.
A modern decompiler (Ghidra, IDA, Binary Ninja) handles this via signature matching. We can plug their headless analyzers into our UF2 pipeline.
Instead of building a decompiler from scratch, the pragmatic engineer builds a wrapper:
