Decompiling firmware is rarely a flawless automated process. Several unique obstacles frequently arise:
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uf2conv.py your_firmware.uf2 --output extracted_firmware.bin uf2 decompiler
// 512 bytes total typedef struct uint32_t magicStart; // 0x0A324655 ('UF2\n') uint32_t flags; // 0x00002000 for families uint32_t targetAddr; // Where this block goes in Flash uint32_t payloadSize; // Usually 256 bytes uint32_t blockNo; // Sequence number uint32_t numBlocks; // Total blocks in file uint32_t familyID; // e.g., SAMD51, RP2040 uint8_t data[476]; // The actual firmware uint32_t magicEnd; // 0x0AB16F30 UF2_Block;
The following table breaks down the structure of a UF2 block:
A is a tool or process used to reverse-engineer firmware stored in the USB Flashing Format (UF2) . Because UF2 is a container format designed for easy flashing, "decompiling" typically involves two main steps: extracting the raw binary data from the UF2 container and then using a standard decompiler to analyze the resulting machine code. 1. Understanding the UF2 Format Decompiling firmware is rarely a flawless automated process
Note: In ARM architectures, an odd-numbered target address indicates execution in "Thumb Mode". The true alignment of the first instruction is found by clearing the lowest bit ( 0x10000104 ).
You will see functions like gpio_set_function , sleep_ms , and loops toggling a GPIO pin. You won't see digitalWrite(LED_BUILTIN, HIGH) , but you will see *(uint32_t*)(0xd0000000 + 0x24) = 1 .
Here is where the "decompiler" starts to look like a "recompiler." We map the binary to the chip's memory map. For an RP2040, Flash starts at 0x10000000 . Because UF2 is a container format designed for
Modern compilers optimize for size or speed by inlining functions, unrolling loops, and omitting frame pointers. This can make the resulting C-like pseudo-code look convoluted and vastly different from the original human-written source.
Since UF2 blocks are structured, you can write a simple script:
Once you have extracted the raw binary firmware, the "real" decompilation work begins. The choice of tools depends on the target architecture, which is almost always embedded-class processors like ARM Cortex-M (Thumb/Thumb-2), ESP32, or RISC-V.