QRception

A QR code generator that can generate itself

Created using the third edition of the QR ISO Standard (ISO/IEC 18004)

This QR code encodes the data of a QR code generating Linux x86-64 executable

Why

Why not?

How to use

Pass in data directly - ./qr_generator "<data>"

Pass in data through a file -./qr_generator "" "<file_path>"

Output is a bitmap file to stdout, pipe it where you see fit

Goals

• Decently featured QR code generator that fits within a QR Code (<= 2953 bytes)
• Features
  • Chooses smallest mode
  • Supports all error correction levels (Low, Medium, Quality, High)
  • Supports numeric, alphanumeric, and byte encoding
  • Supports all versions from 1-40
  • Produces a complete QR code with no errors
  • Fits into QR Code (less than 2953 bytes)

Project Status

There are two versions, the normal version is a typical QR code generator, the max version only produces version 40 (max size) QR codes

Features	Normal	Max Version
Chooses smallest version	✅	❌(Only version 40)
Supports all versions	✅	❌(Only version 40)
Supports all error correction levels	❌(Only Low)	❌(Only Low)
Supports all 3 encoding types	✅	✅
Produces QR Code w/ no errors	✅	✅
Fits into QR Code	❌ (4821 bytes)	✅ (2903 bytes)

Contributing

If you are changing the source code, make sure the tests run. Even if all 40 versions work successfully, use compare_qr_matrix.py at least once and make sure it returns 0.

If you are changing tests, just make sure they run properly on the existing executable. Update requirements.txt if you are adding any python libraries.

If you are changing the build process, just make sure that you update symbol_size.py if anything regarding the object file it works with changes. No real reason to to do this unless some new code breaks the build process.

Warning - The build process may break without any error messages. You will know this has happened if the behavior of qr_generator is different than build/debug/qr_generator.

Overview

Program

Not much to say here. One quirk is that main.c includes the other .c files directly since that led to a smaller binary size in my experience.

Final executable

Old methods for creating final binary

I have always used elf_template.asm as a starter and have only modified it slightly.

Source code -> MASM -> NASM

I used gcc to compile the source code into separate asm files. However, these could not be NASM, so I chose the closest alternative, MASM, and wrote a jank python script to attempt to convert between the two using the errors that I found, then append to the template. Eventually, the program was crashing and faulting in different ways and I realized this was not a reliable strategy.

Source code -> Object file -> NASM

I used gcc to compile the source code to an object file, then used objconv to disassemble the object file into mostly valid NASM. Then I had a python script clean it up and append it to the template.

This also just stopped working eventually.

1. Assembles util/elf_template.asm into a binary file
2. Compiles main.c into an object file, excluding builtins, startfiles, and the stdlib
3. Uses objcopy to only extract .text.startup (main), .text (all other functions), and .rodata (all constants) and sets their ALIGN to 1 so there are no wasted bytes
4. Links the filtered object file with util/linker.ld such that main is at the very start. Formats it as a binary, so the data is just directly put into the file, only address resolution occurs
5. Corrects the elf headers from the template to have the correctly calculated file size
6. Appends the binary file from linking to the elf headers to create an executable. Because of relative addressing all the addresses are still correct.

General repo structure

Repo root

build/ - Stores build artifacts

max_version_generator/ - Stores code for generator that only supports max version (version 40)

src/ - C source code

tests/ - Tests for both final QR validity and some intermediate steps

util/ - Stores utility files that help in the build

qr_generator - Final program

Makefile - Handles building both debug and final executables

Tests overview

segno is a python QR code generation library that is used as a validator for tests

zbarimg is a QR code scanning tool that is used as a scanner for tests

pillow is a python library for imaging and was used to parse bitmap files

test.py - Tests program with QR data of byte and alphanumeric data for all versions

compare_qr_matrix.py - Compares the QR Matrix generated between program and segno

compare_final_message.py - Run this with gdb. Compares the final QR message (data and error correction) between program and segno

compare_data_codewords.py - Run this with gdb. Compares the the data codewords between program and segno

Util overview

Tiny ELF Files is to credit for elf_template.asm

elf_template.asm - Template NASM file that is used as the start of the final elf64 executable

linker.ld - Linker that extracts only the necessary parts out of the object file compiled from the source code

symbol_size.py - Program that calculates and prints out the sizes of the different symbols in the source code for analysis