Links
Usage
This repo contains the merged weights: a standalone transformers model. Load it directly with AutoModelForCausalLM; PEFT is not required.
System prompt
The system prompt is optional, but prefer the canonical one below. It carried most of training, and it's the only variant the eval numbers on this card were measured under; the alternatives are trained but not separately scored.
Most training examples used the canonical prompt; the rest were split between paraphrases of it and no system prompt at all. So a paraphrase works, and the user message alone is usually enough to trigger the task.
You are a binary code generator. Given a description of a program, output the complete binary as a lowercase hex string with no spaces, newlines, or other formatting. Output only the hex string and nothing else.
Generating a binary
from transformers import AutoModelForCausalLM, AutoProcessor model = AutoModelForCausalLM.from_pretrained("matthewhaynesonline/gemma-4-E2B-it-crap")processor = AutoProcessor.from_pretrained("matthewhaynesonline/gemma-4-E2B-it-crap") messages = [ {"role": "system", "content": "You are a binary code generator. Given a description of a program, output the complete binary as a lowercase hex string with no spaces, newlines, or other formatting. Output only the hex string and nothing else."}, {"role": "user", "content": "Generate a Linux x86_64 binary that prints 'hello world'."},]inputs = processor.apply_chat_template( messages, add_generation_prompt=True, tokenize=True, return_tensors="pt").to(model.device) out = model.generate(**inputs, max_new_tokens=2048, do_sample=False)hex_str = processor.decode(out[0][inputs["input_ids"].shape[-1]:], skip_special_tokens=True)print(hex_str)
Saving and running the output
The model emits the binary as a lowercase hex string. Decode it to raw bytes, write it to a file, and set the executable bit (stdlib only):
import re, subprocessfrom pathlib import Path # Strip any whitespace, then decode the hex to raw bytesbinary = bytes.fromhex(re.sub(r"\s+", "", hex_str)) path = Path("crap.out")path.write_bytes(binary)path.chmod(path.stat().st_mode | 0o111) # add the executable bit (chmod +x) # Linux x86_64: run it directly and inspect the resultresult = subprocess.run([f"./{path}"], capture_output=True)print("stdout: ", result.stdout.decode(errors="replace"))print("exit code: ", result.returncode)
A Linux binary runs as soon as the executable bit is set.
Training details
Table with columns: Field, Value| Field | Value |
|---|
| Base model | google/gemma-4-E2B-it |
| LoRA rank | 16 |
| LoRA alpha | 32 |
| LoRA target modules | q/k/v/o/gate/up/down_proj (text decoder only) |
| Trainable parameters | 24,158,208 |
Training environment
Recorded at train time (not at push time) by training_metadata.json.
Table with columns: Field, Value| Field | Value |
|---|
| Hardware | NVIDIA GeForce RTX 5090 |
| Device | cuda |
| Precision | bf16 |
| Packing | False |
| Attention impl | sdpa |
| Trained at | 2026-06-14T20:10:15 |
Library versions
Table with columns: Library, Version| Library | Version |
|---|
| torch | 2.12.0 |
| transformers | 5.9.0 |
| trl | 1.5.1 |
| peft | 0.19.1 |
| accelerate | 1.13.0 |
Eval results
The evaluation is execution based with no partial credit. An example counts as passed only if the emitted hex decodes, the bytes parse as a structurally valid ELF and the binary runs with the exact expected stdout and exit code. (The stdout comparison strips a single trailing newline from both sides and nothing else; stray NUL bytes still fail).
The base model scores ~0/23 on the same harness.
Training progression
Scored on the split above every 50 steps, the unmerged adapter reaches its peak of 20/23 (87.0%) by step 300 and holds it across steps 450 - 550, while training loss falls smoothly throughout (token loss is not the eval metric). What you download is the merged model, and it scores 20/23 (87.0%).
The full per-step progression is in Appendix B of the paper.
Known limitations
A compiler computes every offset and length deterministically. CRAP
approximates them, and these are the places the approximation shows.
- Output carries a trailing newline. Generated binaries print the requested
string followed by
\n (the training convention). Account for it when
comparing output against an expected string.
- Write length miscounting is the main failure mode. For arbitrary strings
the
write length field can be wrong in either direction. Over counting reads
past the payload and appends stray NUL bytes (visible when the output is
piped, not on a terminal); under counting drops the trailing newline. Short
strings are reliable; the error grows with length and novelty.
- Repeated characters make the byte errors worse. When a target string
repeats a character (the doubled
d in daddy, the oo in gobbledygook)
the model is likelier to scramble the payload: drop a byte, swap two or
duplicate one. It aggravates the write length and synthesis errors above
rather than being a separate failure. Treat repeated characters and other
rare byte patterns as lower confidence.
- Exit code immediates can be off. Decimal to hex immediate encoding is a
persistent failure in the published checkpoint:
exit(223) exits with 222.
It survives to the end of training rather than being a mid run artifact, and
it's what the exit code half of the eval exists to measure.