riscv-online-asm

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riscv-online-asm

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RISC-V Online Assembler using Emscripten, Gnu Binutils

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# RISC-V Online Assembler

[![DOI](https://zenodo.org/badge/416230404.svg)](https://doi.org/10.5281/zenodo.21526002)
[![GitHub Release](https://img.shields.io/github/v/release/racerxdl/riscv-online-asm)](https://github.com/racerxdl/riscv-online-asm/releases/latest)
[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://raw.githubusercontent.com/racerxdl/riscv-online-asm/main/LICENSE)
[![Live demo](https://img.shields.io/badge/demo-live-50E3C2)](https://riscvasm.lucasteske.dev/)

Online assembler for RISC-V assembly (all variants that gas supports).

It uses a WebAssembly-compiled version of GNU as, objdump and objcopy to build the assembly.

Built for my RISC-V Emulator series (currently only in portuguese at [https://www.youtube.com/playlist?list=PLEP_M2UAh9q6_2Jtvs9fgOVlRgsruii2m](https://www.youtube.com/playlist?list=PLEP_M2UAh9q6_2Jtvs9fgOVlRgsruii2m))

### Building the WASM toolchain

Requires Docker with the [emscripten/emsdk](https://hub.docker.com/r/emscripten/emsdk) image.

```bash
./build.sh docker     # build via Docker (recommended)
./build.sh            # native build (requires emsdk in PATH)
./build.sh clean      # remove build artifacts
```

The script downloads binutils 2.46.0 source, cross-compiles gas, ld, objcopy and objdump to WebAssembly, and copies the resulting `.wasm` and `.js` glue files into `js/`.

### Legacy manual build

For reference, these are the raw steps the script automates:

```bash
wget https://ftp.gnu.org/gnu/binutils/binutils-2.46.0.tar.xz
tar -xf binutils-2.46.0.tar.xz
mkdir -p build bins
cd build
cat > assets.js <<'JS'
Module['FS'] = FS;
Module['callMain'] = callMain;
JS
emconfigure ../binutils-2.46.0/configure --disable-doc --build=x86 --host=wasm32 --target=riscv64-linux-gnu
emmake make -j4 CFLAGS="-DHAVE_PSIGNAL=1 -DELIDE_CODE -D__GNU_LIBRARY__ -O2 -Wno-unused-but-set-global" LDFLAGS="-s MODULARIZE=1 -s FORCE_FILESYSTEM=1 --post-js $(pwd)/assets.js"
emmake make install DESTDIR="$(pwd)/../bins"
cp binutils/objcopy.wasm binutils/objdump.wasm gas/as-new.wasm ld/ld-new.wasm ../js/
cp ../bins/usr/local/bin/riscv64-linux-gnu-as ../js/riscv64-linux-gnu-as.js
cp ../bins/usr/local/bin/riscv64-linux-gnu-objcopy ../js/riscv64-linux-gnu-objcopy.js
cp ../bins/usr/local/bin/riscv64-linux-gnu-objdump ../js/riscv64-linux-gnu-objdump.js
cp ../bins/usr/local/bin/riscv64-linux-gnu-ld ../js/riscv64-linux-gnu-ld.js
```

## Citation

If this tool helped your research or teaching, a citation is appreciated.

```bibtex
@misc{teske2026riscvasm,
  title={RISC-V Online Assembler},
  author={Teske, Lucas},
  year={2026},
  publisher={Zenodo},
  version={1.0.0},
  doi={10.5281/zenodo.21526003},
  url={https://doi.org/10.5281/zenodo.21526003},
  note={Browser-based RISC-V assembler powered by a WebAssembly build of GNU binutils. Live tool: https://riscvasm.lucasteske.dev/. Source: https://github.com/racerxdl/riscv-online-asm. ORCID: 0009-0002-8526-7662}
}
```

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