wasmrun

A small WebAssembly runtime in C.

日本語版

Limitations

This is a small integer-only runtime intended for learning and experiments.

• WebAssembly binary format v1 only
• Supported sections: type / function / export / code
• Only the i32 value type is supported
• Function results are limited to no result or one i32 result
• Supported instructions: i32.const, local get/set/tee, i32 arithmetic, comparisons, bit operations, shifts, call, return, drop, select, block, loop, resultless if/else, br, br_if
• Unsupported: import / memory / global / table / float / SIMD / multi-value / host functions
• This is not a strict validator; safely running malformed wasm is out of scope

build

make

usage

./wasmrun file.wasm [export] [i32 args...]

When export is omitted, main is called. If main is not found, _start is tried.

examples

Prebuilt .wasm files are included in examples, so you can run them directly.

./wasmrun examples/add.wasm add 40 2
# 42

./wasmrun examples/fact.wasm fact 5
# 120

./wasmrun examples/max.wasm max 3 -5
# 3

./wasmrun examples/max.wasm max -2 7
# 7

After editing a .wat file, regenerate the matching .wasm with wat2wasm.

wat2wasm is part of WABT (The WebAssembly Binary Toolkit). Install it if needed:

# macOS / Homebrew
brew install wabt

# Debian / Ubuntu
sudo apt install wabt

To build WABT from source:

git clone --recursive https://github.com/WebAssembly/wabt
cd wabt
mkdir build
cd build
cmake ..
cmake --build .

Regenerate individual examples:

wat2wasm examples/add.wat -o examples/add.wasm
wat2wasm examples/fact.wat -o examples/fact.wasm
wat2wasm examples/max.wat -o examples/max.wasm

Regenerate all examples:

for f in examples/*.wat; do wat2wasm "$f" -o "${f%.wat}.wasm"; done

embed

Include wasmrun.h from another C program. The implementation is header-only.

#include "wasmrun.h"

Wasmrun m;
wasmrun_init(&m);
wasmrun_load(&m, wasm_bytes, wasm_size);

int32_t args[] = { 40, 2 };
int32_t result;
int has_result;
wasmrun_call_export(&m, "add", args, &result, &has_result);

wasmrun_free(&m);

Compile:

cc -std=c99 -I. your_app.c -o your_app

Included C sample:

cc -std=c99 -Wall -Wextra -O2 examples/simple.c -o simple
./simple
# 42