Run WebAssembly files like standard executable files on Linux, using Lucet

lucet-ondemand.md

The following instructions require Lucet, although they can be easily adapted to other WebAssembly runtimes.

Save the following script as /opt/lucet/bin/lucet-ondemand:

#! /bin/sh

wasm_file="$1"
if [ -n "$wasm_file" ]; then
  if od -x "$wasm_file" | head -n1 | grep -Fq '0000000 6100 6d73 0001'; then
    so_file="$(mktemp).so"
    trap "rm -f $so_file" EXIT
    "/opt/lucet/bin/lucetc-wasi" -o "$so_file" "$wasm_file" && \
      exec "/opt/lucet/bin/lucet-wasi" "$so_file"
  else
    echo "${wasm_file} is not a webassembly file" >&2
  fi
else
  echo "Usage: $0 <wasm file>" >&2
fi

Make it executable:

chmod +x /opt/lucet/bin/lucet-ondemand

Register WebAssembly files to be handled by that script:

sudo bash -c 'echo ":wasm:M::\x00\x61\x73\x6d\x01\x00::/opt/lucet/bin/lucet-ondemand:" > /proc/sys/fs/binfmt_misc/register'

Now, WebAssembly files can be executed directly (make sure that they have the executable bit set, though):

/tmp/example_hello.wasm

Hello world