export_from_mod1_import_to_mod2.py: This code uses the Embedding API to "spins-up" a VM instance, instantiate a module, registers its exports, instantiates another module which imports from the first module, and invokes its exported function.

ewasmify.py is a simple tool for modifying a WebAssembly module's imports and exports to suit one's need.

metering.py: Injects a function call before each sequence of non-control-flow instructions, whose argument is the sum of costs of instructions in the sequence. Also injects helper functions, including the metering function which updates the cycle count and traps when a limit is exceeded.

To run, execute:

python3 metering fibonacci.wasm

Before metering (see fibonacci.wast for full module, and the original fibonacci function in C).

  (func (;0;) (type 0) (param i32) (result i32)
    (local i32 i32 i32)
    i32.const 1
    set_local 1
    block  ;; label = @1
      get_local 0
      i32.const 1
      i32.lt_s
      br_if 0 (;@1;)
      i32.const 1
      set_local 3
      i32.const 0
      set_local 2
      loop  ;; label = @2
        get_local 2
        get_local 3
        i32.add
        set_local 1
        get_local 3
        set_local 2
        get_local 1
        set_local 3
        get_local 0
        i32.const -1
        i32.add
        tee_local 0
        br_if 0 (;@2;)
      end
    end
    get_local 1)

After metering (see fibonacci_metered.wast for full module). Notice injected i32.const n call 1 where n is sum of costs of instructions until the next branch (each instruction costs one for this example). The metering function has index 1 in this example -- this index is handled automatically.

  (func (;0;) (type 0) (param i32) (result i32)
    (local i32 i32 i32)
    i32.const 3
    call 1
    i32.const 1
    set_local 1
    block  ;; label = @1
      i32.const 4
      call 1
      get_local 0
      i32.const 1
      i32.lt_s
      br_if 0 (;@1;)
      i32.const 5
      call 1
      i32.const 1
      set_local 3
      i32.const 0
      set_local 2
      loop  ;; label = @2
        i32.const 13
        call 1
        get_local 2
        get_local 3
        i32.add
        set_local 1
        get_local 3
        set_local 2
        get_local 1
        set_local 3
        get_local 0
        i32.const -1
        i32.add
        tee_local 0
        br_if 0 (;@2;)
        i32.const 1
        call 1
      end
      i32.const 1
      call 1
    end
    i32.const 2
    call 1
    get_local 1)   (;we count an implicit 'end' at the end;)

index.html: Demo to run any file generated by metering.py (e.g. fibonacci_metered.wasm). User specifies the .wasm file, function name, argument, and cycles limit. Because JavaScript doesn't support the i64 type and we want more than 2^32 cycles, we allow arbitrary precision integers imported and exported to and from the wasm module as a sequence of i32s, using helper functions in both JavaScript and injected by metering.py. A trap occurs if the cycles limit is exceeded! To run this demo, a server is needed to serve the .wasm file: execute python3 -m http.server in this directory and visit the given URL in the browser. Notice the 46th Fibonacci numbers overflows i32.

fibonacci...: Various versions of our demo fibonacci module. The _metered.wasm file is generated by metering.py. The .wast versions are generated by wasm2wast.