Wasp is a C++ library designed to make it easy to work with WebAssembly modules. Unlike tools like wabt, it is designed to be used as a library.

It also includes the wasp tool, which has the following commands:

• wasp dump: Dump the contents of a WebAssembly module
• wasp callgraph: Generate a dot graph of the module's callgraph
• wasp cfg: Generate a dot graph of a function's control-flow graph
• wasp dfg: Generate a dot graph of a function's data-flow graph
• wasp validate: Validate a WebAssembly module
• wasp pattern: Find instruction sequence patterns
• wasp wat2wasm: Convert a Wasm text file to a Wasm binary file

You'll need CMake. You can then run CMake, the normal way:

$ mkdir build
$ cd build
$ cmake ..
$ cmake --build .

You'll need CMake. You'll also need Visual Studio (2019 or newer).

Note: Visual Studio 2017 and later come with CMake (and the Ninja build system) out of the box, and should be on your PATH if you open a Developer Command prompt. See https://aka.ms/cmake for more details.

You can run CMake from the command prompt, or use the CMake GUI tool. See Running CMake for more information.

When running from the commandline, create a new directory for the build artifacts, then run cmake from this directory:

> cd [build dir]
> cmake [wasp project root] -DCMAKE_BUILD_TYPE=[config] -DCMAKE_INSTALL_PREFIX=[install directory] -G [generator]

The [config] parameter should be a CMake build type, typically DEBUG or RELEASE.

The [generator] parameter should be the type of project you want to generate, for example "Visual Studio 16 2019". You can see the list of available generators by running cmake --help.

To build the project, you can use Visual Studio, or you can tell CMake to do it:

> cmake --build [wasp project root] --config [config] --target install

This will build and install to the installation directory you provided above.

So, for example, if you want to build the debug configuration on Visual Studio 2019:

> mkdir build
> cd build
> cmake .. -DCMAKE_BUILD_TYPE=DEBUG -DCMAKE_INSTALL_PREFIX=..\ -G "Visual Studio 16 2019"
> cmake --build . --config DEBUG --target install

Disassemble all functions in a module:

$ wasp dump -d mod.wasm

Display all sections in a module:

$ wasp dump -h mod.wasm

Display the contents of the "import" section:

$ wasp dump -j import -x mod.wasm

Write the callgraph as a DOT file to stdout.

$ wasp callgraph mod.wasm

Write the callgraph as a DOT file to file.dot.

$ wasp callgraph mod.wasm -o file.dot

You can use graphviz to convert the DOT file to an SVG:

$ dot -Tsvg file.dot -O

For example, the following wasm file:

(func $a call $b)
(func $b call $c call $d)
(func $c)
(func $d call $a call $b call $d)

Becomes this SVG:

Write the CFG of function 0 as a DOT file to stdout.

$ wasp cfg -f 0 mod.wasm

Write the CFG of function foo as a DOT file to file.dot.

$ wasp cfg -f foo mod.wasm -o file.dot

For example, the following wasm file:

(func $fac (param i64) (result i64)
  (if (result i64) (i64.eq (local.get 0) (i64.const 0))
    (then (i64.const 1))
    (else
      (i64.mul (local.get 0) (call 0 (i64.sub (local.get 0) (i64.const 1)))))))

Becomes this SVG:

Write the DFG of function 0 as a DOT file to stdout.

$ wasp dfg -f 0 mod.wasm

Write the DFG of function foo as a DOT file to file.dot.

$ wasp dfg -f foo mod.wasm -o file.dot

For example, the following wasm file:

(func $fac (param i64) (result i64)
  (if (result i64) (i64.eq (local.get 0) (i64.const 0))
    (then (i64.const 1))
    (else
      (i64.mul (local.get 0) (call 0 (i64.sub (local.get 0) (i64.const 1)))))))

Becomes this SVG:

Validate a module.

$ wasp validate mod.wasm

Validate multiple modules.

$ wasp validate mod1.wasm mod2.wasm mod3.wasm

Print the 10 most common instruction sequences.

$ wasp pattern mod.wasm -d 10

This produces results similar to those shown below. The columns are as follows:

1. How often the instruction sequence occurred
2. The instruction sequence length
3. The instruction sequence
4. A percentage, calculated as 100 * count * sequence length / total instructions.

71333: [2] [i32.const 0 global.set 10] 4.17%
37382: [2] [end end] 2.19%
34937: [2] [i32.const 1 i32.and] 2.04%
25099: [2] [block [] block []] 1.47%
21440: [2] [i32.and if []] 1.25%
20154: [2] [i32.eqz if []] 1.18%
19883: [3] [i32.const 1 i32.and if []] 1.75%
18643: [2] [return end] 1.09%
15857: [3] [block [] block [] block []] 1.39%
15314: [2] [end local.get 0] 0.90%
total instructions: 3417737

Convert test.wat to test.wasm.

$ wasp wat2wasm test.wat

Convert test.wat to something.wasm.

$ wasp wat2wasm test.wat -o something.wasm

Convert test.wat to test.wasm, but skip validation.

$ wasp wat2wasm test.wat --no-validate

Convert test.wat to test.wasm, and enable the SIMD feature.

$ wasp wat2wasm test.wat --enable-simd