wasm

GraalWasm

GraalWasm is a WebAssembly engine implemented in GraalVM. It can interpret and compile WebAssembly programs in the binary format, or be embedded into other programs.

We are working hard towards making GraalWasm more stable and more efficient, as well as to implement various WebAssembly extensions. Feedback, bug reports, and open-source contributions are welcome!

Building GraalWasm

Prerequisites

• Python 3 (required by mx)
• GIT (to download, update, and locate repositories)
• JDK 11+
• emscripten or wasi-sdk for translating C files

Building

To build GraalWasm, you need to follow the standard workflow for Graal projects. We summarize the basic steps below:

1. Create a new folder where your repositories mx and graal should be located:

$ mkdir graalvm
$ cd graalvm

2. Clone mx and add it to the PATH:

$ git clone https://github.com/graalvm/mx.git
$ export PATH=$PWD/mx:$PATH

3. Clone the graal repository and enter the wasm directory:

$ git clone https://github.com/oracle/graal.git
$ cd graal/wasm

4. Set JAVA_HOME:

$ export JAVA_HOME=[path to JDK]

5. Build the project:

$ mx --dy /truffle,/compiler build

These steps will build the wasm.jar file in the mxbuild/dists/jdk<version> directory, which contains the GraalWasm implementation.

Tests and Benchmarks

Test setup

The build command will also create the wasm-tests.jar, which contains the main test cases. To run these tests, the WebAssembly binary toolkit is needed.

1. Download the binary of the WebAssembly binary toolkit(wabt) and extract it.
2. Set WABT_DIR:

$ export WABT_DIR=[path to wabt]/bin

Run basic tests

After building GraalWasm, the WasmTestSuite can be run as follows:

$ mx --dy /truffle,/compiler --jdk jvmci unittest \
  -Dwasmtest.watToWasmExecutable=$WABT_DIR/wat2wasm \
  -Dwasmtest.testFilter="^.*\$" \
  WasmTestSuite

To run a specific test, you can specify a regex for its name with the testFilter flag. Here is an example command that runs all the tests that mention branch in their name:

$ mx --dy /truffle,/compiler --jdk jvmci unittest \
  -Dwasmtest.watToWasmExecutable=$WABT_DIR/wat2wasm \
  -Dwasmtest.testFilter="^.*branch.*\$" \
  WasmTestSuite

This command results in the following output:

--------------------------------------------------------------------------------
Running: BranchBlockSuite (4/16 tests - you have enabled filters)
--------------------------------------------------------------------------------
Using runtime: org.graalvm.compiler.truffle.runtime.hotspot.java.HotSpotTruffleRuntime@7b1d7fff
😍😍😍😍
Finished running: BranchBlockSuite
🍀 4/4 Wasm tests passed.

The WasmTestSuite is the aggregation of all basic tests.

Test setup for additional tests and benchmarks

The GraalWasm repository includes a set of additional tests and benchmarks that are written in C, and are not part of the default build. To compile these programs, you will need to install additional dependencies on your system.

To build these additional tests and benchmarks, you need to:

1. Install the Emscripten SDK. We currently test against Emscripten 1.39.13.

$ cd [preferred emsdk install location]

# Clone repository
$ git clone https://github.com/emscripten-core/emsdk.git

# Move to folder
$ cd emsdk

# Install sdk
$ ./emsdk install [version number]

# Activate sdk
$ ./emsdk activate [version number]

# Set up environment
$ source ./emsdk_env.sh

2. Set EMCC_DIR and GCC_DIR:

$ export EMCC_DIR=[path to emsdk]/upstream/emscripten
$ export GCC_DIR=[path to gcc (usually /usr/bin)]

3. Run emscripten-init:

$ cd grallvm/graal/wasm
$ mx emscripten-init ~/.emscripten [path to emsdk] --local

4. Build with additional dependencies:

$ mx --dy /truffle,/compiler build --all

This will build several additional JARs in mxbuild/dists/jdk<version>: wasm-testcases.jar and wasm-benchmarkcases.jar. These JAR files contain .wasm files that correspond to the tests and the benchmarks whose source code is in C.

Run additional tests

You can run the additional tests as follows:

$ mx --dy /truffle,/compiler --jdk jvmci unittest \
  -Dwasmtest.watToWasmExecutable=$WABT_DIR/wat2wasm \
  -Dwasmtest.testFilter="^.*\$" \
  CSuite

This will result in the following output:

--------------------------------------------------------------------------------
Running: CSuite (1 tests)
--------------------------------------------------------------------------------
Using runtime: org.graalvm.compiler.truffle.runtime.hotspot.java.HotSpotTruffleRuntime@368239c8
😍
Finished running: CSuite
🍀 1/1 Wasm tests passed.

We currently have the following extra test suites:

• CSuite -- set of programs written in the C language
• WatSuite -- set of programs written in textual WebAssembly

Run benchmarks

The GraalWasm project includes a custom JMH-based benchmark suite, which is capable of running WebAssembly benchmark programs. The benchmark programs consist of several special functions, most notably benchmarkRun, which runs the body of the benchmark. The benchmarks are kept in the src/com.oracle.truffle.wasm.benchcases MX project.

For the benchmarks to run NODE_DIR has to be set. You can use the node version that is part of Emscripten, for example:

$ export NODE_DIR=[path to emsdk]/node/14.15.5_64bit/bin

After building the additional benchmarks, as described in the last section, they can be executed as follows:

$ mx --dy /compiler benchmark wasm:WASM_BENCHMARKCASES -- \
  -Dwasmbench.benchmarkName=[benchmark-name] -- \
  CMicroBenchmarkSuite

In the previous command, replace [benchmark-name] with the particular benchmark name, for example, cdf. This runs the JMH wrapper for the test, and produces an output similar to the following:

# Warmup: 10 iterations, 10 s each
# Measurement: 10 iterations, 10 s each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Throughput, ops/time
# Benchmark: com.oracle.truffle.wasm.benchcases.bench.CBenchmarkSuite.run

# Run progress: 0.00% complete, ETA 00:03:20
# Fork: 1 of 1
# Warmup Iteration   1: 0.123 ops/s
# Warmup Iteration   2: 0.298 ops/s
# Warmup Iteration   3: 0.707 ops/s
...
Iteration   9: 0.723 ops/s
Iteration  10: 0.736 ops/s


Result "com.oracle.truffle.wasm.benchcases.bench.CBenchmarkSuite.run":
  0.725 ±(99.9%) 0.012 ops/s [Average]
  (min, avg, max) = (0.711, 0.725, 0.736), stdev = 0.008
  CI (99.9%): [0.714, 0.737] (assumes normal distribution)


# Run complete. Total time: 00:03:47

We currently have the following benchmark suites:

• CMicroBenchmarkSuite -- set of programs written in C
• WatBenchmarkSuite -- set of programs written in textual WebAssembly

Extracting the internal GraalWasm Memory Layout based on a given WebAssembly program

GraalWasm contains a tool for extracting the internal memory layout for a given WebAssembly application. This is useful for detecting the causes of memory overhead.

To execute the memory layout extractor, run:

$ mx --dy /compiler wasm-memory-layout -Djol.magicFieldOffset=true -- [wasm-file]

This prints the memory layout tree of the given file to the console. The application provides additional options:

• --warmup-iterations: to set the number of warmup iterations.
• --entry-point: to set the entry point of the application. This is used to perform linking
• --output: to extract the memory layout into a file instead of the console.

You can also pass all other options available in GraalWasm such as --wasm.Builtins=wasi_snapshot_preview1.

The resulting tree represents a recursive representation of the Objects alive in GraalWasm starting from the WasmContext. The output looks similar to this:

-context: 6598280 Byte [100%]
  -equivalenceClasses: 1320 Byte [0%]
    -table: 80 Byte [0%]
    -table[0]: 384 Byte [0%]
      -key: 72 Byte [0%]
        -paramTypes: 24 Byte [0%]
        -resultTypes: 24 Byte [0%]
      -next: 280 Byte [0%]
        -key: 64 Byte [0%]
          -paramTypes: 24 Byte [0%]
          -resultTypes: 16 Byte [0%]
        -next: 184 Byte [0%]
          -key: 56 Byte [0%]
            -paramTypes: 16 Byte [0%]
            -resultTypes: 16 Byte [0%]
          -next: 96 Byte [0%]
            -key: 64 Byte [0%]
              -paramTypes: 24 Byte [0%]
              -resultTypes: 16 Byte [0%]
    -table[2]: 208 Byte [0%]
      -key: 72 Byte [0%]
        -paramTypes: 24 Byte [0%]
        -resultTypes: 24 Byte [0%]
      -next: 104 Byte [0%]
...

The names represent the names of fields in classes. For example equivalenceClasses is a field in WasmContext. The values next to the names represent the absolute amount of memory in bytes while the number in brackets represent the relative contribution to the overall memory overhead. Names with indices represent array entries such as table[0].

Running WebAssembly programs using a launcher

For the latest GraalWasm release, see the GraalVM dev builds page. If downloading GraalWasm as a separate GraalVM component, you can download it as follows (replace JDK and GraalVM versions with appropriate values):

$ graalvm-ce-java8-21.2.0/bin/gu install --force -L wasm-installable-java8-linux-<version>.jar

This will install a launcher, which runs WebAssembly modules. For example, assuming that compiled the following C program with Emscripten:

#include <stdio.h>

int main() {
  int number = 1;
  int rows = 10;
  for (int i = 1; i <= rows; i++) {
    for (int j = 1; j <= i; j++) {
      printf("%d ", number);
      ++number;
    }
    printf(".\n");
  }
  return 0;
}

You can run the compiled WebAssembly binary as follows:

$ graalvm/bin/wasm --Builtins=memory,env:emscripten floyd.wasm

In this example, the flag --Builtins specifies built-in modules that the Emscripten toolchain assumes.

Embedding GraalWasm inside other programs

GraalWasm can be accessed programmatically with the Polyglot API, which allows embedding GraalWasm into user programs.

Here is a simple example of how to run a WebAssembly program using GraalWasm from a Java application:

import org.graalvm.polyglot.*;
import org.graalvm.polyglot.io.ByteSequence;

byte[]binary=readBytes("example.wasm"); // You need to load the .wasm contents into a byte array.
        Context.Builder contextBuilder=Context.newBuilder("wasm");
        Source.Builder sourceBuilder=Source.newBuilder("wasm",ByteSequence.create(binary),"example");
        Source source=sourceBuilder.build();
        Context context=contextBuilder.build();

        context.eval(source);

        Value mainFunction=context.getBindings("wasm").getMember("example").getMember("_main");
        mainFunction.execute();

For more polyglot-related examples, consult the documentation at the GraalVM website.

Compiling C files with the wasi-sdk

1. Download the wasi-sdk and unpack it.
2. Set WASI_SDK:

   $ export WASI_SDK=[path to wasi-sdk]

3. Compile the C files

   $ $WASI_SDK/bin/clang -O3 -o test.wasm test.c

   To export a specific function use the linker flag -Wl,--export="[function name]".
4. Most applications compiled with the wasi-sdk require WASI. To run a file with WASI enabled use the following command:

   $ graalvm/bin/wasm --Builtins=wasi_snapshot_preview1 test.wasm