Hello World

This chapter will take Hello World as an example to show how to compile a C program to WASM bytecode and run it in WasmEdge.

Prerequisites

Before we start, make sure you have installed the following software:

1. Install WasmEdge

2. Emscripten, a toolchain for compiling C/C++ to WebAssembly. Please refer to the emcc official repository for detailed instructions.

git clone --depth 1 https://github.com/emscripten-core/emsdk.git
cd emsdk
./emsdk install latest
./emsdk activate latest
source ./emsdk_env.sh

Example: Hello World

Compile the C code into Wasm

As the first step is always the "Hello World" program, given below is the C program implementation.

// hello.c

#include<stdio.h>
int main(int argc,char **argv){
  printf("Hello World!\n");
  return 0;
}

Save it in any file and then compile it to WebAssembly with emscripten.

emcc hello.c -o hello.wasm

note

Make sure you either supply -s STANDALONE_WASM flag or specify output as wasm -o your_file_name.wasm

Then run the wasm in wasmedge runtime.

$ wasmedge hello.wasm
Hello World

Run in WasmEdge

Run the compiled wasm with WasmEdge CLI, and you will get the hello world output.

$ wasmedge hello.wasm
Hello, world!

AoT mode

With WasmEdge's AoT compiler, you will get higher performance.

# Compile the wasm file with wasmedge aot compiler
$ wasmedgec hello.wasm hello.wasm
# Run the native binary with wasmedge
$ wasmedge hello.wasm

Example: Add function

We can also pass cmd arguments. For example, add function takes two arguments and prints their sum in this example.

// add.c

#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
  int a,b;
  if(argc==3){
    a = atoi(argv[1]);
    b = atoi(argv[2]);
    printf("%d\n",a+b);
  }
  return 0;
}

Again Compiling to wasm with emcc

emcc add.c -o add.wasm

Running the application in wasmedge runtime

$ wasmedge add.wasm 2 3
5

We can further improve performance by using wasmedge AOT compilation , this feature gives near native performance

$ wasmedgec add.wasm add_aot.wasm
$ wasmedge add_aot.wasm 4 9
13

Example: Fibonacci function

We can also structure our project in separate header and implementation files.

// fibonacci.h

int fib(int n);

// fibonacci.c

#include <stdio.h>
#include "fibonacci.h"

int fib(int n){
  int f1 = 0;
  int f2 = 1;
  if(n<=2){
    if(n==1) return f1;
    else return f2;
  }
  else
    for(int i=2; i<n; i++ ){
      int temp = f2;
      f2=f1+f2;
      f1=temp;
    }
  return f2;
}

// main.c

#include <stdio.h>
#include <stdlib.h>
#include "fibonacci.h"

int main(int argc, char *argv[])
{
  if (argc<2) {
    return 0;
  }
  int n = atoi(argv[1]);
  printf("%d",fib(n));
  return 0;
}

Compiling the program to wasm with emcc

emcc main.c fibonacci.c -o fib.wasm

Running in wasmedge runtime

$ wasmedge fib.wasm 6
5