# "native-lib" sample introduction

This sample demonstrates how to write required interfaces in native library, build it into a shared library and register the shared library to iwasm.

The native library should provide `get_native_lib` API for iwasm to return the native library info, including the module name, the native symbol list and the native symbol count, so that iwasm can use them to regiter the native library, for example:

```C
static int
foo_wrapper(wasm_exec_env_t *exec_env, int x, int y)
{
    return x + y;
}

#define REG_NATIVE_FUNC(func_name, signature) \
    { #func_name, func_name##_wrapper, signature, NULL }

static NativeSymbol native_symbols[] = {
    REG_NATIVE_FUNC(foo, "(ii)i")
};

uint32_t
get_native_lib(char **p_module_name, NativeSymbol **p_native_symbols)
{
    *p_module_name = "env";
    *p_native_symbols = native_symbols;
    return sizeof(native_symbols) / sizeof(NativeSymbol);
}
```

## Preparation

Please install WASI SDK, download the [wasi-sdk release](https://github.com/CraneStation/wasi-sdk/releases) and extract the archive to default path `/opt/wasi-sdk`.

## Build the sample

```bash
mkdir build
cd build
cmake ..
make
```

`iwasm`, one wasm module `test.wasm` and two shared libraries `libtest_add.so`, `libtest_sqrt.so`
will be generated.

## Run workload

```bash
cd build
./iwasm --native-lib=libtest_add.so --native-lib=libtest_sqrt.so wasm-app/test.wasm
```

The output is:

```bash
Hello World!
10 + 20 = 30
sqrt(10, 20) = 500
```