WebAssembly Micro Runtime

WebAssembly Micro Runtime (WAMR) is standalone WebAssembly (WASM) runtime with small footprint. It includes a few components:

• WebAssembly VM core
• WASM application programming API (code available, but compilation is depending on the app manager component)
• Dynamic WASM application management (Not available in github yet. It will be released soon)

Why should we use a WASM runtime out of browser? There are a few points which might be meaningful:

1. WASM is already the LLVM official backend target. That means WASM can run any programming languages which can be compiled to LLVM IR. It is a huge advantage comparing to those language bound runtimes like JS, Lua.
2. WASM is an open standard and the growing trend is so fast as it is supported by the whole web ecosystem
3. WASM is designed to be very friendly for compiling to native binary and gaining the native speed.
4. Potentially change the development practices. Imaging we can do both the WASM application development and validation in a browser, then just download the wasm binary code into the target device.
5. WASM can work without garbage collection. It can be designed to support execution determinics for the time sensitive requirement.

Features

• WASM interpreter (AOT is planned)
• Provide built-in Libc subset, support "side_module=1" EMCC compilation option
• Provide APIs for embedding runtime into production software
• Provide mechanism for exporting native APIs to WASM applications
• Support programming firmware apps in multi languages (C/C++/Java/Rust/Go/TypeScript etc.)
• App sandbox execution environment on embedded OS
• Pure asynchronized programming model
• Menu configuration for easy platform integration
• Support micro service and pub-sub event inter-app communication models
• Easy to extend to support remote FW application management from host or cloud

Architecture

The application manager component handles the packets that the platform recieved from external through any communication buses such as socket, serial port, PSI. A packet type can be either request, response or event. It will service the request with URI "/applet" and call the runtime glue layer interfaces for installing/uninstalling the application. For other URIs, it will filter the resource registeration table and router the request to internal queue of responsible application.

The WebAssembly runtime is the execution environment for WASM applications.

The messaging layer can suppor the API for WASM applications communicate to each other and also the host environment.

When Ahead of Time compilation is enabled, the WASM application can be either bytecode or compiled native binary.

Build WAMR Core

Please follow below instructions to build WAMR core on different platforms.

Linux

Firstly please install library dependencies of lib gcc. Use below installation commands for Ubuntu Linux:

sudo apt install lib32gcc-5-dev
sudo apt-get install g++-multilib

After installing dependencies, build the source code:

cd products/linux/
mkdir build
cd build
cmake ..
make

Zephyr

You need download Zephyr source code first and embeded WAMR into it.

git clone https://github.com/zephyrproject-rtos/zephyr.git
cd zephyr/samples/
cp -a <iwasm_dir>/products/zephyr/simple .
cd simple
ln -s <iwam_dir> iwasm
ln -s <shared_lib_dir> shared-lib
mkdir build && cd build
source ../../../zephyr-env.sh
cmake -GNinja -DBOARD=qemu_x86 ..
ninja

Build WASM app

A popular method to build out WASM binary is to use emcc. Assuming you are using Linux. Please install emcc from Emscripten EMSDK following below steps:

git clone https://github.com/emscripten-core/emsdk.git
emsdk install latest
emsdk activate latest

add ./emsdk_env.sh into path to ease future use, or source it everytime. Emscripten website provides other installtion method beyond Linux.

todo: user should copy the app-libs folder into project and include and build.

You can write a simple test.cas the first sample.

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

int main(int argc, char **argv)
{
  char *buf;

  printf("Hello world!\n");

  buf = malloc(1024);
  if (!buf) {
    printf("malloc buf failed\n");
    return -1;
  }

  printf("buf ptr: %p\n", buf);

  sprintf(buf, "%s", "1234\n");
  printf("buf: %s", buf);

  free(buf);
  return 0;
}

Use below emcc commmand to build the WASM C source code into WASM binary.

emcc -g -O3 *.c -s WASM=1 -s SIDE_MODULE=1 -s ASSERTIONS=1 -s STACK_OVERFLOW_CHECK=2 \
                -s TOTAL_MEMORY=65536 -s TOTAL_STACK=4096 -o test.wasm

You will get test.wasm which is the WASM app binary.

Run WASM app

Assume you are using Linux, the command to run the test.wasm is

cd iwasm/products/linux/bin
./iwasm test.wasm

You will get output:

Hello world!
buf ptr: 0x000101ac
buf: 1234

If you would like to run test app on Zephyr, we have embedded test sample into its OS image. You need to execute

ninja run

Embed WAMR into software production

WAMR can be built into a standalone executable which takes WASM application file name as input, and then execute it. To use it in the embedded environment, you should embed WAMR into your own software product. WASM provides a set of APIs for embedders code to load WASM module, instansiate module and invoke WASM function from native call.

A typical WAMR APIs usage is as below:

  wasm_module_t module;
  wasm_module_inst_t inst;
  wasm_function_inst_t func;
  wasm_exec_env_t env;
  wasm_runtime_init();
  module = wasm_runtime_load(buffer, size, err, err_size);
  inst = wasm_runtime_instantiate(module, 0, err, err_size);
  func = wasm_runtime_lookup_function(inst, "fib", "(i32i32");
  env = wasm_runtime_create_exec_env(stack_size);

  if (!wasm_runtime_call_wasm(inst, env, func, 1, argv_buf) ) {
          wasm_runtime_clear_exception(inst);
    }

  wasm_runtime_destory_exec_env(env);
  wasm_runtime_deinstantiate(inst);
  wasm_runtime_unload(module);
  wasm_runtime_destroy();

WASM application library

In general, there are 3 kinds of APIs for programming the WASM application:

• Built-in APIs: WAMR has already provided a minimal API set for developers.
• 3rd party APIs: Programmer can download include any 3rd party C source code, and added into their own WASM app source tree.
• Platform native APIs: The board vendors define these APIs during their making board firmware. They are provided WASM application to invoke like built-in and 3rd party APIs. In this way board vendors extend APIs which can make programmers develop more complicated WASM apps.

Built-in application library

Built-in APIs include Libc APIs, Base library, Extension library reference.

Libc APIs
It is the minimal Libc APIs like memory allocation and string copy etc. The header files is lib/app-libs/libc/lib-base.h. The API set is listed as below:

void *malloc(size_t size);
void *calloc(size_t n, size_t size);
void free(void *ptr);
int memcmp(const void *s1, const void *s2, size_t n);
void *memcpy(void *dest, const void *src, size_t n);
void *memmove(void *dest, const void *src, size_t n);
void *memset(void *s, int c, size_t n);
int putchar(int c);
int snprintf(char *str, size_t size, const char *format, ...);
int sprintf(char *str, const char *format, ...);
char *strchr(const char *s, int c);
int strcmp(const char *s1, const char *s2);
char *strcpy(char *dest, const char *src);
size_t strlen(const char *s);
int strncmp(const char * str1, const char * str2, size_t n);
char *strncpy(char *dest, const char *src, unsigned long n);

Base library
The basic support like communication, timers etc is already available. The header files is lib/app-libs/base/wasm-app.h, it includes request and response APIs, event pub/sub APIs and timer APIs. Please be noted that they may not work if you have no corresponding framework to work with them. The API set is listed as below:

typedef void(*request_handler_f)(request_t *) ;
typedef void(*response_handler_f)(response_t *, void *) ;

// Request APIs
bool api_register_resource_handler(const char *url, request_handler_f);
void api_send_request(request_t * request, response_handler_f response_handler, void * user_data);
void api_response_send(response_t *response);

// event AP
bool api_publish_event(const char *url,  int fmt, void *payload,  int payload_len);
bool api_subscribe_event(const char * url, request_handler_f handler);

struct user_timer;
typedef struct user_timer * user_timer_t;

// Timer APIs
user_timer_t api_timer_create(int interval, bool is_period, bool auto_start, void(*on_user_timer_update)(user_timer_t
));
void api_timer_cancel(user_timer_t timer);
void api_timer_restart(user_timer_t timer, int interval);

Library extension reference
Currently we provide the sensor APIs as one library extension sample. The header file lib/app-libs/extension/sensor/sensor.h, the API set is listed as below:

sensor_t sensor_open(const char* name, int index,
                                     void(*on_sensor_event)(sensor_t, attr_container_t *, void *),
                                     void *user_data);
bool sensor_config(sensor_t sensor, int interval, int bit_cfg, int delay);
bool sensor_config_with_attr_container(sensor_t sensor, attr_container_t *cfg);
bool sensor_close(sensor_t sensor);

The mechanism of exporting Native API to WASM application

The basic working flow for WASM application calling into the native API is described as following diagram.

WAMR provides the macro EXPORT_WASM_API to enable users to export native API to WASM application. WAMR implemented a base API for timer and messaging by using EXPORT_WASM_API. They can be reference point of extending your own library.

static NativeSymbol extended_native_symbol_defs[] = {
  EXPORT_WASM_API(wasm_register_resource),
  EXPORT_WASM_API(wasm_response_send),
  EXPORT_WASM_API(wasm_post_request),
  EXPORT_WASM_API(wasm_sub_event),
  EXPORT_WASM_API(wasm_create_timer),
  EXPORT_WASM_API(wasm_timer_set_interval),
  EXPORT_WASM_API(wasm_timer_cancel),
  EXPORT_WASM_API(wasm_timer_restart)
};

Security attention: The WebAssembly application is supposed to access its own memory space, the integrator should carefully design the native function to ensure the memory safe. The native API to be exporte to WASM application must follow the rules:

• Only use 32 bits number for parameters
• Don’t passing data structure pointer (do data serialization instead)
• Do the pointer address conversion in native API
• Don’t passing function pointer as callback

Below is a sample of library extension. All invoke across WASM world and native world must be serialized and de-serialized, and native world must do boundary check for every incoming address from WASM world.

Exporting native API steps

WAMR implemented a framework for developers to export APIs. The procedure to expose the platform APIs in three steps:

Step 1. Create a header file
Declare the APIs for WASM application source project to include.

Step 2. Create a source file
Export the platform APIs, for example in products/linux/ext-lib-export.c

#include "lib-export.h"

static NativeSymbol extended_native_symbol_defs[] =
{
};

#include "ext-lib-export.h"

Step 3. Register new APIs
Use macro EXPORT_WASM_API and EXPORT_WASM_API2 to add exported APIs into the array of extended_native_symbol_defs. The pre-defined MACRO EXPORT_WASM_API should be used to declare a function export:

#define EXPORT_WASM_API(symbol)  {#symbol, symbol}

Below code example shows how to extend the library to support customeized():

//lib-export-impl.c
void customized()
{
   // your code
}


// lib-export-dec.h
#ifndef _LIB_EXPORT_DEC_H_
#define _LIB_EXPORT_DEC_H_
#ifdef __cplusplus
extern "C" {
#endif

void customized();

#ifdef __cplusplus
}
#endif
#endif


// ext-lib-export.c
#include "lib-export.h"
#include "lib-export-dec.h"

static NativeSymbol extended_native_symbol_defs[] =
{
  EXPORT_WASM_API(customized)
};

#include "ext-lib-export.h"

Use extended library

In the application source project, it includes the WAMR built-in APIs header file and platform extension header files. Assume the board vendor extend the library which added a API called customized(). The WASM application would be like this:

#include <stdio.h>
#include "lib-export-dec.h" // provided by platform vendor

int main(int argc, char **argv)
{
  int I;
  char *buf = “abcd”;
  customized();                   // customized API provided by platform vendor
  return i;
}

Comming soon...

We are preparing the open source for application manager and related cool samples like inter-application communication, application life cycle management, 2D graphic demo and more. You will get updated soon.

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