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Use WasmEdge Library

When programming with WasmEdge C API, developers should include the required headers and link with the WasmEdge Library. Besides install WasmEdge with the WasmEdge shared library, developers can also build WasmEdge to generate the WasmEdge static library.

Assume the example test.c:

#include <stdio.h>
#include <wasmedge/wasmedge.h>

/* Host function body definition. */
WasmEdge_Result Add(void *Data,
                    const WasmEdge_CallingFrameContext *CallFrameCxt,
                    const WasmEdge_Value *In, WasmEdge_Value *Out) {
  int32_t Val1 = WasmEdge_ValueGetI32(In[0]);
  int32_t Val2 = WasmEdge_ValueGetI32(In[1]);
  printf("Host function \"Add\": %d + %d\n", Val1, Val2);
  Out[0] = WasmEdge_ValueGenI32(Val1 + Val2);
  return WasmEdge_Result_Success;
}

int main() {
  /* Create the VM context. */
  WasmEdge_VMContext *VMCxt = WasmEdge_VMCreate(NULL, NULL);

  /* The WASM module buffer. */
  uint8_t WASM[] = {/* WASM header */
                    0x00, 0x61, 0x73, 0x6D, 0x01, 0x00, 0x00, 0x00,
                    /* Type section */
                    0x01, 0x07, 0x01,
                    /* function type {i32, i32} -> {i32} */
                    0x60, 0x02, 0x7F, 0x7F, 0x01, 0x7F,
                    /* Import section */
                    0x02, 0x13, 0x01,
                    /* module name: "extern" */
                    0x06, 0x65, 0x78, 0x74, 0x65, 0x72, 0x6E,
                    /* extern name: "func-add" */
                    0x08, 0x66, 0x75, 0x6E, 0x63, 0x2D, 0x61, 0x64, 0x64,
                    /* import desc: func 0 */
                    0x00, 0x00,
                    /* Function section */
                    0x03, 0x02, 0x01, 0x00,
                    /* Export section */
                    0x07, 0x0A, 0x01,
                    /* export name: "addTwo" */
                    0x06, 0x61, 0x64, 0x64, 0x54, 0x77, 0x6F,
                    /* export desc: func 0 */
                    0x00, 0x01,
                    /* Code section */
                    0x0A, 0x0A, 0x01,
                    /* code body */
                    0x08, 0x00, 0x20, 0x00, 0x20, 0x01, 0x10, 0x00, 0x0B};

  /* Create the module instance. */
  WasmEdge_String ExportName = WasmEdge_StringCreateByCString("extern");
  WasmEdge_ModuleInstanceContext *HostModCxt =
      WasmEdge_ModuleInstanceCreate(ExportName);
  enum WasmEdge_ValType ParamList[2] = {WasmEdge_ValType_I32,
                                        WasmEdge_ValType_I32};
  enum WasmEdge_ValType ReturnList[1] = {WasmEdge_ValType_I32};
  WasmEdge_FunctionTypeContext *HostFType =
      WasmEdge_FunctionTypeCreate(ParamList, 2, ReturnList, 1);
  WasmEdge_FunctionInstanceContext *HostFunc =
      WasmEdge_FunctionInstanceCreate(HostFType, Add, NULL, 0);
  WasmEdge_FunctionTypeDelete(HostFType);
  WasmEdge_String HostFuncName = WasmEdge_StringCreateByCString("func-add");
  WasmEdge_ModuleInstanceAddFunction(HostModCxt, HostFuncName, HostFunc);
  WasmEdge_StringDelete(HostFuncName);

  WasmEdge_VMRegisterModuleFromImport(VMCxt, HostModCxt);

  /* The parameters and returns arrays. */
  WasmEdge_Value Params[2] = {WasmEdge_ValueGenI32(1234),
                              WasmEdge_ValueGenI32(5678)};
  WasmEdge_Value Returns[1];
  /* Function name. */
  WasmEdge_String FuncName = WasmEdge_StringCreateByCString("addTwo");
  /* Run the WASM function from file. */
  WasmEdge_Result Res = WasmEdge_VMRunWasmFromBuffer(
      VMCxt, WASM, sizeof(WASM), FuncName, Params, 2, Returns, 1);

  if (WasmEdge_ResultOK(Res)) {
    printf("Get the result: %d\n", WasmEdge_ValueGetI32(Returns[0]));
  } else {
    printf("Error message: %s\n", WasmEdge_ResultGetMessage(Res));
  }

  /* Resources deallocations. */
  WasmEdge_VMDelete(VMCxt);
  WasmEdge_StringDelete(FuncName);
  WasmEdge_ModuleInstanceDelete(HostModCxt);
  return 0;
}

This example will execute a WASM, which calls into a host function to add 2 numbers.

To link the executable with the WasmEdge shared library is easy. Just compile the example file after installation of WasmEdge.

$ gcc test.c -lwasmedge -o test
$ ./test
Host function "Add": 1234 + 5678
Get the result: 6912

For preparing the WasmEdge static library, developers should build WasmEdge from source with the options:

# Recommend to use the `wasmedge/wasmedge:latest` docker image. This will provide the required packages.
# In the WasmEdge source directory
cmake -Bbuild -GNinja -DCMAKE_BUILD_TYPE=Release -DWASMEDGE_LINK_LLVM_STATIC=ON -DWASMEDGE_BUILD_SHARED_LIB=Off -DWASMEDGE_BUILD_STATIC_LIB=On -DWASMEDGE_LINK_TOOLS_STATIC=On -DWASMEDGE_BUILD_PLUGINS=Off
cmake --build build
cmake --install build

The cmake option -DWASMEDGE_LINK_LLVM_STATIC=ON will turn on the static library building, and the -DWASMEDGE_BUILD_SHARED_LIB=Off will turn off the shared library building.

After installation, developers can compile the example file:

# Note: only the Linux platforms need the `-lrt`. The MacOS platforms do not need this linker flag.
$ gcc test.c -lwasmedge -lrt -ldl -pthread -lm -lstdc++ -o test
$ ./test
Host function "Add": 1234 + 5678
Get the result: 6912