1 /* 2 Example of instantiating of the WebAssembly module and invoking its exported 3 function. 4 5 You can build using cmake: 6 7 mkdir build && cd build && cmake .. && cmake --build . --target wasmtime-hello 8 */ 9 10 #include <assert.h> 11 #include <stdio.h> 12 #include <stdlib.h> 13 #include <wasm.h> 14 #include <wasmtime.h> 15 16 static void exit_with_error(const char *message, wasmtime_error_t *error, 17 wasm_trap_t *trap); 18 19 static wasm_trap_t *hello_callback(void *env, wasmtime_caller_t *caller, 20 const wasmtime_val_t *args, size_t nargs, 21 wasmtime_val_t *results, size_t nresults) { 22 printf("Calling back...\n"); 23 printf("> Hello World!\n"); 24 return NULL; 25 } 26 27 int main() { 28 int ret = 0; 29 // Set up our compilation context. Note that we could also work with a 30 // `wasm_config_t` here to configure what feature are enabled and various 31 // compilation settings. 32 printf("Initializing...\n"); 33 wasm_engine_t *engine = wasm_engine_new(); 34 assert(engine != NULL); 35 36 // With an engine we can create a *store* which is a long-lived group of wasm 37 // modules. Note that we allocate some custom data here to live in the store, 38 // but here we skip that and specify NULL. 39 wasmtime_store_t *store = wasmtime_store_new(engine, NULL, NULL); 40 assert(store != NULL); 41 wasmtime_context_t *context = wasmtime_store_context(store); 42 43 // Read our input file, which in this case is a wasm text file. 44 FILE *file = fopen("examples/hello.wat", "r"); 45 assert(file != NULL); 46 fseek(file, 0L, SEEK_END); 47 size_t file_size = ftell(file); 48 fseek(file, 0L, SEEK_SET); 49 wasm_byte_vec_t wat; 50 wasm_byte_vec_new_uninitialized(&wat, file_size); 51 if (fread(wat.data, file_size, 1, file) != 1) { 52 printf("> Error loading module!\n"); 53 return 1; 54 } 55 fclose(file); 56 57 // Parse the wat into the binary wasm format 58 wasm_byte_vec_t wasm; 59 wasmtime_error_t *error = wasmtime_wat2wasm(wat.data, wat.size, &wasm); 60 if (error != NULL) 61 exit_with_error("failed to parse wat", error, NULL); 62 wasm_byte_vec_delete(&wat); 63 64 // Now that we've got our binary webassembly we can compile our module. 65 printf("Compiling module...\n"); 66 wasmtime_module_t *module = NULL; 67 error = wasmtime_module_new(engine, (uint8_t *)wasm.data, wasm.size, &module); 68 wasm_byte_vec_delete(&wasm); 69 if (error != NULL) 70 exit_with_error("failed to compile module", error, NULL); 71 72 // Next up we need to create the function that the wasm module imports. Here 73 // we'll be hooking up a thunk function to the `hello_callback` native 74 // function above. Note that we can assign custom data, but we just use NULL 75 // for now). 76 printf("Creating callback...\n"); 77 wasm_functype_t *hello_ty = wasm_functype_new_0_0(); 78 wasmtime_func_t hello; 79 wasmtime_func_new(context, hello_ty, hello_callback, NULL, NULL, &hello); 80 81 // With our callback function we can now instantiate the compiled module, 82 // giving us an instance we can then execute exports from. Note that 83 // instantiation can trap due to execution of the `start` function, so we need 84 // to handle that here too. 85 printf("Instantiating module...\n"); 86 wasm_trap_t *trap = NULL; 87 wasmtime_instance_t instance; 88 wasmtime_extern_t import; 89 import.kind = WASMTIME_EXTERN_FUNC; 90 import.of.func = hello; 91 error = wasmtime_instance_new(context, module, &import, 1, &instance, &trap); 92 if (error != NULL || trap != NULL) 93 exit_with_error("failed to instantiate", error, trap); 94 95 // Lookup our `run` export function 96 printf("Extracting export...\n"); 97 wasmtime_extern_t run; 98 bool ok = wasmtime_instance_export_get(context, &instance, "run", 3, &run); 99 assert(ok); 100 assert(run.kind == WASMTIME_EXTERN_FUNC); 101 102 // And call it! 103 printf("Calling export...\n"); 104 error = wasmtime_func_call(context, &run.of.func, NULL, 0, NULL, 0, &trap); 105 if (error != NULL || trap != NULL) 106 exit_with_error("failed to call function", error, trap); 107 108 // Clean up after ourselves at this point 109 printf("All finished!\n"); 110 ret = 0; 111 112 wasmtime_module_delete(module); 113 wasmtime_store_delete(store); 114 wasm_engine_delete(engine); 115 return ret; 116 } 117 118 static void exit_with_error(const char *message, wasmtime_error_t *error, 119 wasm_trap_t *trap) { 120 fprintf(stderr, "error: %s\n", message); 121 wasm_byte_vec_t error_message; 122 if (error != NULL) { 123 wasmtime_error_message(error, &error_message); 124 wasmtime_error_delete(error); 125 } else { 126 wasm_trap_message(trap, &error_message); 127 wasm_trap_delete(trap); 128 } 129 fprintf(stderr, "%.*s\n", (int)error_message.size, error_message.data); 130 wasm_byte_vec_delete(&error_message); 131 exit(1); 132 } 133