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 (void)env; 23 (void)caller; 24 (void)args; 25 (void)nargs; 26 (void)results; 27 (void)nresults; 28 printf("Calling back...\n"); 29 printf("> Hello World!\n"); 30 return NULL; 31 } 32 33 int main() { 34 int ret = 0; 35 // Set up our compilation context. Note that we could also work with a 36 // `wasm_config_t` here to configure what feature are enabled and various 37 // compilation settings. 38 printf("Initializing...\n"); 39 wasm_engine_t *engine = wasm_engine_new(); 40 assert(engine != NULL); 41 42 // With an engine we can create a *store* which is a long-lived group of wasm 43 // modules. Note that we allocate some custom data here to live in the store, 44 // but here we skip that and specify NULL. 45 wasmtime_store_t *store = wasmtime_store_new(engine, NULL, NULL); 46 assert(store != NULL); 47 wasmtime_context_t *context = wasmtime_store_context(store); 48 49 // Read our input file, which in this case is a wasm text file. 50 FILE *file = fopen("examples/hello.wat", "r"); 51 assert(file != NULL); 52 fseek(file, 0L, SEEK_END); 53 size_t file_size = ftell(file); 54 fseek(file, 0L, SEEK_SET); 55 wasm_byte_vec_t wat; 56 wasm_byte_vec_new_uninitialized(&wat, file_size); 57 if (fread(wat.data, file_size, 1, file) != 1) { 58 printf("> Error loading module!\n"); 59 return 1; 60 } 61 fclose(file); 62 63 // Parse the wat into the binary wasm format 64 wasm_byte_vec_t wasm; 65 wasmtime_error_t *error = wasmtime_wat2wasm(wat.data, wat.size, &wasm); 66 if (error != NULL) 67 exit_with_error("failed to parse wat", error, NULL); 68 wasm_byte_vec_delete(&wat); 69 70 // Now that we've got our binary webassembly we can compile our module. 71 printf("Compiling module...\n"); 72 wasmtime_module_t *module = NULL; 73 error = wasmtime_module_new(engine, (uint8_t *)wasm.data, wasm.size, &module); 74 wasm_byte_vec_delete(&wasm); 75 if (error != NULL) 76 exit_with_error("failed to compile module", error, NULL); 77 78 // Next up we need to create the function that the wasm module imports. Here 79 // we'll be hooking up a thunk function to the `hello_callback` native 80 // function above. Note that we can assign custom data, but we just use NULL 81 // for now). 82 printf("Creating callback...\n"); 83 wasm_functype_t *hello_ty = wasm_functype_new_0_0(); 84 wasmtime_func_t hello; 85 wasmtime_func_new(context, hello_ty, hello_callback, NULL, NULL, &hello); 86 wasm_functype_delete(hello_ty); 87 88 // With our callback function we can now instantiate the compiled module, 89 // giving us an instance we can then execute exports from. Note that 90 // instantiation can trap due to execution of the `start` function, so we need 91 // to handle that here too. 92 printf("Instantiating module...\n"); 93 wasm_trap_t *trap = NULL; 94 wasmtime_instance_t instance; 95 wasmtime_extern_t import; 96 import.kind = WASMTIME_EXTERN_FUNC; 97 import.of.func = hello; 98 error = wasmtime_instance_new(context, module, &import, 1, &instance, &trap); 99 if (error != NULL || trap != NULL) 100 exit_with_error("failed to instantiate", error, trap); 101 102 // Lookup our `run` export function 103 printf("Extracting export...\n"); 104 wasmtime_extern_t run; 105 bool ok = wasmtime_instance_export_get(context, &instance, "run", 3, &run); 106 assert(ok); 107 assert(run.kind == WASMTIME_EXTERN_FUNC); 108 109 // And call it! 110 printf("Calling export...\n"); 111 error = wasmtime_func_call(context, &run.of.func, NULL, 0, NULL, 0, &trap); 112 if (error != NULL || trap != NULL) 113 exit_with_error("failed to call function", error, trap); 114 115 // Clean up after ourselves at this point 116 printf("All finished!\n"); 117 ret = 0; 118 119 wasmtime_module_delete(module); 120 wasmtime_store_delete(store); 121 wasm_engine_delete(engine); 122 return ret; 123 } 124 125 static void exit_with_error(const char *message, wasmtime_error_t *error, 126 wasm_trap_t *trap) { 127 fprintf(stderr, "error: %s\n", message); 128 wasm_byte_vec_t error_message; 129 if (error != NULL) { 130 wasmtime_error_message(error, &error_message); 131 wasmtime_error_delete(error); 132 } else { 133 wasm_trap_message(trap, &error_message); 134 wasm_trap_delete(trap); 135 } 136 fprintf(stderr, "%.*s\n", (int)error_message.size, error_message.data); 137 wasm_byte_vec_delete(&error_message); 138 exit(1); 139 } 140