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
hello_callback(void * env,wasmtime_caller_t * caller,const wasmtime_val_t * args,size_t nargs,wasmtime_val_t * results,size_t nresults)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
main()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
exit_with_error(const char * message,wasmtime_error_t * error,wasm_trap_t * trap)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