Debugging

You can also browse this source code online and clone the wasmtime repository to run the example locally.

This example shows off how to set up a module for dynamic runtime debugging via a native debugger like GDB or LLDB.

main.c

#include <inttypes.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <wasm.h> #include <wasmtime.h> #ifdef WASMTIME_TEST_ONLY // These are the declarations provided from GDB documentation, used to validate // that we actually added some DWARF info: // https://sourceware.org/gdb/current/onlinedocs/gdb.html/Declarations.html#Declarations // // NOTE: These are not required in your code, rather they are used for wasmtime // testing only. typedef enum { JIT_NOACTION = 0, JIT_REGISTER_FN, JIT_UNREGISTER_FN } jit_actions_t; struct jit_code_entry { struct jit_code_entry *next_entry; struct jit_code_entry *prev_entry; const char *symfile_addr; uint64_t symfile_size; }; struct jit_descriptor { uint32_t version; /* This type should be jit_actions_t, but we use uint32_t to be explicit about the bitwidth. */ uint32_t action_flag; struct jit_code_entry *relevant_entry; struct jit_code_entry *first_entry; }; /* * Import the descriptor, defined elsewhere in wasmtime */ extern struct jit_descriptor __jit_debug_descriptor; #endif #define own static void exit_with_error(const char *message, wasmtime_error_t *error, wasm_trap_t *trap); int main(int argc, const char *argv[]) { // Configuring engine to support generating of DWARF info. // lldb can be used to attach to the program and observe // original fib-wasm.c source code and variables. wasm_config_t *config = wasm_config_new(); wasmtime_config_debug_info_set(config, true); wasmtime_config_cranelift_opt_level_set(config, WASMTIME_OPT_LEVEL_NONE); // Initialize. printf("Initializing...\n"); wasm_engine_t *engine = wasm_engine_new_with_config(config); wasmtime_store_t *store = wasmtime_store_new(engine, NULL, NULL); wasmtime_context_t *context = wasmtime_store_context(store); #ifdef WASMTIME_TEST_ONLY // NOTE: This validation is for wasmtime testing and should not be included in // your code. if (__jit_debug_descriptor.first_entry != NULL) { fprintf(stderr, "FAIL: JIT descriptor is already initialized\n"); return 1; } #endif // Load binary. printf("Loading binary...\n"); FILE *file = fopen("target/wasm32-unknown-unknown/debug/fib.wasm", "rb"); if (!file) { printf("> Error opening module!\n"); return 1; } fseek(file, 0L, SEEK_END); size_t file_size = ftell(file); fseek(file, 0L, SEEK_SET); wasm_byte_vec_t binary; wasm_byte_vec_new_uninitialized(&binary, file_size); if (fread(binary.data, file_size, 1, file) != 1) { printf("> Error reading module!\n"); return 1; } fclose(file); // Compile. printf("Compiling module...\n"); wasmtime_module_t *module = NULL; wasmtime_error_t *error = wasmtime_module_new(engine, (uint8_t *)binary.data, binary.size, &module); if (!module) exit_with_error("failed to compile module", error, NULL); wasm_byte_vec_delete(&binary); // Instantiate. printf("Instantiating module...\n"); wasmtime_instance_t instance; wasm_trap_t *trap = NULL; error = wasmtime_instance_new(context, module, NULL, 0, &instance, &trap); if (error != NULL || trap != NULL) exit_with_error("failed to instantiate", error, trap); wasmtime_module_delete(module); #ifdef WASMTIME_TEST_ONLY // NOTE: This validation is for wasmtime testing and should not be included in // your code. if (__jit_debug_descriptor.first_entry == NULL) { fprintf(stderr, "FAIL: JIT descriptor is NOT initialized\n"); return 1; } #endif // Extract export. wasmtime_extern_t fib; bool ok = wasmtime_instance_export_get(context, &instance, "fib", 3, &fib); assert(ok); // Call. printf("Calling fib...\n"); wasmtime_val_t params[1]; params[0].kind = WASMTIME_I32; params[0].of.i32 = 6; wasmtime_val_t results[1]; error = wasmtime_func_call(context, &fib.of.func, params, 1, results, 1, &trap); if (error != NULL || trap != NULL) exit_with_error("failed to call function", error, trap); assert(results[0].kind == WASMTIME_I32); printf("> fib(6) = %d\n", results[0].of.i32); // Shut down. printf("Shutting down...\n"); wasmtime_store_delete(store); wasm_engine_delete(engine); // All done. printf("Done.\n"); return 0; } static void exit_with_error(const char *message, wasmtime_error_t *error, wasm_trap_t *trap) { fprintf(stderr, "error: %s\n", message); wasm_byte_vec_t error_message; if (error != NULL) { wasmtime_error_message(error, &error_message); } else { wasm_trap_message(trap, &error_message); } fprintf(stderr, "%.*s\n", (int)error_message.size, error_message.data); wasm_byte_vec_delete(&error_message); exit(1); }