c-api: Enable debugger DWARF export for guest code

crates/c-api/Cargo.toml

@@ -56,5 +56,6 @@ gc-drc = ["wasmtime/gc-drc"]
 gc-null = ["wasmtime/gc-null"]
 cranelift = ['wasmtime/cranelift']
 winch = ['wasmtime/winch']
+debug-builtins = ['wasmtime/debug-builtins']
 # ... if you add a line above this be sure to change the other locations
 # marked WASMTIME_FEATURE_LIST

crates/c-api/artifact/Cargo.toml

@@ -38,6 +38,7 @@ default = [
   'gc-null',
   'cranelift',
   'winch',
+  'debug-builtins',
   # ... if you add a line above this be sure to change the other locations
   # marked WASMTIME_FEATURE_LIST
 ]
@@ -58,5 +59,6 @@ gc-drc = ["wasmtime-c-api/gc-drc"]
 gc-null = ["wasmtime-c-api/gc-null"]
 cranelift = ["wasmtime-c-api/cranelift"]
 winch = ["wasmtime-c-api/winch"]
+debug-builtins = ["wasmtime-c-api/debug-builtins"]
 # ... if you add a line above this be sure to read the comment at the end of
 # `default`

crates/c-api/build.rs

@@ -19,6 +19,7 @@ const FEATURES: &[&str] = &[
     "GC_NULL",
     "CRANELIFT",
     "WINCH",
+    "DEBUG_BUILTINS",
 ];
 // ... if you add a line above this be sure to change the other locations
 // marked WASMTIME_FEATURE_LIST

crates/c-api/cmake/features.cmake

@@ -43,5 +43,6 @@ feature(gc-null ON)
 feature(async ON)
 feature(cranelift ON)
 feature(winch ON)
+feature(debug-builtins ON)
 # ... if you add a line above this be sure to change the other locations
 # marked WASMTIME_FEATURE_LIST

crates/c-api/include/wasmtime/conf.h.in

@@ -25,6 +25,7 @@
 #cmakedefine WASMTIME_FEATURE_ASYNC
 #cmakedefine WASMTIME_FEATURE_CRANELIFT
 #cmakedefine WASMTIME_FEATURE_WINCH
+#cmakedefine WASMTIME_FEATURE_DEBUG_BUILTINS
 // ... if you add a line above this be sure to change the other locations
 // marked WASMTIME_FEATURE_LIST
 

examples/CMakeLists.txt

@@ -14,6 +14,8 @@ function(CREATE_TARGET TARGET TARGET_PATH)
 		target_compile_options(wasmtime-${TARGET} PRIVATE /W3)
 	endif()
 
+        target_compile_definitions(wasmtime-${TARGET} PRIVATE WASMTIME_TEST_ONLY)
+
 	set_target_properties(wasmtime-${TARGET} PROPERTIES
 		OUTPUT_NAME wasmtime-${TARGET}
 		RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/$<0:>

examples/fib-debug/main.c

@@ -5,6 +5,41 @@
 #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,
@@ -24,6 +59,15 @@ int main(int argc, const char *argv[]) {
   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");
@@ -60,6 +104,15 @@ int main(int argc, const char *argv[]) {
     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);