#1358: Do not dereference jmethodIDs on JDK 26 (#1362)

src/flightRecorder.cpp

@@ -173,31 +173,24 @@ class Lookup {
     }
 
     bool fillJavaMethodInfo(MethodInfo* mi, jmethodID method, bool first_time) {
-        if (VMStructs::hasMethodStructs()) {
-            // Workaround for JDK-8313816
-            VMMethod* vm_method = VMMethod::fromMethodID(method);
-            if (vm_method == NULL || vm_method->id() == NULL) {
-                return false;
-            }
+        if (VMMethod::isStaleMethodId(method)) {
+            return false;
         }
 
-        jvmtiEnv* jvmti = VM::jvmti();
-
         jclass method_class = NULL;
         char* class_name = NULL;
         char* method_name = NULL;
         char* method_sig = NULL;
 
-        if (jvmti->GetMethodName(method, &method_name, &method_sig, NULL) == 0 &&
-            jvmti->GetMethodDeclaringClass(method, &method_class) == 0 &&
-            jvmti->GetClassSignature(method_class, &class_name, NULL) == 0) {
+        jvmtiEnv* jvmti = VM::jvmti();
+        jvmtiError err;
+
+        if ((err = jvmti->GetMethodName(method, &method_name, &method_sig, NULL)) == 0 &&
+            (err = jvmti->GetMethodDeclaringClass(method, &method_class)) == 0 &&
+            (err = jvmti->GetClassSignature(method_class, &class_name, NULL)) == 0) {
             mi->_class = _classes->lookup(class_name + 1, strlen(class_name) - 2);
             mi->_name = _symbols.lookup(method_name);
             mi->_sig = _symbols.lookup(method_sig);
-        } else {
-            mi->_class = _classes->lookup("");
-            mi->_name = _symbols.lookup("jvmtiError");
-            mi->_sig = _symbols.lookup("()L;");
         }
 
         if (method_class) {
@@ -207,6 +200,10 @@ class Lookup {
         jvmti->Deallocate((unsigned char*)method_name);
         jvmti->Deallocate((unsigned char*)class_name);
 
+        if (err != 0) {
+            return false;
+        }
+
         if (first_time && jvmti->GetMethodModifiers(method, &mi->_modifiers) != 0) {
             mi->_modifiers = 0;
         }

src/frameName.cpp

@@ -155,13 +155,9 @@ const char* FrameName::typeSuffix(FrameTypeId type) {
 }
 
 void FrameName::javaMethodName(jmethodID method) {
-    if (VMStructs::hasMethodStructs()) {
-        // Workaround for JDK-8313816
-        VMMethod* vm_method = VMMethod::fromMethodID(method);
-        if (vm_method == NULL || vm_method->id() == NULL) {
-            _str.assign("[stale_jmethodID]");
-            return;
-        }
+    if (VMMethod::isStaleMethodId(method)) {
+        _str.assign("[stale_jmethodID]");
+        return;
     }
 
     jclass method_class = NULL;
@@ -186,6 +182,8 @@ void FrameName::javaMethodName(jmethodID method) {
             }
             _str.append(method_sig);
         }
+    } else if (err == JVMTI_ERROR_INVALID_METHODID) {
+        _str.assign("[stale_jmethodID]");
     } else {
         char buf[32];
         snprintf(buf, sizeof(buf), "[jvmtiError %d]", err);

src/stackWalker.cpp

@@ -53,10 +53,7 @@ static inline void fillFrame(ASGCT_CallFrame& frame, FrameTypeId type, int bci,
 
 static jmethodID getMethodId(VMMethod* method) {
     if (!inDeadZone(method) && aligned((uintptr_t)method)) {
-        jmethodID method_id = method->id();
-        if (!inDeadZone(method_id) && aligned((uintptr_t)method_id) && VMMethod::fromMethodID(method_id) == method) {
-            return method_id;
-        }
+        return method->validatedId();
     }
     return NULL;
 }

src/vmStructs.cpp

@@ -20,6 +20,7 @@ bool VMStructs::_has_stack_structs = false;
 bool VMStructs::_has_class_loader_data = false;
 bool VMStructs::_has_native_thread_id = false;
 bool VMStructs::_has_perm_gen = false;
+bool VMStructs::_can_dereference_jmethod_id = false;
 bool VMStructs::_compact_object_headers = false;
 
 int VMStructs::_klass_name_offset = -1;
@@ -519,6 +520,9 @@ void VMStructs::resolveOffsets() {
             && _thread_exception_offset >= 0
             && _constmethod_size >= 0;
 
+    // Since JDK-8268406, it is no longer possible to get VMMethod* by dereferencing jmethodID
+    _can_dereference_jmethod_id = _has_method_structs && VM::hotspot_version() <= 25;
+
     if (_code_heap_addr != NULL && _code_heap_low_addr != NULL && _code_heap_high_addr != NULL) {
         char* code_heaps = *_code_heap_addr;
         unsigned int code_heap_count = *(unsigned int*)(code_heaps + _array_len_offset);
@@ -665,6 +669,16 @@ jmethodID VMMethod::id() {
     return NULL;
 }
 
+jmethodID VMMethod::validatedId() {
+    jmethodID method_id = id();
+    if (goodPtr(method_id)) {
+        if (!_can_dereference_jmethod_id || *(VMMethod**)method_id == this) {
+            return method_id;
+        }
+    }
+    return NULL;
+}
+
 NMethod* CodeHeap::findNMethod(char* heap, const void* pc) {
     unsigned char* heap_start = *(unsigned char**)(heap + _code_heap_memory_offset + _vs_low_offset);
     unsigned char* segmap = *(unsigned char**)(heap + _code_heap_segmap_offset + _vs_low_offset);

src/vmStructs.h

@@ -26,6 +26,7 @@ class VMStructs {
     static bool _has_class_loader_data;
     static bool _has_native_thread_id;
     static bool _has_perm_gen;
+    static bool _can_dereference_jmethod_id;
     static bool _compact_object_headers;
 
     static int _klass_name_offset;
@@ -385,12 +386,18 @@ class VMThread : VMStructs {
 
 class VMMethod : VMStructs {
   public:
-    static VMMethod* fromMethodID(jmethodID id) {
-        return *(VMMethod**)id;
-    }
-
     jmethodID id();
 
+    // Performs extra validation when VMMethod comes from incomplete frame
+    jmethodID validatedId();
+
+    // Workaround for JDK-8313816
+    static bool isStaleMethodId(jmethodID id) {
+        if (!_can_dereference_jmethod_id) return false;
+        VMMethod* vm_method = *(VMMethod**)id;
+        return vm_method == NULL || vm_method->id() == NULL;
+    }
+
     const char* bytecode() {
         return *(const char**) at(_method_constmethod_offset) + _constmethod_size;
     }