Add defensive checks to SharedLineNumberTable destructor

ddprof-lib/src/main/cpp/flightRecorder.cpp

@@ -1,6 +1,6 @@
 /*
  * Copyright The async-profiler authors
- * Copyright 2025, Datadog, Inc.
+ * Copyright 2025, 2026 Datadog, Inc.
  * SPDX-License-Identifier: Apache-2.0
  */
 
@@ -43,10 +43,22 @@
 static const char *const SETTING_RING[] = {NULL, "kernel", "user", "any"};
 static const char *const SETTING_CSTACK[] = {NULL, "no", "fp", "dwarf", "lbr"};
 
-static void deallocateLineNumberTable(void *ptr) {}
-
 SharedLineNumberTable::~SharedLineNumberTable() {
-  VM::jvmti()->Deallocate((unsigned char *)_ptr);
+  // Always attempt to deallocate if we have a valid pointer
+  // JVMTI spec requires that memory allocated by GetLineNumberTable
+  // must be freed with Deallocate
+  if (_ptr != nullptr) {
+    jvmtiEnv *jvmti = VM::jvmti();
+    if (jvmti != nullptr) {
+      jvmtiError err = jvmti->Deallocate((unsigned char *)_ptr);
+      // If Deallocate fails, log it for debugging (this could indicate a JVM bug)
+      // JVMTI_ERROR_ILLEGAL_ARGUMENT means the memory wasn't allocated by JVMTI
+      // which would be a serious bug in GetLineNumberTable
+      if (err != JVMTI_ERROR_NONE) {
+        TEST_LOG("Unexpected error while deallocating linenumber table: %d", err);
+      }
+    }
+  }
 }
 
 void Lookup::fillNativeMethodInfo(MethodInfo *mi, const char *name,
@@ -151,24 +163,44 @@ void Lookup::fillJavaMethodInfo(MethodInfo *mi, jmethodID method,
         jvmti->GetMethodName(method, &method_name, &method_sig, NULL) == 0) {
 
       if (first_time) {
-        jvmti->GetLineNumberTable(method, &line_number_table_size,
+        jvmtiError line_table_error = jvmti->GetLineNumberTable(method, &line_number_table_size,
                                   &line_number_table);
+        // Defensive: if GetLineNumberTable failed, clean up any potentially allocated memory
+        // Some buggy JVMTI implementations might allocate despite returning an error
+        if (line_table_error != JVMTI_ERROR_NONE) {
+          if (line_number_table != nullptr) {
+            // Try to deallocate to prevent leak from buggy JVM
+            jvmti->Deallocate((unsigned char *)line_number_table);
+          }
+          line_number_table = nullptr;
+          line_number_table_size = 0;
+        }
       }
 
       // Check if the frame is Thread.run or inherits from it
       if (strncmp(method_name, "run", 4) == 0 &&
           strncmp(method_sig, "()V", 3) == 0) {
         jclass Thread_class = jni->FindClass("java/lang/Thread");
-        jmethodID equals = jni->GetMethodID(jni->FindClass("java/lang/Class"),
-                                            "equals", "(Ljava/lang/Object;)Z");
-        jclass klass = method_class;
-        do {
-          entry = jni->CallBooleanMethod(Thread_class, equals, klass);
-          jniExceptionCheck(jni);
-          if (entry) {
-            break;
+        jclass Class_class = jni->FindClass("java/lang/Class");
+        if (Thread_class != nullptr && Class_class != nullptr) {
+          jmethodID equals = jni->GetMethodID(Class_class,
+                                              "equals", "(Ljava/lang/Object;)Z");
+          if (equals != nullptr) {
+            jclass klass = method_class;
+            do {
+              entry = jni->CallBooleanMethod(Thread_class, equals, klass);
+              if (jniExceptionCheck(jni)) {
+                entry = false;
+                break;
+              }
+              if (entry) {
+                break;
+              }
+            } while ((klass = jni->GetSuperclass(klass)) != NULL);
           }
-        } while ((klass = jni->GetSuperclass(klass)) != NULL);
+        }
+        // Clear any exceptions from the reflection calls above
+        jniExceptionCheck(jni);
       } else if (strncmp(method_name, "main", 5) == 0 &&
                  strncmp(method_sig, "(Ljava/lang/String;)V", 21)) {
         // public static void main(String[] args) - 'public static' translates

ddprof-lib/src/main/cpp/vmEntry.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright The async-profiler authors
+ * Copyright 2026, Datadog, Inc.
  * SPDX-License-Identifier: Apache-2.0
  */
 
@@ -514,6 +515,16 @@ void VM::loadMethodIDs(jvmtiEnv *jvmti, JNIEnv *jni, jclass klass) {
     }
   }
 
+  // CRITICAL: GetClassMethods must be called to preallocate jmethodIDs for AsyncGetCallTrace.
+  // AGCT operates in signal handlers where lock acquisition is forbidden, so jmethodIDs must
+  // exist before profiling encounters them. Without preallocation, AGCT cannot identify methods
+  // in stack traces, breaking profiling functionality.
+  //
+  // JVM-internal allocation: This triggers JVM to allocate jmethodIDs internally, which persist
+  // until class unload. High class churn causes significant memory growth, but this is inherent
+  // to AGCT architecture and necessary for signal-safe profiling.
+  //
+  // See: https://mostlynerdless.de/blog/2023/07/17/jmethodids-in-profiling-a-tale-of-nightmares/
   jint method_count;
   jmethodID *methods;
   if (jvmti->GetClassMethods(klass, &method_count, &methods) == 0) {

ddprof-test/build.gradle

@@ -68,6 +68,7 @@ def addCommonTestDependencies(Configuration configuration) {
   configuration.dependencies.add(project.dependencies.create('org.lz4:lz4-java:1.8.0'))
   configuration.dependencies.add(project.dependencies.create('org.xerial.snappy:snappy-java:1.1.10.1'))
   configuration.dependencies.add(project.dependencies.create('com.github.luben:zstd-jni:1.5.5-4'))
+  configuration.dependencies.add(project.dependencies.create('org.ow2.asm:asm:9.6'))
   configuration.dependencies.add(project.dependencies.project(path: ":ddprof-test-tracer"))
 }
 
@@ -277,9 +278,27 @@ tasks.withType(Test).configureEach {
   def keepRecordings = project.hasProperty("keepJFRs") || Boolean.parseBoolean(System.getenv("KEEP_JFRS"))
   environment("CI", project.hasProperty("CI") || Boolean.parseBoolean(System.getenv("CI")))
 
-  jvmArgs "-Dddprof_test.keep_jfrs=${keepRecordings}", '-Djdk.attach.allowAttachSelf', '-Djol.tryWithSudo=true',
-    "-Dddprof_test.config=${config}", "-Dddprof_test.ci=${project.hasProperty('CI')}", "-Dddprof.disable_unsafe=true", '-XX:ErrorFile=build/hs_err_pid%p.log', '-XX:+ResizeTLAB',
-    '-Xmx512m', '-XX:OnError=/tmp/do_stuff.sh', "-Djava.library.path=${outputLibDir.absolutePath}"
+  // Base JVM arguments
+  def jvmArgsList = [
+    "-Dddprof_test.keep_jfrs=${keepRecordings}",
+    '-Djdk.attach.allowAttachSelf',
+    '-Djol.tryWithSudo=true',
+    "-Dddprof_test.config=${config}",
+    "-Dddprof_test.ci=${project.hasProperty('CI')}",
+    "-Dddprof.disable_unsafe=true",
+    '-XX:ErrorFile=build/hs_err_pid%p.log',
+    '-XX:+ResizeTLAB',
+    '-Xmx512m',
+    '-XX:OnError=/tmp/do_stuff.sh',
+    "-Djava.library.path=${outputLibDir.absolutePath}"
+  ]
+
+  // Enable Native Memory Tracking for leak detection tests if requested
+  if (project.hasProperty('enableNMT') || Boolean.parseBoolean(System.getenv("ENABLE_NMT"))) {
+    jvmArgsList.add('-XX:NativeMemoryTracking=detail')
+  }
+
+  jvmArgs jvmArgsList
 
   def javaHome = System.getenv("JAVA_TEST_HOME")
   if (javaHome == null) {