Fix PerfMap crash when Enable IPC command is sent early in startup

src/coreclr/vm/ceemain.cpp

@@ -824,6 +824,10 @@ void EEStartupHelper()
 
         ExecutionManager::Init();
 
+#ifdef FEATURE_PERFMAP
+        PerfMap::SignalDependenciesReady();
+#endif
+
         JitHost::Init();
 
 #ifndef TARGET_UNIX

src/coreclr/vm/perfmap.cpp

@@ -28,6 +28,7 @@
 #endif
 
 Volatile<bool> PerfMap::s_enabled = false;
+Volatile<bool> PerfMap::s_dependenciesReady = false;
 PerfMap * PerfMap::s_Current = nullptr;
 bool PerfMap::s_ShowOptimizationTiers = false;
 bool PerfMap::s_GroupStubsOfSameType = false;
@@ -121,6 +122,17 @@ void PerfMap::Enable(PerfMapType type, bool sendExisting)
 
     if (sendExisting)
     {
+        // When Enable is called very early in startup (e.g., via DiagnosticServer IPC before
+        // SystemDomain::Attach and ExecutionManager::Init), the AppDomain and EEJitManager
+        // may not exist yet. We use s_dependenciesReady (a Volatile<bool>) to guard against
+        // this, rather than null-checking individual pointers which would have race conditions
+        // due to non-Volatile statics like m_pEEJitManager.
+        // Safe to skip: no assemblies are loaded and no code is JIT'd at that point.
+        if (!s_dependenciesReady)
+        {
+            return;
+        }
+
         AppDomain::AssemblyIterator assemblyIterator = GetAppDomain()->IterateAssembliesEx(
             (AssemblyIterationFlags)(kIncludeLoaded | kIncludeExecution));
         CollectibleAssemblyHolder<Assembly *> pAssembly;
@@ -208,6 +220,15 @@ void PerfMap::Disable()
     }
 }
 
+// Signal that all dependencies (AppDomain, ExecutionManager) are ready.
+// This method must be called before any code is JITed or restored from R2R image.
+void PerfMap::SignalDependenciesReady()
+{
+    LIMITED_METHOD_CONTRACT;
+
+    s_dependenciesReady = true;
+}
+
 // Construct a new map for the process.
 PerfMap::PerfMap()
 {

src/coreclr/vm/perfmap.h

@@ -24,6 +24,9 @@ class PerfMap
 private:
     static Volatile<bool> s_enabled;
 
+    // Set to true after all dependencies (AppDomain, ExecutionManager) are initialized.
+    static Volatile<bool> s_dependenciesReady;
+
     // The one and only PerfMap for the process.
     static PerfMap * s_Current;
 
@@ -104,6 +107,9 @@ class PerfMap
     // Close the map and flush any remaining data.
     static void Disable();
 
+    // Signal that all dependencies (AppDomain, ExecutionManager) are ready.
+    static void SignalDependenciesReady();
+
     static bool LowGranularityStubs() { return !s_IndividualAllocationStubReporting; }
 };
 #endif // PERFPID_H