ApplyStartupHook diagnostic IPC command

src/coreclr/System.Private.CoreLib/src/System/StartupHookProvider.CoreCLR.cs

@@ -12,15 +12,15 @@ namespace System
 {
  internal static partial class StartupHookProvider
  {
- private static void ManagedStartup()
+ private static unsafe void ManagedStartup(char* pDiagnosticStartupHooks)
  {
 #if FEATURE_PERFTRACING
  if (EventSource.IsSupported)
  RuntimeEventSource.Initialize();
 #endif
 
  if (IsSupported)
- ProcessStartupHooks();
+ ProcessStartupHooks(new string(pDiagnosticStartupHooks));
  }
  }
 }

src/coreclr/nativeaot/Runtime/eventpipe/ds-rt-aot.h

@@ -272,6 +272,13 @@ ds_rt_disable_perfmap (void)
  return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/assembly.cpp

@@ -52,6 +52,7 @@
 //#define STRICT_JITLOCK_ENTRY_LEAK_DETECTION
 //#define STRICT_CLSINITLOCK_ENTRY_LEAK_DETECTION
 
+LPCWSTR s_wszDiagnosticStartupHookPaths = nullptr;
 
 #ifndef DACCESS_COMPILE
 
@@ -1122,7 +1123,47 @@ bool Assembly::IgnoresAccessChecksTo(Assembly *pAccessedAssembly)
  return GetFriendAssemblyInfo()->IgnoresAccessChecksTo(pAccessedAssembly);
 }
 
+void Assembly::AddDiagnosticStartupHookPath(LPCWSTR wszPath)
+{
+ LPCWSTR wszDiagnosticStartupHookPathsLocal = s_wszDiagnosticStartupHookPaths;
+
+ size_t cchPath = u16_strlen(wszPath);
+ size_t cchDiagnosticStartupHookPathsNew = cchPath;
+ size_t cchDiagnosticStartupHookPathsLocal = 0;
+ if (nullptr != wszDiagnosticStartupHookPathsLocal)
+ {
+ cchDiagnosticStartupHookPathsLocal = u16_strlen(wszDiagnosticStartupHookPathsLocal); 
+ // Add 1 for the path separator
+ cchDiagnosticStartupHookPathsNew += cchDiagnosticStartupHookPathsLocal + 1;
+ }
 
+ size_t currentSize = cchDiagnosticStartupHookPathsNew + 1;
+ LPWSTR wszDiagnosticStartupHookPathsNew = new WCHAR[currentSize];
+ LPWSTR wszCurrent = wszDiagnosticStartupHookPathsNew;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszPath);
+ wszCurrent += cchPath;
+ currentSize -= cchPath;
+
+ if (cchDiagnosticStartupHookPathsLocal > 0)
+ {
+ u16_strcpy_s(wszCurrent, currentSize, PATH_SEPARATOR_STR_W);
+ wszCurrent += 1;
+ currentSize -= 1;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszDiagnosticStartupHookPathsLocal);
+ wszCurrent += cchDiagnosticStartupHookPathsLocal;
+ currentSize -= cchDiagnosticStartupHookPathsLocal;
+ }
+
+ // Expect null terminating character
+ _ASSERTE(currentSize == 1);
+ _ASSERTE(wszCurrent[0] == W('\0'));
+
+ s_wszDiagnosticStartupHookPaths = wszDiagnosticStartupHookPathsNew;
+
+ delete [] wszDiagnosticStartupHookPathsLocal;
+}
 
 enum CorEntryPointType
 {
@@ -1376,7 +1417,7 @@ static void RunMainPost()
  }
 }
 
-static void RunManagedStartup()
+void RunManagedStartup()
 {
  CONTRACTL
  {
@@ -1388,7 +1429,11 @@ static void RunManagedStartup()
  CONTRACTL_END;
 
  MethodDescCallSite managedStartup(METHOD__STARTUP_HOOK_PROVIDER__MANAGED_STARTUP);
- managedStartup.Call(NULL);
+
+ ARG_SLOT args[1];
+ args[0] = PtrToArgSlot(s_wszDiagnosticStartupHookPaths);
+
+ managedStartup.Call(args);
 }
 
 INT32 Assembly::ExecuteMainMethod(PTRARRAYREF *stringArgs, BOOL waitForOtherThreads)

src/coreclr/vm/assembly.hpp

@@ -380,6 +380,8 @@ class Assembly
  }
 #endif
 
+ static void AddDiagnosticStartupHookPath(LPCWSTR wszPath);
+
 
 protected:
 #ifdef FEATURE_COMINTEROP

src/coreclr/vm/corelib.h

@@ -812,7 +812,7 @@ DEFINE_FIELD_U(rgiLastFrameFromForeignExceptionStackTrace, StackFrame
 DEFINE_FIELD_U(iFrameCount, StackFrameHelper, iFrameCount)
 
 DEFINE_CLASS(STARTUP_HOOK_PROVIDER, System, StartupHookProvider)
-DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_RetVoid)
+DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_PtrChar_RetVoid)
 
 DEFINE_CLASS(STREAM, IO, Stream)
 DEFINE_METHOD(STREAM, BEGIN_READ, BeginRead, IM_ArrByte_Int_Int_AsyncCallback_Object_RetIAsyncResult)

src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.h

@@ -329,6 +329,28 @@ ds_rt_disable_perfmap (void)
 #endif // FEATURE_PERFMAP
 }
 
+static ep_char16_t * _ds_rt_coreclr_diagnostic_startup_hook_paths = NULL;
+
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	HRESULT hr = S_OK;
+	// This is set to true when the EE has initialized, which occurs after
+	// the diagnostic suspension point has completed.
+	if (g_fEEStarted)
+	{
+ // TODO: Support loading and executing startup hook after EE has completely initialized.
+ return DS_IPC_E_INVALIDARG;
+	}
+	else
+	{
+ Assembly::AddDiagnosticStartupHookPath(reinterpret_cast<LPCWSTR>(startup_hook_path));
+	}
+
+	return DS_IPC_S_OK;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/metasig.h

@@ -338,6 +338,7 @@ DEFINE_METASIG(SM(IntPtr_Bool_RetVoid, I F, v))
 DEFINE_METASIG(SM(IntPtr_UInt_IntPtr_RetVoid, I K I, v))
 DEFINE_METASIG(SM(IntPtr_RetUInt, I, K))
 DEFINE_METASIG(SM(PtrChar_RetInt, P(u), i))
+DEFINE_METASIG(SM(PtrChar_RetVoid, P(u), v))
 DEFINE_METASIG(SM(IntPtr_IntPtr_RetIntPtr, I I, I))
 DEFINE_METASIG(SM(IntPtr_IntPtr_Int_RetIntPtr, I I i, I))
 DEFINE_METASIG(SM(PtrVoid_PtrVoid_RetVoid, P(v) P(v), v))

src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Suppressions.LibraryBuild.xml

@@ -19,7 +19,7 @@
  <argument>ILLink</argument>
  <argument>IL2026</argument>
  <property name="Scope">member</property>
- <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks()</property>
+ <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks(System.String)</property>
  <property name="Justification">This warning is left in the product so developers get an ILLink warning when trimming an app with System.StartupHookProvider.IsSupported=true.</property>
  </attribute>
  </assembly>

src/libraries/System.Private.CoreLib/src/System/StartupHookProvider.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.Tracing;
 using System.Diagnostics.CodeAnalysis;
@@ -27,15 +28,25 @@ private struct StartupHookNameOrPath
 
  // Parse a string specifying a list of assemblies and types
  // containing a startup hook, and call each hook in turn.
- private static void ProcessStartupHooks()
+ private static void ProcessStartupHooks(string diagnosticStartupHooks)
  {
  if (!IsSupported)
  return;
 
  string? startupHooksVariable = AppContext.GetData("STARTUP_HOOKS") as string;
- if (startupHooksVariable == null)
- {
+ if (null == startupHooksVariable && string.IsNullOrEmpty(diagnosticStartupHooks))
  return;
+
+ List<string> startupHookParts = new();
+
+ if (!string.IsNullOrEmpty(diagnosticStartupHooks))
+ {
+ startupHookParts.AddRange(diagnosticStartupHooks.Split(Path.PathSeparator));
+ }
+
+ if (null != startupHooksVariable)
+ {
+ startupHookParts.AddRange(startupHooksVariable.Split(Path.PathSeparator));
  }
 
  ReadOnlySpan<char> disallowedSimpleAssemblyNameChars = stackalloc char[4]
@@ -47,9 +58,8 @@ private static void ProcessStartupHooks()
  };
 
  // Parse startup hooks variable
- string[] startupHookParts = startupHooksVariable.Split(Path.PathSeparator);
- StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Length];
- for (int i = 0; i < startupHookParts.Length; i++)
+ StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Count];
+ for (int i = 0; i < startupHookParts.Count; i++)
  {
  string startupHookPart = startupHookParts[i];
  if (string.IsNullOrEmpty(startupHookPart))

src/mono/mono/eventpipe/ds-rt-mono.h

@@ -239,6 +239,14 @@ ds_rt_disable_perfmap (void)
 	return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	// TODO: Implement.
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/mono/mono/metadata/object.c

@@ -8135,7 +8135,11 @@ mono_runtime_run_startup_hooks (void)
 	mono_error_cleanup (error);
 	if (!method)
  return;
-	mono_runtime_invoke_checked (method, NULL, NULL, error);
+
+	gpointer args [1];
+	args[0] = mono_string_empty_internal (mono_domain_get ());
+
+	mono_runtime_invoke_checked (method, NULL, args, error);
 	// runtime hooks design doc says not to catch exceptions from the hooks
 	mono_error_raise_exception_deprecated (error);
 }

src/native/eventpipe/ds-process-protocol.c

@@ -89,6 +89,12 @@ process_protocol_helper_disable_perfmap (
 	DiagnosticsIpcMessage *message,
 	DiagnosticsIpcStream *stream);
 
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream);
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -872,6 +878,87 @@ process_protocol_helper_disable_perfmap (
 	ep_exit_error_handler ();
 }
 
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void)
+{
+	return ep_rt_object_alloc (DiagnosticsApplyStartupHookPayload);
+}
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload)
+{
+	ep_return_void_if_nok (payload != NULL);
+	ep_rt_byte_array_free (payload->incoming_buffer);
+	ep_rt_object_free (payload);
+}
+
+static
+uint8_t *
+apply_startup_hook_command_try_parse_payload (
+	uint8_t *buffer,
+	uint16_t buffer_len)
+{
+	EP_ASSERT (buffer != NULL);
+
+	uint8_t * buffer_cursor = buffer;
+	uint32_t buffer_cursor_len = buffer_len;
+
+	DiagnosticsApplyStartupHookPayload *instance = ds_apply_startup_hook_payload_alloc ();
+	ep_raise_error_if_nok (instance != NULL);
+
+	instance->incoming_buffer = buffer;
+
+	if (!ds_ipc_message_try_parse_string_utf16_t (&buffer_cursor, &buffer_cursor_len, &instance->startup_hook_path))
+ ep_raise_error ();
+
+ep_on_exit:
+	return (uint8_t *)instance;
+
+ep_on_error:
+	ds_apply_startup_hook_payload_free (instance);
+	instance = NULL;
+	ep_exit_error_handler ();
+}
+
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream)
+{
+	EP_ASSERT (message != NULL);
+	EP_ASSERT (stream != NULL);
+
+	if (!stream)
+ return false;
+
+	bool result = false;
+	DiagnosticsApplyStartupHookPayload *payload = (DiagnosticsApplyStartupHookPayload *)ds_ipc_message_try_parse_payload (message, apply_startup_hook_command_try_parse_payload);
+	if (!payload) {
+ ds_ipc_message_send_error (stream, DS_IPC_E_BAD_ENCODING);
+ ep_raise_error ();
+	}
+
+	ds_ipc_result_t ipc_result;
+	ipc_result = ds_rt_apply_startup_hook (payload->startup_hook_path);
+	if (ipc_result != DS_IPC_S_OK) {
+ ds_ipc_message_send_error (stream, ipc_result);
+ ep_raise_error ();
+	} else {
+ ds_ipc_message_send_success (stream, ipc_result);
+	}
+
+	result = true;
+
+ep_on_exit:
+	ds_ipc_stream_free (stream);
+	return result;
+
+ep_on_error:
+	EP_ASSERT (!result);
+	ep_exit_error_handler ();
+}
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -916,6 +1003,9 @@ ds_process_protocol_helper_handle_ipc_message (
 	case DS_PROCESS_COMMANDID_DISABLE_PERFMAP:
  result = process_protocol_helper_disable_perfmap (message, stream);
  break;
+	case DS_PROCESS_COMMANDID_APPLY_STARTUP_HOOK:
+ result = process_protocol_helper_apply_startup_hook (message, stream);
+ break;
 	default:
  result = process_protocol_helper_unknown_command (message, stream);
  break;

src/native/eventpipe/ds-process-protocol.h

@@ -190,6 +190,32 @@ ds_enable_perfmap_payload_alloc (void);
 void
 ds_enable_perfmap_payload_free (DiagnosticsEnablePerfmapPayload *payload);
 
+/*
+* DiagnosticsApplyStartupHookPayload
+*/
+
+#if defined(DS_INLINE_GETTER_SETTER) || defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+#else
+struct _DiagnosticsApplyStartupHookPayload_Internal {
+#endif
+	uint8_t * incoming_buffer;
+
+	const ep_char16_t *startup_hook_path;
+};
+
+#if !defined(DS_INLINE_GETTER_SETTER) && !defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+	uint8_t _internal [sizeof (struct _DiagnosticsApplyStartupHookPayload_Internal)];
+};
+#endif
+
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void);
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload);
+
 /*
  * DiagnosticsProcessProtocolHelper.
  */

src/coreclr/System.Private.CoreLib/src/System/StartupHookProvider.CoreCLR.cs

@@ -12,15 +12,15 @@ namespace System
 {
  internal static partial class StartupHookProvider
  {
- private static void ManagedStartup()
+ private static unsafe void ManagedStartup(char* pDiagnosticStartupHooks)
  {
 #if FEATURE_PERFTRACING
  if (EventSource.IsSupported)
  RuntimeEventSource.Initialize();
 #endif
 
  if (IsSupported)
- ProcessStartupHooks();
+ ProcessStartupHooks(new string(pDiagnosticStartupHooks));
  }
  }
 }

src/coreclr/nativeaot/Runtime/eventpipe/ds-rt-aot.h

@@ -272,6 +272,13 @@ ds_rt_disable_perfmap (void)
  return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/assembly.cpp

@@ -52,6 +52,7 @@
 //#define STRICT_JITLOCK_ENTRY_LEAK_DETECTION
 //#define STRICT_CLSINITLOCK_ENTRY_LEAK_DETECTION
 
+LPCWSTR s_wszDiagnosticStartupHookPaths = nullptr;
 
 #ifndef DACCESS_COMPILE
 
@@ -1122,7 +1123,47 @@ bool Assembly::IgnoresAccessChecksTo(Assembly *pAccessedAssembly)
  return GetFriendAssemblyInfo()->IgnoresAccessChecksTo(pAccessedAssembly);
 }
 
+void Assembly::AddDiagnosticStartupHookPath(LPCWSTR wszPath)
+{
+ LPCWSTR wszDiagnosticStartupHookPathsLocal = s_wszDiagnosticStartupHookPaths;
+
+ size_t cchPath = u16_strlen(wszPath);
+ size_t cchDiagnosticStartupHookPathsNew = cchPath;
+ size_t cchDiagnosticStartupHookPathsLocal = 0;
+ if (nullptr != wszDiagnosticStartupHookPathsLocal)
+ {
+ cchDiagnosticStartupHookPathsLocal = u16_strlen(wszDiagnosticStartupHookPathsLocal); 
+ // Add 1 for the path separator
+ cchDiagnosticStartupHookPathsNew += cchDiagnosticStartupHookPathsLocal + 1;
+ }
 
+ size_t currentSize = cchDiagnosticStartupHookPathsNew + 1;
+ LPWSTR wszDiagnosticStartupHookPathsNew = new WCHAR[currentSize];
+ LPWSTR wszCurrent = wszDiagnosticStartupHookPathsNew;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszPath);
+ wszCurrent += cchPath;
+ currentSize -= cchPath;
+
+ if (cchDiagnosticStartupHookPathsLocal > 0)
+ {
+ u16_strcpy_s(wszCurrent, currentSize, PATH_SEPARATOR_STR_W);
+ wszCurrent += 1;
+ currentSize -= 1;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszDiagnosticStartupHookPathsLocal);
+ wszCurrent += cchDiagnosticStartupHookPathsLocal;
+ currentSize -= cchDiagnosticStartupHookPathsLocal;
+ }
+
+ // Expect null terminating character
+ _ASSERTE(currentSize == 1);
+ _ASSERTE(wszCurrent[0] == W('\0'));
+
+ s_wszDiagnosticStartupHookPaths = wszDiagnosticStartupHookPathsNew;
+
+ delete [] wszDiagnosticStartupHookPathsLocal;
+}
 
 enum CorEntryPointType
 {
@@ -1376,7 +1417,7 @@ static void RunMainPost()
  }
 }
 
-static void RunManagedStartup()
+void RunManagedStartup()
 {
  CONTRACTL
  {
@@ -1388,7 +1429,11 @@ static void RunManagedStartup()
  CONTRACTL_END;
 
  MethodDescCallSite managedStartup(METHOD__STARTUP_HOOK_PROVIDER__MANAGED_STARTUP);
- managedStartup.Call(NULL);
+
+ ARG_SLOT args[1];
+ args[0] = PtrToArgSlot(s_wszDiagnosticStartupHookPaths);
+
+ managedStartup.Call(args);
 }
 
 INT32 Assembly::ExecuteMainMethod(PTRARRAYREF *stringArgs, BOOL waitForOtherThreads)

src/coreclr/vm/assembly.hpp

@@ -380,6 +380,8 @@ class Assembly
  }
 #endif
 
+ static void AddDiagnosticStartupHookPath(LPCWSTR wszPath);
+
 
 protected:
 #ifdef FEATURE_COMINTEROP

src/coreclr/vm/corelib.h

@@ -812,7 +812,7 @@ DEFINE_FIELD_U(rgiLastFrameFromForeignExceptionStackTrace, StackFrame
 DEFINE_FIELD_U(iFrameCount, StackFrameHelper, iFrameCount)
 
 DEFINE_CLASS(STARTUP_HOOK_PROVIDER, System, StartupHookProvider)
-DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_RetVoid)
+DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_PtrChar_RetVoid)
 
 DEFINE_CLASS(STREAM, IO, Stream)
 DEFINE_METHOD(STREAM, BEGIN_READ, BeginRead, IM_ArrByte_Int_Int_AsyncCallback_Object_RetIAsyncResult)

src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.h

@@ -329,6 +329,28 @@ ds_rt_disable_perfmap (void)
 #endif // FEATURE_PERFMAP
 }
 
+static ep_char16_t * _ds_rt_coreclr_diagnostic_startup_hook_paths = NULL;
+
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	HRESULT hr = S_OK;
+	// This is set to true when the EE has initialized, which occurs after
+	// the diagnostic suspension point has completed.
+	if (g_fEEStarted)
+	{
+ // TODO: Support loading and executing startup hook after EE has completely initialized.
+ return DS_IPC_E_INVALIDARG;
+	}
+	else
+	{
+ Assembly::AddDiagnosticStartupHookPath(reinterpret_cast<LPCWSTR>(startup_hook_path));
+	}
+
+	return DS_IPC_S_OK;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/metasig.h

@@ -338,6 +338,7 @@ DEFINE_METASIG(SM(IntPtr_Bool_RetVoid, I F, v))
 DEFINE_METASIG(SM(IntPtr_UInt_IntPtr_RetVoid, I K I, v))
 DEFINE_METASIG(SM(IntPtr_RetUInt, I, K))
 DEFINE_METASIG(SM(PtrChar_RetInt, P(u), i))
+DEFINE_METASIG(SM(PtrChar_RetVoid, P(u), v))
 DEFINE_METASIG(SM(IntPtr_IntPtr_RetIntPtr, I I, I))
 DEFINE_METASIG(SM(IntPtr_IntPtr_Int_RetIntPtr, I I i, I))
 DEFINE_METASIG(SM(PtrVoid_PtrVoid_RetVoid, P(v) P(v), v))

src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Suppressions.LibraryBuild.xml

@@ -19,7 +19,7 @@
  <argument>ILLink</argument>
  <argument>IL2026</argument>
  <property name="Scope">member</property>
- <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks()</property>
+ <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks(System.String)</property>
  <property name="Justification">This warning is left in the product so developers get an ILLink warning when trimming an app with System.StartupHookProvider.IsSupported=true.</property>
  </attribute>
  </assembly>

src/libraries/System.Private.CoreLib/src/System/StartupHookProvider.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.Tracing;
 using System.Diagnostics.CodeAnalysis;
@@ -27,15 +28,25 @@ private struct StartupHookNameOrPath
 
  // Parse a string specifying a list of assemblies and types
  // containing a startup hook, and call each hook in turn.
- private static void ProcessStartupHooks()
+ private static void ProcessStartupHooks(string diagnosticStartupHooks)
  {
  if (!IsSupported)
  return;
 
  string? startupHooksVariable = AppContext.GetData("STARTUP_HOOKS") as string;
- if (startupHooksVariable == null)
- {
+ if (null == startupHooksVariable && string.IsNullOrEmpty(diagnosticStartupHooks))
  return;
+
+ List<string> startupHookParts = new();
+
+ if (!string.IsNullOrEmpty(diagnosticStartupHooks))
+ {
+ startupHookParts.AddRange(diagnosticStartupHooks.Split(Path.PathSeparator));
+ }
+
+ if (null != startupHooksVariable)
+ {
+ startupHookParts.AddRange(startupHooksVariable.Split(Path.PathSeparator));
  }
 
  ReadOnlySpan<char> disallowedSimpleAssemblyNameChars = stackalloc char[4]
@@ -47,9 +58,8 @@ private static void ProcessStartupHooks()
  };
 
  // Parse startup hooks variable
- string[] startupHookParts = startupHooksVariable.Split(Path.PathSeparator);
- StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Length];
- for (int i = 0; i < startupHookParts.Length; i++)
+ StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Count];
+ for (int i = 0; i < startupHookParts.Count; i++)
  {
  string startupHookPart = startupHookParts[i];
  if (string.IsNullOrEmpty(startupHookPart))

src/mono/mono/eventpipe/ds-rt-mono.h

@@ -239,6 +239,14 @@ ds_rt_disable_perfmap (void)
 	return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	// TODO: Implement.
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/mono/mono/metadata/object.c

@@ -8135,7 +8135,11 @@ mono_runtime_run_startup_hooks (void)
 	mono_error_cleanup (error);
 	if (!method)
  return;
-	mono_runtime_invoke_checked (method, NULL, NULL, error);
+
+	gpointer args [1];
+	args[0] = mono_string_empty_internal (mono_domain_get ());
+
+	mono_runtime_invoke_checked (method, NULL, args, error);
 	// runtime hooks design doc says not to catch exceptions from the hooks
 	mono_error_raise_exception_deprecated (error);
 }

src/native/eventpipe/ds-process-protocol.c

@@ -89,6 +89,12 @@ process_protocol_helper_disable_perfmap (
 	DiagnosticsIpcMessage *message,
 	DiagnosticsIpcStream *stream);
 
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream);
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -872,6 +878,87 @@ process_protocol_helper_disable_perfmap (
 	ep_exit_error_handler ();
 }
 
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void)
+{
+	return ep_rt_object_alloc (DiagnosticsApplyStartupHookPayload);
+}
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload)
+{
+	ep_return_void_if_nok (payload != NULL);
+	ep_rt_byte_array_free (payload->incoming_buffer);
+	ep_rt_object_free (payload);
+}
+
+static
+uint8_t *
+apply_startup_hook_command_try_parse_payload (
+	uint8_t *buffer,
+	uint16_t buffer_len)
+{
+	EP_ASSERT (buffer != NULL);
+
+	uint8_t * buffer_cursor = buffer;
+	uint32_t buffer_cursor_len = buffer_len;
+
+	DiagnosticsApplyStartupHookPayload *instance = ds_apply_startup_hook_payload_alloc ();
+	ep_raise_error_if_nok (instance != NULL);
+
+	instance->incoming_buffer = buffer;
+
+	if (!ds_ipc_message_try_parse_string_utf16_t (&buffer_cursor, &buffer_cursor_len, &instance->startup_hook_path))
+ ep_raise_error ();
+
+ep_on_exit:
+	return (uint8_t *)instance;
+
+ep_on_error:
+	ds_apply_startup_hook_payload_free (instance);
+	instance = NULL;
+	ep_exit_error_handler ();
+}
+
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream)
+{
+	EP_ASSERT (message != NULL);
+	EP_ASSERT (stream != NULL);
+
+	if (!stream)
+ return false;
+
+	bool result = false;
+	DiagnosticsApplyStartupHookPayload *payload = (DiagnosticsApplyStartupHookPayload *)ds_ipc_message_try_parse_payload (message, apply_startup_hook_command_try_parse_payload);
+	if (!payload) {
+ ds_ipc_message_send_error (stream, DS_IPC_E_BAD_ENCODING);
+ ep_raise_error ();
+	}
+
+	ds_ipc_result_t ipc_result;
+	ipc_result = ds_rt_apply_startup_hook (payload->startup_hook_path);
+	if (ipc_result != DS_IPC_S_OK) {
+ ds_ipc_message_send_error (stream, ipc_result);
+ ep_raise_error ();
+	} else {
+ ds_ipc_message_send_success (stream, ipc_result);
+	}
+
+	result = true;
+
+ep_on_exit:
+	ds_ipc_stream_free (stream);
+	return result;
+
+ep_on_error:
+	EP_ASSERT (!result);
+	ep_exit_error_handler ();
+}
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -916,6 +1003,9 @@ ds_process_protocol_helper_handle_ipc_message (
 	case DS_PROCESS_COMMANDID_DISABLE_PERFMAP:
  result = process_protocol_helper_disable_perfmap (message, stream);
  break;
+	case DS_PROCESS_COMMANDID_APPLY_STARTUP_HOOK:
+ result = process_protocol_helper_apply_startup_hook (message, stream);
+ break;
 	default:
  result = process_protocol_helper_unknown_command (message, stream);
  break;

src/native/eventpipe/ds-process-protocol.h

@@ -190,6 +190,32 @@ ds_enable_perfmap_payload_alloc (void);
 void
 ds_enable_perfmap_payload_free (DiagnosticsEnablePerfmapPayload *payload);
 
+/*
+* DiagnosticsApplyStartupHookPayload
+*/
+
+#if defined(DS_INLINE_GETTER_SETTER) || defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+#else
+struct _DiagnosticsApplyStartupHookPayload_Internal {
+#endif
+	uint8_t * incoming_buffer;
+
+	const ep_char16_t *startup_hook_path;
+};
+
+#if !defined(DS_INLINE_GETTER_SETTER) && !defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+	uint8_t _internal [sizeof (struct _DiagnosticsApplyStartupHookPayload_Internal)];
+};
+#endif
+
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void);
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload);
+
 /*
  * DiagnosticsProcessProtocolHelper.
  */

src/coreclr/System.Private.CoreLib/src/System/StartupHookProvider.CoreCLR.cs

@@ -12,15 +12,15 @@ namespace System
 {
  internal static partial class StartupHookProvider
  {
- private static void ManagedStartup()
+ private static unsafe void ManagedStartup(char* pDiagnosticStartupHooks)
  {
 #if FEATURE_PERFTRACING
  if (EventSource.IsSupported)
  RuntimeEventSource.Initialize();
 #endif
 
  if (IsSupported)
- ProcessStartupHooks();
+ ProcessStartupHooks(new string(pDiagnosticStartupHooks));
  }
  }
 }

src/coreclr/nativeaot/Runtime/eventpipe/ds-rt-aot.h

@@ -272,6 +272,13 @@ ds_rt_disable_perfmap (void)
  return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/assembly.cpp

@@ -52,6 +52,7 @@
 //#define STRICT_JITLOCK_ENTRY_LEAK_DETECTION
 //#define STRICT_CLSINITLOCK_ENTRY_LEAK_DETECTION
 
+LPCWSTR s_wszDiagnosticStartupHookPaths = nullptr;
 
 #ifndef DACCESS_COMPILE
 
@@ -1122,7 +1123,47 @@ bool Assembly::IgnoresAccessChecksTo(Assembly *pAccessedAssembly)
  return GetFriendAssemblyInfo()->IgnoresAccessChecksTo(pAccessedAssembly);
 }
 
+void Assembly::AddDiagnosticStartupHookPath(LPCWSTR wszPath)
+{
+ LPCWSTR wszDiagnosticStartupHookPathsLocal = s_wszDiagnosticStartupHookPaths;
+
+ size_t cchPath = u16_strlen(wszPath);
+ size_t cchDiagnosticStartupHookPathsNew = cchPath;
+ size_t cchDiagnosticStartupHookPathsLocal = 0;
+ if (nullptr != wszDiagnosticStartupHookPathsLocal)
+ {
+ cchDiagnosticStartupHookPathsLocal = u16_strlen(wszDiagnosticStartupHookPathsLocal); 
+ // Add 1 for the path separator
+ cchDiagnosticStartupHookPathsNew += cchDiagnosticStartupHookPathsLocal + 1;
+ }
 
+ size_t currentSize = cchDiagnosticStartupHookPathsNew + 1;
+ LPWSTR wszDiagnosticStartupHookPathsNew = new WCHAR[currentSize];
+ LPWSTR wszCurrent = wszDiagnosticStartupHookPathsNew;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszPath);
+ wszCurrent += cchPath;
+ currentSize -= cchPath;
+
+ if (cchDiagnosticStartupHookPathsLocal > 0)
+ {
+ u16_strcpy_s(wszCurrent, currentSize, PATH_SEPARATOR_STR_W);
+ wszCurrent += 1;
+ currentSize -= 1;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszDiagnosticStartupHookPathsLocal);
+ wszCurrent += cchDiagnosticStartupHookPathsLocal;
+ currentSize -= cchDiagnosticStartupHookPathsLocal;
+ }
+
+ // Expect null terminating character
+ _ASSERTE(currentSize == 1);
+ _ASSERTE(wszCurrent[0] == W('\0'));
+
+ s_wszDiagnosticStartupHookPaths = wszDiagnosticStartupHookPathsNew;
+
+ delete [] wszDiagnosticStartupHookPathsLocal;
+}
 
 enum CorEntryPointType
 {
@@ -1376,7 +1417,7 @@ static void RunMainPost()
  }
 }
 
-static void RunManagedStartup()
+void RunManagedStartup()
 {
  CONTRACTL
  {
@@ -1388,7 +1429,11 @@ static void RunManagedStartup()
  CONTRACTL_END;
 
  MethodDescCallSite managedStartup(METHOD__STARTUP_HOOK_PROVIDER__MANAGED_STARTUP);
- managedStartup.Call(NULL);
+
+ ARG_SLOT args[1];
+ args[0] = PtrToArgSlot(s_wszDiagnosticStartupHookPaths);
+
+ managedStartup.Call(args);
 }
 
 INT32 Assembly::ExecuteMainMethod(PTRARRAYREF *stringArgs, BOOL waitForOtherThreads)

src/coreclr/vm/assembly.hpp

@@ -380,6 +380,8 @@ class Assembly
  }
 #endif
 
+ static void AddDiagnosticStartupHookPath(LPCWSTR wszPath);
+
 
 protected:
 #ifdef FEATURE_COMINTEROP

src/coreclr/vm/corelib.h

@@ -812,7 +812,7 @@ DEFINE_FIELD_U(rgiLastFrameFromForeignExceptionStackTrace, StackFrame
 DEFINE_FIELD_U(iFrameCount, StackFrameHelper, iFrameCount)
 
 DEFINE_CLASS(STARTUP_HOOK_PROVIDER, System, StartupHookProvider)
-DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_RetVoid)
+DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_PtrChar_RetVoid)
 
 DEFINE_CLASS(STREAM, IO, Stream)
 DEFINE_METHOD(STREAM, BEGIN_READ, BeginRead, IM_ArrByte_Int_Int_AsyncCallback_Object_RetIAsyncResult)

src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.h

@@ -329,6 +329,28 @@ ds_rt_disable_perfmap (void)
 #endif // FEATURE_PERFMAP
 }
 
+static ep_char16_t * _ds_rt_coreclr_diagnostic_startup_hook_paths = NULL;
+
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	HRESULT hr = S_OK;
+	// This is set to true when the EE has initialized, which occurs after
+	// the diagnostic suspension point has completed.
+	if (g_fEEStarted)
+	{
+ // TODO: Support loading and executing startup hook after EE has completely initialized.
+ return DS_IPC_E_INVALIDARG;
+	}
+	else
+	{
+ Assembly::AddDiagnosticStartupHookPath(reinterpret_cast<LPCWSTR>(startup_hook_path));
+	}
+
+	return DS_IPC_S_OK;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/metasig.h

@@ -338,6 +338,7 @@ DEFINE_METASIG(SM(IntPtr_Bool_RetVoid, I F, v))
 DEFINE_METASIG(SM(IntPtr_UInt_IntPtr_RetVoid, I K I, v))
 DEFINE_METASIG(SM(IntPtr_RetUInt, I, K))
 DEFINE_METASIG(SM(PtrChar_RetInt, P(u), i))
+DEFINE_METASIG(SM(PtrChar_RetVoid, P(u), v))
 DEFINE_METASIG(SM(IntPtr_IntPtr_RetIntPtr, I I, I))
 DEFINE_METASIG(SM(IntPtr_IntPtr_Int_RetIntPtr, I I i, I))
 DEFINE_METASIG(SM(PtrVoid_PtrVoid_RetVoid, P(v) P(v), v))

src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Suppressions.LibraryBuild.xml

@@ -19,7 +19,7 @@
  <argument>ILLink</argument>
  <argument>IL2026</argument>
  <property name="Scope">member</property>
- <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks()</property>
+ <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks(System.String)</property>
  <property name="Justification">This warning is left in the product so developers get an ILLink warning when trimming an app with System.StartupHookProvider.IsSupported=true.</property>
  </attribute>
  </assembly>

src/libraries/System.Private.CoreLib/src/System/StartupHookProvider.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.Tracing;
 using System.Diagnostics.CodeAnalysis;
@@ -27,15 +28,25 @@ private struct StartupHookNameOrPath
 
  // Parse a string specifying a list of assemblies and types
  // containing a startup hook, and call each hook in turn.
- private static void ProcessStartupHooks()
+ private static void ProcessStartupHooks(string diagnosticStartupHooks)
  {
  if (!IsSupported)
  return;
 
  string? startupHooksVariable = AppContext.GetData("STARTUP_HOOKS") as string;
- if (startupHooksVariable == null)
- {
+ if (null == startupHooksVariable && string.IsNullOrEmpty(diagnosticStartupHooks))
  return;
+
+ List<string> startupHookParts = new();
+
+ if (!string.IsNullOrEmpty(diagnosticStartupHooks))
+ {
+ startupHookParts.AddRange(diagnosticStartupHooks.Split(Path.PathSeparator));
+ }
+
+ if (null != startupHooksVariable)
+ {
+ startupHookParts.AddRange(startupHooksVariable.Split(Path.PathSeparator));
  }
 
  ReadOnlySpan<char> disallowedSimpleAssemblyNameChars = stackalloc char[4]
@@ -47,9 +58,8 @@ private static void ProcessStartupHooks()
  };
 
  // Parse startup hooks variable
- string[] startupHookParts = startupHooksVariable.Split(Path.PathSeparator);
- StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Length];
- for (int i = 0; i < startupHookParts.Length; i++)
+ StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Count];
+ for (int i = 0; i < startupHookParts.Count; i++)
  {
  string startupHookPart = startupHookParts[i];
  if (string.IsNullOrEmpty(startupHookPart))

src/mono/mono/eventpipe/ds-rt-mono.h

@@ -239,6 +239,14 @@ ds_rt_disable_perfmap (void)
 	return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	// TODO: Implement.
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/mono/mono/metadata/object.c

@@ -8135,7 +8135,11 @@ mono_runtime_run_startup_hooks (void)
 	mono_error_cleanup (error);
 	if (!method)
  return;
-	mono_runtime_invoke_checked (method, NULL, NULL, error);
+
+	gpointer args [1];
+	args[0] = mono_string_empty_internal (mono_domain_get ());
+
+	mono_runtime_invoke_checked (method, NULL, args, error);
 	// runtime hooks design doc says not to catch exceptions from the hooks
 	mono_error_raise_exception_deprecated (error);
 }

src/native/eventpipe/ds-process-protocol.c

@@ -89,6 +89,12 @@ process_protocol_helper_disable_perfmap (
 	DiagnosticsIpcMessage *message,
 	DiagnosticsIpcStream *stream);
 
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream);
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -872,6 +878,87 @@ process_protocol_helper_disable_perfmap (
 	ep_exit_error_handler ();
 }
 
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void)
+{
+	return ep_rt_object_alloc (DiagnosticsApplyStartupHookPayload);
+}
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload)
+{
+	ep_return_void_if_nok (payload != NULL);
+	ep_rt_byte_array_free (payload->incoming_buffer);
+	ep_rt_object_free (payload);
+}
+
+static
+uint8_t *
+apply_startup_hook_command_try_parse_payload (
+	uint8_t *buffer,
+	uint16_t buffer_len)
+{
+	EP_ASSERT (buffer != NULL);
+
+	uint8_t * buffer_cursor = buffer;
+	uint32_t buffer_cursor_len = buffer_len;
+
+	DiagnosticsApplyStartupHookPayload *instance = ds_apply_startup_hook_payload_alloc ();
+	ep_raise_error_if_nok (instance != NULL);
+
+	instance->incoming_buffer = buffer;
+
+	if (!ds_ipc_message_try_parse_string_utf16_t (&buffer_cursor, &buffer_cursor_len, &instance->startup_hook_path))
+ ep_raise_error ();
+
+ep_on_exit:
+	return (uint8_t *)instance;
+
+ep_on_error:
+	ds_apply_startup_hook_payload_free (instance);
+	instance = NULL;
+	ep_exit_error_handler ();
+}
+
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream)
+{
+	EP_ASSERT (message != NULL);
+	EP_ASSERT (stream != NULL);
+
+	if (!stream)
+ return false;
+
+	bool result = false;
+	DiagnosticsApplyStartupHookPayload *payload = (DiagnosticsApplyStartupHookPayload *)ds_ipc_message_try_parse_payload (message, apply_startup_hook_command_try_parse_payload);
+	if (!payload) {
+ ds_ipc_message_send_error (stream, DS_IPC_E_BAD_ENCODING);
+ ep_raise_error ();
+	}
+
+	ds_ipc_result_t ipc_result;
+	ipc_result = ds_rt_apply_startup_hook (payload->startup_hook_path);
+	if (ipc_result != DS_IPC_S_OK) {
+ ds_ipc_message_send_error (stream, ipc_result);
+ ep_raise_error ();
+	} else {
+ ds_ipc_message_send_success (stream, ipc_result);
+	}
+
+	result = true;
+
+ep_on_exit:
+	ds_ipc_stream_free (stream);
+	return result;
+
+ep_on_error:
+	EP_ASSERT (!result);
+	ep_exit_error_handler ();
+}
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -916,6 +1003,9 @@ ds_process_protocol_helper_handle_ipc_message (
 	case DS_PROCESS_COMMANDID_DISABLE_PERFMAP:
  result = process_protocol_helper_disable_perfmap (message, stream);
  break;
+	case DS_PROCESS_COMMANDID_APPLY_STARTUP_HOOK:
+ result = process_protocol_helper_apply_startup_hook (message, stream);
+ break;
 	default:
  result = process_protocol_helper_unknown_command (message, stream);
  break;

src/native/eventpipe/ds-process-protocol.h

@@ -190,6 +190,32 @@ ds_enable_perfmap_payload_alloc (void);
 void
 ds_enable_perfmap_payload_free (DiagnosticsEnablePerfmapPayload *payload);
 
+/*
+* DiagnosticsApplyStartupHookPayload
+*/
+
+#if defined(DS_INLINE_GETTER_SETTER) || defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+#else
+struct _DiagnosticsApplyStartupHookPayload_Internal {
+#endif
+	uint8_t * incoming_buffer;
+
+	const ep_char16_t *startup_hook_path;
+};
+
+#if !defined(DS_INLINE_GETTER_SETTER) && !defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+	uint8_t _internal [sizeof (struct _DiagnosticsApplyStartupHookPayload_Internal)];
+};
+#endif
+
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void);
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload);
+
 /*
  * DiagnosticsProcessProtocolHelper.
  */

src/coreclr/System.Private.CoreLib/src/System/StartupHookProvider.CoreCLR.cs

@@ -12,15 +12,15 @@ namespace System
 {
  internal static partial class StartupHookProvider
  {
- private static void ManagedStartup()
+ private static unsafe void ManagedStartup(char* pDiagnosticStartupHooks)
  {
 #if FEATURE_PERFTRACING
  if (EventSource.IsSupported)
  RuntimeEventSource.Initialize();
 #endif
 
  if (IsSupported)
- ProcessStartupHooks();
+ ProcessStartupHooks(new string(pDiagnosticStartupHooks));
  }
  }
 }

src/coreclr/nativeaot/Runtime/eventpipe/ds-rt-aot.h

@@ -272,6 +272,13 @@ ds_rt_disable_perfmap (void)
  return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/assembly.cpp

@@ -52,6 +52,7 @@
 //#define STRICT_JITLOCK_ENTRY_LEAK_DETECTION
 //#define STRICT_CLSINITLOCK_ENTRY_LEAK_DETECTION
 
+LPCWSTR s_wszDiagnosticStartupHookPaths = nullptr;
 
 #ifndef DACCESS_COMPILE
 
@@ -1122,7 +1123,47 @@ bool Assembly::IgnoresAccessChecksTo(Assembly *pAccessedAssembly)
  return GetFriendAssemblyInfo()->IgnoresAccessChecksTo(pAccessedAssembly);
 }
 
+void Assembly::AddDiagnosticStartupHookPath(LPCWSTR wszPath)
+{
+ LPCWSTR wszDiagnosticStartupHookPathsLocal = s_wszDiagnosticStartupHookPaths;
+
+ size_t cchPath = u16_strlen(wszPath);
+ size_t cchDiagnosticStartupHookPathsNew = cchPath;
+ size_t cchDiagnosticStartupHookPathsLocal = 0;
+ if (nullptr != wszDiagnosticStartupHookPathsLocal)
+ {
+ cchDiagnosticStartupHookPathsLocal = u16_strlen(wszDiagnosticStartupHookPathsLocal); 
+ // Add 1 for the path separator
+ cchDiagnosticStartupHookPathsNew += cchDiagnosticStartupHookPathsLocal + 1;
+ }
 
+ size_t currentSize = cchDiagnosticStartupHookPathsNew + 1;
+ LPWSTR wszDiagnosticStartupHookPathsNew = new WCHAR[currentSize];
+ LPWSTR wszCurrent = wszDiagnosticStartupHookPathsNew;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszPath);
+ wszCurrent += cchPath;
+ currentSize -= cchPath;
+
+ if (cchDiagnosticStartupHookPathsLocal > 0)
+ {
+ u16_strcpy_s(wszCurrent, currentSize, PATH_SEPARATOR_STR_W);
+ wszCurrent += 1;
+ currentSize -= 1;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszDiagnosticStartupHookPathsLocal);
+ wszCurrent += cchDiagnosticStartupHookPathsLocal;
+ currentSize -= cchDiagnosticStartupHookPathsLocal;
+ }
+
+ // Expect null terminating character
+ _ASSERTE(currentSize == 1);
+ _ASSERTE(wszCurrent[0] == W('\0'));
+
+ s_wszDiagnosticStartupHookPaths = wszDiagnosticStartupHookPathsNew;
+
+ delete [] wszDiagnosticStartupHookPathsLocal;
+}
 
 enum CorEntryPointType
 {
@@ -1376,7 +1417,7 @@ static void RunMainPost()
  }
 }
 
-static void RunManagedStartup()
+void RunManagedStartup()
 {
  CONTRACTL
  {
@@ -1388,7 +1429,11 @@ static void RunManagedStartup()
  CONTRACTL_END;
 
  MethodDescCallSite managedStartup(METHOD__STARTUP_HOOK_PROVIDER__MANAGED_STARTUP);
- managedStartup.Call(NULL);
+
+ ARG_SLOT args[1];
+ args[0] = PtrToArgSlot(s_wszDiagnosticStartupHookPaths);
+
+ managedStartup.Call(args);
 }
 
 INT32 Assembly::ExecuteMainMethod(PTRARRAYREF *stringArgs, BOOL waitForOtherThreads)

src/coreclr/vm/assembly.hpp

@@ -380,6 +380,8 @@ class Assembly
  }
 #endif
 
+ static void AddDiagnosticStartupHookPath(LPCWSTR wszPath);
+
 
 protected:
 #ifdef FEATURE_COMINTEROP

src/coreclr/vm/corelib.h

@@ -812,7 +812,7 @@ DEFINE_FIELD_U(rgiLastFrameFromForeignExceptionStackTrace, StackFrame
 DEFINE_FIELD_U(iFrameCount, StackFrameHelper, iFrameCount)
 
 DEFINE_CLASS(STARTUP_HOOK_PROVIDER, System, StartupHookProvider)
-DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_RetVoid)
+DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_PtrChar_RetVoid)
 
 DEFINE_CLASS(STREAM, IO, Stream)
 DEFINE_METHOD(STREAM, BEGIN_READ, BeginRead, IM_ArrByte_Int_Int_AsyncCallback_Object_RetIAsyncResult)

src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.h

@@ -329,6 +329,28 @@ ds_rt_disable_perfmap (void)
 #endif // FEATURE_PERFMAP
 }
 
+static ep_char16_t * _ds_rt_coreclr_diagnostic_startup_hook_paths = NULL;
+
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	HRESULT hr = S_OK;
+	// This is set to true when the EE has initialized, which occurs after
+	// the diagnostic suspension point has completed.
+	if (g_fEEStarted)
+	{
+ // TODO: Support loading and executing startup hook after EE has completely initialized.
+ return DS_IPC_E_INVALIDARG;
+	}
+	else
+	{
+ Assembly::AddDiagnosticStartupHookPath(reinterpret_cast<LPCWSTR>(startup_hook_path));
+	}
+
+	return DS_IPC_S_OK;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/metasig.h

@@ -338,6 +338,7 @@ DEFINE_METASIG(SM(IntPtr_Bool_RetVoid, I F, v))
 DEFINE_METASIG(SM(IntPtr_UInt_IntPtr_RetVoid, I K I, v))
 DEFINE_METASIG(SM(IntPtr_RetUInt, I, K))
 DEFINE_METASIG(SM(PtrChar_RetInt, P(u), i))
+DEFINE_METASIG(SM(PtrChar_RetVoid, P(u), v))
 DEFINE_METASIG(SM(IntPtr_IntPtr_RetIntPtr, I I, I))
 DEFINE_METASIG(SM(IntPtr_IntPtr_Int_RetIntPtr, I I i, I))
 DEFINE_METASIG(SM(PtrVoid_PtrVoid_RetVoid, P(v) P(v), v))

src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Suppressions.LibraryBuild.xml

@@ -19,7 +19,7 @@
  <argument>ILLink</argument>
  <argument>IL2026</argument>
  <property name="Scope">member</property>
- <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks()</property>
+ <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks(System.String)</property>
  <property name="Justification">This warning is left in the product so developers get an ILLink warning when trimming an app with System.StartupHookProvider.IsSupported=true.</property>
  </attribute>
  </assembly>

src/libraries/System.Private.CoreLib/src/System/StartupHookProvider.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.Tracing;
 using System.Diagnostics.CodeAnalysis;
@@ -27,15 +28,25 @@ private struct StartupHookNameOrPath
 
  // Parse a string specifying a list of assemblies and types
  // containing a startup hook, and call each hook in turn.
- private static void ProcessStartupHooks()
+ private static void ProcessStartupHooks(string diagnosticStartupHooks)
  {
  if (!IsSupported)
  return;
 
  string? startupHooksVariable = AppContext.GetData("STARTUP_HOOKS") as string;
- if (startupHooksVariable == null)
- {
+ if (null == startupHooksVariable && string.IsNullOrEmpty(diagnosticStartupHooks))
  return;
+
+ List<string> startupHookParts = new();
+
+ if (!string.IsNullOrEmpty(diagnosticStartupHooks))
+ {
+ startupHookParts.AddRange(diagnosticStartupHooks.Split(Path.PathSeparator));
+ }
+
+ if (null != startupHooksVariable)
+ {
+ startupHookParts.AddRange(startupHooksVariable.Split(Path.PathSeparator));
  }
 
  ReadOnlySpan<char> disallowedSimpleAssemblyNameChars = stackalloc char[4]
@@ -47,9 +58,8 @@ private static void ProcessStartupHooks()
  };
 
  // Parse startup hooks variable
- string[] startupHookParts = startupHooksVariable.Split(Path.PathSeparator);
- StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Length];
- for (int i = 0; i < startupHookParts.Length; i++)
+ StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Count];
+ for (int i = 0; i < startupHookParts.Count; i++)
  {
  string startupHookPart = startupHookParts[i];
  if (string.IsNullOrEmpty(startupHookPart))

src/mono/mono/eventpipe/ds-rt-mono.h

@@ -239,6 +239,14 @@ ds_rt_disable_perfmap (void)
 	return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	// TODO: Implement.
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/mono/mono/metadata/object.c

@@ -8135,7 +8135,11 @@ mono_runtime_run_startup_hooks (void)
 	mono_error_cleanup (error);
 	if (!method)
  return;
-	mono_runtime_invoke_checked (method, NULL, NULL, error);
+
+	gpointer args [1];
+	args[0] = mono_string_empty_internal (mono_domain_get ());
+
+	mono_runtime_invoke_checked (method, NULL, args, error);
 	// runtime hooks design doc says not to catch exceptions from the hooks
 	mono_error_raise_exception_deprecated (error);
 }

src/native/eventpipe/ds-process-protocol.c

@@ -89,6 +89,12 @@ process_protocol_helper_disable_perfmap (
 	DiagnosticsIpcMessage *message,
 	DiagnosticsIpcStream *stream);
 
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream);
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -872,6 +878,87 @@ process_protocol_helper_disable_perfmap (
 	ep_exit_error_handler ();
 }
 
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void)
+{
+	return ep_rt_object_alloc (DiagnosticsApplyStartupHookPayload);
+}
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload)
+{
+	ep_return_void_if_nok (payload != NULL);
+	ep_rt_byte_array_free (payload->incoming_buffer);
+	ep_rt_object_free (payload);
+}
+
+static
+uint8_t *
+apply_startup_hook_command_try_parse_payload (
+	uint8_t *buffer,
+	uint16_t buffer_len)
+{
+	EP_ASSERT (buffer != NULL);
+
+	uint8_t * buffer_cursor = buffer;
+	uint32_t buffer_cursor_len = buffer_len;
+
+	DiagnosticsApplyStartupHookPayload *instance = ds_apply_startup_hook_payload_alloc ();
+	ep_raise_error_if_nok (instance != NULL);
+
+	instance->incoming_buffer = buffer;
+
+	if (!ds_ipc_message_try_parse_string_utf16_t (&buffer_cursor, &buffer_cursor_len, &instance->startup_hook_path))
+ ep_raise_error ();
+
+ep_on_exit:
+	return (uint8_t *)instance;
+
+ep_on_error:
+	ds_apply_startup_hook_payload_free (instance);
+	instance = NULL;
+	ep_exit_error_handler ();
+}
+
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream)
+{
+	EP_ASSERT (message != NULL);
+	EP_ASSERT (stream != NULL);
+
+	if (!stream)
+ return false;
+
+	bool result = false;
+	DiagnosticsApplyStartupHookPayload *payload = (DiagnosticsApplyStartupHookPayload *)ds_ipc_message_try_parse_payload (message, apply_startup_hook_command_try_parse_payload);
+	if (!payload) {
+ ds_ipc_message_send_error (stream, DS_IPC_E_BAD_ENCODING);
+ ep_raise_error ();
+	}
+
+	ds_ipc_result_t ipc_result;
+	ipc_result = ds_rt_apply_startup_hook (payload->startup_hook_path);
+	if (ipc_result != DS_IPC_S_OK) {
+ ds_ipc_message_send_error (stream, ipc_result);
+ ep_raise_error ();
+	} else {
+ ds_ipc_message_send_success (stream, ipc_result);
+	}
+
+	result = true;
+
+ep_on_exit:
+	ds_ipc_stream_free (stream);
+	return result;
+
+ep_on_error:
+	EP_ASSERT (!result);
+	ep_exit_error_handler ();
+}
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -916,6 +1003,9 @@ ds_process_protocol_helper_handle_ipc_message (
 	case DS_PROCESS_COMMANDID_DISABLE_PERFMAP:
  result = process_protocol_helper_disable_perfmap (message, stream);
  break;
+	case DS_PROCESS_COMMANDID_APPLY_STARTUP_HOOK:
+ result = process_protocol_helper_apply_startup_hook (message, stream);
+ break;
 	default:
  result = process_protocol_helper_unknown_command (message, stream);
  break;

src/native/eventpipe/ds-process-protocol.h

@@ -190,6 +190,32 @@ ds_enable_perfmap_payload_alloc (void);
 void
 ds_enable_perfmap_payload_free (DiagnosticsEnablePerfmapPayload *payload);
 
+/*
+* DiagnosticsApplyStartupHookPayload
+*/
+
+#if defined(DS_INLINE_GETTER_SETTER) || defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+#else
+struct _DiagnosticsApplyStartupHookPayload_Internal {
+#endif
+	uint8_t * incoming_buffer;
+
+	const ep_char16_t *startup_hook_path;
+};
+
+#if !defined(DS_INLINE_GETTER_SETTER) && !defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+	uint8_t _internal [sizeof (struct _DiagnosticsApplyStartupHookPayload_Internal)];
+};
+#endif
+
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void);
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload);
+
 /*
  * DiagnosticsProcessProtocolHelper.
  */

src/coreclr/System.Private.CoreLib/src/System/StartupHookProvider.CoreCLR.cs

@@ -12,15 +12,15 @@ namespace System
 {
  internal static partial class StartupHookProvider
  {
- private static void ManagedStartup()
+ private static unsafe void ManagedStartup(char* pDiagnosticStartupHooks)
  {
 #if FEATURE_PERFTRACING
  if (EventSource.IsSupported)
  RuntimeEventSource.Initialize();
 #endif
 
  if (IsSupported)
- ProcessStartupHooks();
+ ProcessStartupHooks(new string(pDiagnosticStartupHooks));
  }
  }
 }

src/coreclr/nativeaot/Runtime/eventpipe/ds-rt-aot.h

@@ -272,6 +272,13 @@ ds_rt_disable_perfmap (void)
  return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/assembly.cpp

@@ -52,6 +52,7 @@
 //#define STRICT_JITLOCK_ENTRY_LEAK_DETECTION
 //#define STRICT_CLSINITLOCK_ENTRY_LEAK_DETECTION
 
+LPCWSTR s_wszDiagnosticStartupHookPaths = nullptr;
 
 #ifndef DACCESS_COMPILE
 
@@ -1122,7 +1123,47 @@ bool Assembly::IgnoresAccessChecksTo(Assembly *pAccessedAssembly)
  return GetFriendAssemblyInfo()->IgnoresAccessChecksTo(pAccessedAssembly);
 }
 
+void Assembly::AddDiagnosticStartupHookPath(LPCWSTR wszPath)
+{
+ LPCWSTR wszDiagnosticStartupHookPathsLocal = s_wszDiagnosticStartupHookPaths;
+
+ size_t cchPath = u16_strlen(wszPath);
+ size_t cchDiagnosticStartupHookPathsNew = cchPath;
+ size_t cchDiagnosticStartupHookPathsLocal = 0;
+ if (nullptr != wszDiagnosticStartupHookPathsLocal)
+ {
+ cchDiagnosticStartupHookPathsLocal = u16_strlen(wszDiagnosticStartupHookPathsLocal); 
+ // Add 1 for the path separator
+ cchDiagnosticStartupHookPathsNew += cchDiagnosticStartupHookPathsLocal + 1;
+ }
 
+ size_t currentSize = cchDiagnosticStartupHookPathsNew + 1;
+ LPWSTR wszDiagnosticStartupHookPathsNew = new WCHAR[currentSize];
+ LPWSTR wszCurrent = wszDiagnosticStartupHookPathsNew;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszPath);
+ wszCurrent += cchPath;
+ currentSize -= cchPath;
+
+ if (cchDiagnosticStartupHookPathsLocal > 0)
+ {
+ u16_strcpy_s(wszCurrent, currentSize, PATH_SEPARATOR_STR_W);
+ wszCurrent += 1;
+ currentSize -= 1;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszDiagnosticStartupHookPathsLocal);
+ wszCurrent += cchDiagnosticStartupHookPathsLocal;
+ currentSize -= cchDiagnosticStartupHookPathsLocal;
+ }
+
+ // Expect null terminating character
+ _ASSERTE(currentSize == 1);
+ _ASSERTE(wszCurrent[0] == W('\0'));
+
+ s_wszDiagnosticStartupHookPaths = wszDiagnosticStartupHookPathsNew;
+
+ delete [] wszDiagnosticStartupHookPathsLocal;
+}
 
 enum CorEntryPointType
 {
@@ -1376,7 +1417,7 @@ static void RunMainPost()
  }
 }
 
-static void RunManagedStartup()
+void RunManagedStartup()
 {
  CONTRACTL
  {
@@ -1388,7 +1429,11 @@ static void RunManagedStartup()
  CONTRACTL_END;
 
  MethodDescCallSite managedStartup(METHOD__STARTUP_HOOK_PROVIDER__MANAGED_STARTUP);
- managedStartup.Call(NULL);
+
+ ARG_SLOT args[1];
+ args[0] = PtrToArgSlot(s_wszDiagnosticStartupHookPaths);
+
+ managedStartup.Call(args);
 }
 
 INT32 Assembly::ExecuteMainMethod(PTRARRAYREF *stringArgs, BOOL waitForOtherThreads)

src/coreclr/vm/assembly.hpp

@@ -380,6 +380,8 @@ class Assembly
  }
 #endif
 
+ static void AddDiagnosticStartupHookPath(LPCWSTR wszPath);
+
 
 protected:
 #ifdef FEATURE_COMINTEROP

src/coreclr/vm/corelib.h

@@ -812,7 +812,7 @@ DEFINE_FIELD_U(rgiLastFrameFromForeignExceptionStackTrace, StackFrame
 DEFINE_FIELD_U(iFrameCount, StackFrameHelper, iFrameCount)
 
 DEFINE_CLASS(STARTUP_HOOK_PROVIDER, System, StartupHookProvider)
-DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_RetVoid)
+DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_PtrChar_RetVoid)
 
 DEFINE_CLASS(STREAM, IO, Stream)
 DEFINE_METHOD(STREAM, BEGIN_READ, BeginRead, IM_ArrByte_Int_Int_AsyncCallback_Object_RetIAsyncResult)

src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.h

@@ -329,6 +329,28 @@ ds_rt_disable_perfmap (void)
 #endif // FEATURE_PERFMAP
 }
 
+static ep_char16_t * _ds_rt_coreclr_diagnostic_startup_hook_paths = NULL;
+
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	HRESULT hr = S_OK;
+	// This is set to true when the EE has initialized, which occurs after
+	// the diagnostic suspension point has completed.
+	if (g_fEEStarted)
+	{
+ // TODO: Support loading and executing startup hook after EE has completely initialized.
+ return DS_IPC_E_INVALIDARG;
+	}
+	else
+	{
+ Assembly::AddDiagnosticStartupHookPath(reinterpret_cast<LPCWSTR>(startup_hook_path));
+	}
+
+	return DS_IPC_S_OK;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/metasig.h

@@ -338,6 +338,7 @@ DEFINE_METASIG(SM(IntPtr_Bool_RetVoid, I F, v))
 DEFINE_METASIG(SM(IntPtr_UInt_IntPtr_RetVoid, I K I, v))
 DEFINE_METASIG(SM(IntPtr_RetUInt, I, K))
 DEFINE_METASIG(SM(PtrChar_RetInt, P(u), i))
+DEFINE_METASIG(SM(PtrChar_RetVoid, P(u), v))
 DEFINE_METASIG(SM(IntPtr_IntPtr_RetIntPtr, I I, I))
 DEFINE_METASIG(SM(IntPtr_IntPtr_Int_RetIntPtr, I I i, I))
 DEFINE_METASIG(SM(PtrVoid_PtrVoid_RetVoid, P(v) P(v), v))

src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Suppressions.LibraryBuild.xml

@@ -19,7 +19,7 @@
  <argument>ILLink</argument>
  <argument>IL2026</argument>
  <property name="Scope">member</property>
- <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks()</property>
+ <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks(System.String)</property>
  <property name="Justification">This warning is left in the product so developers get an ILLink warning when trimming an app with System.StartupHookProvider.IsSupported=true.</property>
  </attribute>
  </assembly>

src/libraries/System.Private.CoreLib/src/System/StartupHookProvider.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.Tracing;
 using System.Diagnostics.CodeAnalysis;
@@ -27,15 +28,25 @@ private struct StartupHookNameOrPath
 
  // Parse a string specifying a list of assemblies and types
  // containing a startup hook, and call each hook in turn.
- private static void ProcessStartupHooks()
+ private static void ProcessStartupHooks(string diagnosticStartupHooks)
  {
  if (!IsSupported)
  return;
 
  string? startupHooksVariable = AppContext.GetData("STARTUP_HOOKS") as string;
- if (startupHooksVariable == null)
- {
+ if (null == startupHooksVariable && string.IsNullOrEmpty(diagnosticStartupHooks))
  return;
+
+ List<string> startupHookParts = new();
+
+ if (!string.IsNullOrEmpty(diagnosticStartupHooks))
+ {
+ startupHookParts.AddRange(diagnosticStartupHooks.Split(Path.PathSeparator));
+ }
+
+ if (null != startupHooksVariable)
+ {
+ startupHookParts.AddRange(startupHooksVariable.Split(Path.PathSeparator));
  }
 
  ReadOnlySpan<char> disallowedSimpleAssemblyNameChars = stackalloc char[4]
@@ -47,9 +58,8 @@ private static void ProcessStartupHooks()
  };
 
  // Parse startup hooks variable
- string[] startupHookParts = startupHooksVariable.Split(Path.PathSeparator);
- StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Length];
- for (int i = 0; i < startupHookParts.Length; i++)
+ StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Count];
+ for (int i = 0; i < startupHookParts.Count; i++)
  {
  string startupHookPart = startupHookParts[i];
  if (string.IsNullOrEmpty(startupHookPart))

src/mono/mono/eventpipe/ds-rt-mono.h

@@ -239,6 +239,14 @@ ds_rt_disable_perfmap (void)
 	return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	// TODO: Implement.
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/mono/mono/metadata/object.c

@@ -8135,7 +8135,11 @@ mono_runtime_run_startup_hooks (void)
 	mono_error_cleanup (error);
 	if (!method)
  return;
-	mono_runtime_invoke_checked (method, NULL, NULL, error);
+
+	gpointer args [1];
+	args[0] = mono_string_empty_internal (mono_domain_get ());
+
+	mono_runtime_invoke_checked (method, NULL, args, error);
 	// runtime hooks design doc says not to catch exceptions from the hooks
 	mono_error_raise_exception_deprecated (error);
 }

src/native/eventpipe/ds-process-protocol.c

@@ -89,6 +89,12 @@ process_protocol_helper_disable_perfmap (
 	DiagnosticsIpcMessage *message,
 	DiagnosticsIpcStream *stream);
 
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream);
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -872,6 +878,87 @@ process_protocol_helper_disable_perfmap (
 	ep_exit_error_handler ();
 }
 
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void)
+{
+	return ep_rt_object_alloc (DiagnosticsApplyStartupHookPayload);
+}
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload)
+{
+	ep_return_void_if_nok (payload != NULL);
+	ep_rt_byte_array_free (payload->incoming_buffer);
+	ep_rt_object_free (payload);
+}
+
+static
+uint8_t *
+apply_startup_hook_command_try_parse_payload (
+	uint8_t *buffer,
+	uint16_t buffer_len)
+{
+	EP_ASSERT (buffer != NULL);
+
+	uint8_t * buffer_cursor = buffer;
+	uint32_t buffer_cursor_len = buffer_len;
+
+	DiagnosticsApplyStartupHookPayload *instance = ds_apply_startup_hook_payload_alloc ();
+	ep_raise_error_if_nok (instance != NULL);
+
+	instance->incoming_buffer = buffer;
+
+	if (!ds_ipc_message_try_parse_string_utf16_t (&buffer_cursor, &buffer_cursor_len, &instance->startup_hook_path))
+ ep_raise_error ();
+
+ep_on_exit:
+	return (uint8_t *)instance;
+
+ep_on_error:
+	ds_apply_startup_hook_payload_free (instance);
+	instance = NULL;
+	ep_exit_error_handler ();
+}
+
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream)
+{
+	EP_ASSERT (message != NULL);
+	EP_ASSERT (stream != NULL);
+
+	if (!stream)
+ return false;
+
+	bool result = false;
+	DiagnosticsApplyStartupHookPayload *payload = (DiagnosticsApplyStartupHookPayload *)ds_ipc_message_try_parse_payload (message, apply_startup_hook_command_try_parse_payload);
+	if (!payload) {
+ ds_ipc_message_send_error (stream, DS_IPC_E_BAD_ENCODING);
+ ep_raise_error ();
+	}
+
+	ds_ipc_result_t ipc_result;
+	ipc_result = ds_rt_apply_startup_hook (payload->startup_hook_path);
+	if (ipc_result != DS_IPC_S_OK) {
+ ds_ipc_message_send_error (stream, ipc_result);
+ ep_raise_error ();
+	} else {
+ ds_ipc_message_send_success (stream, ipc_result);
+	}
+
+	result = true;
+
+ep_on_exit:
+	ds_ipc_stream_free (stream);
+	return result;
+
+ep_on_error:
+	EP_ASSERT (!result);
+	ep_exit_error_handler ();
+}
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -916,6 +1003,9 @@ ds_process_protocol_helper_handle_ipc_message (
 	case DS_PROCESS_COMMANDID_DISABLE_PERFMAP:
  result = process_protocol_helper_disable_perfmap (message, stream);
  break;
+	case DS_PROCESS_COMMANDID_APPLY_STARTUP_HOOK:
+ result = process_protocol_helper_apply_startup_hook (message, stream);
+ break;
 	default:
  result = process_protocol_helper_unknown_command (message, stream);
  break;

src/native/eventpipe/ds-process-protocol.h

@@ -190,6 +190,32 @@ ds_enable_perfmap_payload_alloc (void);
 void
 ds_enable_perfmap_payload_free (DiagnosticsEnablePerfmapPayload *payload);
 
+/*
+* DiagnosticsApplyStartupHookPayload
+*/
+
+#if defined(DS_INLINE_GETTER_SETTER) || defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+#else
+struct _DiagnosticsApplyStartupHookPayload_Internal {
+#endif
+	uint8_t * incoming_buffer;
+
+	const ep_char16_t *startup_hook_path;
+};
+
+#if !defined(DS_INLINE_GETTER_SETTER) && !defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+	uint8_t _internal [sizeof (struct _DiagnosticsApplyStartupHookPayload_Internal)];
+};
+#endif
+
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void);
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload);
+
 /*
  * DiagnosticsProcessProtocolHelper.
  */

src/coreclr/System.Private.CoreLib/src/System/StartupHookProvider.CoreCLR.cs

@@ -12,15 +12,15 @@ namespace System
 {
  internal static partial class StartupHookProvider
  {
- private static void ManagedStartup()
+ private static unsafe void ManagedStartup(char* pDiagnosticStartupHooks)
  {
 #if FEATURE_PERFTRACING
  if (EventSource.IsSupported)
  RuntimeEventSource.Initialize();
 #endif
 
  if (IsSupported)
- ProcessStartupHooks();
+ ProcessStartupHooks(new string(pDiagnosticStartupHooks));
  }
  }
 }

src/coreclr/nativeaot/Runtime/eventpipe/ds-rt-aot.h

@@ -272,6 +272,13 @@ ds_rt_disable_perfmap (void)
  return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/assembly.cpp

@@ -52,6 +52,7 @@
 //#define STRICT_JITLOCK_ENTRY_LEAK_DETECTION
 //#define STRICT_CLSINITLOCK_ENTRY_LEAK_DETECTION
 
+LPCWSTR s_wszDiagnosticStartupHookPaths = nullptr;
 
 #ifndef DACCESS_COMPILE
 
@@ -1122,7 +1123,47 @@ bool Assembly::IgnoresAccessChecksTo(Assembly *pAccessedAssembly)
  return GetFriendAssemblyInfo()->IgnoresAccessChecksTo(pAccessedAssembly);
 }
 
+void Assembly::AddDiagnosticStartupHookPath(LPCWSTR wszPath)
+{
+ LPCWSTR wszDiagnosticStartupHookPathsLocal = s_wszDiagnosticStartupHookPaths;
+
+ size_t cchPath = u16_strlen(wszPath);
+ size_t cchDiagnosticStartupHookPathsNew = cchPath;
+ size_t cchDiagnosticStartupHookPathsLocal = 0;
+ if (nullptr != wszDiagnosticStartupHookPathsLocal)
+ {
+ cchDiagnosticStartupHookPathsLocal = u16_strlen(wszDiagnosticStartupHookPathsLocal); 
+ // Add 1 for the path separator
+ cchDiagnosticStartupHookPathsNew += cchDiagnosticStartupHookPathsLocal + 1;
+ }
 
+ size_t currentSize = cchDiagnosticStartupHookPathsNew + 1;
+ LPWSTR wszDiagnosticStartupHookPathsNew = new WCHAR[currentSize];
+ LPWSTR wszCurrent = wszDiagnosticStartupHookPathsNew;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszPath);
+ wszCurrent += cchPath;
+ currentSize -= cchPath;
+
+ if (cchDiagnosticStartupHookPathsLocal > 0)
+ {
+ u16_strcpy_s(wszCurrent, currentSize, PATH_SEPARATOR_STR_W);
+ wszCurrent += 1;
+ currentSize -= 1;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszDiagnosticStartupHookPathsLocal);
+ wszCurrent += cchDiagnosticStartupHookPathsLocal;
+ currentSize -= cchDiagnosticStartupHookPathsLocal;
+ }
+
+ // Expect null terminating character
+ _ASSERTE(currentSize == 1);
+ _ASSERTE(wszCurrent[0] == W('\0'));
+
+ s_wszDiagnosticStartupHookPaths = wszDiagnosticStartupHookPathsNew;
+
+ delete [] wszDiagnosticStartupHookPathsLocal;
+}
 
 enum CorEntryPointType
 {
@@ -1376,7 +1417,7 @@ static void RunMainPost()
  }
 }
 
-static void RunManagedStartup()
+void RunManagedStartup()
 {
  CONTRACTL
  {
@@ -1388,7 +1429,11 @@ static void RunManagedStartup()
  CONTRACTL_END;
 
  MethodDescCallSite managedStartup(METHOD__STARTUP_HOOK_PROVIDER__MANAGED_STARTUP);
- managedStartup.Call(NULL);
+
+ ARG_SLOT args[1];
+ args[0] = PtrToArgSlot(s_wszDiagnosticStartupHookPaths);
+
+ managedStartup.Call(args);
 }
 
 INT32 Assembly::ExecuteMainMethod(PTRARRAYREF *stringArgs, BOOL waitForOtherThreads)

src/coreclr/vm/assembly.hpp

@@ -380,6 +380,8 @@ class Assembly
  }
 #endif
 
+ static void AddDiagnosticStartupHookPath(LPCWSTR wszPath);
+
 
 protected:
 #ifdef FEATURE_COMINTEROP

src/coreclr/vm/corelib.h

@@ -812,7 +812,7 @@ DEFINE_FIELD_U(rgiLastFrameFromForeignExceptionStackTrace, StackFrame
 DEFINE_FIELD_U(iFrameCount, StackFrameHelper, iFrameCount)
 
 DEFINE_CLASS(STARTUP_HOOK_PROVIDER, System, StartupHookProvider)
-DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_RetVoid)
+DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_PtrChar_RetVoid)
 
 DEFINE_CLASS(STREAM, IO, Stream)
 DEFINE_METHOD(STREAM, BEGIN_READ, BeginRead, IM_ArrByte_Int_Int_AsyncCallback_Object_RetIAsyncResult)

src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.h

@@ -329,6 +329,28 @@ ds_rt_disable_perfmap (void)
 #endif // FEATURE_PERFMAP
 }
 
+static ep_char16_t * _ds_rt_coreclr_diagnostic_startup_hook_paths = NULL;
+
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	HRESULT hr = S_OK;
+	// This is set to true when the EE has initialized, which occurs after
+	// the diagnostic suspension point has completed.
+	if (g_fEEStarted)
+	{
+ // TODO: Support loading and executing startup hook after EE has completely initialized.
+ return DS_IPC_E_INVALIDARG;
+	}
+	else
+	{
+ Assembly::AddDiagnosticStartupHookPath(reinterpret_cast<LPCWSTR>(startup_hook_path));
+	}
+
+	return DS_IPC_S_OK;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/metasig.h

@@ -338,6 +338,7 @@ DEFINE_METASIG(SM(IntPtr_Bool_RetVoid, I F, v))
 DEFINE_METASIG(SM(IntPtr_UInt_IntPtr_RetVoid, I K I, v))
 DEFINE_METASIG(SM(IntPtr_RetUInt, I, K))
 DEFINE_METASIG(SM(PtrChar_RetInt, P(u), i))
+DEFINE_METASIG(SM(PtrChar_RetVoid, P(u), v))
 DEFINE_METASIG(SM(IntPtr_IntPtr_RetIntPtr, I I, I))
 DEFINE_METASIG(SM(IntPtr_IntPtr_Int_RetIntPtr, I I i, I))
 DEFINE_METASIG(SM(PtrVoid_PtrVoid_RetVoid, P(v) P(v), v))

src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Suppressions.LibraryBuild.xml

@@ -19,7 +19,7 @@
  <argument>ILLink</argument>
  <argument>IL2026</argument>
  <property name="Scope">member</property>
- <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks()</property>
+ <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks(System.String)</property>
  <property name="Justification">This warning is left in the product so developers get an ILLink warning when trimming an app with System.StartupHookProvider.IsSupported=true.</property>
  </attribute>
  </assembly>

src/libraries/System.Private.CoreLib/src/System/StartupHookProvider.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.Tracing;
 using System.Diagnostics.CodeAnalysis;
@@ -27,15 +28,25 @@ private struct StartupHookNameOrPath
 
  // Parse a string specifying a list of assemblies and types
  // containing a startup hook, and call each hook in turn.
- private static void ProcessStartupHooks()
+ private static void ProcessStartupHooks(string diagnosticStartupHooks)
  {
  if (!IsSupported)
  return;
 
  string? startupHooksVariable = AppContext.GetData("STARTUP_HOOKS") as string;
- if (startupHooksVariable == null)
- {
+ if (null == startupHooksVariable && string.IsNullOrEmpty(diagnosticStartupHooks))
  return;
+
+ List<string> startupHookParts = new();
+
+ if (!string.IsNullOrEmpty(diagnosticStartupHooks))
+ {
+ startupHookParts.AddRange(diagnosticStartupHooks.Split(Path.PathSeparator));
+ }
+
+ if (null != startupHooksVariable)
+ {
+ startupHookParts.AddRange(startupHooksVariable.Split(Path.PathSeparator));
  }
 
  ReadOnlySpan<char> disallowedSimpleAssemblyNameChars = stackalloc char[4]
@@ -47,9 +58,8 @@ private static void ProcessStartupHooks()
  };
 
  // Parse startup hooks variable
- string[] startupHookParts = startupHooksVariable.Split(Path.PathSeparator);
- StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Length];
- for (int i = 0; i < startupHookParts.Length; i++)
+ StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Count];
+ for (int i = 0; i < startupHookParts.Count; i++)
  {
  string startupHookPart = startupHookParts[i];
  if (string.IsNullOrEmpty(startupHookPart))

src/mono/mono/eventpipe/ds-rt-mono.h

@@ -239,6 +239,14 @@ ds_rt_disable_perfmap (void)
 	return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	// TODO: Implement.
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/mono/mono/metadata/object.c

@@ -8135,7 +8135,11 @@ mono_runtime_run_startup_hooks (void)
 	mono_error_cleanup (error);
 	if (!method)
  return;
-	mono_runtime_invoke_checked (method, NULL, NULL, error);
+
+	gpointer args [1];
+	args[0] = mono_string_empty_internal (mono_domain_get ());
+
+	mono_runtime_invoke_checked (method, NULL, args, error);
 	// runtime hooks design doc says not to catch exceptions from the hooks
 	mono_error_raise_exception_deprecated (error);
 }

src/native/eventpipe/ds-process-protocol.c

@@ -89,6 +89,12 @@ process_protocol_helper_disable_perfmap (
 	DiagnosticsIpcMessage *message,
 	DiagnosticsIpcStream *stream);
 
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream);
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -872,6 +878,87 @@ process_protocol_helper_disable_perfmap (
 	ep_exit_error_handler ();
 }
 
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void)
+{
+	return ep_rt_object_alloc (DiagnosticsApplyStartupHookPayload);
+}
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload)
+{
+	ep_return_void_if_nok (payload != NULL);
+	ep_rt_byte_array_free (payload->incoming_buffer);
+	ep_rt_object_free (payload);
+}
+
+static
+uint8_t *
+apply_startup_hook_command_try_parse_payload (
+	uint8_t *buffer,
+	uint16_t buffer_len)
+{
+	EP_ASSERT (buffer != NULL);
+
+	uint8_t * buffer_cursor = buffer;
+	uint32_t buffer_cursor_len = buffer_len;
+
+	DiagnosticsApplyStartupHookPayload *instance = ds_apply_startup_hook_payload_alloc ();
+	ep_raise_error_if_nok (instance != NULL);
+
+	instance->incoming_buffer = buffer;
+
+	if (!ds_ipc_message_try_parse_string_utf16_t (&buffer_cursor, &buffer_cursor_len, &instance->startup_hook_path))
+ ep_raise_error ();
+
+ep_on_exit:
+	return (uint8_t *)instance;
+
+ep_on_error:
+	ds_apply_startup_hook_payload_free (instance);
+	instance = NULL;
+	ep_exit_error_handler ();
+}
+
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream)
+{
+	EP_ASSERT (message != NULL);
+	EP_ASSERT (stream != NULL);
+
+	if (!stream)
+ return false;
+
+	bool result = false;
+	DiagnosticsApplyStartupHookPayload *payload = (DiagnosticsApplyStartupHookPayload *)ds_ipc_message_try_parse_payload (message, apply_startup_hook_command_try_parse_payload);
+	if (!payload) {
+ ds_ipc_message_send_error (stream, DS_IPC_E_BAD_ENCODING);
+ ep_raise_error ();
+	}
+
+	ds_ipc_result_t ipc_result;
+	ipc_result = ds_rt_apply_startup_hook (payload->startup_hook_path);
+	if (ipc_result != DS_IPC_S_OK) {
+ ds_ipc_message_send_error (stream, ipc_result);
+ ep_raise_error ();
+	} else {
+ ds_ipc_message_send_success (stream, ipc_result);
+	}
+
+	result = true;
+
+ep_on_exit:
+	ds_ipc_stream_free (stream);
+	return result;
+
+ep_on_error:
+	EP_ASSERT (!result);
+	ep_exit_error_handler ();
+}
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -916,6 +1003,9 @@ ds_process_protocol_helper_handle_ipc_message (
 	case DS_PROCESS_COMMANDID_DISABLE_PERFMAP:
  result = process_protocol_helper_disable_perfmap (message, stream);
  break;
+	case DS_PROCESS_COMMANDID_APPLY_STARTUP_HOOK:
+ result = process_protocol_helper_apply_startup_hook (message, stream);
+ break;
 	default:
  result = process_protocol_helper_unknown_command (message, stream);
  break;

src/native/eventpipe/ds-process-protocol.h

@@ -190,6 +190,32 @@ ds_enable_perfmap_payload_alloc (void);
 void
 ds_enable_perfmap_payload_free (DiagnosticsEnablePerfmapPayload *payload);
 
+/*
+* DiagnosticsApplyStartupHookPayload
+*/
+
+#if defined(DS_INLINE_GETTER_SETTER) || defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+#else
+struct _DiagnosticsApplyStartupHookPayload_Internal {
+#endif
+	uint8_t * incoming_buffer;
+
+	const ep_char16_t *startup_hook_path;
+};
+
+#if !defined(DS_INLINE_GETTER_SETTER) && !defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+	uint8_t _internal [sizeof (struct _DiagnosticsApplyStartupHookPayload_Internal)];
+};
+#endif
+
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void);
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload);
+
 /*
  * DiagnosticsProcessProtocolHelper.
  */

src/coreclr/System.Private.CoreLib/src/System/StartupHookProvider.CoreCLR.cs

@@ -12,15 +12,15 @@ namespace System
 {
  internal static partial class StartupHookProvider
  {
- private static void ManagedStartup()
+ private static unsafe void ManagedStartup(char* pDiagnosticStartupHooks)
  {
 #if FEATURE_PERFTRACING
  if (EventSource.IsSupported)
  RuntimeEventSource.Initialize();
 #endif
 
  if (IsSupported)
- ProcessStartupHooks();
+ ProcessStartupHooks(new string(pDiagnosticStartupHooks));
  }
  }
 }

src/coreclr/nativeaot/Runtime/eventpipe/ds-rt-aot.h

@@ -272,6 +272,13 @@ ds_rt_disable_perfmap (void)
  return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/assembly.cpp

@@ -52,6 +52,7 @@
 //#define STRICT_JITLOCK_ENTRY_LEAK_DETECTION
 //#define STRICT_CLSINITLOCK_ENTRY_LEAK_DETECTION
 
+LPCWSTR s_wszDiagnosticStartupHookPaths = nullptr;
 
 #ifndef DACCESS_COMPILE
 
@@ -1122,7 +1123,47 @@ bool Assembly::IgnoresAccessChecksTo(Assembly *pAccessedAssembly)
  return GetFriendAssemblyInfo()->IgnoresAccessChecksTo(pAccessedAssembly);
 }
 
+void Assembly::AddDiagnosticStartupHookPath(LPCWSTR wszPath)
+{
+ LPCWSTR wszDiagnosticStartupHookPathsLocal = s_wszDiagnosticStartupHookPaths;
+
+ size_t cchPath = u16_strlen(wszPath);
+ size_t cchDiagnosticStartupHookPathsNew = cchPath;
+ size_t cchDiagnosticStartupHookPathsLocal = 0;
+ if (nullptr != wszDiagnosticStartupHookPathsLocal)
+ {
+ cchDiagnosticStartupHookPathsLocal = u16_strlen(wszDiagnosticStartupHookPathsLocal); 
+ // Add 1 for the path separator
+ cchDiagnosticStartupHookPathsNew += cchDiagnosticStartupHookPathsLocal + 1;
+ }
 
+ size_t currentSize = cchDiagnosticStartupHookPathsNew + 1;
+ LPWSTR wszDiagnosticStartupHookPathsNew = new WCHAR[currentSize];
+ LPWSTR wszCurrent = wszDiagnosticStartupHookPathsNew;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszPath);
+ wszCurrent += cchPath;
+ currentSize -= cchPath;
+
+ if (cchDiagnosticStartupHookPathsLocal > 0)
+ {
+ u16_strcpy_s(wszCurrent, currentSize, PATH_SEPARATOR_STR_W);
+ wszCurrent += 1;
+ currentSize -= 1;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszDiagnosticStartupHookPathsLocal);
+ wszCurrent += cchDiagnosticStartupHookPathsLocal;
+ currentSize -= cchDiagnosticStartupHookPathsLocal;
+ }
+
+ // Expect null terminating character
+ _ASSERTE(currentSize == 1);
+ _ASSERTE(wszCurrent[0] == W('\0'));
+
+ s_wszDiagnosticStartupHookPaths = wszDiagnosticStartupHookPathsNew;
+
+ delete [] wszDiagnosticStartupHookPathsLocal;
+}
 
 enum CorEntryPointType
 {
@@ -1376,7 +1417,7 @@ static void RunMainPost()
  }
 }
 
-static void RunManagedStartup()
+void RunManagedStartup()
 {
  CONTRACTL
  {
@@ -1388,7 +1429,11 @@ static void RunManagedStartup()
  CONTRACTL_END;
 
  MethodDescCallSite managedStartup(METHOD__STARTUP_HOOK_PROVIDER__MANAGED_STARTUP);
- managedStartup.Call(NULL);
+
+ ARG_SLOT args[1];
+ args[0] = PtrToArgSlot(s_wszDiagnosticStartupHookPaths);
+
+ managedStartup.Call(args);
 }
 
 INT32 Assembly::ExecuteMainMethod(PTRARRAYREF *stringArgs, BOOL waitForOtherThreads)

src/coreclr/vm/assembly.hpp

@@ -380,6 +380,8 @@ class Assembly
  }
 #endif
 
+ static void AddDiagnosticStartupHookPath(LPCWSTR wszPath);
+
 
 protected:
 #ifdef FEATURE_COMINTEROP

src/coreclr/vm/corelib.h

@@ -812,7 +812,7 @@ DEFINE_FIELD_U(rgiLastFrameFromForeignExceptionStackTrace, StackFrame
 DEFINE_FIELD_U(iFrameCount, StackFrameHelper, iFrameCount)
 
 DEFINE_CLASS(STARTUP_HOOK_PROVIDER, System, StartupHookProvider)
-DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_RetVoid)
+DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_PtrChar_RetVoid)
 
 DEFINE_CLASS(STREAM, IO, Stream)
 DEFINE_METHOD(STREAM, BEGIN_READ, BeginRead, IM_ArrByte_Int_Int_AsyncCallback_Object_RetIAsyncResult)

src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.h

@@ -329,6 +329,28 @@ ds_rt_disable_perfmap (void)
 #endif // FEATURE_PERFMAP
 }
 
+static ep_char16_t * _ds_rt_coreclr_diagnostic_startup_hook_paths = NULL;
+
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	HRESULT hr = S_OK;
+	// This is set to true when the EE has initialized, which occurs after
+	// the diagnostic suspension point has completed.
+	if (g_fEEStarted)
+	{
+ // TODO: Support loading and executing startup hook after EE has completely initialized.
+ return DS_IPC_E_INVALIDARG;
+	}
+	else
+	{
+ Assembly::AddDiagnosticStartupHookPath(reinterpret_cast<LPCWSTR>(startup_hook_path));
+	}
+
+	return DS_IPC_S_OK;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/metasig.h

@@ -338,6 +338,7 @@ DEFINE_METASIG(SM(IntPtr_Bool_RetVoid, I F, v))
 DEFINE_METASIG(SM(IntPtr_UInt_IntPtr_RetVoid, I K I, v))
 DEFINE_METASIG(SM(IntPtr_RetUInt, I, K))
 DEFINE_METASIG(SM(PtrChar_RetInt, P(u), i))
+DEFINE_METASIG(SM(PtrChar_RetVoid, P(u), v))
 DEFINE_METASIG(SM(IntPtr_IntPtr_RetIntPtr, I I, I))
 DEFINE_METASIG(SM(IntPtr_IntPtr_Int_RetIntPtr, I I i, I))
 DEFINE_METASIG(SM(PtrVoid_PtrVoid_RetVoid, P(v) P(v), v))

src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Suppressions.LibraryBuild.xml

@@ -19,7 +19,7 @@
  <argument>ILLink</argument>
  <argument>IL2026</argument>
  <property name="Scope">member</property>
- <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks()</property>
+ <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks(System.String)</property>
  <property name="Justification">This warning is left in the product so developers get an ILLink warning when trimming an app with System.StartupHookProvider.IsSupported=true.</property>
  </attribute>
  </assembly>

src/libraries/System.Private.CoreLib/src/System/StartupHookProvider.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.Tracing;
 using System.Diagnostics.CodeAnalysis;
@@ -27,15 +28,25 @@ private struct StartupHookNameOrPath
 
  // Parse a string specifying a list of assemblies and types
  // containing a startup hook, and call each hook in turn.
- private static void ProcessStartupHooks()
+ private static void ProcessStartupHooks(string diagnosticStartupHooks)
  {
  if (!IsSupported)
  return;
 
  string? startupHooksVariable = AppContext.GetData("STARTUP_HOOKS") as string;
- if (startupHooksVariable == null)
- {
+ if (null == startupHooksVariable && string.IsNullOrEmpty(diagnosticStartupHooks))
  return;
+
+ List<string> startupHookParts = new();
+
+ if (!string.IsNullOrEmpty(diagnosticStartupHooks))
+ {
+ startupHookParts.AddRange(diagnosticStartupHooks.Split(Path.PathSeparator));
+ }
+
+ if (null != startupHooksVariable)
+ {
+ startupHookParts.AddRange(startupHooksVariable.Split(Path.PathSeparator));
  }
 
  ReadOnlySpan<char> disallowedSimpleAssemblyNameChars = stackalloc char[4]
@@ -47,9 +58,8 @@ private static void ProcessStartupHooks()
  };
 
  // Parse startup hooks variable
- string[] startupHookParts = startupHooksVariable.Split(Path.PathSeparator);
- StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Length];
- for (int i = 0; i < startupHookParts.Length; i++)
+ StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Count];
+ for (int i = 0; i < startupHookParts.Count; i++)
  {
  string startupHookPart = startupHookParts[i];
  if (string.IsNullOrEmpty(startupHookPart))

src/mono/mono/eventpipe/ds-rt-mono.h

@@ -239,6 +239,14 @@ ds_rt_disable_perfmap (void)
 	return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	// TODO: Implement.
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/mono/mono/metadata/object.c

@@ -8135,7 +8135,11 @@ mono_runtime_run_startup_hooks (void)
 	mono_error_cleanup (error);
 	if (!method)
  return;
-	mono_runtime_invoke_checked (method, NULL, NULL, error);
+
+	gpointer args [1];
+	args[0] = mono_string_empty_internal (mono_domain_get ());
+
+	mono_runtime_invoke_checked (method, NULL, args, error);
 	// runtime hooks design doc says not to catch exceptions from the hooks
 	mono_error_raise_exception_deprecated (error);
 }

src/native/eventpipe/ds-process-protocol.c

@@ -89,6 +89,12 @@ process_protocol_helper_disable_perfmap (
 	DiagnosticsIpcMessage *message,
 	DiagnosticsIpcStream *stream);
 
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream);
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -872,6 +878,87 @@ process_protocol_helper_disable_perfmap (
 	ep_exit_error_handler ();
 }
 
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void)
+{
+	return ep_rt_object_alloc (DiagnosticsApplyStartupHookPayload);
+}
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload)
+{
+	ep_return_void_if_nok (payload != NULL);
+	ep_rt_byte_array_free (payload->incoming_buffer);
+	ep_rt_object_free (payload);
+}
+
+static
+uint8_t *
+apply_startup_hook_command_try_parse_payload (
+	uint8_t *buffer,
+	uint16_t buffer_len)
+{
+	EP_ASSERT (buffer != NULL);
+
+	uint8_t * buffer_cursor = buffer;
+	uint32_t buffer_cursor_len = buffer_len;
+
+	DiagnosticsApplyStartupHookPayload *instance = ds_apply_startup_hook_payload_alloc ();
+	ep_raise_error_if_nok (instance != NULL);
+
+	instance->incoming_buffer = buffer;
+
+	if (!ds_ipc_message_try_parse_string_utf16_t (&buffer_cursor, &buffer_cursor_len, &instance->startup_hook_path))
+ ep_raise_error ();
+
+ep_on_exit:
+	return (uint8_t *)instance;
+
+ep_on_error:
+	ds_apply_startup_hook_payload_free (instance);
+	instance = NULL;
+	ep_exit_error_handler ();
+}
+
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream)
+{
+	EP_ASSERT (message != NULL);
+	EP_ASSERT (stream != NULL);
+
+	if (!stream)
+ return false;
+
+	bool result = false;
+	DiagnosticsApplyStartupHookPayload *payload = (DiagnosticsApplyStartupHookPayload *)ds_ipc_message_try_parse_payload (message, apply_startup_hook_command_try_parse_payload);
+	if (!payload) {
+ ds_ipc_message_send_error (stream, DS_IPC_E_BAD_ENCODING);
+ ep_raise_error ();
+	}
+
+	ds_ipc_result_t ipc_result;
+	ipc_result = ds_rt_apply_startup_hook (payload->startup_hook_path);
+	if (ipc_result != DS_IPC_S_OK) {
+ ds_ipc_message_send_error (stream, ipc_result);
+ ep_raise_error ();
+	} else {
+ ds_ipc_message_send_success (stream, ipc_result);
+	}
+
+	result = true;
+
+ep_on_exit:
+	ds_ipc_stream_free (stream);
+	return result;
+
+ep_on_error:
+	EP_ASSERT (!result);
+	ep_exit_error_handler ();
+}
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -916,6 +1003,9 @@ ds_process_protocol_helper_handle_ipc_message (
 	case DS_PROCESS_COMMANDID_DISABLE_PERFMAP:
  result = process_protocol_helper_disable_perfmap (message, stream);
  break;
+	case DS_PROCESS_COMMANDID_APPLY_STARTUP_HOOK:
+ result = process_protocol_helper_apply_startup_hook (message, stream);
+ break;
 	default:
  result = process_protocol_helper_unknown_command (message, stream);
  break;

src/native/eventpipe/ds-process-protocol.h

@@ -190,6 +190,32 @@ ds_enable_perfmap_payload_alloc (void);
 void
 ds_enable_perfmap_payload_free (DiagnosticsEnablePerfmapPayload *payload);
 
+/*
+* DiagnosticsApplyStartupHookPayload
+*/
+
+#if defined(DS_INLINE_GETTER_SETTER) || defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+#else
+struct _DiagnosticsApplyStartupHookPayload_Internal {
+#endif
+	uint8_t * incoming_buffer;
+
+	const ep_char16_t *startup_hook_path;
+};
+
+#if !defined(DS_INLINE_GETTER_SETTER) && !defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+	uint8_t _internal [sizeof (struct _DiagnosticsApplyStartupHookPayload_Internal)];
+};
+#endif
+
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void);
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload);
+
 /*
  * DiagnosticsProcessProtocolHelper.
  */

src/coreclr/System.Private.CoreLib/src/System/StartupHookProvider.CoreCLR.cs

@@ -12,15 +12,15 @@ namespace System
 {
  internal static partial class StartupHookProvider
  {
- private static void ManagedStartup()
+ private static unsafe void ManagedStartup(char* pDiagnosticStartupHooks)
  {
 #if FEATURE_PERFTRACING
  if (EventSource.IsSupported)
  RuntimeEventSource.Initialize();
 #endif
 
  if (IsSupported)
- ProcessStartupHooks();
+ ProcessStartupHooks(new string(pDiagnosticStartupHooks));
  }
  }
 }

src/coreclr/nativeaot/Runtime/eventpipe/ds-rt-aot.h

@@ -272,6 +272,13 @@ ds_rt_disable_perfmap (void)
  return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/assembly.cpp

@@ -52,6 +52,7 @@
 //#define STRICT_JITLOCK_ENTRY_LEAK_DETECTION
 //#define STRICT_CLSINITLOCK_ENTRY_LEAK_DETECTION
 
+LPCWSTR s_wszDiagnosticStartupHookPaths = nullptr;
 
 #ifndef DACCESS_COMPILE
 
@@ -1122,7 +1123,47 @@ bool Assembly::IgnoresAccessChecksTo(Assembly *pAccessedAssembly)
  return GetFriendAssemblyInfo()->IgnoresAccessChecksTo(pAccessedAssembly);
 }
 
+void Assembly::AddDiagnosticStartupHookPath(LPCWSTR wszPath)
+{
+ LPCWSTR wszDiagnosticStartupHookPathsLocal = s_wszDiagnosticStartupHookPaths;
+
+ size_t cchPath = u16_strlen(wszPath);
+ size_t cchDiagnosticStartupHookPathsNew = cchPath;
+ size_t cchDiagnosticStartupHookPathsLocal = 0;
+ if (nullptr != wszDiagnosticStartupHookPathsLocal)
+ {
+ cchDiagnosticStartupHookPathsLocal = u16_strlen(wszDiagnosticStartupHookPathsLocal); 
+ // Add 1 for the path separator
+ cchDiagnosticStartupHookPathsNew += cchDiagnosticStartupHookPathsLocal + 1;
+ }
 
+ size_t currentSize = cchDiagnosticStartupHookPathsNew + 1;
+ LPWSTR wszDiagnosticStartupHookPathsNew = new WCHAR[currentSize];
+ LPWSTR wszCurrent = wszDiagnosticStartupHookPathsNew;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszPath);
+ wszCurrent += cchPath;
+ currentSize -= cchPath;
+
+ if (cchDiagnosticStartupHookPathsLocal > 0)
+ {
+ u16_strcpy_s(wszCurrent, currentSize, PATH_SEPARATOR_STR_W);
+ wszCurrent += 1;
+ currentSize -= 1;
+
+ u16_strcpy_s(wszCurrent, currentSize, wszDiagnosticStartupHookPathsLocal);
+ wszCurrent += cchDiagnosticStartupHookPathsLocal;
+ currentSize -= cchDiagnosticStartupHookPathsLocal;
+ }
+
+ // Expect null terminating character
+ _ASSERTE(currentSize == 1);
+ _ASSERTE(wszCurrent[0] == W('\0'));
+
+ s_wszDiagnosticStartupHookPaths = wszDiagnosticStartupHookPathsNew;
+
+ delete [] wszDiagnosticStartupHookPathsLocal;
+}
 
 enum CorEntryPointType
 {
@@ -1376,7 +1417,7 @@ static void RunMainPost()
  }
 }
 
-static void RunManagedStartup()
+void RunManagedStartup()
 {
  CONTRACTL
  {
@@ -1388,7 +1429,11 @@ static void RunManagedStartup()
  CONTRACTL_END;
 
  MethodDescCallSite managedStartup(METHOD__STARTUP_HOOK_PROVIDER__MANAGED_STARTUP);
- managedStartup.Call(NULL);
+
+ ARG_SLOT args[1];
+ args[0] = PtrToArgSlot(s_wszDiagnosticStartupHookPaths);
+
+ managedStartup.Call(args);
 }
 
 INT32 Assembly::ExecuteMainMethod(PTRARRAYREF *stringArgs, BOOL waitForOtherThreads)

src/coreclr/vm/assembly.hpp

@@ -380,6 +380,8 @@ class Assembly
  }
 #endif
 
+ static void AddDiagnosticStartupHookPath(LPCWSTR wszPath);
+
 
 protected:
 #ifdef FEATURE_COMINTEROP

src/coreclr/vm/corelib.h

@@ -812,7 +812,7 @@ DEFINE_FIELD_U(rgiLastFrameFromForeignExceptionStackTrace, StackFrame
 DEFINE_FIELD_U(iFrameCount, StackFrameHelper, iFrameCount)
 
 DEFINE_CLASS(STARTUP_HOOK_PROVIDER, System, StartupHookProvider)
-DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_RetVoid)
+DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_PtrChar_RetVoid)
 
 DEFINE_CLASS(STREAM, IO, Stream)
 DEFINE_METHOD(STREAM, BEGIN_READ, BeginRead, IM_ArrByte_Int_Int_AsyncCallback_Object_RetIAsyncResult)

src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.h

@@ -329,6 +329,28 @@ ds_rt_disable_perfmap (void)
 #endif // FEATURE_PERFMAP
 }
 
+static ep_char16_t * _ds_rt_coreclr_diagnostic_startup_hook_paths = NULL;
+
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	HRESULT hr = S_OK;
+	// This is set to true when the EE has initialized, which occurs after
+	// the diagnostic suspension point has completed.
+	if (g_fEEStarted)
+	{
+ // TODO: Support loading and executing startup hook after EE has completely initialized.
+ return DS_IPC_E_INVALIDARG;
+	}
+	else
+	{
+ Assembly::AddDiagnosticStartupHookPath(reinterpret_cast<LPCWSTR>(startup_hook_path));
+	}
+
+	return DS_IPC_S_OK;
+}
+
 /*
 * DiagnosticServer.
 */

src/coreclr/vm/metasig.h

@@ -338,6 +338,7 @@ DEFINE_METASIG(SM(IntPtr_Bool_RetVoid, I F, v))
 DEFINE_METASIG(SM(IntPtr_UInt_IntPtr_RetVoid, I K I, v))
 DEFINE_METASIG(SM(IntPtr_RetUInt, I, K))
 DEFINE_METASIG(SM(PtrChar_RetInt, P(u), i))
+DEFINE_METASIG(SM(PtrChar_RetVoid, P(u), v))
 DEFINE_METASIG(SM(IntPtr_IntPtr_RetIntPtr, I I, I))
 DEFINE_METASIG(SM(IntPtr_IntPtr_Int_RetIntPtr, I I i, I))
 DEFINE_METASIG(SM(PtrVoid_PtrVoid_RetVoid, P(v) P(v), v))

src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Suppressions.LibraryBuild.xml

@@ -19,7 +19,7 @@
  <argument>ILLink</argument>
  <argument>IL2026</argument>
  <property name="Scope">member</property>
- <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks()</property>
+ <property name="Target">M:System.StartupHookProvider.ProcessStartupHooks(System.String)</property>
  <property name="Justification">This warning is left in the product so developers get an ILLink warning when trimming an app with System.StartupHookProvider.IsSupported=true.</property>
  </attribute>
  </assembly>

src/libraries/System.Private.CoreLib/src/System/StartupHookProvider.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.Tracing;
 using System.Diagnostics.CodeAnalysis;
@@ -27,15 +28,25 @@ private struct StartupHookNameOrPath
 
  // Parse a string specifying a list of assemblies and types
  // containing a startup hook, and call each hook in turn.
- private static void ProcessStartupHooks()
+ private static void ProcessStartupHooks(string diagnosticStartupHooks)
  {
  if (!IsSupported)
  return;
 
  string? startupHooksVariable = AppContext.GetData("STARTUP_HOOKS") as string;
- if (startupHooksVariable == null)
- {
+ if (null == startupHooksVariable && string.IsNullOrEmpty(diagnosticStartupHooks))
  return;
+
+ List<string> startupHookParts = new();
+
+ if (!string.IsNullOrEmpty(diagnosticStartupHooks))
+ {
+ startupHookParts.AddRange(diagnosticStartupHooks.Split(Path.PathSeparator));
+ }
+
+ if (null != startupHooksVariable)
+ {
+ startupHookParts.AddRange(startupHooksVariable.Split(Path.PathSeparator));
  }
 
  ReadOnlySpan<char> disallowedSimpleAssemblyNameChars = stackalloc char[4]
@@ -47,9 +58,8 @@ private static void ProcessStartupHooks()
  };
 
  // Parse startup hooks variable
- string[] startupHookParts = startupHooksVariable.Split(Path.PathSeparator);
- StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Length];
- for (int i = 0; i < startupHookParts.Length; i++)
+ StartupHookNameOrPath[] startupHooks = new StartupHookNameOrPath[startupHookParts.Count];
+ for (int i = 0; i < startupHookParts.Count; i++)
  {
  string startupHookPart = startupHookParts[i];
  if (string.IsNullOrEmpty(startupHookPart))

src/mono/mono/eventpipe/ds-rt-mono.h

@@ -239,6 +239,14 @@ ds_rt_disable_perfmap (void)
 	return DS_IPC_E_NOTSUPPORTED;
 }
 
+static
+uint32_t
+ds_rt_apply_startup_hook (const ep_char16_t *startup_hook_path)
+{
+	// TODO: Implement.
+	return DS_IPC_E_NOTSUPPORTED;
+}
+
 /*
 * DiagnosticServer.
 */

src/mono/mono/metadata/object.c

@@ -8135,7 +8135,11 @@ mono_runtime_run_startup_hooks (void)
 	mono_error_cleanup (error);
 	if (!method)
  return;
-	mono_runtime_invoke_checked (method, NULL, NULL, error);
+
+	gpointer args [1];
+	args[0] = mono_string_empty_internal (mono_domain_get ());
+
+	mono_runtime_invoke_checked (method, NULL, args, error);
 	// runtime hooks design doc says not to catch exceptions from the hooks
 	mono_error_raise_exception_deprecated (error);
 }

src/native/eventpipe/ds-process-protocol.c

@@ -89,6 +89,12 @@ process_protocol_helper_disable_perfmap (
 	DiagnosticsIpcMessage *message,
 	DiagnosticsIpcStream *stream);
 
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream);
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -872,6 +878,87 @@ process_protocol_helper_disable_perfmap (
 	ep_exit_error_handler ();
 }
 
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void)
+{
+	return ep_rt_object_alloc (DiagnosticsApplyStartupHookPayload);
+}
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload)
+{
+	ep_return_void_if_nok (payload != NULL);
+	ep_rt_byte_array_free (payload->incoming_buffer);
+	ep_rt_object_free (payload);
+}
+
+static
+uint8_t *
+apply_startup_hook_command_try_parse_payload (
+	uint8_t *buffer,
+	uint16_t buffer_len)
+{
+	EP_ASSERT (buffer != NULL);
+
+	uint8_t * buffer_cursor = buffer;
+	uint32_t buffer_cursor_len = buffer_len;
+
+	DiagnosticsApplyStartupHookPayload *instance = ds_apply_startup_hook_payload_alloc ();
+	ep_raise_error_if_nok (instance != NULL);
+
+	instance->incoming_buffer = buffer;
+
+	if (!ds_ipc_message_try_parse_string_utf16_t (&buffer_cursor, &buffer_cursor_len, &instance->startup_hook_path))
+ ep_raise_error ();
+
+ep_on_exit:
+	return (uint8_t *)instance;
+
+ep_on_error:
+	ds_apply_startup_hook_payload_free (instance);
+	instance = NULL;
+	ep_exit_error_handler ();
+}
+
+static
+bool
+process_protocol_helper_apply_startup_hook (
+	DiagnosticsIpcMessage *message,
+	DiagnosticsIpcStream *stream)
+{
+	EP_ASSERT (message != NULL);
+	EP_ASSERT (stream != NULL);
+
+	if (!stream)
+ return false;
+
+	bool result = false;
+	DiagnosticsApplyStartupHookPayload *payload = (DiagnosticsApplyStartupHookPayload *)ds_ipc_message_try_parse_payload (message, apply_startup_hook_command_try_parse_payload);
+	if (!payload) {
+ ds_ipc_message_send_error (stream, DS_IPC_E_BAD_ENCODING);
+ ep_raise_error ();
+	}
+
+	ds_ipc_result_t ipc_result;
+	ipc_result = ds_rt_apply_startup_hook (payload->startup_hook_path);
+	if (ipc_result != DS_IPC_S_OK) {
+ ds_ipc_message_send_error (stream, ipc_result);
+ ep_raise_error ();
+	} else {
+ ds_ipc_message_send_success (stream, ipc_result);
+	}
+
+	result = true;
+
+ep_on_exit:
+	ds_ipc_stream_free (stream);
+	return result;
+
+ep_on_error:
+	EP_ASSERT (!result);
+	ep_exit_error_handler ();
+}
+
 static
 bool
 process_protocol_helper_unknown_command (
@@ -916,6 +1003,9 @@ ds_process_protocol_helper_handle_ipc_message (
 	case DS_PROCESS_COMMANDID_DISABLE_PERFMAP:
  result = process_protocol_helper_disable_perfmap (message, stream);
  break;
+	case DS_PROCESS_COMMANDID_APPLY_STARTUP_HOOK:
+ result = process_protocol_helper_apply_startup_hook (message, stream);
+ break;
 	default:
  result = process_protocol_helper_unknown_command (message, stream);
  break;

src/native/eventpipe/ds-process-protocol.h

@@ -190,6 +190,32 @@ ds_enable_perfmap_payload_alloc (void);
 void
 ds_enable_perfmap_payload_free (DiagnosticsEnablePerfmapPayload *payload);
 
+/*
+* DiagnosticsApplyStartupHookPayload
+*/
+
+#if defined(DS_INLINE_GETTER_SETTER) || defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+#else
+struct _DiagnosticsApplyStartupHookPayload_Internal {
+#endif
+	uint8_t * incoming_buffer;
+
+	const ep_char16_t *startup_hook_path;
+};
+
+#if !defined(DS_INLINE_GETTER_SETTER) && !defined(DS_IMPL_PROCESS_PROTOCOL_GETTER_SETTER)
+struct _DiagnosticsApplyStartupHookPayload {
+	uint8_t _internal [sizeof (struct _DiagnosticsApplyStartupHookPayload_Internal)];
+};
+#endif
+
+DiagnosticsApplyStartupHookPayload *
+ds_apply_startup_hook_payload_alloc (void);
+
+void
+ds_apply_startup_hook_payload_free (DiagnosticsApplyStartupHookPayload *payload);
+
 /*
  * DiagnosticsProcessProtocolHelper.
  */