diff --git a/api/docs/release.dox b/api/docs/release.dox
index 43eedce2ce4..4ad4a01d3ad 100644
--- a/api/docs/release.dox
+++ b/api/docs/release.dox
@@ -169,6 +169,9 @@ Further non-compatibility-affecting changes include:
  - Changed the default drmemtrace offline file format from .gz to .zip and
    added the option -chunk_instr_count to control the split of a file within
    the .zip, which sets the granularity of a fast seek.
+ - Added dr_register_post_attach_event(), dr_unregister_post_attach_event(),
+   dr_register_pre_detach_event(), and dr_unregister_pre_detach_event().
+
 
 The changes between version 9.0.1 and 9.0.0 include the following compatibility
 changes:
diff --git a/core/dynamo.c b/core/dynamo.c
index 45951cba135..1e83b1babcc 100644
--- a/core/dynamo.c
+++ b/core/dynamo.c
@@ -99,6 +99,7 @@ bool dynamo_heap_initialized = false;
 bool dynamo_started = false;
 bool automatic_startup = false;
 bool control_all_threads = false;
+bool dynamo_control_via_attach = false;
 #ifdef WINDOWS
 bool dr_early_injected = false;
 int dr_early_injected_location = INJECT_LOCATION_Invalid;
@@ -2736,6 +2737,7 @@ dr_app_setup(void)
     if (DATASEC_WRITABLE(DATASEC_RARELY_PROT) == 0)
         SELF_UNPROTECT_DATASEC(DATASEC_RARELY_PROT);
     dr_api_entry = true;
+    dynamo_control_via_attach = true;
     res = dynamorio_app_init();
     /* For dr_api_entry, we do not install all our signal handlers during init (to avoid
      * races: i#2335): we delay until dr_app_start().  Plus the vsyscall hook is
@@ -2924,6 +2926,9 @@ dynamorio_take_over_threads(dcontext_t *dcontext)
             os_thread_sleep(1);
     } while (found_threads && attempts < max_takeover_attempts);
     os_process_under_dynamorio_complete(dcontext);
+
+    instrument_post_attach_event();
+
     /* End the barrier to new threads. */
     signal_event(dr_attach_finished);
 
diff --git a/core/globals.h b/core/globals.h
index ce3d1c96579..c88b73aafd6 100644
--- a/core/globals.h
+++ b/core/globals.h
@@ -1,5 +1,5 @@
 /* **********************************************************
- * Copyright (c) 2011-2021 Google, Inc.  All rights reserved.
+ * Copyright (c) 2011-2022 Google, Inc.  All rights reserved.
  * Copyright (c) 2000-2010 VMware, Inc.  All rights reserved.
  * **********************************************************/
 
@@ -431,6 +431,7 @@ extern bool dynamo_exited_log_and_stats; /* are stats and logfile shut down? */
 #endif
 extern bool dynamo_resetting;           /* in middle of global reset? */
 extern bool dynamo_all_threads_synched; /* are all other threads suspended safely? */
+extern bool dynamo_control_via_attach;  /* Attached (vs launched by DR). */
 /* Not guarded by DR_APP_EXPORTS because later detach implementations might not
  * go through the app interface.
  */
diff --git a/core/lib/dr_events.h b/core/lib/dr_events.h
index b45eee4119d..7674164101d 100644
--- a/core/lib/dr_events.h
+++ b/core/lib/dr_events.h
@@ -73,6 +73,60 @@ DR_API
 bool
 dr_unregister_exit_event(void (*func)(void));
 
+DR_API
+/**
+ * Registers a function which is called after all other threads have been taken over
+ * during a process attach event, whether externally triggered or internally triggered
+ * (via dr_app_start() or related functions).  If this process instance was not
+ * initiated by an attach, this registration function returns false.
+ *
+ * The attach methodology operates in a staggered fashion, with each thread being taken
+ * over and executed under DR control in turn.  If the application has many threads,
+ * threads taken over early in this process may execute substantial amounts of
+ * instrumented code before the threads taken over last start executing instrumented
+ * code.  The purpose of this event is to provide a single control point where all
+ * threads are known to be under DR control and running instrumented code.
+ */
+bool
+dr_register_post_attach_event(void (*func)(void));
+
+DR_API
+/**
+ * Unregister a callback function for the post-attach event (see
+ * dr_register_post_attach_event()).  \return true if unregistration is successful and
+ * false if it is not (e.g., \p func was not registered).
+ */
+bool
+dr_unregister_post_attach_event(void (*func)(void));
+
+DR_API
+/**
+ * Registers a function which is called at the start of a full detach of DR from the
+ * current process, whether externally triggered or internally triggered (via
+ * dr_app_stop_and_cleanup() or related functions), as well as at the start of DR
+ * sending all threads native but not cleaning up its own state (through dr_app_stop()).
+ *
+ * The detach methodology operates in a staggered fashion, with each thread being return
+ * to native control in turn.  If the application has many threads, threads detached
+ * late in this process may execute substantial amounts of instrumented code before the
+ * full detach process is complete, while threads detached early are running natively.
+ * The purpose of this event is to provide a single final control point where all
+ * threads are known to be under DR control and running instrumented code.  The exit
+ * event (see dr_register_exit_event()) is not called until after all other threads have
+ * been detached.
+ */
+void
+dr_register_pre_detach_event(void (*func)(void));
+
+DR_API
+/**
+ * Unregister a callback function for the post-attach event (see
+ * dr_register_pre_detach_event()).  \return true if unregistration is successful and
+ * false if it is not (e.g., \p func was not registered).
+ */
+bool
+dr_unregister_pre_detach_event(void (*func)(void));
+
 /**
  * Flags controlling the behavior of basic blocks and traces when emitted
  * into the code cache.  These flags are bitmasks that can be combined by
diff --git a/core/lib/instrument.c b/core/lib/instrument.c
index 497c79bfa11..69594698b42 100644
--- a/core/lib/instrument.c
+++ b/core/lib/instrument.c
@@ -198,6 +198,12 @@ typedef struct _callback_list_t {
 static callback_list_t exit_callbacks = {
     0,
 };
+static callback_list_t post_attach_callbacks = {
+    0,
+};
+static callback_list_t pre_detach_callbacks = {
+    0,
+};
 static callback_list_t thread_init_callbacks = {
     0,
 };
@@ -816,6 +822,8 @@ static void
 free_all_callback_lists()
 {
     free_callback_list(&exit_callbacks);
+    free_callback_list(&post_attach_callbacks);
+    free_callback_list(&pre_detach_callbacks);
     free_callback_list(&thread_init_callbacks);
     free_callback_list(&thread_exit_callbacks);
 #ifdef UNIX
@@ -869,6 +877,20 @@ instrument_exit_event(void)
              NULL);
 }
 
+void
+instrument_post_attach_event(void)
+{
+    if (!dynamo_control_via_attach)
+        return;
+    call_all(post_attach_callbacks, int (*)(), NULL);
+}
+
+void
+instrument_pre_detach_event(void)
+{
+    call_all(pre_detach_callbacks, int (*)(), NULL);
+}
+
 void
 instrument_exit(void)
 {
@@ -971,6 +993,33 @@ dr_unregister_exit_event(void (*func)(void))
     return remove_callback(&exit_callbacks, (void (*)(void))func, true);
 }
 
+bool
+dr_register_post_attach_event(void (*func)(void))
+{
+    if (!dynamo_control_via_attach)
+        return false;
+    add_callback(&post_attach_callbacks, (void (*)(void))func, true);
+    return true;
+}
+
+bool
+dr_unregister_post_attach_event(void (*func)(void))
+{
+    return remove_callback(&post_attach_callbacks, (void (*)(void))func, true);
+}
+
+void
+dr_register_pre_detach_event(void (*func)(void))
+{
+    add_callback(&pre_detach_callbacks, (void (*)(void))func, true);
+}
+
+bool
+dr_unregister_pre_detach_event(void (*func)(void))
+{
+    return remove_callback(&pre_detach_callbacks, (void (*)(void))func, true);
+}
+
 void
 dr_register_bb_event(dr_emit_flags_t (*func)(void *drcontext, void *tag, instrlist_t *bb,
                                              bool for_trace, bool translating))
diff --git a/core/lib/instrument.h b/core/lib/instrument.h
index 57fe0b254a6..8af37af304a 100644
--- a/core/lib/instrument.h
+++ b/core/lib/instrument.h
@@ -1,5 +1,5 @@
 /* **********************************************************
- * Copyright (c) 2010-2021 Google, Inc.  All rights reserved.
+ * Copyright (c) 2010-2022 Google, Inc.  All rights reserved.
  * Copyright (c) 2002-2010 VMware, Inc.  All rights reserved.
  * **********************************************************/
 
@@ -68,6 +68,10 @@ instrument_init(void);
 void
 instrument_exit_event(void);
 void
+instrument_post_attach_event(void);
+void
+instrument_pre_detach_event(void);
+void
 instrument_exit(void);
 bool
 is_in_client_lib(app_pc addr);
diff --git a/core/synch.c b/core/synch.c
index e86cfa1bb38..f5eef1e5c79 100644
--- a/core/synch.c
+++ b/core/synch.c
@@ -1874,6 +1874,8 @@ send_all_other_threads_native(void)
     wait_for_outstanding_nudges();
 #endif
 
+    instrument_pre_detach_event();
+
     /* Suspend all threads except those trying to synch with us */
     if (!synch_with_all_threads(desired_state, &threads, &num_threads,
                                 THREAD_SYNCH_NO_LOCKS_NO_XFER,
@@ -1996,6 +1998,8 @@ detach_on_permanent_stack(bool internal, bool do_cleanup, dr_stats_t *drstats)
     if (!atomic_compare_exchange(&dynamo_detaching_flag, LOCK_FREE_STATE, LOCK_SET_STATE))
         return;
 
+    instrument_pre_detach_event();
+
     /* Unprotect .data for exit cleanup.
      * XXX: more secure to not do this until we've synched, but then need
      * alternative prot for started_detach and init_apc_go_native*
diff --git a/core/unix/os.c b/core/unix/os.c
index fd1c8d5bbd8..4eb8f43f0c7 100644
--- a/core/unix/os.c
+++ b/core/unix/os.c
@@ -752,6 +752,7 @@ our_init(int argc, char **argv, char **envp)
     }
 #endif
     if (takeover) {
+        dynamo_control_via_attach = true;
         if (dynamorio_app_init() == 0 /* success */) {
             dynamorio_app_take_over();
         }
diff --git a/suite/tests/api/startstop.c b/suite/tests/api/startstop.c
index 9b34f07a50e..d4a24b98c2e 100644
--- a/suite/tests/api/startstop.c
+++ b/suite/tests/api/startstop.c
@@ -1,5 +1,5 @@
 /* **********************************************************
- * Copyright (c) 2011-2017 Google, Inc.  All rights reserved.
+ * Copyright (c) 2011-2022 Google, Inc.  All rights reserved.
  * Copyright (c) 2003-2008 VMware, Inc.  All rights reserved.
  * **********************************************************/
 
@@ -115,6 +115,18 @@ event_bb(void *drcontext, void *tag, instrlist_t *bb, bool for_trace, bool trans
     return DR_EMIT_DEFAULT;
 }
 
+static void
+event_post_attach(void)
+{
+    print("in %s\n", __FUNCTION__);
+}
+
+static void
+event_pre_detach(void)
+{
+    print("in %s\n", __FUNCTION__);
+}
+
 static volatile bool sideline_exit = false;
 static void *sideline_continue;
 static void *go_native;
@@ -203,6 +215,9 @@ main(void)
      * just using it for testing.
      */
     dr_register_bb_event(event_bb);
+    if (!dr_register_post_attach_event(event_post_attach))
+        print("Failed to register post-attach event");
+    dr_register_pre_detach_event(event_pre_detach);
 
     /* Wait for all the threads to be scheduled */
     VPRINT("waiting for ready\n");
diff --git a/suite/tests/api/startstop.expect b/suite/tests/api/startstop.expect
index 8276eb7ffd9..4806951cb56 100644
--- a/suite/tests/api/startstop.expect
+++ b/suite/tests/api/startstop.expect
@@ -1 +1,25 @@
+in event_post_attach
+in event_pre_detach
+in event_post_attach
+in event_pre_detach
+in event_post_attach
+in event_pre_detach
+in event_post_attach
+in event_pre_detach
+in event_post_attach
+in event_pre_detach
+in event_post_attach
+in event_pre_detach
+in event_post_attach
+in event_pre_detach
+in event_post_attach
+in event_pre_detach
+in event_post_attach
+in event_pre_detach
+in event_post_attach
+in event_pre_detach
+in event_post_attach
+in event_pre_detach
 all done: 10 iters
+in event_post_attach
+in event_pre_detach
diff --git a/suite/tests/api/static_prepop.c b/suite/tests/api/static_prepop.c
index a34998eb3f6..7e39f1ec5cb 100644
--- a/suite/tests/api/static_prepop.c
+++ b/suite/tests/api/static_prepop.c
@@ -85,12 +85,27 @@ event_exit(void)
     dr_fprintf(STDERR, "Exit event\n");
 }
 
+static void
+event_post_attach(void)
+{
+    dr_fprintf(STDERR, "in %s\n", __FUNCTION__);
+}
+
+static void
+event_pre_detach(void)
+{
+    dr_fprintf(STDERR, "in %s\n", __FUNCTION__);
+}
+
 DR_EXPORT void
 dr_client_main(client_id_t id, int argc, const char *argv[])
 {
     print("in dr_client_main\n");
     dr_register_bb_event(event_bb);
     dr_register_exit_event(event_exit);
+    if (!dr_register_post_attach_event(event_post_attach))
+        print("Failed to register post-attach event");
+    dr_register_pre_detach_event(event_pre_detach);
 
     /* XXX i#975: add some more thorough tests of different events */
 }
diff --git a/suite/tests/api/static_prepop.expect b/suite/tests/api/static_prepop.expect
index fb8582a9368..b515ff53aaa 100644
--- a/suite/tests/api/static_prepop.expect
+++ b/suite/tests/api/static_prepop.expect
@@ -6,7 +6,9 @@ bb asm_label2
 bb asm_label3
 bb asm_return
 pre-DR start
+in event_post_attach
 pre-DR detach
+in event_pre_detach
 Exit event
 pre-DR init
 in dr_client_main
@@ -16,6 +18,8 @@ bb asm_label2
 bb asm_label3
 bb asm_return
 pre-DR start
+in event_post_attach
 pre-DR detach with stats
+in event_pre_detach
 Exit event
 all done
diff --git a/suite/tests/client-interface/events.dll.c b/suite/tests/client-interface/events.dll.c
index 593831caaa4..ce6f624755b 100644
--- a/suite/tests/client-interface/events.dll.c
+++ b/suite/tests/client-interface/events.dll.c
@@ -1,5 +1,5 @@
 /* **********************************************************
- * Copyright (c) 2011-2019 Google, Inc.  All rights reserved.
+ * Copyright (c) 2011-2022 Google, Inc.  All rights reserved.
  * Copyright (c) 2008-2010 VMware, Inc.  All rights reserved.
  * **********************************************************/
 
@@ -737,4 +737,9 @@ dr_init(client_id_t id)
         dr_fprintf(STDERR, "failed to unregister for persist rw events");
     if (!dr_unregister_persist_patch(event_persist_patch))
         dr_fprintf(STDERR, "failed to unregister for persist patch event");
+
+    if (dr_register_post_attach_event(exit_event1))
+        dr_fprintf(STDERR, "should fail to register for post-attach event");
+    if (dr_unregister_post_attach_event(exit_event1))
+        dr_fprintf(STDERR, "should fail to unregister for post-attach event");
 }