Multi-target support

This commit adds multi-target support to GDB.  What this means is that
with this commit, GDB can now be connected to different targets at the
same time.  E.g., you can debug a live native process and a core dump
at the same time, connect to multiple gdbservers, etc.

Actually, the word "target" is overloaded in gdb.  We already have a
target stack, with pushes several target_ops instances on top of one
another.  We also have "info target" already, which means something
completely different to what this patch does.

So from here on, I'll be using the "target connections" term, to mean
an open process_stratum target, pushed on a target stack.  This patch
makes gdb have multiple target stacks, and multiple process_stratum
targets open simultaneously.  The user-visible changes / commands will
also use this terminology, but of course it's all open to debate.

User-interface-wise, not that much changes.  The main difference is
that each inferior may have its own target connection.

A target connection (e.g., a target extended-remote connection) may
support debugging multiple processes, just as before.

Say you're debugging against gdbserver in extended-remote mode, and
you do "add-inferior" to prepare to spawn a new process, like:

 (gdb) target extended-remote :9999
 ...
 (gdb) start
 ...
 (gdb) add-inferior
 Added inferior 2
 (gdb) inferior 2
 [Switching to inferior 2 [<null>] (<noexec>)]
 (gdb) file a.out
 ...
 (gdb) start
 ...

At this point, you have two inferiors connected to the same gdbserver.

With this commit, GDB will maintain a target stack per inferior,
instead of a global target stack.

To preserve the behavior above, by default, "add-inferior" makes the
new inferior inherit a copy of the target stack of the current
inferior.  Same across a fork - the child inherits a copy of the
target stack of the parent.  While the target stacks are copied, the
targets themselves are not.  Instead, target_ops is made a
refcounted_object, which means that target_ops instances are
refcounted, which each inferior counting for a reference.

What if you want to create an inferior and connect it to some _other_
target?  For that, this commit introduces a new "add-inferior
-no-connection" option that makes the new inferior not share the
current inferior's target.  So you could do:

 (gdb) target extended-remote :9999
 Remote debugging using :9999
 ...
 (gdb) add-inferior -no-connection
 [New inferior 2]
 Added inferior 2
 (gdb) inferior 2
 [Switching to inferior 2 [<null>] (<noexec>)]
 (gdb) info inferiors
   Num  Description       Executable
   1    process 18401     target:/home/pedro/tmp/main
 * 2    <null>
 (gdb) tar extended-remote :10000
 Remote debugging using :10000
 ...
 (gdb) info inferiors
   Num  Description       Executable
   1    process 18401     target:/home/pedro/tmp/main
 * 2    process 18450     target:/home/pedro/tmp/main
 (gdb)

A following patch will extended "info inferiors" to include a column
indicating which connection an inferior is bound to, along with a
couple other UI tweaks.

Other than that, debugging is the same as before.  Users interact with
inferiors and threads as before.  The only difference is that
inferiors may be bound to processes running in different machines.

That's pretty much all there is to it in terms of noticeable UI
changes.

On to implementation.

Since we can be connected to different systems at the same time, a
ptid_t is no longer a unique identifier.  Instead a thread can be
identified by a pair of ptid_t and 'process_stratum_target *', the
later being the instance of the process_stratum target that owns the
process/thread.  Note that process_stratum_target inherits from
target_ops, and all process_stratum targets inherit from
process_stratum_target.  In earlier patches, many places in gdb were
converted to refer to threads by thread_info pointer instead of
ptid_t, but there are still places in gdb where we start with a
pid/tid and need to find the corresponding inferior or thread_info
objects.  So you'll see in the patch many places adding a
process_stratum_target parameter to functions that used to take only a
ptid_t.

Since each inferior has its own target stack now, we can always find
the process_stratum target for an inferior.  That is done via a
inf->process_target() convenience method.

Since each inferior has its own target stack, we need to handle the
"beneath" calls when servicing target calls.  The solution I settled
with is just to make sure to switch the current inferior to the
inferior you want before making a target call.  Not relying on global
context is just not feasible in current GDB.  Fortunately, there
aren't that many places that need to do that, because generally most
code that calls target methods already has the current context
pointing to the right inferior/thread.  Note, to emphasize -- there's
no method to "switch to this target stack".  Instead, you switch the
current inferior, and that implicitly switches the target stack.

In some spots, we need to iterate over all inferiors so that we reach
all target stacks.

Native targets are still singletons.  There's always only a single
instance of such targets.

Remote targets however, we'll have one instance per remote connection.

The exec target is still a singleton.  There's only one instance.  I
did not see the point of instanciating more than one exec_target
object.

After vfork, we need to make sure to push the exec target on the new
inferior.  See exec_on_vfork.

For type safety, functions that need a {target, ptid} pair to identify
a thread, take a process_stratum_target pointer for target parameter
instead of target_ops *.  Some shared code in gdb/nat/ also need to
gain a target pointer parameter.  This poses an issue, since gdbserver
doesn't have process_stratum_target, only target_ops.  To fix this,
this commit renames gdbserver's target_ops to process_stratum_target.
I think this makes sense.  There's no concept of target stack in
gdbserver, and gdbserver's target_ops really implements a
process_stratum-like target.

The thread and inferior iterator functions also gain
process_stratum_target parameters.  These are used to be able to
iterate over threads and inferiors of a given target.  Following usual
conventions, if the target pointer is null, then we iterate over
threads and inferiors of all targets.

I tried converting "add-inferior" to the gdb::option framework, as a
preparatory patch, but that stumbled on the fact that gdb::option does
not support file options yet, for "add-inferior -exec".  I have a WIP
patchset that adds that, but it's not a trivial patch, mainly due to
need to integrate readline's filename completion, so I deferred that
to some other time.

In infrun.c/infcmd.c, the main change is that we need to poll events
out of all targets.  See do_target_wait.  Right after collecting an
event, we switch the current inferior to an inferior bound to the
target that reported the event, so that target methods can be used
while handling the event.  This makes most of the code transparent to
multi-targets.  See fetch_inferior_event.

infrun.c:stop_all_threads is interesting -- in this function we need
to stop all threads of all targets.  What the function does is send an
asynchronous stop request to all threads, and then synchronously waits
for events, with target_wait, rinse repeat, until all it finds are
stopped threads.  Now that we have multiple targets, it's not
efficient to synchronously block in target_wait waiting for events out
of one target.  Instead, we implement a mini event loop, with
interruptible_select, select'ing on one file descriptor per target.
For this to work, we need to be able to ask the target for a waitable
file descriptor.  Such file descriptors already exist, they are the
descriptors registered in the main event loop with add_file_handler,
inside the target_async implementations.  This commit adds a new
target_async_wait_fd target method that just returns the file
descriptor in question.  See wait_one / stop_all_threads in infrun.c.

The 'threads_executing' global is made a per-target variable.  Since
it is only relevant to process_stratum_target targets, this is where
it is put, instead of in target_ops.

You'll notice that remote.c includes some FIXME notes.  These refer to
the fact that the global arrays that hold data for the remote packets
supported are still globals.  For example, if we connect to two
different servers/stubs, then each might support different remote
protocol features.  They might even be different architectures, like
e.g., one ARM baremetal stub, and a x86 gdbserver, to debug a
host/controller scenario as a single program.  That isn't going to
work correctly today, because of said globals.  I'm leaving fixing
that for another pass, since it does not appear to be trivial, and I'd
rather land the base work first.  It's already useful to be able to
debug multiple instances of the same server (e.g., a distributed
cluster, where you have full control over the servers installed), so I
think as is it's already reasonable incremental progress.

Current limitations:

 - You can only resume more that one target at the same time if all
   targets support asynchronous debugging, and support non-stop mode.
   It should be possible to support mixed all-stop + non-stop
   backends, but that is left for another time.  This means that
   currently in order to do multi-target with gdbserver you need to
   issue "maint set target-non-stop on".  I would like to make that
   mode be the default, but we're not there yet.  Note that I'm
   talking about how the target backend works, only.  User-visible
   all-stop mode works just fine.

 - As explained above, connecting to different remote servers at the
   same time is likely to produce bad results if they don't support the
   exact set of RSP features.

FreeBSD updates courtesy of John Baldwin.

gdb/ChangeLog:
2020-01-10  Pedro Alves  <palves@redhat.com>
	    John Baldwin  <jhb@FreeBSD.org>

	* aarch64-linux-nat.c
	(aarch64_linux_nat_target::thread_architecture): Adjust.
	* ada-tasks.c (print_ada_task_info): Adjust find_thread_ptid call.
	(task_command_1): Likewise.
	* aix-thread.c (sync_threadlists, aix_thread_target::resume)
	(aix_thread_target::wait, aix_thread_target::fetch_registers)
	(aix_thread_target::store_registers)
	(aix_thread_target::thread_alive): Adjust.
	* amd64-fbsd-tdep.c: Include "inferior.h".
	(amd64fbsd_get_thread_local_address): Pass down target.
	* amd64-linux-nat.c (ps_get_thread_area): Use ps_prochandle
	thread's gdbarch instead of target_gdbarch.
	* break-catch-sig.c (signal_catchpoint_print_it): Adjust call to
	get_last_target_status.
	* break-catch-syscall.c (print_it_catch_syscall): Likewise.
	* breakpoint.c (breakpoints_should_be_inserted_now): Consider all
	inferiors.
	(update_inserted_breakpoint_locations): Skip if inferiors with no
	execution.
	(update_global_location_list): When handling moribund locations,
	find representative inferior for location's pspace, and use thread
	count of its process_stratum target.
	* bsd-kvm.c (bsd_kvm_target_open): Pass target down.
	* bsd-uthread.c (bsd_uthread_target::wait): Use
	as_process_stratum_target and adjust thread_change_ptid and
	add_thread calls.
	(bsd_uthread_target::update_thread_list): Use
	as_process_stratum_target and adjust find_thread_ptid,
	thread_change_ptid and add_thread calls.
	* btrace.c (maint_btrace_packet_history_cmd): Adjust
	find_thread_ptid call.
	* corelow.c (add_to_thread_list): Adjust add_thread call.
	(core_target_open): Adjust add_thread_silent and thread_count
	calls.
	(core_target::pid_to_str): Adjust find_inferior_ptid call.
	* ctf.c (ctf_target_open): Adjust add_thread_silent call.
	* event-top.c (async_disconnect): Pop targets from all inferiors.
	* exec.c (add_target_sections): Push exec target on all inferiors
	sharing the program space.
	(remove_target_sections): Remove the exec target from all
	inferiors sharing the program space.
	(exec_on_vfork): New.
	* exec.h (exec_on_vfork): Declare.
	* fbsd-nat.c (fbsd_add_threads): Add fbsd_nat_target parameter.
	Pass it down.
	(fbsd_nat_target::update_thread_list): Adjust.
	(fbsd_nat_target::resume): Adjust.
	(fbsd_handle_debug_trap): Add fbsd_nat_target parameter.  Pass it
	down.
	(fbsd_nat_target::wait, fbsd_nat_target::post_attach): Adjust.
	* fbsd-tdep.c (fbsd_corefile_thread): Adjust
	get_thread_arch_regcache call.
	* fork-child.c (gdb_startup_inferior): Pass target down to
	startup_inferior and set_executing.
	* gdbthread.h (struct process_stratum_target): Forward declare.
	(add_thread, add_thread_silent, add_thread_with_info)
	(in_thread_list): Add process_stratum_target parameter.
	(find_thread_ptid(inferior*, ptid_t)): New overload.
	(find_thread_ptid, thread_change_ptid): Add process_stratum_target
	parameter.
	(all_threads()): Delete overload.
	(all_threads, all_non_exited_threads): Add process_stratum_target
	parameter.
	(all_threads_safe): Use brace initialization.
	(thread_count): Add process_stratum_target parameter.
	(set_resumed, set_running, set_stop_requested, set_executing)
	(threads_are_executing, finish_thread_state): Add
	process_stratum_target parameter.
	(switch_to_thread): Use is_current_thread.
	* i386-fbsd-tdep.c: Include "inferior.h".
	(i386fbsd_get_thread_local_address): Pass down target.
	* i386-linux-nat.c (i386_linux_nat_target::low_resume): Adjust.
	* inf-child.c (inf_child_target::maybe_unpush_target): Remove
	have_inferiors check.
	* inf-ptrace.c (inf_ptrace_target::create_inferior)
	(inf_ptrace_target::attach): Adjust.
	* infcall.c (run_inferior_call): Adjust.
	* infcmd.c (run_command_1): Pass target to
	scoped_finish_thread_state.
	(proceed_thread_callback): Skip inferiors with no execution.
	(continue_command): Rename 'all_threads' local to avoid hiding
	'all_threads' function.  Adjust get_last_target_status call.
	(prepare_one_step): Adjust set_running call.
	(signal_command): Use user_visible_resume_target.  Compare thread
	pointers instead of inferior_ptid.
	(info_program_command): Adjust to pass down target.
	(attach_command): Mark target's 'thread_executing' flag.
	(stop_current_target_threads_ns): New, factored out from ...
	(interrupt_target_1): ... this.  Switch inferior before making
	target calls.
	* inferior-iter.h
	(struct all_inferiors_iterator, struct all_inferiors_range)
	(struct all_inferiors_safe_range)
	(struct all_non_exited_inferiors_range): Filter on
	process_stratum_target too.  Remove explicit.
	* inferior.c (inferior::inferior): Push dummy target on target
	stack.
	(find_inferior_pid, find_inferior_ptid, number_of_live_inferiors):
	Add process_stratum_target parameter, and pass it down.
	(have_live_inferiors): Adjust.
	(switch_to_inferior_and_push_target): New.
	(add_inferior_command, clone_inferior_command): Handle
	"-no-connection" parameter.  Use
	switch_to_inferior_and_push_target.
	(_initialize_inferior): Mention "-no-connection" option in
	the help of "add-inferior" and "clone-inferior" commands.
	* inferior.h: Include "process-stratum-target.h".
	(interrupt_target_1): Use bool.
	(struct inferior) <push_target, unpush_target, target_is_pushed,
	find_target_beneath, top_target, process_target, target_at,
	m_stack>: New.
	(discard_all_inferiors): Delete.
	(find_inferior_pid, find_inferior_ptid, number_of_live_inferiors)
	(all_inferiors, all_non_exited_inferiors): Add
	process_stratum_target parameter.
	* infrun.c: Include "gdb_select.h" and <unordered_map>.
	(target_last_proc_target): New global.
	(follow_fork_inferior): Push target on new inferior.  Pass target
	to add_thread_silent.  Call exec_on_vfork.  Handle target's
	reference count.
	(follow_fork): Adjust get_last_target_status call.  Also consider
	target.
	(follow_exec): Push target on new inferior.
	(struct execution_control_state) <target>: New field.
	(user_visible_resume_target): New.
	(do_target_resume): Call target_async.
	(resume_1): Set target's threads_executing flag.  Consider resume
	target.
	(commit_resume_all_targets): New.
	(proceed): Also consider resume target.  Skip threads of inferiors
	with no execution.  Commit resumtion in all targets.
	(start_remote): Pass current inferior to wait_for_inferior.
	(infrun_thread_stop_requested): Consider target as well.  Pass
	thread_info pointer to clear_inline_frame_state instead of ptid.
	(infrun_thread_thread_exit): Consider target as well.
	(random_pending_event_thread): New inferior parameter.  Use it.
	(do_target_wait): Rename to ...
	(do_target_wait_1): ... this.  Add inferior parameter, and pass it
	down.
	(threads_are_resumed_pending_p, do_target_wait): New.
	(prepare_for_detach): Adjust calls.
	(wait_for_inferior): New inferior parameter.  Handle it.  Use
	do_target_wait_1 instead of do_target_wait.
	(fetch_inferior_event): Adjust.  Switch to representative
	inferior.  Pass target down.
	(set_last_target_status): Add process_stratum_target parameter.
	Save target in global.
	(get_last_target_status): Add process_stratum_target parameter and
	handle it.
	(nullify_last_target_wait_ptid): Clear 'target_last_proc_target'.
	(context_switch): Check inferior_ptid == null_ptid before calling
	inferior_thread().
	(get_inferior_stop_soon): Pass down target.
	(wait_one): Rename to ...
	(poll_one_curr_target): ... this.
	(struct wait_one_event): New.
	(wait_one): New.
	(stop_all_threads): Adjust.
	(handle_no_resumed, handle_inferior_event): Adjust to consider the
	event's target.
	(switch_back_to_stepped_thread): Also consider target.
	(print_stop_event): Update.
	(normal_stop): Update.  Also consider the resume target.
	* infrun.h (wait_for_inferior): Remove declaration.
	(user_visible_resume_target): New declaration.
	(get_last_target_status, set_last_target_status): New
	process_stratum_target parameter.
	* inline-frame.c (clear_inline_frame_state(ptid_t)): Add
	process_stratum_target parameter, and use it.
	(clear_inline_frame_state (thread_info*)): New.
	* inline-frame.c (clear_inline_frame_state(ptid_t)): Add
	process_stratum_target parameter.
	(clear_inline_frame_state (thread_info*)): Declare.
	* linux-fork.c (delete_checkpoint_command): Pass target down to
	find_thread_ptid.
	(checkpoint_command): Adjust.
	* linux-nat.c (linux_nat_target::follow_fork): Switch to thread
	instead of just tweaking inferior_ptid.
	(linux_nat_switch_fork): Pass target down to thread_change_ptid.
	(exit_lwp): Pass target down to find_thread_ptid.
	(attach_proc_task_lwp_callback): Pass target down to
	add_thread/set_running/set_executing.
	(linux_nat_target::attach): Pass target down to
	thread_change_ptid.
	(get_detach_signal): Pass target down to find_thread_ptid.
	Consider last target status's target.
	(linux_resume_one_lwp_throw, resume_lwp)
	(linux_handle_syscall_trap, linux_handle_extended_wait, wait_lwp)
	(stop_wait_callback, save_stop_reason, linux_nat_filter_event)
	(linux_nat_wait_1, resume_stopped_resumed_lwps): Pass target down.
	(linux_nat_target::async_wait_fd): New.
	(linux_nat_stop_lwp, linux_nat_target::thread_address_space): Pass
	target down.
	* linux-nat.h (linux_nat_target::async_wait_fd): Declare.
	* linux-tdep.c (get_thread_arch_regcache): Pass target down.
	* linux-thread-db.c (struct thread_db_info::process_target): New
	field.
	(add_thread_db_info): Save target.
	(get_thread_db_info): New process_stratum_target parameter.  Also
	match target.
	(delete_thread_db_info): New process_stratum_target parameter.
	Also match target.
	(thread_from_lwp): Adjust to pass down target.
	(thread_db_notice_clone): Pass down target.
	(check_thread_db_callback): Pass down target.
	(try_thread_db_load_1): Always push the thread_db target.
	(try_thread_db_load, record_thread): Pass target down.
	(thread_db_target::detach): Pass target down.  Always unpush the
	thread_db target.
	(thread_db_target::wait, thread_db_target::mourn_inferior): Pass
	target down.  Always unpush the thread_db target.
	(find_new_threads_callback, thread_db_find_new_threads_2)
	(thread_db_target::update_thread_list): Pass target down.
	(thread_db_target::pid_to_str): Pass current inferior down.
	(thread_db_target::get_thread_local_address): Pass target down.
	(thread_db_target::resume, maintenance_check_libthread_db): Pass
	target down.
	* nto-procfs.c (nto_procfs_target::update_thread_list): Adjust.
	* procfs.c (procfs_target::procfs_init_inferior): Declare.
	(proc_set_current_signal, do_attach, procfs_target::wait): Adjust.
	(procfs_init_inferior): Rename to ...
	(procfs_target::procfs_init_inferior): ... this and adjust.
	(procfs_target::create_inferior, procfs_notice_thread)
	(procfs_do_thread_registers): Adjust.
	* ppc-fbsd-tdep.c: Include "inferior.h".
	(ppcfbsd_get_thread_local_address): Pass down target.
	* proc-service.c (ps_xfer_memory): Switch current inferior and
	program space as well.
	(get_ps_regcache): Pass target down.
	* process-stratum-target.c
	(process_stratum_target::thread_address_space)
	(process_stratum_target::thread_architecture): Pass target down.
	* process-stratum-target.h
	(process_stratum_target::threads_executing): New field.
	(as_process_stratum_target): New.
	* ravenscar-thread.c
	(ravenscar_thread_target::update_inferior_ptid): Pass target down.
	(ravenscar_thread_target::wait, ravenscar_add_thread): Pass target
	down.
	* record-btrace.c (record_btrace_target::info_record): Adjust.
	(record_btrace_target::record_method)
	(record_btrace_target::record_is_replaying)
	(record_btrace_target::fetch_registers)
	(get_thread_current_frame_id, record_btrace_target::resume)
	(record_btrace_target::wait, record_btrace_target::stop): Pass
	target down.
	* record-full.c (record_full_wait_1): Switch to event thread.
	Pass target down.
	* regcache.c (regcache::regcache)
	(get_thread_arch_aspace_regcache, get_thread_arch_regcache): Add
	process_stratum_target parameter and handle it.
	(current_thread_target): New global.
	(get_thread_regcache): Add process_stratum_target parameter and
	handle it.  Switch inferior before calling target method.
	(get_thread_regcache): Pass target down.
	(get_thread_regcache_for_ptid): Pass target down.
	(registers_changed_ptid): Add process_stratum_target parameter and
	handle it.
	(registers_changed_thread, registers_changed): Pass target down.
	(test_get_thread_arch_aspace_regcache): New.
	(current_regcache_test): Define a couple local test_target_ops
	instances and use them for testing.
	(readwrite_regcache): Pass process_stratum_target parameter.
	(cooked_read_test, cooked_write_test): Pass mock_target down.
	* regcache.h (get_thread_regcache, get_thread_arch_regcache)
	(get_thread_arch_aspace_regcache): Add process_stratum_target
	parameter.
	(regcache::target): New method.
	(regcache::regcache, regcache::get_thread_arch_aspace_regcache)
	(regcache::registers_changed_ptid): Add process_stratum_target
	parameter.
	(regcache::m_target): New field.
	(registers_changed_ptid): Add process_stratum_target parameter.
	* remote.c (remote_state::supports_vCont_probed): New field.
	(remote_target::async_wait_fd): New method.
	(remote_unpush_and_throw): Add remote_target parameter.
	(get_current_remote_target): Adjust.
	(remote_target::remote_add_inferior): Push target.
	(remote_target::remote_add_thread)
	(remote_target::remote_notice_new_inferior)
	(get_remote_thread_info): Pass target down.
	(remote_target::update_thread_list): Skip threads of inferiors
	bound to other targets.  (remote_target::close): Don't discard
	inferiors.  (remote_target::add_current_inferior_and_thread)
	(remote_target::process_initial_stop_replies)
	(remote_target::start_remote)
	(remote_target::remote_serial_quit_handler): Pass down target.
	(remote_target::remote_unpush_target): New remote_target
	parameter.  Unpush the target from all inferiors.
	(remote_target::remote_unpush_and_throw): New remote_target
	parameter.  Pass it down.
	(remote_target::open_1): Check whether the current inferior has
	execution instead of checking whether any inferior is live.  Pass
	target down.
	(remote_target::remote_detach_1): Pass down target.  Use
	remote_unpush_target.
	(extended_remote_target::attach): Pass down target.
	(remote_target::remote_vcont_probe): Set supports_vCont_probed.
	(remote_target::append_resumption): Pass down target.
	(remote_target::append_pending_thread_resumptions)
	(remote_target::remote_resume_with_hc, remote_target::resume)
	(remote_target::commit_resume): Pass down target.
	(remote_target::remote_stop_ns): Check supports_vCont_probed.
	(remote_target::interrupt_query)
	(remote_target::remove_new_fork_children)
	(remote_target::check_pending_events_prevent_wildcard_vcont)
	(remote_target::remote_parse_stop_reply)
	(remote_target::process_stop_reply): Pass down target.
	(first_remote_resumed_thread): New remote_target parameter.  Pass
	it down.
	(remote_target::wait_as): Pass down target.
	(unpush_and_perror): New remote_target parameter.  Pass it down.
	(remote_target::readchar, remote_target::remote_serial_write)
	(remote_target::getpkt_or_notif_sane_1)
	(remote_target::kill_new_fork_children, remote_target::kill): Pass
	down target.
	(remote_target::mourn_inferior): Pass down target.  Use
	remote_unpush_target.
	(remote_target::core_of_thread)
	(remote_target::remote_btrace_maybe_reopen): Pass down target.
	(remote_target::pid_to_exec_file)
	(remote_target::thread_handle_to_thread_info): Pass down target.
	(remote_target::async_wait_fd): New.
	* riscv-fbsd-tdep.c: Include "inferior.h".
	(riscv_fbsd_get_thread_local_address): Pass down target.
	* sol2-tdep.c (sol2_core_pid_to_str): Pass down target.
	* sol-thread.c (sol_thread_target::wait, ps_lgetregs, ps_lsetregs)
	(ps_lgetfpregs, ps_lsetfpregs, sol_update_thread_list_callback):
	Adjust.
	* solib-spu.c (spu_skip_standalone_loader): Pass down target.
	* solib-svr4.c (enable_break): Pass down target.
	* spu-multiarch.c (parse_spufs_run): Pass down target.
	* spu-tdep.c (spu2ppu_sniffer): Pass down target.
	* target-delegates.c: Regenerate.
	* target.c (g_target_stack): Delete.
	(current_top_target): Return the current inferior's top target.
	(target_has_execution_1): Refer to the passed-in inferior's top
	target.
	(target_supports_terminal_ours): Check whether the initial
	inferior was already created.
	(decref_target): New.
	(target_stack::push): Incref/decref the target.
	(push_target, push_target, unpush_target): Adjust.
	(target_stack::unpush): Defref target.
	(target_is_pushed): Return bool.  Adjust to refer to the current
	inferior's target stack.
	(dispose_inferior): Delete, and inline parts ...
	(target_preopen): ... here.  Only dispose of the current inferior.
	(target_detach): Hold strong target reference while detaching.
	Pass target down.
	(target_thread_name): Add assertion.
	(target_resume): Pass down target.
	(target_ops::beneath, find_target_at): Adjust to refer to the
	current inferior's target stack.
	(get_dummy_target): New.
	(target_pass_ctrlc): Pass the Ctrl-C to the first inferior that
	has a thread running.
	(initialize_targets): Rename to ...
	(_initialize_target): ... this.
	* target.h: Include "gdbsupport/refcounted-object.h".
	(struct target_ops): Inherit refcounted_object.
	(target_ops::shortname, target_ops::longname): Make const.
	(target_ops::async_wait_fd): New method.
	(decref_target): Declare.
	(struct target_ops_ref_policy): New.
	(target_ops_ref): New typedef.
	(get_dummy_target): Declare function.
	(target_is_pushed): Return bool.
	* thread-iter.c (all_matching_threads_iterator::m_inf_matches)
	(all_matching_threads_iterator::all_matching_threads_iterator):
	Handle filter target.
	* thread-iter.h (struct all_matching_threads_iterator, struct
	all_matching_threads_range, class all_non_exited_threads_range):
	Filter by target too.  Remove explicit.
	* thread.c (threads_executing): Delete.
	(inferior_thread): Pass down current inferior.
	(clear_thread_inferior_resources): Pass down thread pointer
	instead of ptid_t.
	(add_thread_silent, add_thread_with_info, add_thread): Add
	process_stratum_target parameter.  Use it for thread and inferior
	searches.
	(is_current_thread): New.
	(thread_info::deletable): Use it.
	(find_thread_ptid, thread_count, in_thread_list)
	(thread_change_ptid, set_resumed, set_running): New
	process_stratum_target parameter.  Pass it down.
	(set_executing): New process_stratum_target parameter.  Pass it
	down.  Adjust reference to 'threads_executing'.
	(threads_are_executing): New process_stratum_target parameter.
	Adjust reference to 'threads_executing'.
	(set_stop_requested, finish_thread_state): New
	process_stratum_target parameter.  Pass it down.
	(switch_to_thread): Also match inferior.
	(switch_to_thread): New process_stratum_target parameter.  Pass it
	down.
	(update_threads_executing): Reimplement.
	* top.c (quit_force): Pop targets from all inferior.
	(gdb_init): Don't call initialize_targets.
	* windows-nat.c (windows_nat_target) <get_windows_debug_event>:
	Declare.
	(windows_add_thread, windows_delete_thread): Adjust.
	(get_windows_debug_event): Rename to ...
	(windows_nat_target::get_windows_debug_event): ... this.  Adjust.
	* tracefile-tfile.c (tfile_target_open): Pass down target.
	* gdbsupport/common-gdbthread.h (struct process_stratum_target):
	Forward declare.
	(switch_to_thread): Add process_stratum_target parameter.
	* mi/mi-interp.c (mi_on_resume_1): Add process_stratum_target
	parameter.  Use it.
	(mi_on_resume): Pass target down.
	* nat/fork-inferior.c (startup_inferior): Add
	process_stratum_target parameter.  Pass it down.
	* nat/fork-inferior.h (startup_inferior): Add
	process_stratum_target parameter.
	* python/py-threadevent.c (py_get_event_thread): Pass target down.

gdb/gdbserver/ChangeLog:
2020-01-10  Pedro Alves  <palves@redhat.com>

	* fork-child.c (post_fork_inferior): Pass target down to
	startup_inferior.
	* inferiors.c (switch_to_thread): Add process_stratum_target
	parameter.
	* lynx-low.c (lynx_target_ops): Now a process_stratum_target.
	* nto-low.c (nto_target_ops): Now a process_stratum_target.
	* linux-low.c (linux_target_ops): Now a process_stratum_target.
	* remote-utils.c (prepare_resume_reply): Pass the target to
	switch_to_thread.
	* target.c (the_target): Now a process_stratum_target.
	(done_accessing_memory): Pass the target to switch_to_thread.
	(set_target_ops): Ajust to use process_stratum_target.
	* target.h (struct target_ops): Rename to ...
	(struct process_stratum_target): ... this.
	(the_target, set_target_ops): Adjust.
	(prepare_to_access_memory): Adjust comment.
	* win32-low.c (child_xfer_memory): Adjust to use
	process_stratum_target.
	(win32_target_ops): Now a process_stratum_target.

1 files changed, 452 insertions, 145 deletions

diff --git a/gdb/infrun.c b/gdb/infrun.c
index bc8a3da..707c053 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -63,6 +63,8 @@
 #include "arch-utils.h"
 #include "gdbsupport/scope-exit.h"
 #include "gdbsupport/forward-scope-exit.h"
+#include "gdb_select.h"
+#include <unordered_map>
 
 /* Prototypes for local functions */
 
@@ -88,6 +90,8 @@ static int maybe_software_singlestep (struct gdbarch *gdbarch, CORE_ADDR pc);
 
 static void resume (gdb_signal sig);
 
+static void wait_for_inferior (inferior *inf);
+
 /* Asynchronous signal handler registered as event loop source for
    when we have pending events ready to be passed to the core.  */
 static struct async_event_handler *infrun_async_inferior_event_token;
@@ -370,9 +374,10 @@ show_stop_on_solib_events (struct ui_file *file, int from_tty,
 
 static int stop_print_frame;
 
-/* This is a cached copy of the pid/waitstatus of the last event
-   returned by target_wait()/deprecated_target_wait_hook().  This
-   information is returned by get_last_target_status().  */
+/* This is a cached copy of the target/ptid/waitstatus of the last
+   event returned by target_wait()/deprecated_target_wait_hook().
+   This information is returned by get_last_target_status().  */
+static process_stratum_target *target_last_proc_target;
 static ptid_t target_last_wait_ptid;
 static struct target_waitstatus target_last_waitstatus;
 
@@ -478,10 +483,12 @@ holding the child stopped.  Try \"set detach-on-fork\" or \
 
 	  scoped_restore_current_pspace_and_thread restore_pspace_thread;
 
-	  inferior_ptid = child_ptid;
-	  add_thread_silent (inferior_ptid);
 	  set_current_inferior (child_inf);
+	  switch_to_no_thread ();
 	  child_inf->symfile_flags = SYMFILE_NO_READ;
+	  push_target (parent_inf->process_target ());
+	  add_thread_silent (child_inf->process_target (), child_ptid);
+	  inferior_ptid = child_ptid;
 
 	  /* If this is a vfork child, then the address-space is
 	     shared with the parent.  */
@@ -490,6 +497,8 @@ holding the child stopped.  Try \"set detach-on-fork\" or \
 	      child_inf->pspace = parent_inf->pspace;
 	      child_inf->aspace = parent_inf->aspace;
 
+	      exec_on_vfork ();
+
 	      /* The parent will be frozen until the child is done
 		 with the shared region.  Keep track of the
 		 parent.  */
@@ -565,52 +574,64 @@ holding the child stopped.  Try \"set detach-on-fork\" or \
 
       parent_pspace = parent_inf->pspace;
 
-      /* If we're vforking, we want to hold on to the parent until the
-	 child exits or execs.  At child exec or exit time we can
-	 remove the old breakpoints from the parent and detach or
-	 resume debugging it.  Otherwise, detach the parent now; we'll
-	 want to reuse it's program/address spaces, but we can't set
-	 them to the child before removing breakpoints from the
-	 parent, otherwise, the breakpoints module could decide to
-	 remove breakpoints from the wrong process (since they'd be
-	 assigned to the same address space).  */
+      process_stratum_target *target = parent_inf->process_target ();
 
-      if (has_vforked)
-	{
-	  gdb_assert (child_inf->vfork_parent == NULL);
-	  gdb_assert (parent_inf->vfork_child == NULL);
-	  child_inf->vfork_parent = parent_inf;
-	  child_inf->pending_detach = 0;
-	  parent_inf->vfork_child = child_inf;
-	  parent_inf->pending_detach = detach_fork;
-	  parent_inf->waiting_for_vfork_done = 0;
-	}
-      else if (detach_fork)
-	{
-	  if (print_inferior_events)
-	    {
-	      /* Ensure that we have a process ptid.  */
-	      ptid_t process_ptid = ptid_t (parent_ptid.pid ());
+      {
+	/* Hold a strong reference to the target while (maybe)
+	   detaching the parent.  Otherwise detaching could close the
+	   target.  */
+	auto target_ref = target_ops_ref::new_reference (target);
+
+	/* If we're vforking, we want to hold on to the parent until
+	   the child exits or execs.  At child exec or exit time we
+	   can remove the old breakpoints from the parent and detach
+	   or resume debugging it.  Otherwise, detach the parent now;
+	   we'll want to reuse it's program/address spaces, but we
+	   can't set them to the child before removing breakpoints
+	   from the parent, otherwise, the breakpoints module could
+	   decide to remove breakpoints from the wrong process (since
+	   they'd be assigned to the same address space).  */
+
+	if (has_vforked)
+	  {
+	    gdb_assert (child_inf->vfork_parent == NULL);
+	    gdb_assert (parent_inf->vfork_child == NULL);
+	    child_inf->vfork_parent = parent_inf;
+	    child_inf->pending_detach = 0;
+	    parent_inf->vfork_child = child_inf;
+	    parent_inf->pending_detach = detach_fork;
+	    parent_inf->waiting_for_vfork_done = 0;
+	  }
+	else if (detach_fork)
+	  {
+	    if (print_inferior_events)
+	      {
+		/* Ensure that we have a process ptid.  */
+		ptid_t process_ptid = ptid_t (parent_ptid.pid ());
+
+		target_terminal::ours_for_output ();
+		fprintf_filtered (gdb_stdlog,
+				  _("[Detaching after fork from "
+				    "parent %s]\n"),
+				  target_pid_to_str (process_ptid).c_str ());
+	      }
 
-	      target_terminal::ours_for_output ();
-	      fprintf_filtered (gdb_stdlog,
-				_("[Detaching after fork from "
-				  "parent %s]\n"),
-				target_pid_to_str (process_ptid).c_str ());
-	    }
+	    target_detach (parent_inf, 0);
+	    parent_inf = NULL;
+	  }
 
-	  target_detach (parent_inf, 0);
-	}
+	/* Note that the detach above makes PARENT_INF dangling.  */
 
-      /* Note that the detach above makes PARENT_INF dangling.  */
+	/* Add the child thread to the appropriate lists, and switch
+	   to this new thread, before cloning the program space, and
+	   informing the solib layer about this new process.  */
 
-      /* Add the child thread to the appropriate lists, and switch to
-	 this new thread, before cloning the program space, and
-	 informing the solib layer about this new process.  */
+	set_current_inferior (child_inf);
+	push_target (target);
+      }
 
+      add_thread_silent (target, child_ptid);
       inferior_ptid = child_ptid;
-      add_thread_silent (inferior_ptid);
-      set_current_inferior (child_inf);
 
       /* If this is a vfork child, then the address-space is shared
 	 with the parent.  If we detached from the parent, then we can
@@ -619,6 +640,8 @@ holding the child stopped.  Try \"set detach-on-fork\" or \
 	{
 	  child_inf->pspace = parent_pspace;
 	  child_inf->aspace = child_inf->pspace->aspace;
+
+	  exec_on_vfork ();
 	}
       else
 	{
@@ -665,11 +688,12 @@ follow_fork (void)
 
   if (!non_stop)
     {
+      process_stratum_target *wait_target;
       ptid_t wait_ptid;
       struct target_waitstatus wait_status;
 
       /* Get the last target status returned by target_wait().  */
-      get_last_target_status (&wait_ptid, &wait_status);
+      get_last_target_status (&wait_target, &wait_ptid, &wait_status);
 
       /* If not stopped at a fork event, then there's nothing else to
 	 do.  */
@@ -680,14 +704,14 @@ follow_fork (void)
       /* Check if we switched over from WAIT_PTID, since the event was
 	 reported.  */
       if (wait_ptid != minus_one_ptid
-	  && inferior_ptid != wait_ptid)
+	  && (current_inferior ()->process_target () != wait_target
+	      || inferior_ptid != wait_ptid))
 	{
 	  /* We did.  Switch back to WAIT_PTID thread, to tell the
 	     target to follow it (in either direction).  We'll
 	     afterwards refuse to resume, and inform the user what
 	     happened.  */
-	  thread_info *wait_thread
-	    = find_thread_ptid (wait_ptid);
+	  thread_info *wait_thread = find_thread_ptid (wait_target, wait_ptid);
 	  switch_to_thread (wait_thread);
 	  should_resume = 0;
 	}
@@ -733,6 +757,7 @@ follow_fork (void)
 	parent = inferior_ptid;
 	child = tp->pending_follow.value.related_pid;
 
+	process_stratum_target *parent_targ = tp->inf->process_target ();
 	/* Set up inferior(s) as specified by the caller, and tell the
 	   target to do whatever is necessary to follow either parent
 	   or child.  */
@@ -748,7 +773,7 @@ follow_fork (void)
 	       or another.  The previous selected thread may be gone
 	       from the lists by now, but if it is still around, need
 	       to clear the pending follow request.  */
-	    tp = find_thread_ptid (parent);
+	    tp = find_thread_ptid (parent_targ, parent);
 	    if (tp)
 	      tp->pending_follow.kind = TARGET_WAITKIND_SPURIOUS;
 
@@ -759,7 +784,7 @@ follow_fork (void)
 	    /* If we followed the child, switch to it...  */
 	    if (follow_child)
 	      {
-		thread_info *child_thr = find_thread_ptid (child);
+		thread_info *child_thr = find_thread_ptid (parent_targ, child);
 		switch_to_thread (child_thr);
 
 		/* ... and preserve the stepping state, in case the
@@ -1188,9 +1213,11 @@ follow_exec (ptid_t ptid, const char *exec_file_target)
       inf->pid = pid;
       target_follow_exec (inf, exec_file_target);
 
-      set_current_inferior (inf);
-      set_current_program_space (inf->pspace);
-      add_thread (ptid);
+      inferior *org_inferior = current_inferior ();
+      switch_to_inferior_no_thread (inf);
+      push_target (org_inferior->process_target ());
+      thread_info *thr = add_thread (inf->process_target (), ptid);
+      switch_to_thread (thr);
     }
   else
     {
@@ -1884,6 +1911,7 @@ displaced_step_fixup (thread_info *event_thread, enum gdb_signal signal)
    discarded between events.  */
 struct execution_control_state
 {
+  process_stratum_target *target;
   ptid_t ptid;
   /* The thread that got the event, if this was a thread event; NULL
      otherwise.  */
@@ -2140,6 +2168,16 @@ user_visible_resume_ptid (int step)
   return resume_ptid;
 }
 
+/* See infrun.h.  */
+
+process_stratum_target *
+user_visible_resume_target (ptid_t resume_ptid)
+{
+  return (resume_ptid == minus_one_ptid && sched_multi
+	  ? NULL
+	  : current_inferior ()->process_target ());
+}
+
 /* Return a ptid representing the set of threads that we will resume,
    in the perspective of the target, assuming run control handling
    does not require leaving some threads stopped (e.g., stepping past
@@ -2204,6 +2242,9 @@ do_target_resume (ptid_t resume_ptid, int step, enum gdb_signal sig)
   target_resume (resume_ptid, step, sig);
 
   target_commit_resume ();
+
+  if (target_can_async_p ())
+    target_async (1);
 }
 
 /* Resume the inferior.  SIG is the signal to give the inferior
@@ -2247,6 +2288,7 @@ resume_1 (enum gdb_signal sig)
 			      currently_stepping (tp));
 	}
 
+      tp->inf->process_target ()->threads_executing = true;
       tp->resumed = 1;
 
       /* FIXME: What should we do if we are supposed to resume this
@@ -2732,10 +2774,12 @@ clear_proceed_status (int step)
   if (!non_stop && inferior_ptid != null_ptid)
     {
       ptid_t resume_ptid = user_visible_resume_ptid (step);
+      process_stratum_target *resume_target
+	= user_visible_resume_target (resume_ptid);
 
       /* In all-stop mode, delete the per-thread status of all threads
 	 we're about to resume, implicitly and explicitly.  */
-      for (thread_info *tp : all_non_exited_threads (resume_ptid))
+      for (thread_info *tp : all_non_exited_threads (resume_target, resume_ptid))
 	clear_proceed_status_thread (tp);
     }
 
@@ -2812,6 +2856,31 @@ schedlock_applies (struct thread_info *tp)
 					    execution_direction)));
 }
 
+/* Calls target_commit_resume on all targets.  */
+
+static void
+commit_resume_all_targets ()
+{
+  scoped_restore_current_thread restore_thread;
+
+  /* Map between process_target and a representative inferior.  This
+     is to avoid committing a resume in the same target more than
+     once.  Resumptions must be idempotent, so this is an
+     optimization.  */
+  std::unordered_map<process_stratum_target *, inferior *> conn_inf;
+
+  for (inferior *inf : all_non_exited_inferiors ())
+    if (inf->has_execution ())
+      conn_inf[inf->process_target ()] = inf;
+
+  for (const auto &ci : conn_inf)
+    {
+      inferior *inf = ci.second;
+      switch_to_inferior_no_thread (inf);
+      target_commit_resume ();
+    }
+}
+
 /* Basic routine for continuing the program in various fashions.
 
    ADDR is the address to resume at, or -1 for resume where stopped.
@@ -2826,7 +2895,6 @@ proceed (CORE_ADDR addr, enum gdb_signal siggnal)
   struct regcache *regcache;
   struct gdbarch *gdbarch;
   CORE_ADDR pc;
-  ptid_t resume_ptid;
   struct execution_control_state ecss;
   struct execution_control_state *ecs = &ecss;
   int started;
@@ -2858,6 +2926,11 @@ proceed (CORE_ADDR addr, enum gdb_signal siggnal)
 
   gdb_assert (!thread_is_in_step_over_chain (cur_thr));
 
+  ptid_t resume_ptid
+    = user_visible_resume_ptid (cur_thr->control.stepping_command);
+  process_stratum_target *resume_target
+    = user_visible_resume_target (resume_ptid);
+
   if (addr == (CORE_ADDR) -1)
     {
       if (pc == cur_thr->suspend.stop_pc
@@ -2887,12 +2960,10 @@ proceed (CORE_ADDR addr, enum gdb_signal siggnal)
   if (siggnal != GDB_SIGNAL_DEFAULT)
     cur_thr->suspend.stop_signal = siggnal;
 
-  resume_ptid = user_visible_resume_ptid (cur_thr->control.stepping_command);
-
   /* If an exception is thrown from this point on, make sure to
      propagate GDB's knowledge of the executing state to the
      frontend/user running state.  */
-  scoped_finish_thread_state finish_state (resume_ptid);
+  scoped_finish_thread_state finish_state (resume_target, resume_ptid);
 
   /* Even if RESUME_PTID is a wildcard, and we end up resuming fewer
      threads (e.g., we might need to set threads stepping over
@@ -2901,7 +2972,7 @@ proceed (CORE_ADDR addr, enum gdb_signal siggnal)
      inferior function, as in that case we pretend the inferior
      doesn't run at all.  */
   if (!cur_thr->control.in_infcall)
-   set_running (resume_ptid, 1);
+    set_running (resume_target, resume_ptid, 1);
 
   if (debug_infrun)
     fprintf_unfiltered (gdb_stdlog,
@@ -2936,7 +3007,8 @@ proceed (CORE_ADDR addr, enum gdb_signal siggnal)
      threads.  */
   if (!non_stop && !schedlock_applies (cur_thr))
     {
-      for (thread_info *tp : all_non_exited_threads (resume_ptid))
+      for (thread_info *tp : all_non_exited_threads (resume_target,
+						     resume_ptid))
 	{
 	  switch_to_thread_no_regs (tp);
 
@@ -2993,9 +3065,20 @@ proceed (CORE_ADDR addr, enum gdb_signal siggnal)
       {
 	/* In all-stop, but the target is always in non-stop mode.
 	   Start all other threads that are implicitly resumed too.  */
-      for (thread_info *tp : all_non_exited_threads (resume_ptid))
-        {
-	  switch_to_thread_no_regs (tp);
+	for (thread_info *tp : all_non_exited_threads (resume_target,
+						       resume_ptid))
+	  {
+	    switch_to_thread_no_regs (tp);
+
+	  if (!tp->inf->has_execution ())
+	    {
+	      if (debug_infrun)
+		fprintf_unfiltered (gdb_stdlog,
+				    "infrun: proceed: [%s] target has "
+				    "no execution\n",
+				    target_pid_to_str (tp->ptid).c_str ());
+	      continue;
+	    }
 
 	  if (tp->resumed)
 	    {
@@ -3039,7 +3122,7 @@ proceed (CORE_ADDR addr, enum gdb_signal siggnal)
       }
   }
 
-  target_commit_resume ();
+  commit_resume_all_targets ();
 
   finish_state.release ();
 
@@ -3061,10 +3144,8 @@ proceed (CORE_ADDR addr, enum gdb_signal siggnal)
 void
 start_remote (int from_tty)
 {
-  struct inferior *inferior;
-
-  inferior = current_inferior ();
-  inferior->control.stop_soon = STOP_QUIETLY_REMOTE;
+  inferior *inf = current_inferior ();
+  inf->control.stop_soon = STOP_QUIETLY_REMOTE;
 
   /* Always go on waiting for the target, regardless of the mode.  */
   /* FIXME: cagney/1999-09-23: At present it isn't possible to
@@ -3080,7 +3161,7 @@ start_remote (int from_tty)
      target_open() return to the caller an indication that the target
      is currently running and GDB state should be set to the same as
      for an async run.  */
-  wait_for_inferior ();
+  wait_for_inferior (inf);
 
   /* Now that the inferior has stopped, do any bookkeeping like
      loading shared libraries.  We want to do this before normal_stop,
@@ -3131,11 +3212,13 @@ static int switch_back_to_stepped_thread (struct execution_control_state *ecs);
 static void
 infrun_thread_stop_requested (ptid_t ptid)
 {
+  process_stratum_target *curr_target = current_inferior ()->process_target ();
+
   /* PTID was requested to stop.  If the thread was already stopped,
      but the user/frontend doesn't know about that yet (e.g., the
      thread had been temporarily paused for some step-over), set up
      for reporting the stop now.  */
-  for (thread_info *tp : all_threads (ptid))
+  for (thread_info *tp : all_threads (curr_target, ptid))
     {
       if (tp->state != THREAD_RUNNING)
 	continue;
@@ -3161,7 +3244,7 @@ infrun_thread_stop_requested (ptid_t ptid)
 
       /* Clear the inline-frame state, since we're re-processing the
 	 stop.  */
-      clear_inline_frame_state (tp->ptid);
+      clear_inline_frame_state (tp);
 
       /* If this thread was paused because some other thread was
 	 doing an inline-step over, let that finish first.  Once
@@ -3180,7 +3263,8 @@ infrun_thread_stop_requested (ptid_t ptid)
 static void
 infrun_thread_thread_exit (struct thread_info *tp, int silent)
 {
-  if (target_last_wait_ptid == tp->ptid)
+  if (target_last_proc_target == tp->inf->process_target ()
+      && target_last_wait_ptid == tp->ptid)
     nullify_last_target_wait_ptid ();
 }
 
@@ -3276,19 +3360,20 @@ print_target_wait_results (ptid_t waiton_ptid, ptid_t result_ptid,
    had events.  */
 
 static struct thread_info *
-random_pending_event_thread (ptid_t waiton_ptid)
+random_pending_event_thread (inferior *inf, ptid_t waiton_ptid)
 {
   int num_events = 0;
 
-  auto has_event = [] (thread_info *tp)
+  auto has_event = [&] (thread_info *tp)
     {
-      return (tp->resumed
+      return (tp->ptid.matches (waiton_ptid)
+	      && tp->resumed
 	      && tp->suspend.waitstatus_pending_p);
     };
 
   /* First see how many events we have.  Count only resumed threads
      that have an event pending.  */
-  for (thread_info *tp : all_non_exited_threads (waiton_ptid))
+  for (thread_info *tp : inf->non_exited_threads ())
     if (has_event (tp))
       num_events++;
 
@@ -3305,7 +3390,7 @@ random_pending_event_thread (ptid_t waiton_ptid)
 			num_events, random_selector);
 
   /* Select the Nth thread that has had an event.  */
-  for (thread_info *tp : all_non_exited_threads (waiton_ptid))
+  for (thread_info *tp : inf->non_exited_threads ())
     if (has_event (tp))
       if (random_selector-- == 0)
 	return tp;
@@ -3315,10 +3400,12 @@ random_pending_event_thread (ptid_t waiton_ptid)
 
 /* Wrapper for target_wait that first checks whether threads have
    pending statuses to report before actually asking the target for
-   more events.  */
+   more events.  INF is the inferior we're using to call target_wait
+   on.  */
 
 static ptid_t
-do_target_wait (ptid_t ptid, struct target_waitstatus *status, int options)
+do_target_wait_1 (inferior *inf, ptid_t ptid,
+		  target_waitstatus *status, int options)
 {
   ptid_t event_ptid;
   struct thread_info *tp;
@@ -3327,7 +3414,7 @@ do_target_wait (ptid_t ptid, struct target_waitstatus *status, int options)
      pending.  */
   if (ptid == minus_one_ptid || ptid.is_pid ())
     {
-      tp = random_pending_event_thread (ptid);
+      tp = random_pending_event_thread (inf, ptid);
     }
   else
     {
@@ -3337,7 +3424,7 @@ do_target_wait (ptid_t ptid, struct target_waitstatus *status, int options)
 			    target_pid_to_str (ptid).c_str ());
 
       /* We have a specific thread to check.  */
-      tp = find_thread_ptid (ptid);
+      tp = find_thread_ptid (inf, ptid);
       gdb_assert (tp != NULL);
       if (!tp->suspend.waitstatus_pending_p)
 	tp = NULL;
@@ -3444,6 +3531,109 @@ do_target_wait (ptid_t ptid, struct target_waitstatus *status, int options)
   return event_ptid;
 }
 
+/* Returns true if INF has any resumed thread with a status
+   pending.  */
+
+static bool
+threads_are_resumed_pending_p (inferior *inf)
+{
+  for (thread_info *tp : inf->non_exited_threads ())
+    if (tp->resumed
+	&& tp->suspend.waitstatus_pending_p)
+      return true;
+
+  return false;
+}
+
+/* Wrapper for target_wait that first checks whether threads have
+   pending statuses to report before actually asking the target for
+   more events. Polls for events from all inferiors/targets.  */
+
+static bool
+do_target_wait (ptid_t wait_ptid, execution_control_state *ecs, int options)
+{
+  int num_inferiors = 0;
+  int random_selector;
+
+  /* For fairness, we pick the first inferior/target to poll at
+     random, and then continue polling the rest of the inferior list
+     starting from that one in a circular fashion until the whole list
+     is polled once.  */
+
+  auto inferior_matches = [&wait_ptid] (inferior *inf)
+    {
+      return (inf->process_target () != NULL
+	      && (threads_are_executing (inf->process_target ())
+		  || threads_are_resumed_pending_p (inf))
+	      && ptid_t (inf->pid).matches (wait_ptid));
+    };
+
+  /* First see how many resumed inferiors we have.  */
+  for (inferior *inf : all_inferiors ())
+    if (inferior_matches (inf))
+      num_inferiors++;
+
+  if (num_inferiors == 0)
+    {
+      ecs->ws.kind = TARGET_WAITKIND_IGNORE;
+      return false;
+    }
+
+  /* Now randomly pick an inferior out of those that were resumed.  */
+  random_selector = (int)
+    ((num_inferiors * (double) rand ()) / (RAND_MAX + 1.0));
+
+  if (debug_infrun && num_inferiors > 1)
+    fprintf_unfiltered (gdb_stdlog,
+			"infrun: Found %d inferiors, starting at #%d\n",
+			num_inferiors, random_selector);
+
+  /* Select the Nth inferior that was resumed.  */
+
+  inferior *selected = nullptr;
+
+  for (inferior *inf : all_inferiors ())
+    if (inferior_matches (inf))
+      if (random_selector-- == 0)
+	{
+	  selected = inf;
+	  break;
+	}
+
+  /* Now poll for events out of each of the resumed inferior's
+     targets, starting from the selected one.  */
+
+  auto do_wait = [&] (inferior *inf)
+  {
+    switch_to_inferior_no_thread (inf);
+
+    ecs->ptid = do_target_wait_1 (inf, wait_ptid, &ecs->ws, options);
+    ecs->target = inf->process_target ();
+    return (ecs->ws.kind != TARGET_WAITKIND_IGNORE);
+  };
+
+  /* Needed in all-stop+target-non-stop mode, because we end up here
+     spuriously after the target is all stopped and we've already
+     reported the stop to the user, polling for events.  */
+  scoped_restore_current_thread restore_thread;
+
+  int inf_num = selected->num;
+  for (inferior *inf = selected; inf != NULL; inf = inf->next)
+    if (inferior_matches (inf))
+      if (do_wait (inf))
+	return true;
+
+  for (inferior *inf = inferior_list;
+       inf != NULL && inf->num < inf_num;
+       inf = inf->next)
+    if (inferior_matches (inf))
+      if (do_wait (inf))
+	return true;
+
+  ecs->ws.kind = TARGET_WAITKIND_IGNORE;
+  return false;
+}
+
 /* Prepare and stabilize the inferior for detaching it.  E.g.,
    detaching while a thread is displaced stepping is a recipe for
    crashing it, as nothing would readjust the PC out of the scratch
@@ -3483,7 +3673,7 @@ prepare_for_detach (void)
 	 don't get any event.  */
       target_dcache_invalidate ();
 
-      ecs->ptid = do_target_wait (pid_ptid, &ecs->ws, 0);
+      do_target_wait (pid_ptid, ecs, 0);
 
       if (debug_infrun)
 	print_target_wait_results (pid_ptid, ecs->ptid, &ecs->ws);
@@ -3491,7 +3681,8 @@ prepare_for_detach (void)
       /* If an error happens while handling the event, propagate GDB's
 	 knowledge of the executing state to the frontend/user running
 	 state.  */
-      scoped_finish_thread_state finish_state (minus_one_ptid);
+      scoped_finish_thread_state finish_state (inf->process_target (),
+					       minus_one_ptid);
 
       /* Now figure out what to do with the result of the result.  */
       handle_inferior_event (ecs);
@@ -3519,8 +3710,8 @@ prepare_for_detach (void)
    When this function actually returns it means the inferior
    should be left stopped and GDB should read more commands.  */
 
-void
-wait_for_inferior (void)
+static void
+wait_for_inferior (inferior *inf)
 {
   if (debug_infrun)
     fprintf_unfiltered
@@ -3531,13 +3722,13 @@ wait_for_inferior (void)
   /* If an error happens while handling the event, propagate GDB's
      knowledge of the executing state to the frontend/user running
      state.  */
-  scoped_finish_thread_state finish_state (minus_one_ptid);
+  scoped_finish_thread_state finish_state
+    (inf->process_target (), minus_one_ptid);
 
   while (1)
     {
       struct execution_control_state ecss;
       struct execution_control_state *ecs = &ecss;
-      ptid_t waiton_ptid = minus_one_ptid;
 
       memset (ecs, 0, sizeof (*ecs));
 
@@ -3549,10 +3740,11 @@ wait_for_inferior (void)
 	 don't get any event.  */
       target_dcache_invalidate ();
 
-      ecs->ptid = do_target_wait (waiton_ptid, &ecs->ws, 0);
+      ecs->ptid = do_target_wait_1 (inf, minus_one_ptid, &ecs->ws, 0);
+      ecs->target = inf->process_target ();
 
       if (debug_infrun)
-	print_target_wait_results (waiton_ptid, ecs->ptid, &ecs->ws);
+	print_target_wait_results (minus_one_ptid, ecs->ptid, &ecs->ws);
 
       /* Now figure out what to do with the result of the result.  */
       handle_inferior_event (ecs);
@@ -3678,7 +3870,6 @@ fetch_inferior_event (void *client_data)
   struct execution_control_state ecss;
   struct execution_control_state *ecs = &ecss;
   int cmd_done = 0;
-  ptid_t waiton_ptid = minus_one_ptid;
 
   memset (ecs, 0, sizeof (*ecs));
 
@@ -3719,17 +3910,28 @@ fetch_inferior_event (void *client_data)
       = make_scoped_restore (&execution_direction,
 			     target_execution_direction ());
 
-    ecs->ptid = do_target_wait (waiton_ptid, &ecs->ws,
-				target_can_async_p () ? TARGET_WNOHANG : 0);
+    if (!do_target_wait (minus_one_ptid, ecs, TARGET_WNOHANG))
+      return;
+
+    gdb_assert (ecs->ws.kind != TARGET_WAITKIND_IGNORE);
+
+    /* Switch to the target that generated the event, so we can do
+       target calls.  Any inferior bound to the target will do, so we
+       just switch to the first we find.  */
+    for (inferior *inf : all_inferiors (ecs->target))
+      {
+	switch_to_inferior_no_thread (inf);
+	break;
+      }
 
     if (debug_infrun)
-      print_target_wait_results (waiton_ptid, ecs->ptid, &ecs->ws);
+      print_target_wait_results (minus_one_ptid, ecs->ptid, &ecs->ws);
 
     /* If an error happens while handling the event, propagate GDB's
        knowledge of the executing state to the frontend/user running
        state.  */
     ptid_t finish_ptid = !target_is_non_stop_p () ? minus_one_ptid : ecs->ptid;
-    scoped_finish_thread_state finish_state (finish_ptid);
+    scoped_finish_thread_state finish_state (ecs->target, finish_ptid);
 
     /* Get executed before scoped_restore_current_thread above to apply
        still for the thread which has thrown the exception.  */
@@ -3743,7 +3945,7 @@ fetch_inferior_event (void *client_data)
 
     if (!ecs->wait_some_more)
       {
-	struct inferior *inf = find_inferior_ptid (ecs->ptid);
+	struct inferior *inf = find_inferior_ptid (ecs->target, ecs->ptid);
 	int should_stop = 1;
 	struct thread_info *thr = ecs->event_thread;
 
@@ -3848,8 +4050,10 @@ init_thread_stepping_state (struct thread_info *tss)
 /* See infrun.h.  */
 
 void
-set_last_target_status (ptid_t ptid, struct target_waitstatus status)
+set_last_target_status (process_stratum_target *target, ptid_t ptid,
+			target_waitstatus status)
 {
+  target_last_proc_target = target;
   target_last_wait_ptid = ptid;
   target_last_waitstatus = status;
 }
@@ -3857,8 +4061,11 @@ set_last_target_status (ptid_t ptid, struct target_waitstatus status)
 /* See infrun.h.  */
 
 void
-get_last_target_status (ptid_t *ptid, struct target_waitstatus *status)
+get_last_target_status (process_stratum_target **target, ptid_t *ptid,
+			target_waitstatus *status)
 {
+  if (target != nullptr)
+    *target = target_last_proc_target;
   if (ptid != nullptr)
     *ptid = target_last_wait_ptid;
   if (status != nullptr)
@@ -3870,6 +4077,7 @@ get_last_target_status (ptid_t *ptid, struct target_waitstatus *status)
 void
 nullify_last_target_wait_ptid (void)
 {
+  target_last_proc_target = nullptr;
   target_last_wait_ptid = minus_one_ptid;
   target_last_waitstatus = {};
 }
@@ -3881,7 +4089,8 @@ context_switch (execution_control_state *ecs)
 {
   if (debug_infrun
       && ecs->ptid != inferior_ptid
-      && ecs->event_thread != inferior_thread ())
+      && (inferior_ptid == null_ptid
+	  || ecs->event_thread != inferior_thread ()))
     {
       fprintf_unfiltered (gdb_stdlog, "infrun: Switching context from %s ",
 			  target_pid_to_str (inferior_ptid).c_str ());
@@ -4206,20 +4415,19 @@ fill_in_stop_func (struct gdbarch *gdbarch,
 static enum stop_kind
 get_inferior_stop_soon (execution_control_state *ecs)
 {
-  struct inferior *inf = find_inferior_ptid (ecs->ptid);
+  struct inferior *inf = find_inferior_ptid (ecs->target, ecs->ptid);
 
   gdb_assert (inf != NULL);
   return inf->control.stop_soon;
 }
 
-/* Wait for one event.  Store the resulting waitstatus in WS, and
-   return the event ptid.  */
+/* Poll for one event out of the current target.  Store the resulting
+   waitstatus in WS, and return the event ptid.  Does not block.  */
 
 static ptid_t
-wait_one (struct target_waitstatus *ws)
+poll_one_curr_target (struct target_waitstatus *ws)
 {
   ptid_t event_ptid;
-  ptid_t wait_ptid = minus_one_ptid;
 
   overlay_cache_invalid = 1;
 
@@ -4230,16 +4438,101 @@ wait_one (struct target_waitstatus *ws)
   target_dcache_invalidate ();
 
   if (deprecated_target_wait_hook)
-    event_ptid = deprecated_target_wait_hook (wait_ptid, ws, 0);
+    event_ptid = deprecated_target_wait_hook (minus_one_ptid, ws, TARGET_WNOHANG);
   else
-    event_ptid = target_wait (wait_ptid, ws, 0);
+    event_ptid = target_wait (minus_one_ptid, ws, TARGET_WNOHANG);
 
   if (debug_infrun)
-    print_target_wait_results (wait_ptid, event_ptid, ws);
+    print_target_wait_results (minus_one_ptid, event_ptid, ws);
 
   return event_ptid;
 }
 
+/* An event reported by wait_one.  */
+
+struct wait_one_event
+{
+  /* The target the event came out of.  */
+  process_stratum_target *target;
+
+  /* The PTID the event was for.  */
+  ptid_t ptid;
+
+  /* The waitstatus.  */
+  target_waitstatus ws;
+};
+
+/* Wait for one event out of any target.  */
+
+static wait_one_event
+wait_one ()
+{
+  while (1)
+    {
+      for (inferior *inf : all_inferiors ())
+	{
+	  process_stratum_target *target = inf->process_target ();
+	  if (target == NULL
+	      || !target->is_async_p ()
+	      || !target->threads_executing)
+	    continue;
+
+	  switch_to_inferior_no_thread (inf);
+
+	  wait_one_event event;
+	  event.target = target;
+	  event.ptid = poll_one_curr_target (&event.ws);
+
+	  if (event.ws.kind == TARGET_WAITKIND_NO_RESUMED)
+	    {
+	      /* If nothing is resumed, remove the target from the
+		 event loop.  */
+	      target_async (0);
+	    }
+	  else if (event.ws.kind != TARGET_WAITKIND_IGNORE)
+	    return event;
+	}
+
+      /* Block waiting for some event.  */
+
+      fd_set readfds;
+      int nfds = 0;
+
+      FD_ZERO (&readfds);
+
+      for (inferior *inf : all_inferiors ())
+	{
+	  process_stratum_target *target = inf->process_target ();
+	  if (target == NULL
+	      || !target->is_async_p ()
+	      || !target->threads_executing)
+	    continue;
+
+	  int fd = target->async_wait_fd ();
+	  FD_SET (fd, &readfds);
+	  if (nfds <= fd)
+	    nfds = fd + 1;
+	}
+
+      if (nfds == 0)
+	{
+	  /* No waitable targets left.  All must be stopped.  */
+	  return {NULL, minus_one_ptid, {TARGET_WAITKIND_NO_RESUMED}};
+	}
+
+      QUIT;
+
+      int numfds = interruptible_select (nfds, &readfds, 0, NULL, 0);
+      if (numfds < 0)
+	{
+	  if (errno == EINTR)
+	    continue;
+	  else
+	    perror_with_name ("interruptible_select");
+	}
+    }
+}
+
 /* Generate a wrapper for target_stopped_by_REASON that works on PTID
    instead of the current thread.  */
 #define THREAD_STOPPED_BY(REASON)		\
@@ -4262,7 +4555,7 @@ THREAD_STOPPED_BY (hw_breakpoint)
 /* Save the thread's event and stop reason to process it later.  */
 
 static void
-save_waitstatus (struct thread_info *tp, struct target_waitstatus *ws)
+save_waitstatus (struct thread_info *tp, const target_waitstatus *ws)
 {
   if (debug_infrun)
     {
@@ -4362,8 +4655,6 @@ stop_all_threads (void)
 			    "iterations=%d\n", pass, iterations);
       while (1)
 	{
-	  ptid_t event_ptid;
-	  struct target_waitstatus ws;
 	  int need_wait = 0;
 
 	  update_thread_list ();
@@ -4421,28 +4712,29 @@ stop_all_threads (void)
 	  if (pass > 0)
 	    pass = -1;
 
-	  event_ptid = wait_one (&ws);
+	  wait_one_event event = wait_one ();
+
 	  if (debug_infrun)
 	    {
 	      fprintf_unfiltered (gdb_stdlog,
 				  "infrun: stop_all_threads %s %s\n",
-				  target_waitstatus_to_string (&ws).c_str (),
-				  target_pid_to_str (event_ptid).c_str ());
+				  target_waitstatus_to_string (&event.ws).c_str (),
+				  target_pid_to_str (event.ptid).c_str ());
 	    }
 
-	  if (ws.kind == TARGET_WAITKIND_NO_RESUMED
-	      || ws.kind == TARGET_WAITKIND_THREAD_EXITED
-	      || ws.kind == TARGET_WAITKIND_EXITED
-	      || ws.kind == TARGET_WAITKIND_SIGNALLED)
+	  if (event.ws.kind == TARGET_WAITKIND_NO_RESUMED
+	      || event.ws.kind == TARGET_WAITKIND_THREAD_EXITED
+	      || event.ws.kind == TARGET_WAITKIND_EXITED
+	      || event.ws.kind == TARGET_WAITKIND_SIGNALLED)
 	    {
 	      /* All resumed threads exited
 		 or one thread/process exited/signalled.  */
 	    }
 	  else
 	    {
-	      thread_info *t = find_thread_ptid (event_ptid);
+	      thread_info *t = find_thread_ptid (event.target, event.ptid);
 	      if (t == NULL)
-		t = add_thread (event_ptid);
+		t = add_thread (event.target, event.ptid);
 
 	      t->stop_requested = 0;
 	      t->executing = 0;
@@ -4451,15 +4743,15 @@ stop_all_threads (void)
 
 	      /* This may be the first time we see the inferior report
 		 a stop.  */
-	      inferior *inf = find_inferior_ptid (event_ptid);
+	      inferior *inf = find_inferior_ptid (event.target, event.ptid);
 	      if (inf->needs_setup)
 		{
 		  switch_to_thread_no_regs (t);
 		  setup_inferior (0);
 		}
 
-	      if (ws.kind == TARGET_WAITKIND_STOPPED
-		  && ws.value.sig == GDB_SIGNAL_0)
+	      if (event.ws.kind == TARGET_WAITKIND_STOPPED
+		  && event.ws.value.sig == GDB_SIGNAL_0)
 		{
 		  /* We caught the event that we intended to catch, so
 		     there's no event pending.  */
@@ -4488,7 +4780,7 @@ stop_all_threads (void)
 
 		  if (debug_infrun)
 		    {
-		      std::string statstr = target_waitstatus_to_string (&ws);
+		      std::string statstr = target_waitstatus_to_string (&event.ws);
 
 		      fprintf_unfiltered (gdb_stdlog,
 					  "infrun: target_wait %s, saving "
@@ -4500,10 +4792,10 @@ stop_all_threads (void)
 		    }
 
 		  /* Record for later.  */
-		  save_waitstatus (t, &ws);
+		  save_waitstatus (t, &event.ws);
 
-		  sig = (ws.kind == TARGET_WAITKIND_STOPPED
-			 ? ws.value.sig : GDB_SIGNAL_0);
+		  sig = (event.ws.kind == TARGET_WAITKIND_STOPPED
+			 ? event.ws.value.sig : GDB_SIGNAL_0);
 
 		  if (displaced_step_fixup (t, sig) < 0)
 		    {
@@ -4601,7 +4893,7 @@ handle_no_resumed (struct execution_control_state *ecs)
      the synchronous command show "no unwaited-for " to the user.  */
   update_thread_list ();
 
-  for (thread_info *thread : all_non_exited_threads ())
+  for (thread_info *thread : all_non_exited_threads (ecs->target))
     {
       if (thread->executing
 	  || thread->suspend.waitstatus_pending_p)
@@ -4621,7 +4913,7 @@ handle_no_resumed (struct execution_control_state *ecs)
      process exited meanwhile (thus updating the thread list results
      in an empty thread list).  In this case we know we'll be getting
      a process exit event shortly.  */
-  for (inferior *inf : all_non_exited_inferiors ())
+  for (inferior *inf : all_non_exited_inferiors (ecs->target))
     {
       thread_info *thread = any_live_thread_of_inferior (inf);
       if (thread == NULL)
@@ -4691,8 +4983,8 @@ handle_inferior_event (struct execution_control_state *ecs)
       && handle_no_resumed (ecs))
     return;
 
-  /* Cache the last pid/waitstatus.  */
-  set_last_target_status (ecs->ptid, ecs->ws);
+  /* Cache the last target/ptid/waitstatus.  */
+  set_last_target_status (ecs->target, ecs->ptid, ecs->ws);
 
   /* Always clear state belonging to the previous time we stopped.  */
   stop_stack_dummy = STOP_NONE;
@@ -4709,10 +5001,10 @@ handle_inferior_event (struct execution_control_state *ecs)
   if (ecs->ws.kind != TARGET_WAITKIND_EXITED
       && ecs->ws.kind != TARGET_WAITKIND_SIGNALLED)
     {
-      ecs->event_thread = find_thread_ptid (ecs->ptid);
+      ecs->event_thread = find_thread_ptid (ecs->target, ecs->ptid);
       /* If it's a new thread, add it to the thread database.  */
       if (ecs->event_thread == NULL)
-	ecs->event_thread = add_thread (ecs->ptid);
+	ecs->event_thread = add_thread (ecs->target, ecs->ptid);
 
       /* Disable range stepping.  If the next step request could use a
 	 range, this will be end up re-enabled then.  */
@@ -4784,10 +5076,10 @@ handle_inferior_event (struct execution_control_state *ecs)
     else
       mark_ptid = ecs->ptid;
 
-    set_executing (mark_ptid, 0);
+    set_executing (ecs->target, mark_ptid, 0);
 
     /* Likewise the resumed flag.  */
-    set_resumed (mark_ptid, 0);
+    set_resumed (ecs->target, mark_ptid, 0);
   }
 
   switch (ecs->ws.kind)
@@ -4888,7 +5180,7 @@ handle_inferior_event (struct execution_control_state *ecs)
     case TARGET_WAITKIND_EXITED:
     case TARGET_WAITKIND_SIGNALLED:
       inferior_ptid = ecs->ptid;
-      set_current_inferior (find_inferior_ptid (ecs->ptid));
+      set_current_inferior (find_inferior_ptid (ecs->target, ecs->ptid));
       set_current_program_space (current_inferior ()->pspace);
       handle_vfork_child_exec_or_exit (0);
       target_terminal::ours ();	/* Must do this before mourn anyway.  */
@@ -4961,7 +5253,7 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
 	if (displaced_step_in_progress_thread (ecs->event_thread))
 	  {
 	    struct inferior *parent_inf
-	      = find_inferior_ptid (ecs->ptid);
+	      = find_inferior_ptid (ecs->target, ecs->ptid);
 	    struct regcache *child_regcache;
 	    CORE_ADDR parent_pc;
 
@@ -4992,7 +5284,8 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
 	       list yet at this point.  */
 
 	    child_regcache
-	      = get_thread_arch_aspace_regcache (ecs->ws.value.related_pid,
+	      = get_thread_arch_aspace_regcache (parent_inf->process_target (),
+						 ecs->ws.value.related_pid,
 						 gdbarch,
 						 parent_inf->aspace);
 	    /* Read PC value of parent process.  */
@@ -5060,10 +5353,16 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
 
 	  ecs->event_thread->suspend.stop_signal = GDB_SIGNAL_0;
 
+	  process_stratum_target *targ
+	    = ecs->event_thread->inf->process_target ();
+
 	  should_resume = follow_fork ();
 
+	  /* Note that one of these may be an invalid pointer,
+	     depending on detach_fork.  */
 	  thread_info *parent = ecs->event_thread;
-	  thread_info *child = find_thread_ptid (ecs->ws.value.related_pid);
+	  thread_info *child
+	    = find_thread_ptid (targ, ecs->ws.value.related_pid);
 
 	  /* At this point, the parent is marked running, and the
 	     child is marked stopped.  */
@@ -5876,7 +6175,7 @@ handle_signal_stop (struct execution_control_state *ecs)
   if (random_signal)
     {
       /* Signal not for debugging purposes.  */
-      struct inferior *inf = find_inferior_ptid (ecs->ptid);
+      struct inferior *inf = find_inferior_ptid (ecs->target, ecs->ptid);
       enum gdb_signal stop_signal = ecs->event_thread->suspend.stop_signal;
 
       if (debug_infrun)
@@ -6934,7 +7233,8 @@ switch_back_to_stepped_thread (struct execution_control_state *ecs)
 	  /* Ignore threads of processes the caller is not
 	     resuming.  */
 	  if (!sched_multi
-	      && tp->ptid.pid () != ecs->ptid.pid ())
+	      && (tp->inf->process_target () != ecs->target
+		  || tp->inf->pid != ecs->ptid.pid ()))
 	    continue;
 
 	  /* When stepping over a breakpoint, we lock all threads
@@ -7875,7 +8175,7 @@ print_stop_event (struct ui_out *uiout, bool displays)
   struct target_waitstatus last;
   struct thread_info *tp;
 
-  get_last_target_status (nullptr, &last);
+  get_last_target_status (nullptr, nullptr, &last);
 
   {
     scoped_restore save_uiout = make_scoped_restore (&current_uiout, uiout);
@@ -7995,7 +8295,7 @@ normal_stop (void)
 {
   struct target_waitstatus last;
 
-  get_last_target_status (nullptr, &last);
+  get_last_target_status (nullptr, nullptr, &last);
 
   new_stop_id ();
 
@@ -8004,10 +8304,10 @@ normal_stop (void)
      frontend/user running state.  A QUIT is an easy exception to see
      here, so do this before any filtered output.  */
 
-  gdb::optional<scoped_finish_thread_state> maybe_finish_thread_state;
+  ptid_t finish_ptid = null_ptid;
 
   if (!non_stop)
-    maybe_finish_thread_state.emplace (minus_one_ptid);
+    finish_ptid = minus_one_ptid;
   else if (last.kind == TARGET_WAITKIND_SIGNALLED
 	   || last.kind == TARGET_WAITKIND_EXITED)
     {
@@ -8017,10 +8317,17 @@ normal_stop (void)
 	 linux-fork.c automatically switches to another fork from
 	 within target_mourn_inferior.  */
       if (inferior_ptid != null_ptid)
-	maybe_finish_thread_state.emplace (ptid_t (inferior_ptid.pid ()));
+	finish_ptid = ptid_t (inferior_ptid.pid ());
     }
   else if (last.kind != TARGET_WAITKIND_NO_RESUMED)
-    maybe_finish_thread_state.emplace (inferior_ptid);
+    finish_ptid = inferior_ptid;
+
+  gdb::optional<scoped_finish_thread_state> maybe_finish_thread_state;
+  if (finish_ptid != null_ptid)
+    {
+      maybe_finish_thread_state.emplace
+	(user_visible_resume_target (finish_ptid), finish_ptid);
+    }
 
   /* As we're presenting a stop, and potentially removing breakpoints,
      update the thread list so we can tell whether there are threads