[PATCH v2][PR 30630] gdb/remote: fix assertion failure during startup

Tue Jul 30 04:16:06 GMT 2024

Ensure that calls to `remote_state::mark_async_event_handler` are only
made when the target is in async mode:
- Replace the check for `target_can_async_p` in
`remote_target::queued_stop_reply` with `target_is_async_p`.
- Add a check in `remote_notif_stop_can_get_pending_events`.

During early startup, `process_initial_stop_replies` was called before
asynchronous mode was enabled. The function then called
`remote_target::queued_stop_reply`, which then tried to mark the event
handler on all targets claiming async support, regardless of whether
async mode had been enabled or not. This triggered an assertion fail if
there had been queued stop replies.

The bug can be reproduced when running in non-stop mode while connected
to a custom build of `gdbserver`. This build always returns an extra
library stop notification due to the system libraries loading extra
add-ons right after program startup.

gdb/gdb -ex "set non-stop on" -ex "set debug remote 1" \
        -ex "target remote $VM_HOST:6666"

Remote debugging using 192.168.154.176:6666
[remote] start_remote_1: enter
  [remote] Sending packet: $qSupported:multiprocess+;swbreak+;hwbreak+;qRelocInsn+;fork-events+;vfork-events+;exec-events+;vContSupported+;QThreadEvents+;QThreadOptions+;no-resumed+;memory-tagging+;xmlRegisters=i386#72
  [remote] Received Ack
  [remote] Packet received: PacketSize=2001f;QPassSignals+;QProgramSignals+;QStartupWithShell+;QEnvironmentHexEncoded+;QEnvironmentReset+;QEnvironmentUnset+;QSetWorkingDir+;QCatchSyscalls+;qXfer:libraries:read+;qXfer:features:read+;QStartNoAckMode+;qXfer:osdata:read+;multiprocess+;fork-events+;exec-events+;QNonStop+;QDisableRandomization+;qXfer:threads:read+;BreakpointCommands+;qXfer:exec-file:read+;vContSupported+;QThreadEvents+;no-resumed+
  [remote] packet_ok: Packet qSupported (supported-packets) is supported
  [remote] Sending packet: $vCont?#49
  [remote] Received Ack
  [remote] Packet received: vCont;c;C;t
  [remote] packet_ok: Packet vCont (verbose-resume) is supported
  [remote] Sending packet: $vMustReplyEmpty#3a
  [remote] Received Ack
  [remote] Packet received:
  [remote] Sending packet: $QStartNoAckMode#b0
  [remote] Received Ack
  [remote] Packet received: OK

  [remote] Sending packet: $QNonStop:1#8d
  [remote] Packet received: OK
  [remote] Sending packet: $qXfer:threads:read::0,1000#92
  [remote]   Notification received: Stop:T0006:20310801007f0000;07:a8300801007f0000;10:a13c110000000000;thread:p85a.0;library:;
  [remote] Packet received: l<threads>\n<thread id="p85a.0" name="cat"/>\n</threads>\n
  [remote] Sending packet: $vStopped#55
  [remote] Packet received: OK
  [remote] Sending packet: $qAttached:85a#97
  [remote] Packet received: 0
  [remote] packet_ok: Packet qAttached (query-attached) is supported
  [remote] Sending packet: $qXfer:exec-file:read:85a:0,1000#e7
  [remote] Packet received: l/boot/system/bin/cat
  [remote] Sending packet: $vFile:setfs:0#bf
  [remote] Packet received:
  [remote] packet_ok: Packet vFile:setfs (hostio-setfs) is NOT supported
  [remote] Sending packet: $vFile:open:6a7573742070726f62696e67,0,1c0#ed
  [remote] Packet received: F-1,2
  [remote] packet_ok: Packet vFile:open (hostio-open) is supported
Reading /boot/system/bin/cat from remote target...
warning: File transfers from remote targets can be slow. Use "set sysroot" to access files locally instead.

  [remote] Sending packet: $QPassSignals:#f3
  [remote] Packet received: OK
  [remote] wait: enter
../../gdb-haiku/gdb/remote.c:504: internal-error: mark_async_event_handler: Assertion `this->is_async_p ()' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
----- Backtrace -----
0x7f6328d6b0b5 gdb_internal_backtrace_1
        ../../gdb-haiku/gdb/bt-utils.c:121
0x7f6328d6b0b5 _Z22gdb_internal_backtracev
        ../../gdb-haiku/gdb/bt-utils.c:167
0x7f6329145214 internal_vproblem
        ../../gdb-haiku/gdb/utils.c:420
0x7f6329145540 _Z15internal_verrorPKciS0_P13__va_list_tag
        ../../gdb-haiku/gdb/utils.c:500
0x7f632929ecc4 _Z18internal_error_locPKciS0_z
        ../../gdb-haiku/gdbsupport/errors.cc:57
0x7f632902f48d _ZN12remote_state24mark_async_event_handlerEv
        ../../gdb-haiku/gdb/remote.c:504
0x7f63290375d4 _ZN12remote_state24mark_async_event_handlerEv
        ../../gdb-haiku/gdb/remote.c:7912
0x7f63290375d4 _ZN13remote_target17queued_stop_replyE6ptid_t
        ../../gdb-haiku/gdb/remote.c:7908
0x7f6329042b21 _ZN13remote_target7wait_nsE6ptid_tP17target_waitstatus10enum_flagsI16target_wait_flagE
        ../../gdb-haiku/gdb/remote.c:8602
0x7f6329043466 _ZN13remote_target4waitE6ptid_tP17target_waitstatus10enum_flagsI16target_wait_flagE
        ../../gdb-haiku/gdb/remote.c:8804
0x7f63290f1c45 _Z11target_wait6ptid_tP17target_waitstatus10enum_flagsI16target_wait_flagE
        ../../gdb-haiku/gdb/target.c:2579
0x7f63290460bb _ZN13remote_target28process_initial_stop_repliesEi
        ../../gdb-haiku/gdb/remote.c:4906
0x7f632904c847 _ZN13remote_target14start_remote_1Eii
        ../../gdb-haiku/gdb/remote.c:5365
0x7f632904ce3c _ZN13remote_target12start_remoteEii
        ../../gdb-haiku/gdb/remote.c:5417
0x7f632904ce3c _ZN13remote_target6open_1EPKcii
        ../../gdb-haiku/gdb/remote.c:6279
0x7f63290f2ba8 open_target
        ../../gdb-haiku/gdb/target.c:837
0x7f6328d9f9b4 _Z8cmd_funcP16cmd_list_elementPKci
        ../../gdb-haiku/gdb/cli/cli-decode.c:2741
0x7f6329102e64 _Z15execute_commandPKci
---
 gdb/remote.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/gdb/remote.c b/gdb/remote.c
index 4948a54e322..c6f05c4af30 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -7710,8 +7710,11 @@ remote_notif_stop_can_get_pending_events (remote_target *remote,
      instead.  If we fetch all queued events from stub, remote stub
      may exit and we have no chance to process them back in
      remote_wait_ns.  */
-  remote_state *rs = remote->get_remote_state ();
-  rs->mark_async_event_handler ();
+  if (target_is_async_p ())
+    {
+      remote_state *rs = remote->get_remote_state ();
+      rs->mark_async_event_handler ();
+    }
   return 0;
 }

@@ -7908,7 +7911,7 @@ remote_target::queued_stop_reply (ptid_t ptid)
   remote_state *rs = get_remote_state ();
   stop_reply_up r = remote_notif_remove_queued_reply (ptid);

-  if (!rs->stop_reply_queue.empty () && target_can_async_p ())
+  if (!rs->stop_reply_queue.empty () && target_is_async_p ())
     {
       /* There's still at least an event left.  */
       rs->mark_async_event_handler ();
--
2.39.1.windows.1

