[PATCH] Fix amd_dbgapi_target::wait's handling of TARGET_WAITKIND_IGNORE

[Pedro Alves <pedro@palves.net>]

On Windows, a ROCgdb downstream testcase
(gdb.rocm/register-watchpoint.exp, which we can't upstream yet due to
missing support for DWARF 6 features upstream) currently fails with a
timeout, like so:

  (gdb) PASS: gdb.rocm/register-watchpoint.exp: continue to breakpoint: bit_extract_kernel
  watch $s32
  Watchpoint 3: $s32
  (gdb) PASS: gdb.rocm/register-watchpoint.exp: watchpoint on a stack pointer of the first wave
  continue
  Continuing.
  FAIL: gdb.rocm/register-watchpoint.exp: continue (timeout)

Running the test manualy with some extra logging, we see:

  [infrun] stop_all_threads:   6/7 waits_needed                          << extra
  [amd-dbgapi] wait: ptid = -1.0.0
  [windows events] get_windows_debug_event: kernel event for pid=7036 tid=0x4e8 code=EXCEPTION_DEBUG_EVENT
  [windows events] get_windows_debug_event: get_windows_debug_event - unexpected stop in suspended thread 0x4e8
  [windows events] continue_last_debug_event: ContinueDebugEvent (cpid=7036, ctid=0x4e8, DBG_REPLY_LATER)
  [windows events] wait: get_windows_debug_event returned [0.0.0 : status->kind = IGNORE, fake=0]
  [infrun] print_target_wait_results: target_wait (-1.0.0 [process -1], status) =
  [infrun] print_target_wait_results:   0.0.0 [process 0],
  [infrun] print_target_wait_results:   status->kind = IGNORE
  [infrun] print_target_wait_results:   from target 1 (native)
  [infrun] wait_one: about to block in interruptible_select              << extra

So we're in stop_all_threads, and we've pulled the stop events for all
CPU threads already, but then we hang in interruptible_select waiting
for the last stop event, which happens to be for the GPU wave.

In wait_one, before the interruptible_select call, we poll events from
the target, via target_wait with WNOHANG, and so we get here:

    ptid_t
    amd_dbgapi_target::wait (ptid_t ptid, struct target_waitstatus *ws,
			     target_wait_flags target_options)
    {
  ...
      ptid_t event_ptid = beneath ()->wait (ptid, ws, target_options);
      if (event_ptid != minus_one_ptid)
	{
  ...
	  return event_ptid;
	}
  ... handle dbgapi events ...

So above, we call the beneath target's wait.  On Windows that may hit
that "get_windows_debug_event - unexpected stop in suspended thread
0x4e8" path, which makes windows_nat_target::wait return
TARGET_WAITKIND_IGNORE.  The Windows target pairs that with event_ptid
== ptid_t(0,0,0) though, so the 'if then' branch is taken and we
return the TARGET_WAITKIND_IGNORE to the core without looking for
dbgapi events.  The event for the wave stop at this point has already
been flushed from the dbgapi library into amd-dbgapi-target's dbgapi
local event queue, and so wait_one ends up deadlocked in
interruptible_select, which results in the timeouts observed.

Nothing specifies that TARGET_WAITKIND_IGNORE must be returned with
minus_one_ptid.  infrun never looks at the event ptid if the status is
TARGET_WAITKIND_IGNORE.  So fix this by tweaking
amd_dbgapi_target::wait to not assume that either.

Change-Id: I6cbbeebdc8146e361ead72829b59f82531c90fc7
---
 gdb/amd-dbgapi-target.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/gdb/amd-dbgapi-target.c b/gdb/amd-dbgapi-target.c
index 610a484becd..d0424044e0c 100644
--- a/gdb/amd-dbgapi-target.c
+++ b/gdb/amd-dbgapi-target.c
@@ -1690,7 +1690,8 @@ amd_dbgapi_target::wait (ptid_t ptid, struct target_waitstatus *ws,
   amd_dbgapi_debug_printf ("ptid = %s", ptid.to_string ().c_str ());
 
   ptid_t event_ptid = beneath ()->wait (ptid, ws, target_options);
-  if (event_ptid != minus_one_ptid)
+  if (ws->kind () != TARGET_WAITKIND_NO_RESUMED
+      && ws->kind () != TARGET_WAITKIND_IGNORE)
     {
       if (ws->kind () == TARGET_WAITKIND_EXITED
 	  || ws->kind () == TARGET_WAITKIND_SIGNALLED)
@@ -1703,9 +1704,6 @@ amd_dbgapi_target::wait (ptid_t ptid, struct target_waitstatus *ws,
       return event_ptid;
     }
 
-  gdb_assert (ws->kind () == TARGET_WAITKIND_NO_RESUMED
-	      || ws->kind () == TARGET_WAITKIND_IGNORE);
-
   /* Flush the async handler first.  */
   if (target_is_async_p ())
     async_event_handler_clear ();

base-commit: fd3cf86c638b7fdc0ccb64e178ec43ccd7e9d3f9
-- 
2.54.0