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

[Lancelot SIX <lancelot.six@amd.com>]

On Fri, Jun 19, 2026 at 06:01:51PM +0100, Pedro Alves wrote:
> 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

Hi,

Thas looks good to me, thanks!

Approved-by: Lancelot Six <lancelot.six@amd.com> (amdgpu)

Best,
Lancelot.

> ---
>  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