From b1497491008b9351fa95c5f08fbe361a014dabba Mon Sep 17 00:00:00 2001
From: Pedro Alves <pedro@palves.net>
Date: Tue, 9 May 2023 10:27:04 +0100
Subject: [PATCH] Windows gdb+gdbserver: Move suspending thread to when
 returning event

The current code suspends a thread just before calling
GetThreadContext.  You can only call GetThreadContext if the thread is
suspended.  But, after WaitForDebugEvent, all threads are implicitly
suspended.  So I don't think we even needed to call SuspendThread
explictly at all before our GetThreadContext calls.

However, suspending threads when we're about to present a stop to gdb
simplifies adding non-stop support later.  This way, the windows
SuspendThread state corresponds to whether a thread is suspended or
resumed from the core's perspective.  Curiously, I noticed that Wine's
winedbg does something similar:
https://github.com/wine-mirror/wine/blob/234943344f7495d1e072338f0e06fa2d5cbf0aa1/programs/winedbg/gdbproxy.c#L651

This makes it much easier to reason about a thread's suspend state,
and simplifies adding non-stop mode later on.

Change-Id: Ifd6889a8afc041fad33cd1c4500e38941da6781b
---
 gdb/windows-nat.c      | 12 +++++-------
 gdbserver/win32-low.cc |  5 +++++
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index f1ec8837e82..a81a7eebfe9 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -706,7 +706,6 @@ windows_nat_target::fetch_registers (struct regcache *regcache, int r)
      {
        if (context->ContextFlags == 0)
 	 {
-	   th->suspend ();
 	   context->ContextFlags = WindowsContext<decltype(context)>::all;
 	   CHECK (get_thread_context (th->h, context));
 	 }
@@ -1233,12 +1232,6 @@ windows_nat_target::windows_continue (DWORD continue_status, int id,
 
 	th->resume ();
       }
-    else
-      {
-	/* When single-stepping a specific thread, other threads must
-	   be suspended.  */
-	th->suspend ();
-      }
 
   std::optional<unsigned> err;
   do_synchronously ([&] ()
@@ -1717,6 +1710,11 @@ windows_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 		  th->stopped_at_software_breakpoint = true;
 		  th->pc_adjusted = false;
 		}
+
+	      /* All-stop, suspend all threads until they are
+		 explicitly resumed.  */
+	      for (auto &thr : windows_process.thread_list)
+		thr->suspend ();
 	    }
 
 	  return result;
diff --git a/gdbserver/win32-low.cc b/gdbserver/win32-low.cc
index c99248d37cb..a23a41b9c02 100644
--- a/gdbserver/win32-low.cc
+++ b/gdbserver/win32-low.cc
@@ -1194,6 +1194,11 @@ win32_process_target::wait (ptid_t ptid, target_waitstatus *ourstatus,
 	    OUTMSG2 (("Child Stopped with signal = %d \n",
 		      ourstatus->sig ()));
 	    maybe_adjust_pc ();
+
+	    /* All-stop, suspend all threads until they are explicitly
+	       resumed.  */
+	    for_each_thread (suspend_one_thread);
+
 	    return debug_event_ptid (&windows_process.current_event);
 	  }
 	default:
-- 
2.47.2