[PATCH v3 01/11] Windows gdb+gdbserver: Check whether DBG_REPLY_LATER is available

[Pedro Alves <pedro@palves.net>]

Per
<https://learn.microsoft.com/en-us/windows/win32/api/debugapi/nf-debugapi-continuedebugevent>,
DBG_REPLY_LATER is "Supported in Windows 10, version 1507 or above, ..."

Since we support versions of Windows older than 10, we need to know
whether DBG_REPLY_LATER is available.  And we need to know this before
starting any inferior.

This adds a function that probes for support (and caches the result),
by trying to call ContinueDebugEvent on pid=0,tid=0 with
DBG_REPLY_LATER, and inspecting the resulting error.

Suggested-by: Hannes Domani <ssbssa@yahoo.de>
Suggested-by: Eli Zaretskii <eliz@gnu.org>
Approved-By: Tom Tromey <tom@tromey.com>
Change-Id: Ia27b981aeecaeef430ec90cebc5b3abdce00449d
commit-id:9098a060
---
 gdb/nat/windows-nat.c | 20 ++++++++++++++++++++
 gdb/nat/windows-nat.h |  9 +++++++++
 2 files changed, 29 insertions(+)

diff --git a/gdb/nat/windows-nat.c b/gdb/nat/windows-nat.c
index c6434348607..cf30a66a0c1 100644
--- a/gdb/nat/windows-nat.c
+++ b/gdb/nat/windows-nat.c
@@ -917,6 +917,26 @@ disable_randomization_available ()
 
 /* See windows-nat.h.  */
 
+bool
+dbg_reply_later_available ()
+{
+  static int available = -1;
+  if (available == -1)
+    {
+      /* DBG_REPLY_LATER is supported since Windows 10, Version 1507.
+	 If supported, this fails with ERROR_INVALID_HANDLE (tested on
+	 Win10 and Win11).  If not supported, it fails with
+	 ERROR_INVALID_PARAMETER (tested on Win7).  */
+      if (ContinueDebugEvent (0, 0, DBG_REPLY_LATER))
+	internal_error (_("ContinueDebugEvent call should not "
+			  "have succeeded"));
+      available = (GetLastError () != ERROR_INVALID_PARAMETER);
+    }
+  return available;
+}
+
+/* See windows-nat.h.  */
+
 bool
 initialize_loadable ()
 {
diff --git a/gdb/nat/windows-nat.h b/gdb/nat/windows-nat.h
index 45d186f771a..0a503232718 100644
--- a/gdb/nat/windows-nat.h
+++ b/gdb/nat/windows-nat.h
@@ -535,6 +535,15 @@ enum_process_modules (WOW64_CONTEXT *, HANDLE process,
 }
 #endif
 
+/* This is available starting with Windows 10.  */
+#ifndef DBG_REPLY_LATER
+# define DBG_REPLY_LATER 0x40010001L
+#endif
+
+/* Return true if it's possible to use DBG_REPLY_LATER with
+   ContinueDebugEvent on this host.  */
+extern bool dbg_reply_later_available ();
+
 /* Load any functions which may not be available in ancient versions
    of Windows.  */
 
-- 
2.53.0