From 6c6084d66c4ec111a3e3c9f4af5518d929313fef Mon Sep 17 00:00:00 2001
From: "jan.nijtmans" <nijtmans@users.sourceforge.net>
Date: Tue, 4 Feb 2014 08:35:02 +0000
Subject: Fix [http://core.tcl.tk/tcl/info/651e828a52|651e828a52]: Wrong
 Windows version reported for Windows 8.1

---
 win/tkWinX.c | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/win/tkWinX.c b/win/tkWinX.c
index 60e5e90..a37fa0a 100644
--- a/win/tkWinX.c
+++ b/win/tkWinX.c
@@ -166,20 +166,31 @@ TkGetServerInfo(
     Tk_Window tkwin)		/* Token for window; this selects a particular
 				 * display and server. */
 {
-    char buffer[60];
+    static char buffer[32]; /* Empty string means not initialized yet. */
     OSVERSIONINFOW os;
 
-    os.dwOSVersionInfoSize = sizeof(OSVERSIONINFOW);
-    GetVersionExW(&os);
-    sprintf(buffer, "Windows %d.%d %d %s", (int)os.dwMajorVersion,
-	    (int)os.dwMinorVersion, (int)os.dwBuildNumber,
+    if (!buffer[0]) {
+	HANDLE handle = LoadLibraryW(L"NTDLL");
+	int(*getversion)(void *) = (int(*)(void *))GetProcAddress(handle, "RtlGetVersion");
+	os.dwOSVersionInfoSize = sizeof(OSVERSIONINFOW);
+	if (!getversion || getversion(&os)) {
+	    GetVersionExW(&os);
+	}
+	if (handle) {
+	    FreeLibrary(handle);
+	}
+	/* Write the first character last, preventing multi-thread issues. */
+	sprintf(buffer+1, "indows %d.%d %d %s", (int)os.dwMajorVersion,
+		(int)os.dwMinorVersion, (int)os.dwBuildNumber,
 #ifdef _WIN64
-	    "Win64"
+		"Win64"
 #else
-	    "Win32"
+		"Win32"
 #endif
-	    );
-    Tcl_SetResult(interp, buffer, TCL_VOLATILE);
+	);
+	buffer[0] = 'W';
+    }
+    Tcl_SetResult(interp, buffer, TCL_STATIC);
 }
 
 /*
-- 
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