RFA: Support Windows extended error numbers in safe_strerror

[Daniel Jacobowitz <drow@false.org>]

This is an improved version of a patch Mark Mitchell submitted last
year.  If you give strerror() anything above 42 (sys_nerr) on Windows,
it gives you back "Unknown error" - particularly unfortunate since
WSAECONNREFUSED is way above there, so connecting to a closed socket
will give you a generic error message.  This patch lets us try an
OS-specific interface to fetch an error string.

[Actually you need my next patch too to get the connection refused message;
right now you'll get a timeout.]

Any comments on this patch?

-- 
Daniel Jacobowitz
CodeSourcery

2006-02-03  Daniel Jacobowitz  <dan@codesourcery.com>

	* utils.c (safe_strerror): Try to use FormatMessage for otherwise
	unknown messages on Windows.

Index: src/gdb/utils.c
===================================================================
--- src.orig/gdb/utils.c	2006-02-03 15:13:03.000000000 -0500
+++ src/gdb/utils.c	2006-02-03 15:16:24.000000000 -0500
@@ -1,8 +1,8 @@
 /* General utility routines for GDB, the GNU debugger.
 
    Copyright (C) 1986, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
-   1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005 Free
-   Software Foundation, Inc.
+   1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
+   Free Software Foundation, Inc.
 
    This file is part of GDB.
 
@@ -36,6 +36,10 @@
 #include <pc.h>
 #endif
 
+#ifdef USE_WIN32API
+#include <windows.h>
+#endif
+
 /* SunOS's curses.h has a '#define reg register' in it.  Thank you Sun. */
 #ifdef reg
 #undef reg
@@ -847,7 +851,34 @@ safe_strerror (int errnum)
 {
   char *msg;
 
-  msg = strerror (errnum);
+#ifdef USE_WIN32API
+  /* On Windows, strerror never returns NULL, but it returns a useless
+     string for anything above sys_nerr.  Try a little harder to find
+     a system-provided error message in that case.  */
+  if (errnum >= sys_nerr)
+    {
+      static char *buffer;
+
+      if (buffer)
+	LocalFree (buffer);
+
+      if (FormatMessage (FORMAT_MESSAGE_ALLOCATE_BUFFER
+			 | FORMAT_MESSAGE_FROM_SYSTEM,
+			 NULL, errnum,
+			 MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+			 (LPTSTR) &buffer, 0, NULL) != 0)
+	{
+	  if (strcmp (buffer + strlen (buffer) - 3, ".\r\n") == 0)
+	    buffer[strlen (buffer) - 3] = '\0';
+	  return buffer;
+	}
+      else
+	msg = NULL;
+    }
+  else
+#endif
+    msg = strerror (errnum);
+
   if (msg == NULL)
     {
       static char buf[32];