Cygwin: exceptions: check ExceptionFlags for EXCEPTION_NONCONTINUABLE

So far, exception::handle returned prematurely if the value of
EXCEPTION_RECORD::ExceptionFlags was non-0.

Starting with Windows 11 we're getting into trouble with that,
if the exception is software generated, for instance by calling
"throw" in a C++ application.

In that case EXCEPTION_SOFTWARE_ORIGINATE (0x80) is set in
EXCEPTION_RECORD::ExceptionFlags.

Change the condition for exiting prematurely to do this only if
any other flag except EXCEPTION_SOFTWARE_ORIGINATE is set in
EXCEPTION_RECORD::ExceptionFlags.

Fixes: Silent change in Windows exception handling
Signed-off-by: Corinna Vinschen <[email protected]>

(cherry picked from commit 0d73c04)

Author: github-cygwin

winsup/cygwin/exceptions.cc

@@ -659,7 +659,7 @@ exception::handle (EXCEPTION_RECORD *e, exception_list *frame, CONTEXT *in,
 
   /* If we're exiting, tell Windows to keep looking for an
      exception handler.  */
-  if (exit_state || e->ExceptionFlags)
+  if (exit_state || (e->ExceptionFlags & ~EXCEPTION_SOFTWARE_ORIGINATE))
     return ExceptionContinueSearch;
 
   siginfo_t si = {};

winsup/cygwin/local_includes/winlean.h

@@ -111,6 +111,10 @@ details. */
 #define DOMAIN_ALIAS_RID_DEVICE_OWNERS		(__MSABI_LONG(0x00000247))
 #endif
 
+#ifndef EXCEPTION_SOFTWARE_ORIGINATE
+#define EXCEPTION_SOFTWARE_ORIGINATE		0x80
+#endif
+
 /* So-called "Microsoft Account" SIDs (S-1-11-...) have a netbios domain name
    "MicrosoftAccounts".  The new "Application Container SIDs" (S-1-15-...)
    have a netbios domain name "APPLICATION PACKAGE AUTHORITY"

winsup/cygwin/release/3.6.1

@@ -23,3 +23,7 @@ Fixes:
 
 - Disallow accounts from the BUILTIN, NT AUTHORITY, NT SERVICE domains
   as USER entry in a POSIX ACL.  Only allow USER_OBJ, GROUP_OBJ and GROUP.
+
+- Accommodate a change in Windows exception handling affecting software
+  generated exceptions.
+  Addresses: https://cygwin.com/pipermail/cygwin/2025-March/257808.html