[newlib-cygwin] Cygwin: main exception handler (64-bit): continue GCC exceptions

[Ken Brown <kbrown@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=74cf7dabcb69ea0608163ba84ecc3d798d5b0421

commit 74cf7dabcb69ea0608163ba84ecc3d798d5b0421
Author: Ken Brown <kbrown@cornell.edu>
Date:   Mon Aug 17 16:24:59 2020 -0400

    Cygwin: main exception handler (64-bit): continue GCC exceptions
    
    This is necessary in order to be consistent with the following comment
    in the definition of _Unwind_RaiseException() in the GCC source file
    libgcc/unwind-seh.c:
    
         The exception handler installed in crt0 will continue any GCC
         exception that reaches there (and isn't marked non-continuable).
    
    Previously we failed to do this and, as a consequence, the C++ runtime
    didn't call std::terminate after an unhandled exception.
    
    This fixes the problem reported here:
    
      https://cygwin.com/pipermail/cygwin/2019-October/242795.html
      https://sourceware.org/pipermail/cygwin/2020-August/245897.html

Diff:
---
 winsup/cygwin/exceptions.cc | 19 +++++++++++++++++++
 winsup/cygwin/release/3.1.7 |  4 ++++
 2 files changed, 23 insertions(+)

diff --git a/winsup/cygwin/exceptions.cc b/winsup/cygwin/exceptions.cc
index 0d9e8f70e..61406e5d1 100644
--- a/winsup/cygwin/exceptions.cc
+++ b/winsup/cygwin/exceptions.cc
@@ -762,6 +762,25 @@ exception::handle (EXCEPTION_RECORD *e, exception_list *frame, CONTEXT *in,
 	 handling.  */
       return ExceptionContinueExecution;
 
+#ifdef __x86_64__
+/* From the GCC source file libgcc/unwind-seh.c. */
+#define STATUS_USER_DEFINED		(1U << 29)
+#define GCC_MAGIC			(('G' << 16) | ('C' << 8) | 'C')
+#define GCC_EXCEPTION(TYPE)		\
+       (STATUS_USER_DEFINED | ((TYPE) << 24) | GCC_MAGIC)
+#define STATUS_GCC_THROW		GCC_EXCEPTION (0)
+#define STATUS_GCC_UNWIND		GCC_EXCEPTION (1)
+#define STATUS_GCC_FORCED		GCC_EXCEPTION (2)
+
+    case STATUS_GCC_THROW:
+    case STATUS_GCC_UNWIND:
+    case STATUS_GCC_FORCED:
+      /* According to a comment in the GCC function
+	 _Unwind_RaiseException(), GCC expects us to continue all the
+	 (continuable) GCC exceptions that reach us. */
+      return ExceptionContinueExecution;
+#endif
+
     default:
       /* If we don't recognize the exception, we have to assume that
 	 we are doing structured exception handling, and we let
diff --git a/winsup/cygwin/release/3.1.7 b/winsup/cygwin/release/3.1.7
index 2f4856495..83cff2b46 100644
--- a/winsup/cygwin/release/3.1.7
+++ b/winsup/cygwin/release/3.1.7
@@ -11,3 +11,7 @@ Bug Fixes:
 
 - Fix an mmap issue that could cause failure with errno EFBIG
   Partially addresses: https://sourceware.org/pipermail/cygwin/2020-July/245557.html
+
+- Fix the behavior of C++ apps after an unhandled exception (64-bit only)
+  Addresses: https://cygwin.com/pipermail/cygwin/2019-October/242795.html
+             https://cygwin.com/pipermail/cygwin/2020-August/245897.html