From aec8d9056db3e340009d1f19fd070d161f6f080c Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Sun, 28 Jan 2018 17:29:13 +0200
Subject: [PATCH 1/3] Test that assigning to boost::throws() crashes

---
 test/Jamfile.v2             |  1 +
 test/throws_assign_fail.cpp | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)
 create mode 100644 test/throws_assign_fail.cpp

diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index bf90d08..55183b8 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -125,6 +125,7 @@ else
          [ run single_instance_test.cpp single_instance_lib1 single_instance_lib2 : : : <link>static : single_instance_lib_static ]
          [ run single_instance_test.cpp single_instance_lib1 single_instance_lib2 : : : <link>shared : single_instance_lib_shared ]
          [ system-run before_main_test.cpp ]
+         [ run-fail throws_assign_fail.cpp ]
          ;
 
 # Quick (CI) test
diff --git a/test/throws_assign_fail.cpp b/test/throws_assign_fail.cpp
new file mode 100644
index 0000000..8453577
--- /dev/null
+++ b/test/throws_assign_fail.cpp
@@ -0,0 +1,28 @@
+
+// Copyright 2018 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+
+#include <boost/system/error_code.hpp>
+
+using namespace boost::system;
+
+static void f( error_code & ec )
+{
+    ec = error_code();
+}
+
+#if defined(_WIN32)
+# include <windows.h> // SetErrorMode
+#endif
+
+int main()
+{
+#if defined(_WIN32)
+
+    SetErrorMode( SetErrorMode( 0 ) | SEM_NOGPFAULTERRORBOX );
+
+#endif
+
+    // this should crash
+    f( boost::throws() );
+}

From 0433e561b5e2802979348cc8ce18c41f07ca0470 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Mon, 29 Jan 2018 02:29:14 +0200
Subject: [PATCH 2/3] Change the invalid address of boost::throws() to 8 from
 1, so that it's properly aligned

---
 include/boost/system/error_code.hpp | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/boost/system/error_code.hpp b/include/boost/system/error_code.hpp
index 712d73e..f31155d 100644
--- a/include/boost/system/error_code.hpp
+++ b/include/boost/system/error_code.hpp
@@ -578,10 +578,14 @@ namespace boost
     inline system::error_code* throws()
     {
       // See github.com/boostorg/system/pull/12 by visigoth for why the return
-      // is poisoned with (1) rather than (0). A test, test_throws_usage(), has
-      // been added to error_code_test.cpp, and as visigoth mentioned it fails
-      // on clang for release builds with a return of 0 but works fine with (1).
-      return reinterpret_cast<system::error_code*>(1);
+      // is poisoned with nonzero rather than (0). A test, test_throws_usage(),
+      // has been added to error_code_test.cpp, and as visigoth mentioned it
+      // fails on clang for release builds with a return of 0 but works fine
+      // with (1).
+      // Since the undefined behavior sanitizer (-fsanitize=undefined) does not
+      // allow a reference to be formed to the unaligned address of (1), we use
+      // (8) instead.
+      return reinterpret_cast<system::error_code*>(8);
     }
   }
 

From 6ea02e2668c16218c7881f36908dafdbabd3c8a7 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Mon, 29 Jan 2018 02:36:50 +0200
Subject: [PATCH 3/3] Reenable test_throws_usage() under UBSAN

---
 test/error_code_test.cpp | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/test/error_code_test.cpp b/test/error_code_test.cpp
index 1f96c59..7965541 100644
--- a/test/error_code_test.cpp
+++ b/test/error_code_test.cpp
@@ -22,7 +22,6 @@
 #include <cstring>
 #include <functional>
 #include <boost/cerrno.hpp>
-#include <boost/config/pragma_message.hpp>
 
 //  Although using directives are not the best programming practice, testing
 //  with a boost::system using directive increases use scenario coverage.
@@ -247,17 +246,8 @@ int main( int, char ** )
   BOOST_TEST( econd.message() != "" );
   BOOST_TEST( econd.message().substr( 0, 13) != "Unknown error" );
 
-#if !defined(UBSAN)
-
-  // the current implementation of boost::throws() relies on undefined behavior
   test_throws_usage();
 
-#else
-
-  BOOST_PRAGMA_MESSAGE("Skipping test_throws_usage() due to UBSAN");
-
-#endif
-
 #ifdef BOOST_WINDOWS_API
   std::cout << "Windows tests...\n";
   // these tests probe the Windows errc decoder