[libc++] Avoid UB in the no-exceptions mode in a few places

Summary:
A few places in the library seem to behave unexpectedly when the library
is compiled or used with exceptions disabled. For example, not throwing
an exception when a pointer is NULL can lead us to dereference the pointer
later on, which is UB. This patch fixes such occurences.

It's hard to tell whether there are other places where the no-exceptions
mode misbehaves like this, because the replacement for throwing an
exception does not always seem to be abort()ing, but at least this
patch will improve the situation somewhat.

See http://lists.llvm.org/pipermail/libcxx-dev/2019-January/000172.html

Reviewers: mclow.lists, EricWF

Subscribers: christof, jkorous, dexonsmith, libcxx-commits

Differential Revision: https://reviews.llvm.org/D57761

llvm-svn: 353850

3 files changed, 14 insertions, 12 deletions

diff --git a/libcxx/include/ios b/libcxx/include/ios
index 96336396302..96e84eb3835 100644
--- a/libcxx/include/ios
+++ b/libcxx/include/ios
@@ -425,6 +425,16 @@ public:
     virtual ~failure() throw();
 };
 
+_LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
+void __throw_failure(char const* __msg) {
+#ifndef _LIBCPP_NO_EXCEPTIONS
+    throw ios_base::failure(__msg);
+#else
+    ((void)__msg);
+    _VSTD::abort();
+#endif
+}
+
 class _LIBCPP_TYPE_VIS ios_base::Init
 {
 public:
diff --git a/libcxx/include/map b/libcxx/include/map
index 47f5c678bcc..e21dd5a8454 100644
--- a/libcxx/include/map
+++ b/libcxx/include/map
@@ -1535,10 +1535,8 @@ map<_Key, _Tp, _Compare, _Allocator>::at(const key_type& __k)
 {
     __parent_pointer __parent;
     __node_base_pointer& __child = __tree_.__find_equal(__parent, __k);
-#ifndef _LIBCPP_NO_EXCEPTIONS
     if (__child == nullptr)
-        throw out_of_range("map::at:  key not found");
-#endif  // _LIBCPP_NO_EXCEPTIONS
+        __throw_out_of_range("map::at:  key not found");
     return static_cast<__node_pointer>(__child)->__value_.__get_value().second;
 }
 
@@ -1548,10 +1546,8 @@ map<_Key, _Tp, _Compare, _Allocator>::at(const key_type& __k) const
 {
     __parent_pointer __parent;
     __node_base_pointer __child = __tree_.__find_equal(__parent, __k);
-#ifndef _LIBCPP_NO_EXCEPTIONS
     if (__child == nullptr)
-        throw out_of_range("map::at:  key not found");
-#endif  // _LIBCPP_NO_EXCEPTIONS
+        __throw_out_of_range("map::at:  key not found");
     return static_cast<__node_pointer>(__child)->__value_.__get_value().second;
 }
 
diff --git a/libcxx/include/unordered_map b/libcxx/include/unordered_map
index 87278b07d74..7ae9805d81d 100644
--- a/libcxx/include/unordered_map
+++ b/libcxx/include/unordered_map
@@ -1602,10 +1602,8 @@ _Tp&
 unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::at(const key_type& __k)
 {
     iterator __i = find(__k);
-#ifndef _LIBCPP_NO_EXCEPTIONS
     if (__i == end())
-        throw out_of_range("unordered_map::at: key not found");
-#endif  // _LIBCPP_NO_EXCEPTIONS
+        __throw_out_of_range("unordered_map::at: key not found");
     return __i->second;
 }
 
@@ -1614,10 +1612,8 @@ const _Tp&
 unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::at(const key_type& __k) const
 {
     const_iterator __i = find(__k);
-#ifndef _LIBCPP_NO_EXCEPTIONS
     if (__i == end())
-        throw out_of_range("unordered_map::at: key not found");
-#endif  // _LIBCPP_NO_EXCEPTIONS
+        __throw_out_of_range("unordered_map::at: key not found");
     return __i->second;
 }