ubsan: Unbreak ubsan_cxx runtime library on Windows.

This was originally broken by r258744 which introduced a weak reference
from ubsan to ubsan_cxx. This reference does not work directly on
Windows because COFF has no direct concept of weak symbols. The fix is
to use /alternatename to create a weak external reference to ubsan_cxx.

Also fix the definition (and the name, so that we drop cached values)
of the cmake flag that controls whether to build ubsan_cxx. Now the
user-controllable flag is always on, and we turn it off internally
depending on whether we support building it.

Differential Revision: https://reviews.llvm.org/D37882

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@313391 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 32 insertions, 8 deletions

diff --git a/lib/ubsan/ubsan_handlers.cc b/lib/ubsan/ubsan_handlers.cc
index 06438a5d3..93f6ee2ab 100644
--- a/lib/ubsan/ubsan_handlers.cc
+++ b/lib/ubsan/ubsan_handlers.cc
@@ -652,16 +652,33 @@ static void handleCFIBadIcall(CFICheckFailData *Data, ValueHandle Function,
 }
 
 namespace __ubsan {
+
 #ifdef UBSAN_CAN_USE_CXXABI
+
+#ifdef _WIN32
+
+extern "C" void __ubsan_handle_cfi_bad_type_default(CFICheckFailData *Data,
+                                                    ValueHandle Vtable,
+                                                    bool ValidVtable,
+                                                    ReportOptions Opts) {
+  Die();
+}
+
+WIN_WEAK_ALIAS(__ubsan_handle_cfi_bad_type, __ubsan_handle_cfi_bad_type_default)
+#else
 SANITIZER_WEAK_ATTRIBUTE
-void HandleCFIBadType(CFICheckFailData *Data, ValueHandle Vtable,
-                      bool ValidVtable, ReportOptions Opts);
+#endif
+void __ubsan_handle_cfi_bad_type(CFICheckFailData *Data, ValueHandle Vtable,
+                                 bool ValidVtable, ReportOptions Opts);
+
 #else
-static void HandleCFIBadType(CFICheckFailData *Data, ValueHandle Vtable,
-                             bool ValidVtable, ReportOptions Opts) {
+static void __ubsan_handle_cfi_bad_type(CFICheckFailData *Data,
+                                        ValueHandle Vtable,
+                                        bool ValidVtable, ReportOptions Opts) {
   Die();
 }
 #endif
+
 }  // namespace __ubsan
 
 void __ubsan::__ubsan_handle_cfi_check_fail(CFICheckFailData *Data,
@@ -671,7 +688,7 @@ void __ubsan::__ubsan_handle_cfi_check_fail(CFICheckFailData *Data,
   if (Data->CheckKind == CFITCK_ICall)
     handleCFIBadIcall(Data, Value, Opts);
   else
-    HandleCFIBadType(Data, Value, ValidVtable, Opts);
+    __ubsan_handle_cfi_bad_type(Data, Value, ValidVtable, Opts);
 }
 
 void __ubsan::__ubsan_handle_cfi_check_fail_abort(CFICheckFailData *Data,
@@ -681,7 +698,7 @@ void __ubsan::__ubsan_handle_cfi_check_fail_abort(CFICheckFailData *Data,
   if (Data->CheckKind == CFITCK_ICall)
     handleCFIBadIcall(Data, Value, Opts);
   else
-    HandleCFIBadType(Data, Value, ValidVtable, Opts);
+    __ubsan_handle_cfi_bad_type(Data, Value, ValidVtable, Opts);
   Die();
 }
 
diff --git a/lib/ubsan/ubsan_handlers.h b/lib/ubsan/ubsan_handlers.h
index 5a9e902ce..311776b9f 100644
--- a/lib/ubsan/ubsan_handlers.h
+++ b/lib/ubsan/ubsan_handlers.h
@@ -192,6 +192,13 @@ struct CFICheckFailData {
 /// \brief Handle control flow integrity failures.
 RECOVERABLE(cfi_check_fail, CFICheckFailData *Data, ValueHandle Function,
             uptr VtableIsValid)
+
+struct ReportOptions;
+
+extern "C" SANITIZER_INTERFACE_ATTRIBUTE void __ubsan_handle_cfi_bad_type(
+    CFICheckFailData *Data, ValueHandle Vtable, bool ValidVtable,
+    ReportOptions Opts);
+
 }
 
 #endif // UBSAN_HANDLERS_H
diff --git a/lib/ubsan/ubsan_handlers_cxx.cc b/lib/ubsan/ubsan_handlers_cxx.cc
index d97ec4813..e15abc64e 100644
--- a/lib/ubsan/ubsan_handlers_cxx.cc
+++ b/lib/ubsan/ubsan_handlers_cxx.cc
@@ -95,8 +95,8 @@ void __ubsan::__ubsan_handle_dynamic_type_cache_miss_abort(
 }
 
 namespace __ubsan {
-void HandleCFIBadType(CFICheckFailData *Data, ValueHandle Vtable,
-                      bool ValidVtable, ReportOptions Opts) {
+void __ubsan_handle_cfi_bad_type(CFICheckFailData *Data, ValueHandle Vtable,
+                                 bool ValidVtable, ReportOptions Opts) {
   SourceLocation Loc = Data->Loc.acquire();
   ErrorType ET = ErrorType::CFIBadType;