[cfi] Safe handling of unaddressable vtable pointers (clang).

Avoid crashing when printing diagnostics for vtable-related CFI
errors. In diagnostic mode, the frontend does an additional check of
the vtable pointer against the set of all known vtable addresses and
lets the runtime handler know if it is safe to inspect the vtable.

http://reviews.llvm.org/D16823

llvm-svn: 259716

1 files changed, 25 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 4d7f62750a1..a30e62499fa 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -4021,6 +4021,20 @@ llvm::Metadata *CodeGenModule::CreateMetadataIdentifierForType(QualType T) {
   return InternalId;
 }
 
+/// Returns whether this module needs the "all-vtables" bitset.
+bool CodeGenModule::NeedAllVtablesBitSet() const {
+  // Returns true if at least one of vtable-based CFI checkers is enabled and
+  // is not in the trapping mode.
+  return ((LangOpts.Sanitize.has(SanitizerKind::CFIVCall) &&
+           !CodeGenOpts.SanitizeTrap.has(SanitizerKind::CFIVCall)) ||
+          (LangOpts.Sanitize.has(SanitizerKind::CFINVCall) &&
+           !CodeGenOpts.SanitizeTrap.has(SanitizerKind::CFINVCall)) ||
+          (LangOpts.Sanitize.has(SanitizerKind::CFIDerivedCast) &&
+           !CodeGenOpts.SanitizeTrap.has(SanitizerKind::CFIDerivedCast)) ||
+          (LangOpts.Sanitize.has(SanitizerKind::CFIUnrelatedCast) &&
+           !CodeGenOpts.SanitizeTrap.has(SanitizerKind::CFIUnrelatedCast)));
+}
+
 void CodeGenModule::CreateVTableBitSetEntry(llvm::NamedMDNode *BitsetsMD,
                                             llvm::GlobalVariable *VTable,
                                             CharUnits Offset,
@@ -4043,6 +4057,17 @@ void CodeGenModule::CreateVTableBitSetEntry(llvm::NamedMDNode *BitsetsMD,
       BitsetsMD->addOperand(llvm::MDTuple::get(getLLVMContext(), BitsetOps2));
     }
   }
+
+  if (NeedAllVtablesBitSet()) {
+    llvm::Metadata *MD = llvm::MDString::get(getLLVMContext(), "all-vtables");
+    llvm::Metadata *BitsetOps[] = {
+        MD, llvm::ConstantAsMetadata::get(VTable),
+        llvm::ConstantAsMetadata::get(
+            llvm::ConstantInt::get(Int64Ty, Offset.getQuantity()))};
+    // Avoid adding a node to BitsetsMD twice.
+    if (!llvm::MDTuple::getIfExists(getLLVMContext(), BitsetOps))
+      BitsetsMD->addOperand(llvm::MDTuple::get(getLLVMContext(), BitsetOps));
+  }
 }
 
 // Fills in the supplied string map with the set of target features for the