[ubsan] Diagnose noreturn functions which return

Diagnose 'unreachable' UB when a noreturn function returns.

  1. Insert a check at the end of functions marked noreturn.

  2. A decl may be marked noreturn in the caller TU, but not marked in
     the TU where it's defined. To diagnose this scenario, strip away the
     noreturn attribute on the callee and insert check after calls to it.

Testing: check-clang, check-ubsan, check-ubsan-minimal, D40700

rdar://33660464

Differential Revision: https://reviews.llvm.org/D40698

llvm-svn: 321231

1 files changed, 17 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index eea074e0307..38d7344572d 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -2758,6 +2758,12 @@ static llvm::StoreInst *findDominatingStoreToReturnValue(CodeGenFunction &CGF) {
 void CodeGenFunction::EmitFunctionEpilog(const CGFunctionInfo &FI,
                                          bool EmitRetDbgLoc,
                                          SourceLocation EndLoc) {
+  if (FI.isNoReturn()) {
+    // Noreturn functions don't return.
+    EmitUnreachable(EndLoc);
+    return;
+  }
+
   if (CurCodeDecl && CurCodeDecl->hasAttr<NakedAttr>()) {
     // Naked functions don't have epilogues.
     Builder.CreateUnreachable();
@@ -3718,7 +3724,8 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
                                  const CGCallee &Callee,
                                  ReturnValueSlot ReturnValue,
                                  const CallArgList &CallArgs,
-                                 llvm::Instruction **callOrInvoke) {
+                                 llvm::Instruction **callOrInvoke,
+                                 SourceLocation Loc) {
   // FIXME: We no longer need the types from CallArgs; lift up and simplify.
 
   assert(Callee.isOrdinary());
@@ -4241,7 +4248,15 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
       EmitLifetimeEnd(llvm::ConstantInt::get(Int64Ty, UnusedReturnSize),
                       SRetPtr.getPointer());
 
-    Builder.CreateUnreachable();
+    // Strip away the noreturn attribute to better diagnose unreachable UB.
+    if (SanOpts.has(SanitizerKind::Unreachable)) {
+      if (auto *F = CS.getCalledFunction())
+        F->removeFnAttr(llvm::Attribute::NoReturn);
+      CS.removeAttribute(llvm::AttributeList::FunctionIndex,
+                         llvm::Attribute::NoReturn);
+    }
+
+    EmitUnreachable(Loc);
     Builder.ClearInsertionPoint();
 
     // FIXME: For now, emit a dummy basic block because expr emitters in