[ubsan] Have -fsanitize=vptr emit a null check if -fsanitize=null isn't available

In r309007, I made -fsanitize=null a hard prerequisite for -fsanitize=vptr. I
did not see the need for the two checks to have separate null checking logic
for the same pointer. I expected the two checks to either always be enabled
together, or to be mutually compatible.

In the mailing list discussion re: r309007 it became clear that that isn't the
case. If a codebase is -fsanitize=vptr clean but not -fsanitize=null clean,
it's useful to have -fsanitize=vptr emit its own null check. That's what this
patch does: with it, -fsanitize=vptr can be used without -fsanitize=null.

Differential Revision: https://reviews.llvm.org/D36112

llvm-svn: 309846

2 files changed, 4 insertions, 11 deletions

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index e9ad05cf666..ec48b2cc86e 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -694,17 +694,17 @@ void CodeGenFunction::EmitTypeCheck(TypeCheckKind TCK, SourceLocation Loc,
   //    -- the [pointer or glvalue] is used to access a non-static data member
   //       or call a non-static member function
   CXXRecordDecl *RD = Ty->getAsCXXRecordDecl();
-  bool HasNullCheck = IsGuaranteedNonNull || IsNonNull;
   if (SanOpts.has(SanitizerKind::Vptr) &&
-      !SkippedChecks.has(SanitizerKind::Vptr) && HasNullCheck &&
+      !SkippedChecks.has(SanitizerKind::Vptr) &&
       (TCK == TCK_MemberAccess || TCK == TCK_MemberCall ||
        TCK == TCK_DowncastPointer || TCK == TCK_DowncastReference ||
        TCK == TCK_UpcastToVirtualBase) &&
       RD && RD->hasDefinition() && RD->isDynamicClass()) {
     // Ensure that the pointer is non-null before loading it. If there is no
-    // compile-time guarantee, reuse the run-time null check.
+    // compile-time guarantee, reuse the run-time null check or emit a new one.
     if (!IsGuaranteedNonNull) {
-      assert(IsNonNull && "Missing run-time null check");
+      if (!IsNonNull)
+        IsNonNull = Builder.CreateIsNotNull(Ptr);
       if (!Done)
         Done = createBasicBlock("vptr.null");
       llvm::BasicBlock *VptrNotNull = createBasicBlock("vptr.not.null");
diff --git a/clang/lib/Driver/SanitizerArgs.cpp b/clang/lib/Driver/SanitizerArgs.cpp
index f4fe06af25f..2a3ae51734d 100644
--- a/clang/lib/Driver/SanitizerArgs.cpp
+++ b/clang/lib/Driver/SanitizerArgs.cpp
@@ -307,13 +307,6 @@ SanitizerArgs::SanitizerArgs(const ToolChain &TC,
     Kinds &= ~Vptr;
   }
 
-  // Disable -fsanitize=vptr if -fsanitize=null is not enabled (the vptr
-  // instrumentation is broken without run-time null checks).
-  if ((Kinds & Vptr) && !(Kinds & Null)) {
-    Kinds &= ~Vptr;
-    D.Diag(diag::warn_drv_disabling_vptr_no_null_check);
-  }
-
   // Check that LTO is enabled if we need it.
   if ((Kinds & NeedsLTO) && !D.isUsingLTO()) {
     D.Diag(diag::err_drv_argument_only_allowed_with)