Do not warn about format strings that are indexed string literals.

[meikeb]

Summary

The warning for a format string not being a string literal and therefore
being potentially insecure is overly strict for indices into string
literals. This fix checks if the index into the string literal is
precomputable. If that's the case it will check if the suffix of that
string literal is a valid format string string literal. It will still
issue the aforementioned warning for out of range indices into the
string literal.

[srhines]

lib/Sema/SemaChecking.cpp

3941

It might be good to mention that Offset now goes back to the caller to allow for checking of string literal suffixes.

3987

separately

[meikeb]

Fix typo.

[meikeb]

lib/Sema/SemaChecking.cpp

3941

I'm not sure if that should be mentioned here because it is a very high level comment and the suffix of a string literal is a string literal itself.

[rsmith]

Please also handle expressions of the form &"str"[i]. We warn (under -Wstring-plus-int) for "str" + i and suggest rewriting into that form, so we should also handle that form here.

lib/Sema/SemaChecking.cpp

3949

Why is this passed by reference? It's just an input, not an output, right?

4146–4151

This doesn't seem like it preserves enough information for the downstream code to give correct caret diagnostics pointing at locations within the string. It seems like it would be extremely complicated to maintain the necessary invariants to make that work (you'd need to create a fake string literal source buffer so that the StringLiteralParser can reparse it, for whichever of the string literal tokens the offset ends up within). Have you looked at how much work it'd be to feed a starting offset into CheckFormatString instead?

4166–4167

What happens if one of these expressions is value-dependent? The evaluator can crash or assert if given a value-dependent expression. If we don't defer these checks in dependent contexts, you'll need to handle that possibility somehow.

Example:

template<int N> void f(const char *p) {
  printf("blah blah %s" + N, p);
}

4174–4177

This will assert if the result doesn't fit into 64 bits, and it's not guaranteed to (if one of the operands was cast to __int128, for instance). You could use getLimitedValue instead, with some suitable limit.

[meikeb]

lib/Sema/SemaChecking.cpp

4166–4167

I think I don't understand what you are trying to tell me. Especially the example you provided does just fine and behaves as I expected. As far as I followed EvaluateAsInt it does not assert but returns false if we don't get a constexpr here. We warn under -Wformat-nonliteral for value-dependent string literals.

Could you explain this more or provide an example that triggers an assert or explain what behavior is wrong regarding the provided example? Thanks!

[rsmith]

lib/Sema/SemaChecking.cpp

4166–4167

We should not warn for that example, since (for instance) calling f<0> is fine (we should warn for f<11>, though, since it has no format specifiers).

While EvaluateAsInt happens to not assert for that particular value-dependent input, it does assert for some other value-dependent cases. It's not easy for me to find you such a case, because Clang is currently careful to never call this function on a value-dependent expression, but perhaps this will trigger an assert:

struct S { constexpr S(int n) : n(n) {} int n; };
template<int N> void f(const char *p) {
  printf("blah blah %s" + S(N).n, p);
}

[meikeb]

Fix the mentioned issues.

[meikeb]

lib/Sema/SemaChecking.cpp

4166–4167

I hope this additional check fixes this issue. As far as I read the code there were none such asserts in isIntegerConstantExpr(). Thanks for explaining this!

[rsmith]

lib/Sema/SemaChecking.cpp

3842–3843

I can't tell from this declaration what this function is for -- what does "reckon up" mean?

3880

Typo "retruning"

3891–3892

I think you can simplify this to return FExpr->getString().drop_front(Offset);

4143

You should presumably also do this if Offset is >= the length of the string literal (we want printf and friends to at least find the trailing nul byte).

4148–4149

Does this need to be heap-allocated?

4166–4167

OK, I've now checked and the value-dependent case is handled up on line 3953. So just calling EvaluateAsInt here is fine after all.

[meikeb]

Fix mentioned issues.

[meikeb]

Thanks for taking the time and doing these great reviews! Really appreciated!

lib/Sema/SemaChecking.cpp

4143–4151

The = case is part of a different warning. It's checked in CheckFormatString.

[srhines]

My comment is mostly naming considerations to improve clarity. I do have concerns though about the unhandled else path.

lib/Sema/SemaChecking.cpp

3842–3927

Is "computeStringLiteralOffset" or "calculate..." a better name here?

3844

Is "Operand" better than "Addend"? In particular, there is the possibility that we do subtraction of the value instead of addition, so "Addend" makes it a bit confusing. Of course, I then would expect "OperandIsRight" instead of "AddendIsRight" too.

3852

Align -> Canonicalize or Adjust

This is confusing here as "Align" already has too many overloaded meanings in programming (that could be relevant to bitwidths). Canonicalize or Adjust don't have this problem.

3860

Ov -> Overflow

3865

What happens if someone passes something that isn't caught by these two cases? Should we be returning an indicator that the calculation failed? If not, should we assert here?

3867

2 places to fix: "a offset" -> "an offset"

[meikeb]

Fix typos and add assert to sum up offset helper.

[meikeb]

I explained why I chose the names that you commented on. Feel free to add your thoughts if you still think another name would be more fitting.

lib/Sema/SemaChecking.cpp

3842–3927

I thought about that but decided to go with sumUp because compute or calculate sounds like this function would do what we actually do what the caller of this function does (computing the offset). This is just a nice helper to sum up the offset we already have with another piece of offset.

3844

Clang summarizes sub and add as "additive" operands. This is why I think this is fitting. Operand is misleading because it includes a lot more operands than add and sub imo.

3860

I named that in compliance with clang naming. E.g. sadd_ov. It is common in this file to abbreviate variable names with 1-3 characters.

[rsmith]

This basically looks fine to me now. I'm not 100% sold on sumUpStringLiteralOffset being the best name, but I think we have better things to worry about, and it's good enough. Just a couple of minor style issues then I think this is good to go.

lib/Sema/SemaChecking.cpp

3866–3867

Rather than assert(false && XXX);, use either llvm_unreachable(XXX) or change the previous case to be:

else {
  assert(AddendIsRight && BinOpKind == BO_Sub &&
         "operator must be ...");

4148–4149

You can write this more simply as

FormatStringLiteral FStr(StrE, Offset.sextOrTrunc(64).getSExtValue());

[meikeb]

Try to improve offset sum helper function name and fix style issues.

[rsmith]

lib/Sema/SemaChecking.cpp

3864–3867

The suggestion was to remove the condition in the else if and put the assertion inside its body, rather than duplicating it here:

if (BinOpKind == BO_Add)
  // handle add
else {
  assert(it's a subtract);
  // handle sub
}

[meikeb]

Correct assert position in offset sum helper function.

[meikeb]

lib/Sema/SemaChecking.cpp

3864–3867

This is way better. Thank you.

[meikeb]

Thanks for reviewing my patch! It would be great if someone could submit this patch for me.

[srhines]

I will take care of submitting this. Thanks for the reviews everybody!

lib/Sema/SemaChecking.cpp

 
 enum StringLiteralCheckType {
   SLCT_NotALiteral,
   SLCT_UncheckedLiteral,
   SLCT_CheckedLiteral
 };
 } // end anonymous namespace
 
-static void CheckFormatString(Sema &S, const StringLiteral *FExpr,
+static void reckonUpOffset(llvm::APSInt &Offset, llvm::APSInt Addend,
+                           BinaryOperatorKind BinOpKind, bool AddendIsRight) {
+  unsigned BitWidth = Offset.getBitWidth();
+  unsigned AddendBitWidth = Addend.getBitWidth();
+  // There might be negative interim results.
+  if (Addend.isUnsigned()) {
+    Addend = Addend.zext(++AddendBitWidth);
+    Addend.setIsSigned(true);
+  }
+  // Align the bit width of the APSInts.
+  if (AddendBitWidth > BitWidth) {
+    Offset = Offset.sext(AddendBitWidth);
+    BitWidth = AddendBitWidth;
+  } else if (BitWidth > AddendBitWidth) {
+    Addend = Addend.sext(BitWidth);
+  }
+
+  bool Ov = false;
+  llvm::APSInt ResOffset = Offset;
+  if (BinOpKind == BO_Add)
+    ResOffset = Offset.sadd_ov(Addend, Ov);
+  else if (AddendIsRight && BinOpKind == BO_Sub)
+    ResOffset = Offset.ssub_ov(Addend, Ov);
+
+  // We add a offset to a pointer here so we should support a offset as big as
+  // possible.
+  if (Ov) {
+    assert(BitWidth <= UINT_MAX / 2 && "index (intermediate) result too big");
+    Offset.sext(2 * BitWidth);
+    reckonUpOffset(Offset, Addend, BinOpKind, AddendIsRight);
+    return;
+  }
+
+  Offset = ResOffset;
+}
+
+namespace {
+// This is a wrapper class around StringLiteral to support offsetted string
+// literals as format strings. It takes the offset into account when retruning
+// the string and its length or the source locations to display notes correctly.
+class FormatStringLiteral {
+  const StringLiteral *FExpr;
+  int64_t Offset;
+
+ public:
+  FormatStringLiteral(const StringLiteral *fexpr, int64_t Offset = 0)
+      : FExpr(fexpr), Offset(Offset) {}
+
+  StringRef getString() const {
+    return StringRef(FExpr->getString().data() + Offset,
+                     FExpr->getLength() - Offset);
+  }
+
+  unsigned getByteLength() const {
+    return FExpr->getByteLength() - getCharByteWidth() * Offset;
+  }
+  unsigned getLength() const { return FExpr->getLength() - Offset; }
+  unsigned getCharByteWidth() const { return FExpr->getCharByteWidth(); }
+
+  StringLiteral::StringKind getKind() const { return FExpr->getKind(); }
+
+  QualType getType() const { return FExpr->getType(); }
+
+  bool isAscii() const { return FExpr->isAscii(); }
+  bool isWide() const { return FExpr->isWide(); }
+  bool isUTF8() const { return FExpr->isUTF8(); }
+  bool isUTF16() const { return FExpr->isUTF16(); }
+  bool isUTF32() const { return FExpr->isUTF32(); }
+  bool isPascal() const { return FExpr->isPascal(); }
+
+  SourceLocation getLocationOfByte(
+      unsigned ByteNo, const SourceManager &SM, const LangOptions &Features,
+      const TargetInfo &Target, unsigned *StartToken = nullptr,
+      unsigned *StartTokenByteOffset = nullptr) const {
+    return FExpr->getLocationOfByte(ByteNo + Offset, SM, Features, Target,
+                                    StartToken, StartTokenByteOffset);
+  }
+
+  SourceLocation getLocStart() const LLVM_READONLY {
+    return FExpr->getLocStart().getLocWithOffset(Offset);
+  }
+  SourceLocation getLocEnd() const LLVM_READONLY { return FExpr->getLocEnd(); }
+};
+}  // end anonymous namespace
+
+static void CheckFormatString(Sema &S, const FormatStringLiteral *FExpr,
                               const Expr *OrigFormatExpr,
                               ArrayRef<const Expr *> Args,
                               bool HasVAListArg, unsigned format_idx,
                               unsigned firstDataArg,
                               Sema::FormatStringType Type,
                               bool inFunctionCall,
                               Sema::VariadicCallType CallType,
                               llvm::SmallBitVector &CheckedVarArgs,
                               UncoveredArgHandler &UncoveredArg);
 
 // Determine if an expression is a string literal or constant string.
 // If this function returns false on the arguments to a function expecting a
 // format string, we will usually need to emit a warning.
 // True string literals are then checked by CheckFormatString.
 static StringLiteralCheckType
 checkFormatStringExpr(Sema &S, const Expr *E, ArrayRef<const Expr *> Args,
                       bool HasVAListArg, unsigned format_idx,
                       unsigned firstDataArg, Sema::FormatStringType Type,
                       Sema::VariadicCallType CallType, bool InFunctionCall,
                       llvm::SmallBitVector &CheckedVarArgs,
-                      UncoveredArgHandler &UncoveredArg) {
+                      UncoveredArgHandler &UncoveredArg,
+                      llvm::APSInt Offset) {
  tryAgain:
+  assert(Offset.isSigned() && "invalid offset");
+
   if (E->isTypeDependent() || E->isValueDependent())
     return SLCT_NotALiteral;
 
   E = E->IgnoreParenCasts();
 
   if (E->isNullPointerConstant(S.Context, Expr::NPC_ValueDependentIsNotNull))
     // Technically -Wformat-nonliteral does not warn about this case.
     // The behavior of printf and friends in this case is implementation
case Stmt::ConditionalOperatorClass: {
     bool Cond;
     if (C->getCond()->EvaluateAsBooleanCondition(Cond, S.getASTContext())) {
       if (Cond)
         CheckRight = false;
       else
         CheckLeft = false;
     }
 
+    // We need to maintain the offsets for the right and the left hand side
+    // separately to check if every possible indexed expression is a valid
+    // string literal. They might have different offsets for different string
+    // literals in the end.
     StringLiteralCheckType Left;
     if (!CheckLeft)
       Left = SLCT_UncheckedLiteral;
     else {
       Left = checkFormatStringExpr(S, C->getTrueExpr(), Args,
                                    HasVAListArg, format_idx, firstDataArg,
                                    Type, CallType, InFunctionCall,
-                                   CheckedVarArgs, UncoveredArg);
-      if (Left == SLCT_NotALiteral || !CheckRight)
+                                   CheckedVarArgs, UncoveredArg, Offset);
+      if (Left == SLCT_NotALiteral || !CheckRight) {
         return Left;
       }
+    }
 
     StringLiteralCheckType Right =
         checkFormatStringExpr(S, C->getFalseExpr(), Args,
                               HasVAListArg, format_idx, firstDataArg,
                               Type, CallType, InFunctionCall, CheckedVarArgs,
-                              UncoveredArg);
+                              UncoveredArg, Offset);
 
     return (CheckLeft && Left < Right) ? Left : Right;
   }
 
   case Stmt::ImplicitCastExprClass: {
     E = cast<ImplicitCastExpr>(E)->getSubExpr();
     goto tryAgain;
   }
if (const VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl())) {
           // Look through initializers like const char c[] = { "foo" }
           if (const InitListExpr *InitList = dyn_cast<InitListExpr>(Init)) {
             if (InitList->isStringLiteralInit())
               Init = InitList->getInit(0)->IgnoreParenImpCasts();
           }
           return checkFormatStringExpr(S, Init, Args,
                                        HasVAListArg, format_idx,
                                        firstDataArg, Type, CallType,
-                                       /*InFunctionCall*/false, CheckedVarArgs,
-                                       UncoveredArg);
+                                       /*InFunctionCall*/ false, CheckedVarArgs,
+                                       UncoveredArg, Offset);
         }
       }
 
       // For vprintf* functions (i.e., HasVAListArg==true), we add a
       // special check to see if the format string is a function parameter
       // of the function calling the printf function.  If the function
       // has an attribute indicating it is a printf-like function, then we
       // should suppress warnings concerning non-literals being used in a call
if (const NamedDecl *ND = dyn_cast_or_null<NamedDecl>(CE->getCalleeDecl())) {
         if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(ND))
           if (MD->isInstance())
             --ArgIndex;
         const Expr *Arg = CE->getArg(ArgIndex - 1);
 
         return checkFormatStringExpr(S, Arg, Args,
                                      HasVAListArg, format_idx, firstDataArg,
                                      Type, CallType, InFunctionCall,
-                                     CheckedVarArgs, UncoveredArg);
+                                     CheckedVarArgs, UncoveredArg, Offset);
       } else if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(ND)) {
         unsigned BuiltinID = FD->getBuiltinID();
         if (BuiltinID == Builtin::BI__builtin___CFStringMakeConstantString ||
             BuiltinID == Builtin::BI__builtin___NSStringMakeConstantString) {
           const Expr *Arg = CE->getArg(0);
           return checkFormatStringExpr(S, Arg, Args,
                                        HasVAListArg, format_idx,
                                        firstDataArg, Type, CallType,
                                        InFunctionCall, CheckedVarArgs,
-                                       UncoveredArg);
+                                       UncoveredArg, Offset);
         }
       }
     }
 
     return SLCT_NotALiteral;
   }
   case Stmt::ObjCStringLiteralClass:
   case Stmt::StringLiteralClass: {
     const StringLiteral *StrE = nullptr;
 
     if (const ObjCStringLiteral *ObjCFExpr = dyn_cast<ObjCStringLiteral>(E))
       StrE = ObjCFExpr->getString();
     else
       StrE = cast<StringLiteral>(E);
 
     if (StrE) {
-      CheckFormatString(S, StrE, E, Args, HasVAListArg, format_idx,
+      if (Offset.isNegative()) {
+        // TODO: It would be better to have an explicit warning for out of
+        // bounds literals.
+        return SLCT_NotALiteral;
+      }
+      FormatStringLiteral *FStr =
+          new FormatStringLiteral(StrE, Offset.sextOrTrunc(64).getSExtValue());
+      CheckFormatString(S, FStr, E, Args, HasVAListArg, format_idx,
                         firstDataArg, Type, InFunctionCall, CallType,
                         CheckedVarArgs, UncoveredArg);
       return SLCT_CheckedLiteral;
     }
 
     return SLCT_NotALiteral;
   }
+  case Stmt::BinaryOperatorClass: {
+    llvm::APSInt LResult;
+    llvm::APSInt RResult;
+
+    const BinaryOperator *BinOp = cast<BinaryOperator>(E);
+
+    // A string literal + an int offset is still a string literal.
+    if (BinOp->isAdditiveOp()) {
+      bool LIsInt = false;
+      bool RIsInt = false;
+      // Prevent asserts triggering in EvaluateAsInt by checking if we deal with
+      // integer constant expressions first.
+      if (BinOp->getLHS()->isIntegerConstantExpr(S.Context))
+        LIsInt = BinOp->getLHS()->EvaluateAsInt(LResult, S.Context);
+      if (BinOp->getRHS()->isIntegerConstantExpr(S.Context))
+        RIsInt = BinOp->getRHS()->EvaluateAsInt(RResult, S.Context);
+
+      if (LIsInt != RIsInt) {
+        BinaryOperatorKind BinOpKind = BinOp->getOpcode();
+
+        if (LIsInt) {
+          if (BinOpKind == BO_Add) {
+            reckonUpOffset(Offset, LResult, BinOpKind, RIsInt);
+            E = BinOp->getRHS();
+            goto tryAgain;
+          }
+        } else {
+          reckonUpOffset(Offset, RResult, BinOpKind, RIsInt);
+          E = BinOp->getLHS();
+          goto tryAgain;
+        }
+      }
+
+      return SLCT_NotALiteral;
+    }
+  }
+  case Stmt::UnaryOperatorClass: {
+    const UnaryOperator *UnaOp = cast<UnaryOperator>(E);
+    auto ASE = dyn_cast<ArraySubscriptExpr>(UnaOp->getSubExpr());
+    if (UnaOp->getOpcode() == clang::UO_AddrOf && ASE) {
+      if (ASE->getRHS()->isIntegerConstantExpr(S.Context) &&
+          ASE->getRHS()->EvaluateAsInt(IndexResult, S.Context)) {
+        llvm::APSInt IndexResult;
+        reckonUpOffset(Offset, IndexResult, BO_Add, /*RHS is int*/ true);
+        E = ASE->getBase();
+        goto tryAgain;
+      }
+    }
+
+    return SLCT_NotALiteral;
+  }
 
   default:
     return SLCT_NotALiteral;
   }
 }
 
 Sema::FormatStringType Sema::GetFormatStringType(const FormatAttr *Format) {
   return llvm::StringSwitch<FormatStringType>(Format->getType()->getName())
bool Sema::CheckFormatArguments(ArrayRef<const Expr *> Args,
   // Format string can be either ObjC string (e.g. @"%d") or
   // C string (e.g. "%d")
   // ObjC string uses the same format specifiers as C string, so we can use
   // the same format string checking logic for both ObjC and C strings.
   UncoveredArgHandler UncoveredArg;
   StringLiteralCheckType CT =
       checkFormatStringExpr(*this, OrigFormatExpr, Args, HasVAListArg,
                             format_idx, firstDataArg, Type, CallType,
-                            /*IsFunctionCall*/true, CheckedVarArgs,
-                            UncoveredArg);
+                            /*IsFunctionCall*/ true, CheckedVarArgs,
+                            UncoveredArg,
+                            /*no string offset*/ llvm::APSInt(64, false) = 0);
 
   // Generate a diagnostic where an uncovered argument is detected.
   if (UncoveredArg.hasUncoveredArg()) {
     unsigned ArgIdx = UncoveredArg.getUncoveredArg() + firstDataArg;
     assert(ArgIdx < Args.size() && "ArgIdx outside bounds");
     UncoveredArg.Diagnose(*this, /*IsFunctionCall*/true, Args[ArgIdx]);
   }
 
bool Sema::CheckFormatArguments(ArrayRef<const Expr *> Args,
   }
   return false;
 }
 
 namespace {
 class CheckFormatHandler : public analyze_format_string::FormatStringHandler {
 protected:
   Sema &S;
-  const StringLiteral *FExpr;
+  const FormatStringLiteral *FExpr;
   const Expr *OrigFormatExpr;
   const unsigned FirstDataArg;
   const unsigned NumDataArgs;
   const char *Beg; // Start of format string.
   const bool HasVAListArg;
   ArrayRef<const Expr *> Args;
   unsigned FormatIdx;
   llvm::SmallBitVector CoveredArgs;
   bool usesPositionalArgs;
   bool atFirstArg;
   bool inFunctionCall;
   Sema::VariadicCallType CallType;
   llvm::SmallBitVector &CheckedVarArgs;
   UncoveredArgHandler &UncoveredArg;
 
 public:
-  CheckFormatHandler(Sema &s, const StringLiteral *fexpr,
+  CheckFormatHandler(Sema &s, const FormatStringLiteral *fexpr,
                      const Expr *origFormatExpr, unsigned firstDataArg,
                      unsigned numDataArgs, const char *beg, bool hasVAListArg,
                      ArrayRef<const Expr *> Args,
                      unsigned formatIdx, bool inFunctionCall,
                      Sema::VariadicCallType callType,
                      llvm::SmallBitVector &CheckedVarArgs,
                      UncoveredArgHandler &UncoveredArg)
     : S(s), FExpr(fexpr), OrigFormatExpr(origFormatExpr),
getSpecifierRange(const char *startSpecifier, unsigned specifierLen) {
 
   // Advance the end SourceLocation by one due to half-open ranges.
   End = End.getLocWithOffset(1);
 
   return CharSourceRange::getCharRange(Start, End);
 }
 
 SourceLocation CheckFormatHandler::getLocationOfByte(const char *x) {
-  return S.getLocationOfStringLiteralByte(FExpr, x - Beg);
+  return FExpr->getLocationOfByte(x - Beg, S.getSourceManager(),
+                                  S.getLangOpts(), S.Context.getTargetInfo());
 }
 
 void CheckFormatHandler::HandleIncompleteSpecifier(const char *startSpecifier,
                                                    unsigned specifierLen){
   EmitFormatDiagnostic(S.PDiag(diag::warn_printf_incomplete_specifier),
                        getLocationOfByte(startSpecifier),
                        /*IsStringLocation*/true,
                        getSpecifierRange(startSpecifier, specifierLen));

 
 //===--- CHECK: Printf format string checking ------------------------------===//
 
 namespace {
 class CheckPrintfHandler : public CheckFormatHandler {
   bool ObjCContext;
 
 public:
-  CheckPrintfHandler(Sema &s, const StringLiteral *fexpr,
+  CheckPrintfHandler(Sema &s, const FormatStringLiteral *fexpr,
                      const Expr *origFormatExpr, unsigned firstDataArg,
                      unsigned numDataArgs, bool isObjC,
                      const char *beg, bool hasVAListArg,
                      ArrayRef<const Expr *> Args,
                      unsigned formatIdx, bool inFunctionCall,
                      Sema::VariadicCallType CallType,
                      llvm::SmallBitVector &CheckedVarArgs,
                      UncoveredArgHandler &UncoveredArg)
CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
   return true;
 }
 
 //===--- CHECK: Scanf format string checking ------------------------------===//
 
 namespace {  
 class CheckScanfHandler : public CheckFormatHandler {
 public:
-  CheckScanfHandler(Sema &s, const StringLiteral *fexpr,
+  CheckScanfHandler(Sema &s, const FormatStringLiteral *fexpr,
                     const Expr *origFormatExpr, unsigned firstDataArg,
                     unsigned numDataArgs, const char *beg, bool hasVAListArg,
                     ArrayRef<const Expr *> Args,
                     unsigned formatIdx, bool inFunctionCall,
                     Sema::VariadicCallType CallType,
                     llvm::SmallBitVector &CheckedVarArgs,
                     UncoveredArgHandler &UncoveredArg)
     : CheckFormatHandler(s, fexpr, origFormatExpr, firstDataArg,
EmitFormatDiagnostic(S.PDiag(diag)
                          Ex->getLocStart(),
                          /*IsStringLocation*/ false,
                          getSpecifierRange(startSpecifier, specifierLen));
   }
 
   return true;
 }
 
-static void CheckFormatString(Sema &S, const StringLiteral *FExpr,
+static void CheckFormatString(Sema &S, const FormatStringLiteral *FExpr,
                               const Expr *OrigFormatExpr,
                               ArrayRef<const Expr *> Args,
                               bool HasVAListArg, unsigned format_idx,
                               unsigned firstDataArg,
                               Sema::FormatStringType Type,
                               bool inFunctionCall,
                               Sema::VariadicCallType CallType,
                               llvm::SmallBitVector &CheckedVarArgs,

test/Sema/format-strings.c

 // <rdar://problem/14178260>
 extern void test_format_security_extra_args(const char*, int, ...)
     __attribute__((__format__(__printf__, 1, 3)));
 void test_format_security_pos(char* string) {
   test_format_security_extra_args(string, 5); // expected-warning {{format string is not a string literal (potentially insecure)}}
   // expected-note@-1{{treat the string as an argument to avoid this}}
 }
 #pragma GCC diagnostic warning "-Wformat-nonliteral"
+
+void test_char_pointer_arithmetic(int b) {
+  const char s1[] = "string";
+  const char s2[] = "%s string";
+
+  printf(s1 - 1);  // expected-warning {{format string is not a string literal (potentially insecure)}}
+  // expected-note@-1{{treat the string as an argument to avoid this}}
+
+  printf(s1 + 2);  // no-warning
+  printf(s2 + 2);  // no-warning
+
+  const char s3[] = "%s string";
+  printf((s3 + 2) - 2);  // expected-warning{{more '%' conversions than data arguments}}
+  // expected-note@-2{{format string is defined here}}
+  printf(2 + s2);             // no-warning
+  printf(6 + s2 - 2);         // no-warning
+  printf(2 + (b ? s1 : s2));  // no-warning
+
+  const char s5[] = "string %s";
+  printf(2 + (b ? s2 : s5));  // expected-warning{{more '%' conversions than data arguments}}
+  // expected-note@-2{{format string is defined here}}
+  printf(2 + (b ? s2 : s5), "");      // no-warning
+  printf(2 + (b ? s1 : s2 - 2), "");  // no-warning
+
+  const char s6[] = "%s string";
+  printf(2 + (b ? s1 : s6 - 2));  // expected-warning{{more '%' conversions than data arguments}}
+  // expected-note@-2{{format string is defined here}}
+  printf(1 ? s2 + 2 : s2);  // no-warning
+  printf(0 ? s2 : s2 + 2);  // no-warning
+  printf(2 + s2 + 5 * 3 - 16, "");  // expected-warning{{data argument not used}}
+
+  const char s7[] = "%s string %s %s";
+  printf(s7 + 3, "");  // expected-warning{{more '%' conversions than data arguments}}
+  // expected-note@-2{{format string is defined here}}
+}