[clang] [Clang] Add wraps attribute (for granular integer overflow handling) (PR #86618)
Justin Stitt via cfe-commits
cfe-commits at lists.llvm.org
Thu Jun 27 12:59:43 PDT 2024
https://github.com/JustinStitt updated https://github.com/llvm/llvm-project/pull/86618
>From af16c497b1323983d55f92d6cfb9ab2c99a21639 Mon Sep 17 00:00:00 2001
From: Justin Stitt <justinstitt at google.com>
Date: Tue, 5 Mar 2024 03:14:49 +0000
Subject: [PATCH] implement wraps attribute
Signed-off-by: Justin Stitt <justinstitt at google.com>
---
clang/docs/ReleaseNotes.rst | 10 +++
clang/include/clang/AST/Expr.h | 3 +
clang/include/clang/AST/Type.h | 2 +
clang/include/clang/Basic/Attr.td | 7 ++
clang/include/clang/Basic/AttrDocs.td | 68 +++++++++++++++++++
clang/include/clang/Basic/DiagnosticGroups.td | 6 ++
.../clang/Basic/DiagnosticSemaKinds.td | 7 ++
clang/lib/AST/Expr.cpp | 9 +++
clang/lib/AST/ExprConstant.cpp | 4 +-
clang/lib/AST/Type.cpp | 4 ++
clang/lib/AST/TypePrinter.cpp | 3 +
clang/lib/CodeGen/CGExprScalar.cpp | 47 +++++++++----
clang/lib/Sema/Sema.cpp | 3 +
clang/lib/Sema/SemaChecking.cpp | 33 ++++++++-
clang/lib/Sema/SemaDeclAttr.cpp | 8 ++-
clang/lib/Sema/SemaType.cpp | 15 ++++
clang/test/CodeGen/integer-overflow.c | 66 ++++++++++++++++++
clang/test/CodeGen/unsigned-overflow.c | 63 ++++++++++++++---
...a-attribute-supported-attributes-list.test | 1 +
clang/test/Sema/attr-wraps.c | 43 ++++++++++++
20 files changed, 376 insertions(+), 26 deletions(-)
create mode 100644 clang/test/Sema/attr-wraps.c
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index df579ae398c5e..1c8abb79a8a9a 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -525,6 +525,16 @@ Attribute Changes in Clang
The attributes declare constraints about a function's behavior pertaining to blocking and
heap memory allocation.
+- Introduced ``__attribute((wraps))__`` which can be added to type or variable
+ declarations. Using an attributed type or variable in an arithmetic
+ expression will define the overflow behavior for that expression as having
+ two's complement wrap-around. These expressions cannot trigger integer
+ overflow warnings or sanitizer warnings. They also cannot be optimized away
+ by some eager UB optimizations.
+
+ This attribute is only valid for C, as there are built-in language
+ alternatives for other languages.
+
Improvements to Clang's diagnostics
-----------------------------------
- Clang now applies syntax highlighting to the code snippets it
diff --git a/clang/include/clang/AST/Expr.h b/clang/include/clang/AST/Expr.h
index 3bc8cae4d8c86..acd2645720217 100644
--- a/clang/include/clang/AST/Expr.h
+++ b/clang/include/clang/AST/Expr.h
@@ -4061,6 +4061,9 @@ class BinaryOperator : public Expr {
return getFPFeaturesInEffect(LO).getAllowFEnvAccess();
}
+ /// Does one of the subexpressions have the wraps attribute?
+ bool hasWrappingOperand(const ASTContext &Ctx) const;
+
protected:
BinaryOperator(const ASTContext &Ctx, Expr *lhs, Expr *rhs, Opcode opc,
QualType ResTy, ExprValueKind VK, ExprObjectKind OK,
diff --git a/clang/include/clang/AST/Type.h b/clang/include/clang/AST/Type.h
index 62836ec5c6312..9de19094298da 100644
--- a/clang/include/clang/AST/Type.h
+++ b/clang/include/clang/AST/Type.h
@@ -1457,6 +1457,8 @@ class QualType {
return getQualifiers().hasStrongOrWeakObjCLifetime();
}
+ bool hasWrapsAttr() const;
+
// true when Type is objc's weak and weak is enabled but ARC isn't.
bool isNonWeakInMRRWithObjCWeak(const ASTContext &Context) const;
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 0c469e389eff0..81e48a7638ea6 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -4630,3 +4630,10 @@ def ClspvLibclcBuiltin: InheritableAttr {
let Documentation = [ClspvLibclcBuiltinDoc];
let SimpleHandler = 1;
}
+
+def Wraps : DeclOrTypeAttr {
+ let Spellings = [Clang<"wraps">];
+ let Subjects = SubjectList<[Var, TypedefName, Field]>;
+ let Documentation = [WrapsDocs];
+ let LangOpts = [COnly];
+}
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 8d8f058281684..cf34bba7dea7f 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -8176,3 +8176,71 @@ of ``nonallocating`` by the compiler.
}];
}
+def WrapsDocs : Documentation {
+ let Category = DocCatField;
+ let Content = [{
+This attribute can be used with type or variable declarations to denote that
+arithmetic containing these marked components have defined overflow behavior.
+Specifically, the behavior is defined as being consistent with two's complement
+wrap-around. For the purposes of sanitizers or warnings that concern themselves
+with the definedness of integer arithmetic, they will cease to instrument or
+warn about arithmetic that directly involves a "wrapping" component.
+
+For example, ``-fsanitize=signed-integer-overflow`` or ``-Winteger-overflow``
+will not warn about suspicious overflowing arithmetic -- assuming correct usage
+of the wraps attribute.
+
+This example shows some basic usage of ``__attribute__((wraps))`` on a type
+definition when building with ``-fsanitize=signed-integer-overflow``
+
+.. code-block:: c
+
+ typedef int __attribute__((wraps)) wrapping_int;
+
+ void foo() {
+ wrapping_int a = INT_MAX;
+ ++a; // no sanitizer warning
+ }
+
+ int main() { foo(); }
+
+In the following example, we use ``__attribute__((wraps))`` on a variable to
+disable overflow instrumentation for arithmetic expressions it appears in. We
+do so with a popular overflow-checking pattern which we might not want to trip
+sanitizers (like ``-fsanitize=unsigned-integer-overflow``).
+
+.. code-block:: c
+
+ void foo(int offset) {
+ unsigned int A __attribute__((wraps)) = UINT_MAX;
+
+ // check for overflow using a common pattern, however we may accidentally
+ // perform a real overflow thus triggering sanitizers to step in. Since "A"
+ // is "wrapping", we can avoid sanitizer warnings.
+ if (A + offset < A) {
+ // handle overflow manually
+ // ...
+ return;
+ }
+
+ // now, handle non-overflow case ...
+ }
+
+The above example demonstrates some of the power and elegance this attribute
+provides. We can use code patterns we are already familiar with (like ``if (x +
+y < x)``) while gaining control over the overflow behavior on a case-by-case
+basis.
+
+When combined with ``-fwrapv``, this attribute can still be applied as normal
+but has no function apart from annotating types and variables for readers. This
+is because ``-fwrapv`` defines all arithmetic as being "wrapping", rendering
+this attribute's efforts redundant.
+
+When using this attribute without ``-fwrapv`` and without any sanitizers, it
+still has an impact on the definedness of arithmetic expressions containing
+wrapping components. Since the behavior of said expressions is now technically
+defined, the compiler will forgo some eager optimizations that are used on
+expressions containing UB.
+}];
+}
+
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 1c4f305fb5d00..4055b5ff34807 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -1539,3 +1539,9 @@ def BitIntExtension : DiagGroup<"bit-int-extension">;
// Warnings about misuse of ExtractAPI options.
def ExtractAPIMisuse : DiagGroup<"extractapi-misuse">;
+
+// Warnings regarding the usage of __attribute__((wraps)) on non-integer types.
+def UselessWrapsAttr : DiagGroup<"useless-wraps-attribute">;
+
+// Warnings about the wraps attribute getting implicitly discarded
+def ImpDiscardedWrapsAttr : DiagGroup<"implicitly-discarded-wraps-attribute">;
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 46ad359751d7d..38fbffd07d8d3 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6601,6 +6601,13 @@ def warn_counted_by_attr_elt_type_unknown_size :
Warning<err_counted_by_attr_pointee_unknown_size.Summary>,
InGroup<BoundsSafetyCountedByEltTyUnknownSize>;
+def warn_wraps_attr_var_decl_type_not_integer : Warning<
+ "using attribute 'wraps' with non-integer type '%0' has no function">,
+ InGroup<UselessWrapsAttr>;
+def warn_wraps_attr_maybe_lost : Warning<
+ "'wraps' attribute may be implicitly discarded when converted to %0">,
+ InGroup<ImpDiscardedWrapsAttr>;
+
let CategoryName = "ARC Semantic Issue" in {
// ARC-mode diagnostics.
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 6af1b5683e08b..88d1350c52064 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -2237,6 +2237,11 @@ bool BinaryOperator::isNullPointerArithmeticExtension(ASTContext &Ctx,
return true;
}
+bool BinaryOperator::hasWrappingOperand(const ASTContext &Ctx) const {
+ return getLHS()->getType().hasWrapsAttr() ||
+ getRHS()->getType().hasWrapsAttr();
+}
+
SourceLocExpr::SourceLocExpr(const ASTContext &Ctx, SourceLocIdentKind Kind,
QualType ResultTy, SourceLocation BLoc,
SourceLocation RParenLoc,
@@ -4774,6 +4779,8 @@ BinaryOperator::BinaryOperator(const ASTContext &Ctx, Expr *lhs, Expr *rhs,
if (hasStoredFPFeatures())
setStoredFPFeatures(FPFeatures);
setDependence(computeDependence(this));
+ if (hasWrappingOperand(Ctx))
+ setType(Ctx.getAttributedType(attr::Wraps, getType(), getType()));
}
BinaryOperator::BinaryOperator(const ASTContext &Ctx, Expr *lhs, Expr *rhs,
@@ -4791,6 +4798,8 @@ BinaryOperator::BinaryOperator(const ASTContext &Ctx, Expr *lhs, Expr *rhs,
if (hasStoredFPFeatures())
setStoredFPFeatures(FPFeatures);
setDependence(computeDependence(this));
+ if (hasWrappingOperand(Ctx))
+ setType(Ctx.getAttributedType(attr::Wraps, getType(), getType()));
}
BinaryOperator *BinaryOperator::CreateEmpty(const ASTContext &C,
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index fe4b9a569ab87..cc5af1bdc2022 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -2781,7 +2781,7 @@ static bool CheckedIntArithmetic(EvalInfo &Info, const Expr *E,
APSInt Value(Op(LHS.extend(BitWidth), RHS.extend(BitWidth)), false);
Result = Value.trunc(LHS.getBitWidth());
if (Result.extend(BitWidth) != Value) {
- if (Info.checkingForUndefinedBehavior())
+ if (Info.checkingForUndefinedBehavior() && !E->getType().hasWrapsAttr())
Info.Ctx.getDiagnostics().Report(E->getExprLoc(),
diag::warn_integer_constant_overflow)
<< toString(Result, 10, Result.isSigned(), /*formatAsCLiteral=*/false,
@@ -14176,7 +14176,7 @@ bool IntExprEvaluator::VisitUnaryOperator(const UnaryOperator *E) {
if (!Result.isInt()) return Error(E);
const APSInt &Value = Result.getInt();
if (Value.isSigned() && Value.isMinSignedValue() && E->canOverflow()) {
- if (Info.checkingForUndefinedBehavior())
+ if (Info.checkingForUndefinedBehavior() && !E->getType().hasWrapsAttr())
Info.Ctx.getDiagnostics().Report(E->getExprLoc(),
diag::warn_integer_constant_overflow)
<< toString(Value, 10, Value.isSigned(), /*formatAsCLiteral=*/false,
diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
index d8b885870de3a..5d6c4154c349c 100644
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -2875,6 +2875,10 @@ bool QualType::isTriviallyEqualityComparableType(
CanonicalType, /*CheckIfTriviallyCopyable=*/false);
}
+bool QualType::hasWrapsAttr() const {
+ return !isNull() && getTypePtr()->hasAttr(attr::Wraps);
+}
+
bool QualType::isNonWeakInMRRWithObjCWeak(const ASTContext &Context) const {
return !Context.getLangOpts().ObjCAutoRefCount &&
Context.getLangOpts().ObjCWeak &&
diff --git a/clang/lib/AST/TypePrinter.cpp b/clang/lib/AST/TypePrinter.cpp
index 7c87fd587880e..94613235e5838 100644
--- a/clang/lib/AST/TypePrinter.cpp
+++ b/clang/lib/AST/TypePrinter.cpp
@@ -1995,6 +1995,9 @@ void TypePrinter::printAttributedAfter(const AttributedType *T,
case attr::AArch64SVEPcs: OS << "aarch64_sve_pcs"; break;
case attr::AMDGPUKernelCall: OS << "amdgpu_kernel"; break;
case attr::IntelOclBicc: OS << "inteloclbicc"; break;
+ case attr::Wraps:
+ OS << "wraps";
+ break;
case attr::PreserveMost:
OS << "preserve_most";
break;
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index f40f3c273206b..fb3982295825e 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -156,6 +156,10 @@ struct BinOpInfo {
}
return false;
}
+
+ /// Does the BinaryOperator have the wraps attribute?
+ /// If so, we can elide overflow sanitizer checks.
+ bool hasWrappingOperand() const { return E->getType().hasWrapsAttr(); }
};
static bool MustVisitNullValue(const Expr *E) {
@@ -736,7 +740,8 @@ class ScalarExprEmitter
// Binary Operators.
Value *EmitMul(const BinOpInfo &Ops) {
- if (Ops.Ty->isSignedIntegerOrEnumerationType()) {
+ if (Ops.Ty->isSignedIntegerOrEnumerationType() &&
+ !Ops.hasWrappingOperand()) {
switch (CGF.getLangOpts().getSignedOverflowBehavior()) {
case LangOptions::SOB_Defined:
if (!CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow))
@@ -772,7 +777,8 @@ class ScalarExprEmitter
if (Ops.Ty->isUnsignedIntegerType() &&
CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow) &&
- !CanElideOverflowCheck(CGF.getContext(), Ops))
+ !CanElideOverflowCheck(CGF.getContext(), Ops) &&
+ !Ops.hasWrappingOperand())
return EmitOverflowCheckedBinOp(Ops);
if (Ops.LHS->getType()->isFPOrFPVectorTy()) {
@@ -1104,7 +1110,7 @@ void ScalarExprEmitter::EmitIntegerTruncationCheck(Value *Src, QualType SrcType,
// If the comparison result is 'i1 false', then the truncation was lossy.
// Do we care about this type of truncation?
- if (!CGF.SanOpts.has(Check.second.second))
+ if (!CGF.SanOpts.has(Check.second.second) || DstType.hasWrapsAttr())
return;
llvm::Constant *StaticArgs[] = {
@@ -1337,6 +1343,14 @@ void CodeGenFunction::EmitBitfieldConversionCheck(Value *Src, QualType SrcType,
bool SrcSigned = SrcType->isSignedIntegerOrEnumerationType();
bool DstSigned = DstType->isSignedIntegerOrEnumerationType();
+ bool SrcWraps = SrcType.hasWrapsAttr();
+ bool DstWraps = DstType.hasWrapsAttr();
+
+ // The wraps attribute should silence any sanitizer warnings
+ // regarding truncation or overflow
+ if (SrcWraps || DstWraps)
+ return;
+
CodeGenFunction::SanitizerScope SanScope(this);
std::pair<ScalarExprEmitter::ImplicitConversionCheckKind,
@@ -2870,6 +2884,9 @@ ScalarExprEmitter::EmitScalarPrePostIncDec(const UnaryOperator *E, LValue LV,
} else if (type->isIntegerType()) {
QualType promotedType;
bool canPerformLossyDemotionCheck = false;
+ BinOpInfo Ops = createBinOpInfoFromIncDec(
+ E, value, isInc, E->getFPFeaturesInEffect(CGF.getLangOpts()));
+
if (CGF.getContext().isPromotableIntegerType(type)) {
promotedType = CGF.getContext().getPromotedIntegerType(type);
assert(promotedType != type && "Shouldn't promote to the same type.");
@@ -2926,10 +2943,12 @@ ScalarExprEmitter::EmitScalarPrePostIncDec(const UnaryOperator *E, LValue LV,
// Note that signed integer inc/dec with width less than int can't
// overflow because of promotion rules; we're just eliding a few steps
// here.
- } else if (E->canOverflow() && type->isSignedIntegerOrEnumerationType()) {
+ } else if (E->canOverflow() && type->isSignedIntegerOrEnumerationType() &&
+ !Ops.hasWrappingOperand()) {
value = EmitIncDecConsiderOverflowBehavior(E, value, isInc);
} else if (E->canOverflow() && type->isUnsignedIntegerType() &&
- CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow)) {
+ CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow) &&
+ !Ops.hasWrappingOperand()) {
value = EmitOverflowCheckedBinOp(createBinOpInfoFromIncDec(
E, value, isInc, E->getFPFeaturesInEffect(CGF.getLangOpts())));
} else {
@@ -3718,7 +3737,8 @@ Value *ScalarExprEmitter::EmitDiv(const BinOpInfo &Ops) {
if ((CGF.SanOpts.has(SanitizerKind::IntegerDivideByZero) ||
CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow)) &&
Ops.Ty->isIntegerType() &&
- (Ops.mayHaveIntegerDivisionByZero() || Ops.mayHaveIntegerOverflow())) {
+ (Ops.mayHaveIntegerDivisionByZero() || Ops.mayHaveIntegerOverflow()) &&
+ !Ops.hasWrappingOperand()) {
llvm::Value *Zero = llvm::Constant::getNullValue(ConvertType(Ops.Ty));
EmitUndefinedBehaviorIntegerDivAndRemCheck(Ops, Zero, true);
} else if (CGF.SanOpts.has(SanitizerKind::FloatDivideByZero) &&
@@ -3767,7 +3787,8 @@ Value *ScalarExprEmitter::EmitRem(const BinOpInfo &Ops) {
if ((CGF.SanOpts.has(SanitizerKind::IntegerDivideByZero) ||
CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow)) &&
Ops.Ty->isIntegerType() &&
- (Ops.mayHaveIntegerDivisionByZero() || Ops.mayHaveIntegerOverflow())) {
+ (Ops.mayHaveIntegerDivisionByZero() || Ops.mayHaveIntegerOverflow()) &&
+ !Ops.hasWrappingOperand()) {
CodeGenFunction::SanitizerScope SanScope(&CGF);
llvm::Value *Zero = llvm::Constant::getNullValue(ConvertType(Ops.Ty));
EmitUndefinedBehaviorIntegerDivAndRemCheck(Ops, Zero, false);
@@ -4132,7 +4153,7 @@ Value *ScalarExprEmitter::EmitAdd(const BinOpInfo &op) {
op.RHS->getType()->isPointerTy())
return emitPointerArithmetic(CGF, op, CodeGenFunction::NotSubtraction);
- if (op.Ty->isSignedIntegerOrEnumerationType()) {
+ if (op.Ty->isSignedIntegerOrEnumerationType() && !op.hasWrappingOperand()) {
switch (CGF.getLangOpts().getSignedOverflowBehavior()) {
case LangOptions::SOB_Defined:
if (!CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow))
@@ -4165,7 +4186,7 @@ Value *ScalarExprEmitter::EmitAdd(const BinOpInfo &op) {
if (op.Ty->isUnsignedIntegerType() &&
CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow) &&
- !CanElideOverflowCheck(CGF.getContext(), op))
+ !CanElideOverflowCheck(CGF.getContext(), op) && !op.hasWrappingOperand())
return EmitOverflowCheckedBinOp(op);
if (op.LHS->getType()->isFPOrFPVectorTy()) {
@@ -4288,7 +4309,7 @@ Value *ScalarExprEmitter::EmitFixedPointBinOp(const BinOpInfo &op) {
Value *ScalarExprEmitter::EmitSub(const BinOpInfo &op) {
// The LHS is always a pointer if either side is.
if (!op.LHS->getType()->isPointerTy()) {
- if (op.Ty->isSignedIntegerOrEnumerationType()) {
+ if (op.Ty->isSignedIntegerOrEnumerationType() && !op.hasWrappingOperand()) {
switch (CGF.getLangOpts().getSignedOverflowBehavior()) {
case LangOptions::SOB_Defined:
if (!CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow))
@@ -4321,7 +4342,8 @@ Value *ScalarExprEmitter::EmitSub(const BinOpInfo &op) {
if (op.Ty->isUnsignedIntegerType() &&
CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow) &&
- !CanElideOverflowCheck(CGF.getContext(), op))
+ !CanElideOverflowCheck(CGF.getContext(), op) &&
+ !op.hasWrappingOperand())
return EmitOverflowCheckedBinOp(op);
if (op.LHS->getType()->isFPOrFPVectorTy()) {
@@ -4441,7 +4463,8 @@ Value *ScalarExprEmitter::EmitShl(const BinOpInfo &Ops) {
bool SanitizeSignedBase = CGF.SanOpts.has(SanitizerKind::ShiftBase) &&
Ops.Ty->hasSignedIntegerRepresentation() &&
!CGF.getLangOpts().isSignedOverflowDefined() &&
- !CGF.getLangOpts().CPlusPlus20;
+ !CGF.getLangOpts().CPlusPlus20 &&
+ !Ops.hasWrappingOperand();
bool SanitizeUnsignedBase =
CGF.SanOpts.has(SanitizerKind::UnsignedShiftBase) &&
Ops.Ty->hasUnsignedIntegerRepresentation();
diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index 3f8f2f027172d..3cb8866158ee1 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -735,6 +735,9 @@ ExprResult Sema::ImpCastExprToType(Expr *E, QualType Ty,
QualType ExprTy = Context.getCanonicalType(E->getType());
QualType TypeTy = Context.getCanonicalType(Ty);
+ if (E->getType().getTypePtr()->isIntegerType() && E->getType().hasWrapsAttr())
+ Ty = Context.getAttributedType(attr::Wraps, Ty, Ty);
+
if (ExprTy == TypeTy)
return E;
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 87988519e7691..512a6ca117785 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -11237,7 +11237,8 @@ static void AnalyzeAssignment(Sema &S, BinaryOperator *E) {
// We want to recurse on the RHS as normal unless we're assigning to
// a bitfield.
if (FieldDecl *Bitfield = E->getLHS()->getSourceBitField()) {
- if (AnalyzeBitFieldAssignment(S, Bitfield, E->getRHS(),
+ if (!E->hasWrappingOperand(S.Context) &&
+ AnalyzeBitFieldAssignment(S, Bitfield, E->getRHS(),
E->getOperatorLoc())) {
// Recurse, ignoring any implicit conversions on the RHS.
return AnalyzeImplicitConversions(S, E->getRHS()->IgnoreParenImpCasts(),
@@ -11477,11 +11478,37 @@ static bool IsImplicitBoolFloatConversion(Sema &S, Expr *Ex, bool ToBool) {
FloatCandidateBT && (FloatCandidateBT->isFloatingPoint()));
}
+/// Check to see if the wraps attribute may have been lost through a function
+/// call. For cases where we are unsure, assume not.
+static bool IsWrapsAttrLost(Sema &S, const CallExpr *TheCall,
+ const FunctionDecl *FD, unsigned i) {
+ // We may not have a FunctionDecl if this CallExpr is associated virtual,
+ // templated or overloaded functions.
+ if (!FD)
+ return false;
+
+ if (i >= TheCall->getNumArgs() || i >= FD->getNumParams())
+ return false;
+
+ const QualType ProvidedArgTy = TheCall->getArg(i)->getType();
+ const QualType PrototypedArgTy = FD->getParamDecl(i)->getType();
+
+ return ProvidedArgTy.hasWrapsAttr() && !PrototypedArgTy.hasWrapsAttr();
+}
+
static void CheckImplicitArgumentConversions(Sema &S, CallExpr *TheCall,
SourceLocation CC) {
unsigned NumArgs = TheCall->getNumArgs();
+ const FunctionDecl *FD = TheCall->getDirectCallee();
+
for (unsigned i = 0; i < NumArgs; ++i) {
Expr *CurrA = TheCall->getArg(i);
+
+ if (IsWrapsAttrLost(S, TheCall, FD, i))
+ S.Diag(CurrA->getSourceRange().getBegin(),
+ diag::warn_wraps_attr_maybe_lost)
+ << FD->getParamDecl(i)->getType();
+
if (!IsImplicitBoolFloatConversion(S, CurrA, true))
continue;
@@ -12080,7 +12107,7 @@ static void CheckImplicitConversion(Sema &S, Expr *E, QualType T,
S.Context, E, S.isConstantEvaluatedContext(), /*Approximate=*/true);
IntRange TargetRange = IntRange::forTargetOfCanonicalType(S.Context, Target);
- if (LikelySourceRange.Width > TargetRange.Width) {
+ if (LikelySourceRange.Width > TargetRange.Width && !T.hasWrapsAttr()) {
// If the source is a constant, use a default-on diagnostic.
// TODO: this should happen for bitfield stores, too.
Expr::EvalResult Result;
@@ -12128,7 +12155,7 @@ static void CheckImplicitConversion(Sema &S, Expr *E, QualType T,
if (TargetRange.Width == LikelySourceRange.Width &&
!TargetRange.NonNegative && LikelySourceRange.NonNegative &&
- Source->isSignedIntegerType()) {
+ Source->isSignedIntegerType() && !T.hasWrapsAttr()) {
// Warn when doing a signed to signed conversion, warn if the positive
// source value is exactly the width of the target type, which will
// cause a negative value to be stored.
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 99b400307d644..b58da23777715 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -3951,6 +3951,10 @@ void Sema::AddAlignValueAttr(Decl *D, const AttributeCommonInfo &CI, Expr *E) {
D->addAttr(::new (Context) AlignValueAttr(Context, CI, E));
}
+static void handleWrapsAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+ D->addAttr(::new (S.Context) WrapsAttr(S.Context, AL));
+}
+
static void handleAlignedAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
if (AL.hasParsedType()) {
const ParsedType &TypeArg = AL.getTypeArg();
@@ -6900,10 +6904,12 @@ ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D, const ParsedAttr &AL,
case ParsedAttr::AT_AvailableOnlyInDefaultEvalMethod:
handleAvailableOnlyInDefaultEvalMethod(S, D, AL);
break;
-
case ParsedAttr::AT_CountedBy:
handleCountedByAttrField(S, D, AL);
break;
+ case ParsedAttr::AT_Wraps:
+ handleWrapsAttr(S, D, AL);
+ break;
// Microsoft attributes:
case ParsedAttr::AT_LayoutVersion:
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 53b9083c95c1b..5e8ae6b77241d 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -6522,6 +6522,18 @@ static void HandleBTFTypeTagAttribute(QualType &Type, const ParsedAttr &Attr,
::new (Ctx) BTFTypeTagAttr(Ctx, Attr, BTFTypeTag), Type);
}
+static void handleWrapsAttr(QualType &Type, const ParsedAttr &Attr,
+ TypeProcessingState &State) {
+ Sema &S = State.getSema();
+ ASTContext &Ctx = S.Context;
+
+ if (!Type->isIntegerType())
+ S.Diag(Attr.getLoc(), diag::warn_wraps_attr_var_decl_type_not_integer)
+ << Type.getAsString();
+
+ Type = State.getAttributedType(::new (Ctx) WrapsAttr(Ctx, Attr), Type, Type);
+}
+
/// HandleAddressSpaceTypeAttribute - Process an address_space attribute on the
/// specified type. The attribute contains 1 argument, the id of the address
/// space for the type.
@@ -8624,6 +8636,9 @@ static void processTypeAttrs(TypeProcessingState &state, QualType &type,
HandleBTFTypeTagAttribute(type, attr, state);
attr.setUsedAsTypeAttr();
break;
+ case ParsedAttr::AT_Wraps:
+ handleWrapsAttr(type, attr, state);
+ break;
case ParsedAttr::AT_MayAlias:
// FIXME: This attribute needs to actually be handled, but if we ignore
diff --git a/clang/test/CodeGen/integer-overflow.c b/clang/test/CodeGen/integer-overflow.c
index 461b026d39615..cb6cb201b55f9 100644
--- a/clang/test/CodeGen/integer-overflow.c
+++ b/clang/test/CodeGen/integer-overflow.c
@@ -105,3 +105,69 @@ void test1(void) {
// TRAPV: call ptr @llvm.frameaddress.p0(i32 0)
// CATCH_UB: call ptr @llvm.frameaddress.p0(i32 0)
}
+
+// Tests for integer overflow using __attribute__((wraps))
+typedef int __attribute__((wraps)) wrapping_int;
+
+void test2(void) {
+ // DEFAULT-LABEL: define{{.*}} void @test2
+ // WRAPV-LABEL: define{{.*}} void @test2
+ // TRAPV-LABEL: define{{.*}} void @test2
+ extern volatile wrapping_int a, b, c;
+
+ // Basically, all cases should match the WRAPV case since this attribute
+ // effectively enables wrapv for expressions containing wrapping types.
+
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: add i32
+ a = b + c;
+
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: sub i32
+ a = b - c;
+
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: mul i32
+ a = b * c;
+
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: sub i32 0,
+ a = -b;
+
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: add i32 {{.*}}, 1
+ ++b;
+
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: add i32 {{.*}}, -1
+ --b;
+
+ // Less trivial cases
+ extern volatile wrapping_int u, v;
+ extern volatile int w;
+
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: add i32
+ if (u + v < u) {}
+
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: add i32
+ for (;u + v < u;) {}
+
+ // this (w+1) should have instrumentation
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: call {{.*}} @llvm.sadd.with.overflow.i32
+ u = (w+1) + v;
+
+ // no parts of this expression should have instrumentation
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: add i32 {{.*}}, 1
+ u = (v+1) + w;
+
+ // downcast off the wraps attribute
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: call { i32, i1 } @llvm.sadd.with.overflow.i32
+ u = (int) u + (int) v;
+
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: call { i32, i1 } @llvm.sadd.with.overflow.i32
+ u = (int) u + w;
+
+ // persist wraps attribute through implicit integer promotion
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: store i8 127, ptr [[D1:%.*]]
+ // DEFAULT,WRAPV,TRAPV,CATCH_UB,TRAPV_HANDLER: mul{{.*}} = mul i32
+ // would look like mul{{.*}} = mul nsw i32
+ // if overflow behavior was not defined.
+ char __attribute__((wraps)) d;
+ d = 127;
+ w = d*d*d*d*d; // d is promoted to int, then calculation is made.
+ // wraps prevents instrumentation even through promotion
+}
diff --git a/clang/test/CodeGen/unsigned-overflow.c b/clang/test/CodeGen/unsigned-overflow.c
index 6c2f0c1efc145..471a06e5fa63f 100644
--- a/clang/test/CodeGen/unsigned-overflow.c
+++ b/clang/test/CodeGen/unsigned-overflow.c
@@ -5,6 +5,11 @@
unsigned long li, lj, lk;
unsigned int ii, ij, ik;
+// The wraps attribute disables sanitizer instrumentation for arithmetic
+// expressions containing these types.
+unsigned long __attribute__((wraps)) li_w, lj_w, lk_w;
+unsigned int __attribute__((wraps)) ii_w, ij_w, ik_w;
+
extern void opaquelong(unsigned long);
extern void opaqueint(unsigned int);
@@ -18,6 +23,11 @@ void testlongadd(void) {
// CHECK-NEXT: [[T5:%.*]] = extractvalue { i64, i1 } [[T3]], 1
// CHECK: call void @__ubsan_handle_add_overflow
li = lj + lk;
+
+ // CHECK: [[T6:%.*]] = load i64, ptr @lj_w
+ // CHECK-NEXT: [[T7:%.*]] = load i64, ptr @lk_w
+ // CHECK-NEXT: add i64 [[T6]], [[T7]]
+ li_w = lj_w + lk_w;
}
// CHECK-LABEL: define{{.*}} void @testlongsub()
@@ -30,6 +40,11 @@ void testlongsub(void) {
// CHECK-NEXT: [[T5:%.*]] = extractvalue { i64, i1 } [[T3]], 1
// CHECK: call void @__ubsan_handle_sub_overflow
li = lj - lk;
+
+ // CHECK: [[T6:%.*]] = load i64, ptr @lj_w
+ // CHECK-NEXT: [[T7:%.*]] = load i64, ptr @lk_w
+ // CHECK-NEXT: sub i64 [[T6]], [[T7]]
+ li_w = lj_w - lk_w;
}
// CHECK-LABEL: define{{.*}} void @testlongmul()
@@ -42,28 +57,39 @@ void testlongmul(void) {
// CHECK-NEXT: [[T5:%.*]] = extractvalue { i64, i1 } [[T3]], 1
// CHECK: call void @__ubsan_handle_mul_overflow
li = lj * lk;
+
+ // CHECK: [[T6:%.*]] = load i64, ptr @lj_w
+ // CHECK-NEXT: [[T7:%.*]] = load i64, ptr @lk_w
+ // CHECK-NEXT: mul i64 [[T6]], [[T7]]
+ li_w = lj_w * lk_w;
}
// CHECK-LABEL: define{{.*}} void @testlongpostinc()
void testlongpostinc(void) {
- opaquelong(li++);
-
// CHECK: [[T1:%.*]] = load i64, ptr @li
// CHECK-NEXT: [[T2:%.*]] = call { i64, i1 } @llvm.uadd.with.overflow.i64(i64 [[T1]], i64 1)
// CHECK-NEXT: [[T3:%.*]] = extractvalue { i64, i1 } [[T2]], 0
// CHECK-NEXT: [[T4:%.*]] = extractvalue { i64, i1 } [[T2]], 1
// CHECK: call void @__ubsan_handle_add_overflow
+ opaquelong(li++);
+
+ // CHECK: [[T5:%.*]] = load i64, ptr @li_w
+ // CHECK-NEXT: add i64 [[T5]], 1
+ opaquelong(li_w++);
}
// CHECK-LABEL: define{{.*}} void @testlongpreinc()
void testlongpreinc(void) {
- opaquelong(++li);
-
// CHECK: [[T1:%.*]] = load i64, ptr @li
// CHECK-NEXT: [[T2:%.*]] = call { i64, i1 } @llvm.uadd.with.overflow.i64(i64 [[T1]], i64 1)
// CHECK-NEXT: [[T3:%.*]] = extractvalue { i64, i1 } [[T2]], 0
// CHECK-NEXT: [[T4:%.*]] = extractvalue { i64, i1 } [[T2]], 1
// CHECK: call void @__ubsan_handle_add_overflow
+ opaquelong(++li);
+
+ // CHECK: [[T5:%.*]] = load i64, ptr @li_w
+ // CHECK-NEXT: add i64 [[T5]], 1
+ opaquelong(++li_w);
}
// CHECK-LABEL: define{{.*}} void @testintadd()
@@ -76,6 +102,11 @@ void testintadd(void) {
// CHECK-NEXT: [[T5:%.*]] = extractvalue { i32, i1 } [[T3]], 1
// CHECK: call void @__ubsan_handle_add_overflow
ii = ij + ik;
+
+ // CHECK: [[T6:%.*]] = load i32, ptr @ij_w
+ // CHECK-NEXT: [[T7:%.*]] = load i32, ptr @ik_w
+ // CHECK-NEXT: add i32 [[T6]], [[T7]]
+ ii_w = ij_w + ik_w;
}
// CHECK-LABEL: define{{.*}} void @testintsub()
@@ -88,6 +119,11 @@ void testintsub(void) {
// CHECK-NEXT: [[T5:%.*]] = extractvalue { i32, i1 } [[T3]], 1
// CHECK: call void @__ubsan_handle_sub_overflow
ii = ij - ik;
+
+ // CHECK: [[T6:%.*]] = load i32, ptr @ij_w
+ // CHECK-NEXT: [[T7:%.*]] = load i32, ptr @ik_w
+ // CHECK-NEXT: sub i32 [[T6]], [[T7]]
+ ii_w = ij_w - ik_w;
}
// CHECK-LABEL: define{{.*}} void @testintmul()
@@ -100,26 +136,37 @@ void testintmul(void) {
// CHECK-NEXT: [[T5:%.*]] = extractvalue { i32, i1 } [[T3]], 1
// CHECK: call void @__ubsan_handle_mul_overflow
ii = ij * ik;
+
+ // CHECK: [[T6:%.*]] = load i32, ptr @ij_w
+ // CHECK-NEXT: [[T7:%.*]] = load i32, ptr @ik_w
+ // CHECK-NEXT: mul i32 [[T6]], [[T7]]
+ ii_w = ij_w * ik_w;
}
// CHECK-LABEL: define{{.*}} void @testintpostinc()
void testintpostinc(void) {
- opaqueint(ii++);
-
// CHECK: [[T1:%.*]] = load i32, ptr @ii
// CHECK-NEXT: [[T2:%.*]] = call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 [[T1]], i32 1)
// CHECK-NEXT: [[T3:%.*]] = extractvalue { i32, i1 } [[T2]], 0
// CHECK-NEXT: [[T4:%.*]] = extractvalue { i32, i1 } [[T2]], 1
// CHECK: call void @__ubsan_handle_add_overflow
+ opaqueint(ii++);
+
+ // CHECK: [[T5:%.*]] = load i32, ptr @ii_w
+ // CHECK-NEXT: add i32 [[T5]], 1
+ opaqueint(ii_w++);
}
// CHECK-LABEL: define{{.*}} void @testintpreinc()
void testintpreinc(void) {
- opaqueint(++ii);
-
// CHECK: [[T1:%.*]] = load i32, ptr @ii
// CHECK-NEXT: [[T2:%.*]] = call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 [[T1]], i32 1)
// CHECK-NEXT: [[T3:%.*]] = extractvalue { i32, i1 } [[T2]], 0
// CHECK-NEXT: [[T4:%.*]] = extractvalue { i32, i1 } [[T2]], 1
// CHECK: call void @__ubsan_handle_add_overflow
+ opaqueint(++ii);
+
+ // CHECK: [[T5:%.*]] = load i32, ptr @ii_w
+ // CHECK-NEXT: add i32 [[T5]], 1
+ opaqueint(++ii_w);
}
diff --git a/clang/test/Misc/pragma-attribute-supported-attributes-list.test b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
index 99732694f72a5..935d0ab86b0f0 100644
--- a/clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -211,6 +211,7 @@
// CHECK-NEXT: WebAssemblyImportModule (SubjectMatchRule_function)
// CHECK-NEXT: WebAssemblyImportName (SubjectMatchRule_function)
// CHECK-NEXT: WorkGroupSizeHint (SubjectMatchRule_function)
+// CHECK-NEXT: Wraps (SubjectMatchRule_variable, SubjectMatchRule_type_alias, SubjectMatchRule_field)
// CHECK-NEXT: XRayInstrument (SubjectMatchRule_function, SubjectMatchRule_objc_method)
// CHECK-NEXT: XRayLogArgs (SubjectMatchRule_function, SubjectMatchRule_objc_method)
// CHECK-NEXT: ZeroCallUsedRegs (SubjectMatchRule_function)
diff --git a/clang/test/Sema/attr-wraps.c b/clang/test/Sema/attr-wraps.c
new file mode 100644
index 0000000000000..cb30200f072f2
--- /dev/null
+++ b/clang/test/Sema/attr-wraps.c
@@ -0,0 +1,43 @@
+// RUN: %clang_cc1 %s -verify -fsyntax-only -triple x86_64-pc-linux-gnu
+typedef int __attribute__((wraps)) wrapping_int;
+typedef unsigned __attribute__((wraps)) wrapping_u32;
+
+int implicit_truncation(void) {
+ const wrapping_int A = 1;
+ return 2147483647 + A; // no warning
+}
+
+struct R {
+ wrapping_int a: 2; // test bitfield sign change -- no warning
+ wrapping_u32 b: 1; // test bitfield overflow/truncation -- no warning
+ int baseline: 2; // baseline, should warn
+};
+
+void bitfields_truncation(void) {
+ struct R r;
+ r.a = 2; // this value changes from 2 to -2
+ ++r.a;
+
+ r.b = 2; // changes from 2 to 0
+ ++r.b;
+
+ // expected-warning at +1 {{to bit-field changes value from}}
+ r.baseline = 2;
+}
+
+extern void implicitly_discards_wraps_attribute(int discards);
+
+int discard_test(void) {
+ wrapping_int A = 1;
+ // expected-warning at +1 {{'wraps' attribute may be implicitly discarded}}
+ implicitly_discards_wraps_attribute(A);
+
+ int B = A; // assignments don't warn right now -- probably too noisy
+ return A; // neither do non-wrapping return types
+}
+
+float useless_wraps_attribute(void) {
+ // expected-warning at +1 {{using attribute 'wraps' with non-integer type}}
+ float __attribute__((wraps)) A = 3.14;
+ return A;
+}
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