This patch implements PR#22821.
Taking the address of a packed member is dangerous since the reduced
alignment of the pointee is lost. This can lead to memory alignment
faults in some architectures if the pointer value is dereferenced.
This change adds a new warning to clang emitted when taking the address
of a packed member. A packed member is either a field/data member
declared as attribute((packed)) or belonging to a struct/class
declared as such. The associated flag is -Waddress-of-packed-member.
Conversions (either implicit or via a valid casting) to pointer types
with lower or equal alignment requirements (e.g. void* or char*)
will silence the warning.
Differential Revision: https://reviews.llvm.org/D20561
llvm-svn: 278483
diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index e83dd07..e19020c 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -256,6 +256,7 @@
Op.CheckConstCast();
if (Op.SrcExpr.isInvalid())
return ExprError();
+ DiscardMisalignedMemberAddress(DestType.getTypePtr(), E);
}
return Op.complete(CXXConstCastExpr::Create(Context, Op.ResultType,
Op.ValueKind, Op.SrcExpr.get(), DestTInfo,
@@ -279,6 +280,7 @@
Op.CheckReinterpretCast();
if (Op.SrcExpr.isInvalid())
return ExprError();
+ DiscardMisalignedMemberAddress(DestType.getTypePtr(), E);
}
return Op.complete(CXXReinterpretCastExpr::Create(Context, Op.ResultType,
Op.ValueKind, Op.Kind, Op.SrcExpr.get(),
@@ -291,6 +293,7 @@
Op.CheckStaticCast();
if (Op.SrcExpr.isInvalid())
return ExprError();
+ DiscardMisalignedMemberAddress(DestType.getTypePtr(), E);
}
return Op.complete(CXXStaticCastExpr::Create(Context, Op.ResultType,
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index c1781c2..6edb251 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -8383,6 +8383,8 @@
DiagnoseNullConversion(S, E, T, CC);
+ S.DiscardMisalignedMemberAddress(Target, E);
+
if (!Source->isIntegerType() || !Target->isIntegerType())
return;
@@ -9453,6 +9455,7 @@
CheckUnsequencedOperations(E);
if (!IsConstexpr && !E->isValueDependent())
CheckForIntOverflow(E);
+ DiagnoseMisalignedMembers();
}
void Sema::CheckBitFieldInitialization(SourceLocation InitLoc,
@@ -10998,3 +11001,67 @@
<< ArgumentExpr->getSourceRange()
<< TypeTagExpr->getSourceRange();
}
+
+void Sema::AddPotentialMisalignedMembers(Expr *E, RecordDecl *RD, ValueDecl *MD,
+ CharUnits Alignment) {
+ MisalignedMembers.emplace_back(E, RD, MD, Alignment);
+}
+
+void Sema::DiagnoseMisalignedMembers() {
+ for (MisalignedMember &m : MisalignedMembers) {
+ Diag(m.E->getLocStart(), diag::warn_taking_address_of_packed_member)
+ << m.MD << m.RD << m.E->getSourceRange();
+ }
+ MisalignedMembers.clear();
+}
+
+void Sema::DiscardMisalignedMemberAddress(const Type *T, Expr *E) {
+ if (!T->isPointerType())
+ return;
+ if (isa<UnaryOperator>(E) &&
+ cast<UnaryOperator>(E)->getOpcode() == UO_AddrOf) {
+ auto *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
+ if (isa<MemberExpr>(Op)) {
+ auto MA = std::find(MisalignedMembers.begin(), MisalignedMembers.end(),
+ MisalignedMember(Op));
+ if (MA != MisalignedMembers.end() &&
+ Context.getTypeAlignInChars(T->getPointeeType()) <= MA->Alignment)
+ MisalignedMembers.erase(MA);
+ }
+ }
+}
+
+void Sema::RefersToMemberWithReducedAlignment(
+ Expr *E,
+ std::function<void(Expr *, RecordDecl *, ValueDecl *, CharUnits)> Action) {
+ const auto *ME = dyn_cast<MemberExpr>(E);
+ while (ME && isa<FieldDecl>(ME->getMemberDecl())) {
+ QualType BaseType = ME->getBase()->getType();
+ if (ME->isArrow())
+ BaseType = BaseType->getPointeeType();
+ RecordDecl *RD = BaseType->getAs<RecordType>()->getDecl();
+
+ ValueDecl *MD = ME->getMemberDecl();
+ bool ByteAligned = Context.getTypeAlignInChars(MD->getType()).isOne();
+ if (ByteAligned) // Attribute packed does not have any effect.
+ break;
+
+ if (!ByteAligned &&
+ (RD->hasAttr<PackedAttr>() || (MD->hasAttr<PackedAttr>()))) {
+ CharUnits Alignment = std::min(Context.getTypeAlignInChars(MD->getType()),
+ Context.getTypeAlignInChars(BaseType));
+ // Notify that this expression designates a member with reduced alignment
+ Action(E, RD, MD, Alignment);
+ break;
+ }
+ ME = dyn_cast<MemberExpr>(ME->getBase());
+ }
+}
+
+void Sema::CheckAddressOfPackedMember(Expr *rhs) {
+ using namespace std::placeholders;
+ RefersToMemberWithReducedAlignment(
+ rhs, std::bind(&Sema::AddPotentialMisalignedMembers, std::ref(*this), _1,
+ _2, _3, _4));
+}
+
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 81b57ca..5a437d2 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -6022,7 +6022,9 @@
CheckTollFreeBridgeCast(castType, CastExpr);
CheckObjCBridgeRelatedCast(castType, CastExpr);
-
+
+ DiscardMisalignedMemberAddress(castType.getTypePtr(), CastExpr);
+
return BuildCStyleCastExpr(LParenLoc, castTInfo, RParenLoc, CastExpr);
}
@@ -10614,6 +10616,8 @@
if (op->getType()->isObjCObjectType())
return Context.getObjCObjectPointerType(op->getType());
+ CheckAddressOfPackedMember(op);
+
return Context.getPointerType(op->getType());
}
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 35accac..386c7ab 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -6660,12 +6660,16 @@
getAssignmentAction(Entity), CCK);
if (CurInitExprRes.isInvalid())
return ExprError();
+
+ S.DiscardMisalignedMemberAddress(Step->Type.getTypePtr(), CurInit.get());
+
CurInit = CurInitExprRes;
if (Step->Kind == SK_ConversionSequenceNoNarrowing &&
S.getLangOpts().CPlusPlus && !CurInit.get()->isValueDependent())
DiagnoseNarrowingInInitList(S, *Step->ICS, SourceType, Entity.getType(),
CurInit.get());
+
break;
}