Hi majnemer, rsmith, rnk,
Support MS-ABI's concept of "Required Alignment" imposed by __declspec(align())
This patch implements required alignment in a way that makes
__declspec(align()) and #pragma pack play correctly together. In the MS-ABI,
__declspec(align()) is a hard rule and cannot be overridden by #pragma pack.
This cases each record to have two interesting alignments "preferred alignment"
(which matches Itanium's concept of alignment) and "required alignment" which
is an alignment that must never be violated, even in the case of #pragma pack.
This patch introduces the concept of Required Alignment to the record builder
and tracks/uses it appropriately. Test cases are included.
This patch should address the following bugs:
http://llvm.org/bugs/show_bug.cgi?id=18025
http://llvm.org/bugs/show_bug.cgi?id=18026
http://llvm-reviews.chandlerc.com/D2283
Files:
include/clang/AST/RecordLayout.h
lib/AST/RecordLayout.cpp
lib/AST/RecordLayoutBuilder.cpp
test/Layout/ms-x86-pack-and-align.cpp
Index: include/clang/AST/RecordLayout.h
===================================================================
--- include/clang/AST/RecordLayout.h
+++ include/clang/AST/RecordLayout.h
@@ -82,6 +82,10 @@
/// which is the alignment of the object without virtual bases.
CharUnits NonVirtualAlign;
+ /// RequiredAlignment - The required alignment of the object. In the MS-ABI
+ /// the __declspec(align()) trumps #pramga pack and must always be obeyed.
+ CharUnits RequiredAlignment;
+
/// SizeOfLargestEmptySubobject - The size of the largest empty subobject
/// (either a base or a member). Will be zero if the class doesn't contain
/// any empty subobjects.
@@ -100,10 +104,6 @@
/// a primary base class.
bool HasExtendableVFPtr : 1;
- /// AlignAfterVBases - Force appropriate alignment after virtual bases are
- /// laid out in MS-C++-ABI.
- bool AlignAfterVBases : 1;
-
/// PrimaryBase - The primary base info for this record.
llvm::PointerIntPair<const CXXRecordDecl *, 1, bool> PrimaryBase;
@@ -138,12 +138,12 @@
CharUnits vbptroffset,
CharUnits datasize,
const uint64_t *fieldoffsets, unsigned fieldcount,
+ CharUnits requiredAlignment,
CharUnits nonvirtualsize, CharUnits nonvirtualalign,
CharUnits SizeOfLargestEmptySubobject,
const CXXRecordDecl *PrimaryBase,
bool IsPrimaryBaseVirtual,
const CXXRecordDecl *BaseSharingVBPtr,
- bool ForceAlign,
const BaseOffsetsMapTy& BaseOffsets,
const VBaseOffsetsMapTy& VBaseOffsets);
@@ -267,9 +267,9 @@
return !CXXInfo->VBPtrOffset.isNegative();
}
- bool getAlignAfterVBases() const {
+ CharUnits getRequiredAlignment() const {
assert(CXXInfo && "Record layout does not have C++ specific info!");
- return CXXInfo->AlignAfterVBases;
+ return CXXInfo->RequiredAlignment;
}
/// getVBPtrOffset - Get the offset for virtual base table pointer.
Index: lib/AST/RecordLayout.cpp
===================================================================
--- lib/AST/RecordLayout.cpp
+++ lib/AST/RecordLayout.cpp
@@ -48,13 +48,13 @@
CharUnits datasize,
const uint64_t *fieldoffsets,
unsigned fieldcount,
+ CharUnits requiredAlignment,
CharUnits nonvirtualsize,
CharUnits nonvirtualalign,
CharUnits SizeOfLargestEmptySubobject,
const CXXRecordDecl *PrimaryBase,
bool IsPrimaryBaseVirtual,
const CXXRecordDecl *BaseSharingVBPtr,
- bool AlignAfterVBases,
const BaseOffsetsMapTy& BaseOffsets,
const VBaseOffsetsMapTy& VBaseOffsets)
: Size(size), DataSize(datasize), Alignment(alignment), FieldOffsets(0),
@@ -67,6 +67,7 @@
CXXInfo->PrimaryBase.setPointer(PrimaryBase);
CXXInfo->PrimaryBase.setInt(IsPrimaryBaseVirtual);
+ CXXInfo->RequiredAlignment = requiredAlignment;
CXXInfo->NonVirtualSize = nonvirtualsize;
CXXInfo->NonVirtualAlign = nonvirtualalign;
CXXInfo->SizeOfLargestEmptySubobject = SizeOfLargestEmptySubobject;
@@ -76,7 +77,6 @@
CXXInfo->VBPtrOffset = vbptroffset;
CXXInfo->HasExtendableVFPtr = hasExtendableVFPtr;
CXXInfo->BaseSharingVBPtr = BaseSharingVBPtr;
- CXXInfo->AlignAfterVBases = AlignAfterVBases;
#ifndef NDEBUG
Index: lib/AST/RecordLayoutBuilder.cpp
===================================================================
--- lib/AST/RecordLayoutBuilder.cpp
+++ lib/AST/RecordLayoutBuilder.cpp
@@ -2064,6 +2064,7 @@
void updateAlignment(CharUnits NewAlignment) {
Alignment = std::max(Alignment, NewAlignment);
}
+ CharUnits getBaseAlignment(const ASTRecordLayout& Layout);
/// \brief Gets the size and alignment taking attributes into account.
std::pair<CharUnits, CharUnits> getAdjustedFieldInfo(const FieldDecl *FD);
/// \brief Places a field at offset 0.
@@ -2089,9 +2090,9 @@
SmallVector<uint64_t, 16> FieldOffsets;
/// \brief The maximum allowed field alignment. This is set by #pragma pack.
CharUnits MaxFieldAlignment;
- /// \brief Alignment does not occur for virtual bases unless something
- /// forces it to by explicitly using __declspec(align())
- bool AlignAfterVBases : 1;
+ /// \brief The alignment that this record must obey. This is imposed by
+ /// __declspec(align()) on the record itself or one of its fields or bases.
+ CharUnits RequiredAlignment;
bool IsUnion : 1;
/// \brief True if the last field laid out was a bitfield and was not 0
/// width.
@@ -2148,6 +2149,16 @@
};
} // namespace
+CharUnits
+MicrosoftRecordLayoutBuilder::getBaseAlignment(const ASTRecordLayout& Layout) {
+ CharUnits BaseAlignment = Layout.getAlignment();
+ if (!MaxFieldAlignment.isZero())
+ BaseAlignment = std::min(BaseAlignment,
+ std::max(MaxFieldAlignment,
+ Layout.getRequiredAlignment()));
+ return BaseAlignment;
+}
+
std::pair<CharUnits, CharUnits>
MicrosoftRecordLayoutBuilder::getAdjustedFieldInfo(const FieldDecl *FD) {
std::pair<CharUnits, CharUnits> FieldInfo =
@@ -2174,9 +2185,18 @@
// Respect alignment attributes.
if (unsigned fieldAlign = FD->getMaxAlignment()) {
CharUnits FieldAlign = Context.toCharUnitsFromBits(fieldAlign);
- AlignAfterVBases = true;
+ RequiredAlignment = std::max(RequiredAlignment, FieldAlign);
FieldInfo.second = std::max(FieldInfo.second, FieldAlign);
}
+ // Respect attributes applied inside field base types.
+ if (const RecordType *RT =
+ FD->getType()->getBaseElementTypeUnsafe()->getAs<RecordType>()) {
+ const ASTRecordLayout &Layout = Context.getASTRecordLayout(RT->getDecl());
+ RequiredAlignment = std::max(RequiredAlignment,
+ Layout.getRequiredAlignment());
+ FieldInfo.second = std::max(FieldInfo.second,
+ Layout.getRequiredAlignment());
+ }
return FieldInfo;
}
@@ -2186,7 +2206,10 @@
Size = CharUnits::Zero();
Alignment = CharUnits::One();
- AlignAfterVBases = false;
+ // In 64-bit mode we always perform an alignment step after laying out vbases.
+ // In 32-bit mode we do not. The check to see if we need to perform alignment
+ // checks the RequiredAlignment field and performs alignment if it isn't 0.
+ RequiredAlignment = Is64BitMode ? CharUnits::One() : CharUnits::Zero();
// Compute the maximum field alignment.
MaxFieldAlignment = CharUnits::Zero();
@@ -2236,7 +2259,6 @@
SharedVBPtrBase = 0;
PrimaryBase = 0;
VirtualAlignment = CharUnits::One();
- AlignAfterVBases = Is64BitMode;
// If the record has a dynamic base class, attempt to choose a primary base
// class. It is the first (in direct base class order) non-virtual dynamic
@@ -2247,12 +2269,12 @@
const CXXRecordDecl *BaseDecl =
cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
const ASTRecordLayout &Layout = Context.getASTRecordLayout(BaseDecl);
- // Handle forced alignment.
- if (Layout.getAlignAfterVBases())
- AlignAfterVBases = true;
+ // Handle required alignment.
+ RequiredAlignment = std::max(RequiredAlignment,
+ Layout.getRequiredAlignment());
// Handle virtual bases.
if (i->isVirtual()) {
- VirtualAlignment = std::max(VirtualAlignment, Layout.getAlignment());
+ VirtualAlignment = std::max(VirtualAlignment, getBaseAlignment(Layout));
HasVBPtr = true;
continue;
}
@@ -2266,7 +2288,7 @@
SharedVBPtrBase = BaseDecl;
HasVBPtr = true;
}
- updateAlignment(Layout.getAlignment());
+ updateAlignment(getBaseAlignment(Layout));
}
// Use LayoutFields to compute the alignment of the fields. The layout
@@ -2335,7 +2357,7 @@
if (LazyEmptyBase) {
const ASTRecordLayout &LazyLayout =
Context.getASTRecordLayout(LazyEmptyBase);
- Size = Size.RoundUpToAlignment(LazyLayout.getAlignment());
+ Size = Size.RoundUpToAlignment(getBaseAlignment(LazyLayout));
// If the last non-virtual base has a vbptr we add a byte of padding for no
// obvious reason.
if (LastNonVirtualBaseHasVBPtr)
@@ -2360,7 +2382,7 @@
}
// Insert the base here.
- CharUnits BaseOffset = Size.RoundUpToAlignment(Layout->getAlignment());
+ CharUnits BaseOffset = Size.RoundUpToAlignment(getBaseAlignment(*Layout));
Bases.insert(std::make_pair(RD, BaseOffset));
Size = BaseOffset + Layout->getDataSize();
// Note: we don't update alignment here because it was accounted
@@ -2536,7 +2558,7 @@
if (LazyEmptyBase) {
const ASTRecordLayout &LazyLayout =
Context.getASTRecordLayout(LazyEmptyBase);
- Size = Size.RoundUpToAlignment(LazyLayout.getAlignment());
+ Size = Size.RoundUpToAlignment(getBaseAlignment(LazyLayout));
VBases.insert(
std::make_pair(LazyEmptyBase, ASTRecordLayout::VBaseInfo(Size, false)));
// Empty bases only consume space when followed by another empty base.
@@ -2560,7 +2582,7 @@
}
CharUnits BaseNVSize = Layout.getNonVirtualSize();
- CharUnits BaseAlign = Layout.getAlignment();
+ CharUnits BaseAlign = getBaseAlignment(Layout);
// vtordisps are always 4 bytes (even in 64-bit mode)
if (HasVtordisp)
@@ -2580,7 +2602,7 @@
// Flush the lazy virtual base.
layoutVirtualBase(0, false);
- if (RD->vbases_begin() == RD->vbases_end() || AlignAfterVBases)
+ if (RD->vbases_begin() == RD->vbases_end() || !RequiredAlignment.isZero())
Size = Size.RoundUpToAlignment(Alignment);
if (Size.isZero())
@@ -2588,9 +2610,10 @@
}
void MicrosoftRecordLayoutBuilder::honorDeclspecAlign(const RecordDecl *RD) {
- if (unsigned MaxAlign = RD->getMaxAlignment()) {
- AlignAfterVBases = true;
- updateAlignment(Context.toCharUnitsFromBits(MaxAlign));
+ RequiredAlignment = std::max(RequiredAlignment,
+ Context.toCharUnitsFromBits(RD->getMaxAlignment()));
+ if (!RequiredAlignment.isZero()) {
+ updateAlignment(RequiredAlignment);
Size = Size.RoundUpToAlignment(Alignment);
}
}
@@ -2688,9 +2711,9 @@
Builder.HasExtendableVFPtr && !Builder.PrimaryBase,
Builder.HasExtendableVFPtr,
Builder.VBPtrOffset, Builder.DataSize, Builder.FieldOffsets.data(),
- Builder.FieldOffsets.size(), Builder.DataSize,
+ Builder.FieldOffsets.size(),Builder.RequiredAlignment, Builder.DataSize,
Builder.NonVirtualAlignment, CharUnits::Zero(), Builder.PrimaryBase,
- false, Builder.SharedVBPtrBase, Builder.AlignAfterVBases, Builder.Bases,
+ false, Builder.SharedVBPtrBase, Builder.Bases,
Builder.VBases);
} else {
Builder.layout(D);
@@ -2753,12 +2776,14 @@
DataSize,
Builder.FieldOffsets.data(),
Builder.FieldOffsets.size(),
+ /*RequiredAlignment *used by MS-ABI)*/
+ CharUnits::Zero(),
NonVirtualSize,
Builder.NonVirtualAlignment,
EmptySubobjects.SizeOfLargestEmptySubobject,
Builder.PrimaryBase,
Builder.PrimaryBaseIsVirtual,
- 0, true,
+ 0,
Builder.Bases, Builder.VBases);
} else {
RecordLayoutBuilder Builder(*this, /*EmptySubobjects=*/0);
Index: test/Layout/ms-x86-pack-and-align.cpp
===================================================================
--- test/Layout/ms-x86-pack-and-align.cpp
+++ test/Layout/ms-x86-pack-and-align.cpp
@@ -0,0 +1,120 @@
+// RUN: %clang_cc1 -fno-rtti -emit-llvm-only -triple i686-pc-win32 -fdump-record-layouts -fsyntax-only -cxx-abi microsoft %s 2>&1 \
+// RUN: | FileCheck %s
+// RUN: %clang_cc1 -fno-rtti -emit-llvm-only -triple x86_64-pc-win32 -fdump-record-layouts -fsyntax-only -cxx-abi microsoft %s 2>/dev/null \
+// RUN: | FileCheck %s -check-prefix CHECK-X64
+
+extern "C" int printf(const char *fmt, ...);
+char buffer[419430400];
+
+struct A {
+ char a;
+ A() {
+ printf("A = %d\n", (int)((char*)this - buffer));
+ printf("A.a = %d\n", (int)((char*)&a - buffer));
+ }
+};
+
+struct B {
+ __declspec(align(4)) long long a;
+ B() {
+ printf("B = %d\n", (int)((char*)this - buffer));
+ printf("B.a = %d\n", (int)((char*)&a - buffer));
+ }
+};
+
+#pragma pack(push, 2)
+struct X {
+ B a;
+ char b;
+ int c;
+ X() {
+ printf("X = %d\n", (int)((char*)this - buffer));
+ printf("X.a = %d\n", (int)((char*)&a - buffer));
+ printf("X.b = %d\n", (int)((char*)&b - buffer));
+ printf("X.c = %d\n", (int)((char*)&c - buffer));
+ }
+};
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: 0 | struct X
+// CHECK: 0 | struct B a
+// CHECK: 0 | long long a
+// CHECK: 8 | char b
+// CHECK: 10 | int c
+// CHECK: | [sizeof=16, align=4
+// CHECK: | nvsize=16, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64: 0 | struct X
+// CHECK-X64: 0 | struct B a
+// CHECK-X64: 0 | long long a
+// CHECK-X64: 8 | char b
+// CHECK-X64: 10 | int c
+// CHECK-X64: | [sizeof=16, align=4
+// CHECK-X64: | nvsize=16, nvalign=4]
+
+struct Y : A, B {
+ char a;
+ int b;
+ Y() {
+ printf("Y = %d\n", (int)((char*)this - buffer));
+ printf("Y.a = %d\n", (int)((char*)&a - buffer));
+ printf("Y.b = %d\n", (int)((char*)&b - buffer));
+ }
+};
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: 0 | struct Y
+// CHECK: 0 | struct A (base)
+// CHECK: 0 | char a
+// CHECK: 4 | struct B (base)
+// CHECK: 4 | long long a
+// CHECK: 12 | char a
+// CHECK: 14 | int b
+// CHECK: | [sizeof=20, align=4
+// CHECK: | nvsize=20, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64: 0 | struct Y
+// CHECK-X64: 0 | struct A (base)
+// CHECK-X64: 0 | char a
+// CHECK-X64: 4 | struct B (base)
+// CHECK-X64: 4 | long long a
+// CHECK-X64: 12 | char a
+// CHECK-X64: 14 | int b
+// CHECK-X64: | [sizeof=20, align=4
+// CHECK-X64: | nvsize=20, nvalign=4]
+
+struct Z : virtual B {
+ char a;
+ int b;
+ Z() {
+ printf("Z = %d\n", (int)((char*)this - buffer));
+ printf("Z.a = %d\n", (int)((char*)&a - buffer));
+ printf("Z.b = %d\n", (int)((char*)&b - buffer));
+ }
+};
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: 0 | struct Z
+// CHECK: 0 | (Z vbtable pointer)
+// CHECK: 4 | char a
+// CHECK: 6 | int b
+// CHECK: 12 | struct B (virtual base)
+// CHECK: 12 | long long a
+// CHECK: | [sizeof=20, align=4
+// CHECK: | nvsize=10, nvalign=2]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64: 0 | struct Z
+// CHECK-X64: 0 | (Z vbtable pointer)
+// CHECK-X64: 8 | char a
+// CHECK-X64: 10 | int b
+// CHECK-X64: 16 | struct B (virtual base)
+// CHECK-X64: 16 | long long a
+// CHECK-X64: | [sizeof=24, align=4
+// CHECK-X64: | nvsize=14, nvalign=2]
+
+#pragma pack(pop)
+
+int a[
+sizeof(X)+
+sizeof(Y)+
+sizeof(Z)];
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