[PATCH] MS ABI: vptr injection should obey alignment requirements
David Majnemer
david.majnemer at gmail.com
Sun Feb 2 17:29:14 PST 2014
Hi whunt, rnk, rsmith,
vptr injection must inject padding equivalent to the alignment of the
most aligned non-virtual subobject, not the alignment of the enclosing
record.
To fascilitate this change, don't let record layout observe the
alignment of the record until we've injected our vptrs. Also, do not
allow the alignment of vbases to affect required alignment until just
before we insert the vtordisp field.
http://llvm-reviews.chandlerc.com/D2674
Files:
lib/AST/RecordLayoutBuilder.cpp
test/Layout/ms-x86-pack-and-align.cpp
Index: lib/AST/RecordLayoutBuilder.cpp
===================================================================
--- lib/AST/RecordLayoutBuilder.cpp
+++ lib/AST/RecordLayoutBuilder.cpp
@@ -2277,6 +2277,8 @@
initializeLayout(RD);
layoutFields(RD);
DataSize = Size = Size.RoundUpToAlignment(Alignment);
+ RequiredAlignment = std::max(
+ RequiredAlignment, Context.toCharUnitsFromBits(RD->getMaxAlignment()));
finalizeLayout(RD);
}
@@ -2287,6 +2289,8 @@
layoutFields(RD);
injectVPtrs(RD);
DataSize = Size = Size.RoundUpToAlignment(Alignment);
+ RequiredAlignment = std::max(
+ RequiredAlignment, Context.toCharUnitsFromBits(RD->getMaxAlignment()));
layoutVirtualBases(RD);
finalizeLayout(RD);
}
@@ -2300,8 +2304,6 @@
// 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();
- RequiredAlignment = std::max(RequiredAlignment,
- Context.toCharUnitsFromBits(RD->getMaxAlignment()));
// Compute the maximum field alignment.
MaxFieldAlignment = CharUnits::Zero();
// Honor the default struct packing maximum alignment flag.
@@ -2352,14 +2354,14 @@
i != e; ++i) {
const CXXRecordDecl *BaseDecl = i->getType()->getAsCXXRecordDecl();
const ASTRecordLayout &BaseLayout = Context.getASTRecordLayout(BaseDecl);
- // Track RequiredAlignment for all bases in this pass.
- RequiredAlignment = std::max(RequiredAlignment,
- BaseLayout.getRequiredAlignment());
// Mark and skip virtual bases.
if (i->isVirtual()) {
HasVBPtr = true;
continue;
}
+ // Track RequiredAlignment for all bases in this pass.
+ RequiredAlignment = std::max(RequiredAlignment,
+ BaseLayout.getRequiredAlignment());
// Check fo a base to share a VBPtr with.
if (!SharedVBPtrBase && BaseLayout.hasVBPtr()) {
SharedVBPtrBase = BaseDecl;
@@ -2525,7 +2527,8 @@
CharUnits FieldStart = VBPtrOffset + PointerInfo.Size;
// Make sure that the amount we push the fields back by is a multiple of the
// alignment.
- CharUnits Offset = (FieldStart - InjectionSite).RoundUpToAlignment(Alignment);
+ CharUnits Offset = (FieldStart - InjectionSite).RoundUpToAlignment(
+ std::max(RequiredAlignment, Alignment));
// Increase the size of the object and push back all fields by the offset
// amount.
Size += Offset;
@@ -2547,11 +2550,12 @@
return;
// Make sure that the amount we push the struct back by is a multiple of the
// alignment.
- CharUnits Offset = PointerInfo.Size.RoundUpToAlignment(Alignment);
+ CharUnits Offset = PointerInfo.Size.RoundUpToAlignment(
+ std::max(RequiredAlignment, Alignment));
// Increase the size of the object and push back all fields, the vbptr and all
// bases by the offset amount.
Size += Offset;
- for (SmallVector<uint64_t, 16>::iterator i = FieldOffsets.begin(),
+ for (SmallVectorImpl<uint64_t>::iterator i = FieldOffsets.begin(),
e = FieldOffsets.end();
i != e; ++i)
*i += Context.toBits(Offset);
@@ -2646,6 +2650,14 @@
// The alignment of the vtordisp is at least the required alignment of the
// entire record. This requirement may be present to support vtordisp
// injection.
+ for (CXXRecordDecl::base_class_const_iterator i = RD->vbases_begin(),
+ e = RD->vbases_end();
+ i != e; ++i) {
+ const CXXRecordDecl *BaseDecl = i->getType()->getAsCXXRecordDecl();
+ const ASTRecordLayout &BaseLayout = Context.getASTRecordLayout(BaseDecl);
+ RequiredAlignment =
+ std::max(RequiredAlignment, BaseLayout.getRequiredAlignment());
+ }
VtorDispAlignment = std::max(VtorDispAlignment, RequiredAlignment);
// Compute the vtordisp set.
llvm::SmallPtrSet<const CXXRecordDecl *, 2> HasVtordispSet =
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
@@ -371,6 +371,49 @@
// CHECK-X64-NEXT: | [sizeof=4, align=2
// CHECK-X64-NEXT: | nvsize=3, nvalign=2]
+#pragma pack(1)
+struct L {
+ virtual void fun() {}
+ __declspec(align(256)) int Field;
+};
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT: 0 | struct L
+// CHECK-NEXT: 0 | (L vftable pointer)
+// CHECK-NEXT: 256 | int Field
+// CHECK-NEXT: | [sizeof=512, align=256
+// CHECK-NEXT: | nvsize=260, nvalign=256]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64-NEXT: 0 | struct L
+// CHECK-X64-NEXT: 0 | (L vftable pointer)
+// CHECK-X64-NEXT: 256 | int Field
+// CHECK-X64-NEXT: | [sizeof=512, align=256
+// CHECK-X64-NEXT: | nvsize=260, nvalign=256]
+
+#pragma pack()
+struct MA {};
+#pragma pack(1)
+struct MB : virtual MA {
+ __declspec(align(256)) int Field;
+};
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT: 0 | struct MB
+// CHECK-NEXT: 0 | (MB vbtable pointer)
+// CHECK-NEXT: 256 | int Field
+// CHECK-NEXT: 260 | struct MA (virtual base) (empty)
+// CHECK-NEXT: | [sizeof=512, align=256
+// CHECK-NEXT: | nvsize=260, nvalign=256]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64-NEXT: 0 | struct MB
+// CHECK-X64-NEXT: 0 | (MB vbtable pointer)
+// CHECK-X64-NEXT: 256 | int Field
+// CHECK-X64-NEXT: 260 | struct MA (virtual base) (empty)
+// CHECK-X64-NEXT: | [sizeof=512, align=256
+// CHECK-X64-NEXT: | nvsize=260, nvalign=256]
+
int a[
sizeof(X)+
sizeof(Y)+
@@ -387,4 +430,6 @@
sizeof(D2)+
sizeof(JC)+
sizeof(KB)+
+sizeof(L)+
+sizeof(MB)+
0];
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