Index: cfe/trunk/docs/ReleaseNotes.rst =================================================================== --- cfe/trunk/docs/ReleaseNotes.rst +++ cfe/trunk/docs/ReleaseNotes.rst @@ -78,6 +78,12 @@ standard-layout if all base classes and the first data member (or bit-field) can be laid out at offset zero. +- Clang's handling of the GCC ``packed`` class attribute in C++ has been fixed + to apply only to non-static data members and not to base classes. This fixes + an ABI difference between Clang and GCC, but creates an ABI difference between + Clang 7 and earlier versions. The old behavior can be restored by setting + ``-fclang-abi-compat`` to ``6`` or earlier. + - ... New Compiler Flags Index: cfe/trunk/lib/AST/RecordLayoutBuilder.cpp =================================================================== --- cfe/trunk/lib/AST/RecordLayoutBuilder.cpp +++ cfe/trunk/lib/AST/RecordLayoutBuilder.cpp @@ -967,7 +967,7 @@ void ItaniumRecordLayoutBuilder::EnsureVTablePointerAlignment( CharUnits UnpackedBaseAlign) { - CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign; + CharUnits BaseAlign = Packed ? CharUnits::One() : UnpackedBaseAlign; // The maximum field alignment overrides base align. if (!MaxFieldAlignment.isZero()) { @@ -1175,9 +1175,14 @@ HasExternalLayout = External.getExternalVBaseOffset(Base->Class, Offset); } + // Clang <= 6 incorrectly applied the 'packed' attribute to base classes. + // Per GCC's documentation, it only applies to non-static data members. CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlignment(); - CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign; - + CharUnits BaseAlign = (Packed && Context.getLangOpts().getClangABICompat() <= + LangOptions::ClangABI::Ver6) + ? CharUnits::One() + : UnpackedBaseAlign; + // If we have an empty base class, try to place it at offset 0. if (Base->Class->isEmpty() && (!HasExternalLayout || Offset == CharUnits::Zero()) && Index: cfe/trunk/test/CodeGenCXX/alignment.cpp =================================================================== --- cfe/trunk/test/CodeGenCXX/alignment.cpp +++ cfe/trunk/test/CodeGenCXX/alignment.cpp @@ -1,4 +1,5 @@ -// RUN: %clang_cc1 %s -emit-llvm -o - -triple=x86_64-apple-darwin10 | FileCheck %s +// RUN: %clang_cc1 %s -emit-llvm -o - -triple=x86_64-apple-darwin10 | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-NOCOMPAT +// RUN: %clang_cc1 %s -emit-llvm -o - -triple=x86_64-apple-darwin10 -fclang-abi-compat=6.0 | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-V6COMPAT extern int int_source(); extern void int_sink(int x); @@ -54,11 +55,13 @@ // CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B]]* // CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8* // CHECK: [[TRUNC:%.*]] = trunc i32 [[CALL]] to i8 - // CHECK: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-V6COMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-NOCOMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4 // CHECK: [[T0:%.*]] = and i8 [[TRUNC]], 3 // CHECK: [[T1:%.*]] = and i8 [[OLD_VALUE]], -4 // CHECK: [[T2:%.*]] = or i8 [[T1]], [[T0]] - // CHECK: store i8 [[T2]], i8* [[FIELD_P]], align 2 + // CHECK-V6COMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 2 + // CHECK-NOCOMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 4 c.onebit = int_source(); // CHECK: [[C_P:%.*]] = load [[C]]*, [[C]]** @@ -66,7 +69,8 @@ // CHECK: [[T1:%.*]] = getelementptr inbounds i8, i8* [[T0]], i64 8 // CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B]]* // CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8* - // CHECK: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-V6COMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-NOCOMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4 // CHECK: [[T0:%.*]] = shl i8 [[VALUE]], 6 // CHECK: [[T1:%.*]] = ashr i8 [[T0]], 6 // CHECK: [[T2:%.*]] = sext i8 [[T1]] to i32 @@ -83,11 +87,13 @@ // CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B]]* // CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8* // CHECK: [[TRUNC:%.*]] = trunc i32 [[CALL]] to i8 - // CHECK: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-V6COMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-NOCOMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4 // CHECK: [[T0:%.*]] = and i8 [[TRUNC]], 3 // CHECK: [[T1:%.*]] = and i8 [[OLD_VALUE]], -4 // CHECK: [[T2:%.*]] = or i8 [[T1]], [[T0]] - // CHECK: store i8 [[T2]], i8* [[FIELD_P]], align 2 + // CHECK-V6COMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 2 + // CHECK-NOCOMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 4 c->onebit = int_source(); // CHECK: [[C_P:%.*]] = load [[C:%.*]]*, [[C]]** @@ -95,7 +101,8 @@ // CHECK: [[T1:%.*]] = getelementptr inbounds i8, i8* [[T0]], i64 8 // CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B:%.*]]* // CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8* - // CHECK: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-V6COMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-NOCOMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4 // CHECK: [[T0:%.*]] = shl i8 [[VALUE]], 6 // CHECK: [[T1:%.*]] = ashr i8 [[T0]], 6 // CHECK: [[T2:%.*]] = sext i8 [[T1]] to i32 @@ -107,7 +114,8 @@ // in an alignment-2 variable. // CHECK-LABEL: @_ZN5test01dEv void d() { - // CHECK: [[C_P:%.*]] = alloca [[C:%.*]], align 2 + // CHECK-V6COMPAT: [[C_P:%.*]] = alloca [[C:%.*]], align 2 + // CHECK-NOCOMPAT: [[C_P:%.*]] = alloca [[C:%.*]], align 4 C c; // CHECK: [[CALL:%.*]] = call i32 @_Z10int_sourcev() @@ -116,18 +124,21 @@ // CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B]]* // CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8* // CHECK: [[TRUNC:%.*]] = trunc i32 [[CALL]] to i8 - // CHECK: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-V6COMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-NOCOMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4 // CHECK: [[T0:%.*]] = and i8 [[TRUNC]], 3 // CHECK: [[T1:%.*]] = and i8 [[OLD_VALUE]], -4 // CHECK: [[T2:%.*]] = or i8 [[T1]], [[T0]] - // CHECK: store i8 [[T2]], i8* [[FIELD_P]], align 2 + // CHECK-V6COMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 2 + // CHECK-NOCOMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 4 c.onebit = int_source(); // CHECK: [[T0:%.*]] = bitcast [[C]]* [[C_P]] to i8* // CHECK: [[T1:%.*]] = getelementptr inbounds i8, i8* [[T0]], i64 8 // CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B:%.*]]* // CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8* - // CHECK: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-V6COMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2 + // CHECK-NOCOMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4 // CHECK: [[T0:%.*]] = shl i8 [[VALUE]], 6 // CHECK: [[T1:%.*]] = ashr i8 [[T0]], 6 // CHECK: [[T2:%.*]] = sext i8 [[T1]] to i32 Index: cfe/trunk/test/SemaCXX/class-layout.cpp =================================================================== --- cfe/trunk/test/SemaCXX/class-layout.cpp +++ cfe/trunk/test/SemaCXX/class-layout.cpp @@ -1,5 +1,6 @@ // RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++98 -Wno-inaccessible-base // RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base +// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=6 -DCLANG_ABI_COMPAT=6 // expected-no-diagnostics #define SA(n, p) int a##n[(p) ? 1 : -1] @@ -570,3 +571,36 @@ SA(0, sizeof(might_use_tail_padding) == 80); } } // namespace PR16537 + +namespace PR37275 { + struct X { char c; }; + + struct A { int n; }; + _Static_assert(_Alignof(A) == _Alignof(int), ""); + + // __attribute__((packed)) does not apply to base classes. + struct __attribute__((packed)) B : X, A {}; +#if defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 6 + _Static_assert(_Alignof(B) == 1, ""); + _Static_assert(__builtin_offsetof(B, n) == 1, ""); +#else + _Static_assert(_Alignof(B) == _Alignof(int), ""); + _Static_assert(__builtin_offsetof(B, n) == 4, ""); +#endif + + // #pragma pack does, though. +#pragma pack(push, 2) + struct C : X, A {}; + _Static_assert(_Alignof(C) == 2, ""); + _Static_assert(__builtin_offsetof(C, n) == 2, ""); + + struct __attribute__((packed)) D : X, A {}; +#if defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 6 + _Static_assert(_Alignof(D) == 1, ""); + _Static_assert(__builtin_offsetof(D, n) == 1, ""); +#else + _Static_assert(_Alignof(D) == 2, ""); + _Static_assert(__builtin_offsetof(D, n) == 2, ""); +#endif +#pragma pack(pop) +}