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GCC ABI Compatibility: Preserve alignment of non-pod members in packed structs
This matches GCC: https://godbolt.org/z/sM5q95PGY I realize this is an API break for clang+clang - so I'm totally open to discussing how we should deal with that. If Apple wants to keep the Clang layout indefinitely, if we want to put a flag on this so non-Apple folks can opt out of this fix/new behavior. Differential Revision: https://reviews.llvm.org/D117616
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@ -236,6 +236,12 @@ ABI Changes in Clang
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is still in the process of being stabilized, so this type should not yet be
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used in interfaces that require ABI stability.
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- GCC doesn't pack non-POD members in packed structs unless the packed
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attribute is also specified on the member. Clang historically did perform
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such packing. Clang now matches the gcc behavior (except on Darwin and PS4).
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You can switch back to the old ABI behavior with the flag:
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``-fclang-abi-compat=13.0``.
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OpenMP Support in Clang
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-----------------------
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@ -181,6 +181,10 @@ public:
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/// global-scope inline variables incorrectly.
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Ver12,
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/// Attempt to be ABI-compatible with code generated by Clang 13.0.x.
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/// This causes clang to not pack non-POD members of packed structs.
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Ver13,
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/// Conform to the underlying platform's C and C++ ABIs as closely
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/// as we can.
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Latest
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@ -1887,7 +1887,12 @@ void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
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UnfilledBitsInLastUnit = 0;
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LastBitfieldStorageUnitSize = 0;
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bool FieldPacked = Packed || D->hasAttr<PackedAttr>();
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llvm::Triple Target = Context.getTargetInfo().getTriple();
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bool FieldPacked = (Packed && (!FieldClass || FieldClass->isPOD() ||
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Context.getLangOpts().getClangABICompat() <=
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LangOptions::ClangABI::Ver13 ||
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Target.isPS4() || Target.isOSDarwin())) ||
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D->hasAttr<PackedAttr>();
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AlignRequirementKind AlignRequirement = AlignRequirementKind::None;
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CharUnits FieldSize;
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@ -3560,6 +3560,8 @@ void CompilerInvocation::GenerateLangArgs(const LangOptions &Opts,
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GenerateArg(Args, OPT_fclang_abi_compat_EQ, "11.0", SA);
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else if (Opts.getClangABICompat() == LangOptions::ClangABI::Ver12)
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GenerateArg(Args, OPT_fclang_abi_compat_EQ, "12.0", SA);
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else if (Opts.getClangABICompat() == LangOptions::ClangABI::Ver13)
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GenerateArg(Args, OPT_fclang_abi_compat_EQ, "13.0", SA);
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if (Opts.getSignReturnAddressScope() ==
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LangOptions::SignReturnAddressScopeKind::All)
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@ -4062,6 +4064,8 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
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Opts.setClangABICompat(LangOptions::ClangABI::Ver11);
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else if (Major <= 12)
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Opts.setClangABICompat(LangOptions::ClangABI::Ver12);
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else if (Major <= 13)
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Opts.setClangABICompat(LangOptions::ClangABI::Ver13);
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} else if (Ver != "latest") {
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Diags.Report(diag::err_drv_invalid_value)
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<< A->getAsString(Args) << A->getValue();
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@ -1,6 +1,9 @@
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// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++98 -Wno-inaccessible-base
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// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base
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// RUN: %clang_cc1 -triple x86_64-apple-darwin %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -DCLANG_ABI_COMPAT=13
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// RUN: %clang_cc1 -triple x86_64-scei-ps4 %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -DCLANG_ABI_COMPAT=6
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// 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
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// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=13 -DCLANG_ABI_COMPAT=13
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// expected-no-diagnostics
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#define SA(n, p) int a##n[(p) ? 1 : -1]
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@ -604,3 +607,37 @@ namespace PR37275 {
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#endif
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#pragma pack(pop)
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}
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namespace non_pod {
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struct t1 {
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protected:
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int a;
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};
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// GCC prints warning: ignoring packed attribute because of unpacked non-POD field 't1 t2::v1'`
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struct t2 {
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char c1;
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short s1;
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char c2;
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t1 v1;
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} __attribute__((packed));
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#if defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 13
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_Static_assert(_Alignof(t1) == 4, "");
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_Static_assert(_Alignof(t2) == 1, "");
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#else
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_Static_assert(_Alignof(t1) == 4, "");
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_Static_assert(_Alignof(t2) == 4, "");
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#endif
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_Static_assert(sizeof(t2) == 8, ""); // it's still packing the rest of the struct
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} // namespace non_pod
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namespace non_pod_packed {
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struct t1 {
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protected:
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int a;
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} __attribute__((packed));
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struct t2 {
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t1 v1;
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} __attribute__((packed));
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_Static_assert(_Alignof(t1) == 1, "");
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_Static_assert(_Alignof(t2) == 1, "");
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} // namespace non_pod_packed
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