1 //===-------------------- InterpBuiltinBitCast.cpp --------------*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 #include "InterpBuiltinBitCast.h" 9 #include "BitcastBuffer.h" 10 #include "Boolean.h" 11 #include "Context.h" 12 #include "Floating.h" 13 #include "Integral.h" 14 #include "InterpState.h" 15 #include "MemberPointer.h" 16 #include "Pointer.h" 17 #include "Record.h" 18 #include "clang/AST/ASTContext.h" 19 #include "clang/AST/RecordLayout.h" 20 #include "clang/Basic/TargetInfo.h" 21 22 using namespace clang; 23 using namespace clang::interp; 24 25 /// Implement __builtin_bit_cast and related operations. 26 /// Since our internal representation for data is more complex than 27 /// something we can simply memcpy or memcmp, we first bitcast all the data 28 /// into a buffer, which we then later use to copy the data into the target. 29 30 // TODO: 31 // - Try to minimize heap allocations. 32 // - Optimize the common case of only pushing and pulling full 33 // bytes to/from the buffer. 34 35 /// Used to iterate over pointer fields. 36 using DataFunc = llvm::function_ref<bool(const Pointer &P, PrimType Ty, 37 Bits BitOffset, bool PackedBools)>; 38 39 #define BITCAST_TYPE_SWITCH(Expr, B) \ 40 do { \ 41 switch (Expr) { \ 42 TYPE_SWITCH_CASE(PT_Sint8, B) \ 43 TYPE_SWITCH_CASE(PT_Uint8, B) \ 44 TYPE_SWITCH_CASE(PT_Sint16, B) \ 45 TYPE_SWITCH_CASE(PT_Uint16, B) \ 46 TYPE_SWITCH_CASE(PT_Sint32, B) \ 47 TYPE_SWITCH_CASE(PT_Uint32, B) \ 48 TYPE_SWITCH_CASE(PT_Sint64, B) \ 49 TYPE_SWITCH_CASE(PT_Uint64, B) \ 50 TYPE_SWITCH_CASE(PT_IntAP, B) \ 51 TYPE_SWITCH_CASE(PT_IntAPS, B) \ 52 TYPE_SWITCH_CASE(PT_Bool, B) \ 53 default: \ 54 llvm_unreachable("Unhandled bitcast type"); \ 55 } \ 56 } while (0) 57 58 #define BITCAST_TYPE_SWITCH_FIXED_SIZE(Expr, B) \ 59 do { \ 60 switch (Expr) { \ 61 TYPE_SWITCH_CASE(PT_Sint8, B) \ 62 TYPE_SWITCH_CASE(PT_Uint8, B) \ 63 TYPE_SWITCH_CASE(PT_Sint16, B) \ 64 TYPE_SWITCH_CASE(PT_Uint16, B) \ 65 TYPE_SWITCH_CASE(PT_Sint32, B) \ 66 TYPE_SWITCH_CASE(PT_Uint32, B) \ 67 TYPE_SWITCH_CASE(PT_Sint64, B) \ 68 TYPE_SWITCH_CASE(PT_Uint64, B) \ 69 TYPE_SWITCH_CASE(PT_Bool, B) \ 70 default: \ 71 llvm_unreachable("Unhandled bitcast type"); \ 72 } \ 73 } while (0) 74 75 static void swapBytes(std::byte *M, size_t N) { 76 for (size_t I = 0; I != (N / 2); ++I) 77 std::swap(M[I], M[N - 1 - I]); 78 } 79 80 /// We use this to recursively iterate over all fields and elements of a pointer 81 /// and extract relevant data for a bitcast. 82 static bool enumerateData(const Pointer &P, const Context &Ctx, Bits Offset, 83 Bits BitsToRead, DataFunc F) { 84 const Descriptor *FieldDesc = P.getFieldDesc(); 85 assert(FieldDesc); 86 87 // Primitives. 88 if (FieldDesc->isPrimitive()) 89 return F(P, FieldDesc->getPrimType(), Offset, /*PackedBools=*/false); 90 91 // Primitive arrays. 92 if (FieldDesc->isPrimitiveArray()) { 93 QualType ElemType = FieldDesc->getElemQualType(); 94 size_t ElemSizeInBits = Ctx.getASTContext().getTypeSize(ElemType); 95 PrimType ElemT = *Ctx.classify(ElemType); 96 // Special case, since the bools here are packed. 97 bool PackedBools = FieldDesc->getType()->isExtVectorBoolType(); 98 unsigned NumElems = FieldDesc->getNumElems(); 99 bool Ok = true; 100 for (unsigned I = P.getIndex(); I != NumElems; ++I) { 101 Ok = Ok && F(P.atIndex(I), ElemT, Offset, PackedBools); 102 Offset += PackedBools ? 1 : ElemSizeInBits; 103 if (Offset >= BitsToRead) 104 break; 105 } 106 return Ok; 107 } 108 109 // Composite arrays. 110 if (FieldDesc->isCompositeArray()) { 111 QualType ElemType = FieldDesc->getElemQualType(); 112 size_t ElemSizeInBits = Ctx.getASTContext().getTypeSize(ElemType); 113 for (unsigned I = 0; I != FieldDesc->getNumElems(); ++I) { 114 enumerateData(P.atIndex(I).narrow(), Ctx, Offset, BitsToRead, F); 115 Offset += ElemSizeInBits; 116 if (Offset >= BitsToRead) 117 break; 118 } 119 return true; 120 } 121 122 // Records. 123 if (FieldDesc->isRecord()) { 124 const Record *R = FieldDesc->ElemRecord; 125 const ASTRecordLayout &Layout = 126 Ctx.getASTContext().getASTRecordLayout(R->getDecl()); 127 bool Ok = true; 128 129 for (const Record::Field &Fi : R->fields()) { 130 if (Fi.isUnnamedBitField()) 131 continue; 132 Pointer Elem = P.atField(Fi.Offset); 133 Bits BitOffset = 134 Offset + Bits(Layout.getFieldOffset(Fi.Decl->getFieldIndex())); 135 Ok = Ok && enumerateData(Elem, Ctx, BitOffset, BitsToRead, F); 136 } 137 for (const Record::Base &B : R->bases()) { 138 Pointer Elem = P.atField(B.Offset); 139 CharUnits ByteOffset = 140 Layout.getBaseClassOffset(cast<CXXRecordDecl>(B.Decl)); 141 Bits BitOffset = Offset + Bits(Ctx.getASTContext().toBits(ByteOffset)); 142 Ok = Ok && enumerateData(Elem, Ctx, BitOffset, BitsToRead, F); 143 // FIXME: We should only (need to) do this when bitcasting OUT of the 144 // buffer, not when copying data into it. 145 if (Ok) 146 Elem.initialize(); 147 } 148 149 return Ok; 150 } 151 152 llvm_unreachable("Unhandled data type"); 153 } 154 155 static bool enumeratePointerFields(const Pointer &P, const Context &Ctx, 156 Bits BitsToRead, DataFunc F) { 157 return enumerateData(P, Ctx, Bits::zero(), BitsToRead, F); 158 } 159 160 // This function is constexpr if and only if To, From, and the types of 161 // all subobjects of To and From are types T such that... 162 // (3.1) - is_union_v<T> is false; 163 // (3.2) - is_pointer_v<T> is false; 164 // (3.3) - is_member_pointer_v<T> is false; 165 // (3.4) - is_volatile_v<T> is false; and 166 // (3.5) - T has no non-static data members of reference type 167 // 168 // NOTE: This is a version of checkBitCastConstexprEligibilityType() in 169 // ExprConstant.cpp. 170 static bool CheckBitcastType(InterpState &S, CodePtr OpPC, QualType T, 171 bool IsToType) { 172 enum { 173 E_Union = 0, 174 E_Pointer, 175 E_MemberPointer, 176 E_Volatile, 177 E_Reference, 178 }; 179 enum { C_Member, C_Base }; 180 181 auto diag = [&](int Reason) -> bool { 182 const Expr *E = S.Current->getExpr(OpPC); 183 S.FFDiag(E, diag::note_constexpr_bit_cast_invalid_type) 184 << static_cast<int>(IsToType) << (Reason == E_Reference) << Reason 185 << E->getSourceRange(); 186 return false; 187 }; 188 auto note = [&](int Construct, QualType NoteType, SourceRange NoteRange) { 189 S.Note(NoteRange.getBegin(), diag::note_constexpr_bit_cast_invalid_subtype) 190 << NoteType << Construct << T.getUnqualifiedType() << NoteRange; 191 return false; 192 }; 193 194 T = T.getCanonicalType(); 195 196 if (T->isUnionType()) 197 return diag(E_Union); 198 if (T->isPointerType()) 199 return diag(E_Pointer); 200 if (T->isMemberPointerType()) 201 return diag(E_MemberPointer); 202 if (T.isVolatileQualified()) 203 return diag(E_Volatile); 204 205 if (const RecordDecl *RD = T->getAsRecordDecl()) { 206 if (const auto *CXXRD = dyn_cast<CXXRecordDecl>(RD)) { 207 for (const CXXBaseSpecifier &BS : CXXRD->bases()) { 208 if (!CheckBitcastType(S, OpPC, BS.getType(), IsToType)) 209 return note(C_Base, BS.getType(), BS.getBeginLoc()); 210 } 211 } 212 for (const FieldDecl *FD : RD->fields()) { 213 if (FD->getType()->isReferenceType()) 214 return diag(E_Reference); 215 if (!CheckBitcastType(S, OpPC, FD->getType(), IsToType)) 216 return note(C_Member, FD->getType(), FD->getSourceRange()); 217 } 218 } 219 220 if (T->isArrayType() && 221 !CheckBitcastType(S, OpPC, S.getASTContext().getBaseElementType(T), 222 IsToType)) 223 return false; 224 225 return true; 226 } 227 228 static bool readPointerToBuffer(const Context &Ctx, const Pointer &FromPtr, 229 BitcastBuffer &Buffer, bool ReturnOnUninit) { 230 const ASTContext &ASTCtx = Ctx.getASTContext(); 231 Endian TargetEndianness = 232 ASTCtx.getTargetInfo().isLittleEndian() ? Endian::Little : Endian::Big; 233 234 return enumeratePointerFields( 235 FromPtr, Ctx, Buffer.size(), 236 [&](const Pointer &P, PrimType T, Bits BitOffset, 237 bool PackedBools) -> bool { 238 CharUnits ObjectReprChars = ASTCtx.getTypeSizeInChars(P.getType()); 239 Bits BitWidth = Bits(ASTCtx.toBits(ObjectReprChars)); 240 Bits FullBitWidth = BitWidth; 241 242 if (const FieldDecl *FD = P.getField(); FD && FD->isBitField()) { 243 BitWidth = Bits(std::min(FD->getBitWidthValue(ASTCtx), 244 (unsigned)FullBitWidth.getQuantity())); 245 } else if (T == PT_Bool && PackedBools) 246 BitWidth = Bits(1); 247 248 if (BitWidth.isZero()) 249 return true; 250 251 // Bits will be left uninitialized and diagnosed when reading. 252 if (!P.isInitialized()) 253 return true; 254 255 if (T == PT_Ptr) { 256 assert(P.getType()->isNullPtrType()); 257 // Clang treats nullptr_t has having NO bits in its value 258 // representation. So, we accept it here and leave its bits 259 // uninitialized. 260 return true; 261 } 262 263 assert(P.isInitialized()); 264 auto Buff = 265 std::make_unique<std::byte[]>(ObjectReprChars.getQuantity()); 266 // Work around floating point types that contain unused padding bytes. 267 // This is really just `long double` on x86, which is the only 268 // fundamental type with padding bytes. 269 if (T == PT_Float) { 270 const Floating &F = P.deref<Floating>(); 271 Bits NumBits = Bits( 272 llvm::APFloatBase::getSizeInBits(F.getAPFloat().getSemantics())); 273 assert(NumBits.isFullByte()); 274 assert(NumBits.getQuantity() <= FullBitWidth.getQuantity()); 275 F.bitcastToMemory(Buff.get()); 276 // Now, only (maybe) swap the actual size of the float, excluding the 277 // padding bits. 278 if (llvm::sys::IsBigEndianHost) 279 swapBytes(Buff.get(), NumBits.roundToBytes()); 280 281 Buffer.markInitialized(BitOffset, NumBits); 282 } else { 283 BITCAST_TYPE_SWITCH(T, { P.deref<T>().bitcastToMemory(Buff.get()); }); 284 285 if (llvm::sys::IsBigEndianHost) 286 swapBytes(Buff.get(), FullBitWidth.roundToBytes()); 287 Buffer.markInitialized(BitOffset, BitWidth); 288 } 289 290 Buffer.pushData(Buff.get(), BitOffset, BitWidth, TargetEndianness); 291 return true; 292 }); 293 } 294 295 bool clang::interp::DoBitCast(InterpState &S, CodePtr OpPC, const Pointer &Ptr, 296 std::byte *Buff, Bits BitWidth, Bits FullBitWidth, 297 bool &HasIndeterminateBits) { 298 assert(Ptr.isLive()); 299 assert(Ptr.isBlockPointer()); 300 assert(Buff); 301 assert(BitWidth <= FullBitWidth); 302 assert(FullBitWidth.isFullByte()); 303 assert(BitWidth.isFullByte()); 304 305 BitcastBuffer Buffer(FullBitWidth); 306 size_t BuffSize = FullBitWidth.roundToBytes(); 307 if (!CheckBitcastType(S, OpPC, Ptr.getType(), /*IsToType=*/false)) 308 return false; 309 310 bool Success = readPointerToBuffer(S.getContext(), Ptr, Buffer, 311 /*ReturnOnUninit=*/false); 312 HasIndeterminateBits = !Buffer.rangeInitialized(Bits::zero(), BitWidth); 313 314 const ASTContext &ASTCtx = S.getASTContext(); 315 Endian TargetEndianness = 316 ASTCtx.getTargetInfo().isLittleEndian() ? Endian::Little : Endian::Big; 317 auto B = 318 Buffer.copyBits(Bits::zero(), BitWidth, FullBitWidth, TargetEndianness); 319 320 std::memcpy(Buff, B.get(), BuffSize); 321 322 if (llvm::sys::IsBigEndianHost) 323 swapBytes(Buff, BitWidth.roundToBytes()); 324 325 return Success; 326 } 327 bool clang::interp::DoBitCastPtr(InterpState &S, CodePtr OpPC, 328 const Pointer &FromPtr, Pointer &ToPtr) { 329 const ASTContext &ASTCtx = S.getASTContext(); 330 CharUnits ObjectReprChars = ASTCtx.getTypeSizeInChars(ToPtr.getType()); 331 332 return DoBitCastPtr(S, OpPC, FromPtr, ToPtr, ObjectReprChars.getQuantity()); 333 } 334 335 bool clang::interp::DoBitCastPtr(InterpState &S, CodePtr OpPC, 336 const Pointer &FromPtr, Pointer &ToPtr, 337 size_t Size) { 338 assert(FromPtr.isLive()); 339 assert(FromPtr.isBlockPointer()); 340 assert(ToPtr.isBlockPointer()); 341 342 QualType FromType = FromPtr.getType(); 343 QualType ToType = ToPtr.getType(); 344 345 if (!CheckBitcastType(S, OpPC, ToType, /*IsToType=*/true)) 346 return false; 347 if (!CheckBitcastType(S, OpPC, FromType, /*IsToType=*/false)) 348 return false; 349 350 const ASTContext &ASTCtx = S.getASTContext(); 351 BitcastBuffer Buffer(Bytes(Size).toBits()); 352 readPointerToBuffer(S.getContext(), FromPtr, Buffer, 353 /*ReturnOnUninit=*/false); 354 355 // Now read the values out of the buffer again and into ToPtr. 356 Endian TargetEndianness = 357 ASTCtx.getTargetInfo().isLittleEndian() ? Endian::Little : Endian::Big; 358 bool Success = enumeratePointerFields( 359 ToPtr, S.getContext(), Buffer.size(), 360 [&](const Pointer &P, PrimType T, Bits BitOffset, 361 bool PackedBools) -> bool { 362 QualType PtrType = P.getType(); 363 CharUnits ObjectReprChars = ASTCtx.getTypeSizeInChars(PtrType); 364 Bits FullBitWidth = Bits(ASTCtx.toBits(ObjectReprChars)); 365 if (T == PT_Float) { 366 const auto &Semantics = ASTCtx.getFloatTypeSemantics(PtrType); 367 Bits NumBits = Bits(llvm::APFloatBase::getSizeInBits(Semantics)); 368 assert(NumBits.isFullByte()); 369 assert(NumBits.getQuantity() <= FullBitWidth.getQuantity()); 370 auto M = Buffer.copyBits(BitOffset, NumBits, FullBitWidth, 371 TargetEndianness); 372 373 if (llvm::sys::IsBigEndianHost) 374 swapBytes(M.get(), NumBits.roundToBytes()); 375 376 P.deref<Floating>() = Floating::bitcastFromMemory(M.get(), Semantics); 377 P.initialize(); 378 return true; 379 } 380 381 Bits BitWidth; 382 if (const FieldDecl *FD = P.getField(); FD && FD->isBitField()) 383 BitWidth = Bits(std::min(FD->getBitWidthValue(ASTCtx), 384 (unsigned)FullBitWidth.getQuantity())); 385 else if (T == PT_Bool && PackedBools) 386 BitWidth = Bits(1); 387 else 388 BitWidth = FullBitWidth; 389 390 // If any of the bits are uninitialized, we need to abort unless the 391 // target type is std::byte or unsigned char. 392 bool Initialized = Buffer.rangeInitialized(BitOffset, BitWidth); 393 if (!Initialized) { 394 if (!PtrType->isStdByteType() && 395 !PtrType->isSpecificBuiltinType(BuiltinType::UChar) && 396 !PtrType->isSpecificBuiltinType(BuiltinType::Char_U)) { 397 const Expr *E = S.Current->getExpr(OpPC); 398 S.FFDiag(E, diag::note_constexpr_bit_cast_indet_dest) 399 << PtrType << S.getLangOpts().CharIsSigned 400 << E->getSourceRange(); 401 402 return false; 403 } 404 return true; 405 } 406 407 auto Memory = Buffer.copyBits(BitOffset, BitWidth, FullBitWidth, 408 TargetEndianness); 409 if (llvm::sys::IsBigEndianHost) 410 swapBytes(Memory.get(), FullBitWidth.roundToBytes()); 411 412 BITCAST_TYPE_SWITCH_FIXED_SIZE(T, { 413 if (BitWidth.nonZero()) 414 P.deref<T>() = T::bitcastFromMemory(Memory.get(), T::bitWidth()) 415 .truncate(BitWidth.getQuantity()); 416 else 417 P.deref<T>() = T::zero(); 418 }); 419 P.initialize(); 420 return true; 421 }); 422 423 return Success; 424 } 425