MCStreamer.h revision 440596ffe5bb77a202acb36d5eadd158976ff39a
1//===- MCStreamer.h - High-level Streaming Machine Code Output --*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file declares the MCStreamer class. 11// 12//===----------------------------------------------------------------------===// 13 14#ifndef LLVM_MC_MCSTREAMER_H 15#define LLVM_MC_MCSTREAMER_H 16 17#include "llvm/ADT/SmallVector.h" 18#include "llvm/Support/DataTypes.h" 19#include "llvm/MC/MCDirectives.h" 20#include "llvm/MC/MCDwarf.h" 21#include "llvm/MC/MCWin64EH.h" 22 23namespace llvm { 24 class MCAsmInfo; 25 class MCCodeEmitter; 26 class MCContext; 27 class MCExpr; 28 class MCInst; 29 class MCInstPrinter; 30 class MCSection; 31 class MCSymbol; 32 class StringRef; 33 class TargetAsmBackend; 34 class TargetLoweringObjectFile; 35 class Twine; 36 class raw_ostream; 37 class formatted_raw_ostream; 38 39 /// MCStreamer - Streaming machine code generation interface. This interface 40 /// is intended to provide a programatic interface that is very similar to the 41 /// level that an assembler .s file provides. It has callbacks to emit bytes, 42 /// handle directives, etc. The implementation of this interface retains 43 /// state to know what the current section is etc. 44 /// 45 /// There are multiple implementations of this interface: one for writing out 46 /// a .s file, and implementations that write out .o files of various formats. 47 /// 48 class MCStreamer { 49 MCContext &Context; 50 51 MCStreamer(const MCStreamer&); // DO NOT IMPLEMENT 52 MCStreamer &operator=(const MCStreamer&); // DO NOT IMPLEMENT 53 54 bool EmitEHFrame; 55 bool EmitDebugFrame; 56 57 std::vector<MCDwarfFrameInfo> FrameInfos; 58 MCDwarfFrameInfo *getCurrentFrameInfo(); 59 void EnsureValidFrame(); 60 61 std::vector<MCWin64EHUnwindInfo> W64UnwindInfos; 62 MCWin64EHUnwindInfo *CurrentW64UnwindInfo; 63 void setCurrentW64UnwindInfo(MCWin64EHUnwindInfo *Frame); 64 void EnsureValidW64UnwindInfo(); 65 66 const MCSymbol* LastNonPrivate; 67 68 /// SectionStack - This is stack of current and previous section 69 /// values saved by PushSection. 70 SmallVector<std::pair<const MCSection *, 71 const MCSection *>, 4> SectionStack; 72 73 protected: 74 MCStreamer(MCContext &Ctx); 75 76 const MCExpr *BuildSymbolDiff(MCContext &Context, const MCSymbol *A, 77 const MCSymbol *B); 78 79 const MCExpr *ForceExpAbs(MCStreamer *Streamer, MCContext &Context, 80 const MCExpr* Expr); 81 82 void EmitFrames(bool usingCFI); 83 84 public: 85 virtual ~MCStreamer(); 86 87 MCContext &getContext() const { return Context; } 88 89 unsigned getNumFrameInfos() { 90 return FrameInfos.size(); 91 } 92 93 const MCDwarfFrameInfo &getFrameInfo(unsigned i) { 94 return FrameInfos[i]; 95 } 96 97 /// @name Assembly File Formatting. 98 /// @{ 99 100 /// isVerboseAsm - Return true if this streamer supports verbose assembly 101 /// and if it is enabled. 102 virtual bool isVerboseAsm() const { return false; } 103 104 /// hasRawTextSupport - Return true if this asm streamer supports emitting 105 /// unformatted text to the .s file with EmitRawText. 106 virtual bool hasRawTextSupport() const { return false; } 107 108 /// AddComment - Add a comment that can be emitted to the generated .s 109 /// file if applicable as a QoI issue to make the output of the compiler 110 /// more readable. This only affects the MCAsmStreamer, and only when 111 /// verbose assembly output is enabled. 112 /// 113 /// If the comment includes embedded \n's, they will each get the comment 114 /// prefix as appropriate. The added comment should not end with a \n. 115 virtual void AddComment(const Twine &T) {} 116 117 /// GetCommentOS - Return a raw_ostream that comments can be written to. 118 /// Unlike AddComment, you are required to terminate comments with \n if you 119 /// use this method. 120 virtual raw_ostream &GetCommentOS(); 121 122 /// AddBlankLine - Emit a blank line to a .s file to pretty it up. 123 virtual void AddBlankLine() {} 124 125 /// @} 126 127 /// @name Symbol & Section Management 128 /// @{ 129 130 /// getCurrentSection - Return the current section that the streamer is 131 /// emitting code to. 132 const MCSection *getCurrentSection() const { 133 if (!SectionStack.empty()) 134 return SectionStack.back().first; 135 return NULL; 136 } 137 138 /// getPreviousSection - Return the previous section that the streamer is 139 /// emitting code to. 140 const MCSection *getPreviousSection() const { 141 if (!SectionStack.empty()) 142 return SectionStack.back().second; 143 return NULL; 144 } 145 146 /// ChangeSection - Update streamer for a new active section. 147 /// 148 /// This is called by PopSection and SwitchSection, if the current 149 /// section changes. 150 virtual void ChangeSection(const MCSection *) = 0; 151 152 /// pushSection - Save the current and previous section on the 153 /// section stack. 154 void PushSection() { 155 SectionStack.push_back(std::make_pair(getCurrentSection(), 156 getPreviousSection())); 157 } 158 159 /// popSection - Restore the current and previous section from 160 /// the section stack. Calls ChangeSection as needed. 161 /// 162 /// Returns false if the stack was empty. 163 bool PopSection() { 164 if (SectionStack.size() <= 1) 165 return false; 166 const MCSection *oldSection = SectionStack.pop_back_val().first; 167 const MCSection *curSection = SectionStack.back().first; 168 169 if (oldSection != curSection) 170 ChangeSection(curSection); 171 return true; 172 } 173 174 /// SwitchSection - Set the current section where code is being emitted to 175 /// @p Section. This is required to update CurSection. 176 /// 177 /// This corresponds to assembler directives like .section, .text, etc. 178 void SwitchSection(const MCSection *Section) { 179 assert(Section && "Cannot switch to a null section!"); 180 const MCSection *curSection = SectionStack.back().first; 181 SectionStack.back().second = curSection; 182 if (Section != curSection) { 183 SectionStack.back().first = Section; 184 ChangeSection(Section); 185 } 186 } 187 188 /// InitSections - Create the default sections and set the initial one. 189 virtual void InitSections() = 0; 190 191 /// EmitLabel - Emit a label for @p Symbol into the current section. 192 /// 193 /// This corresponds to an assembler statement such as: 194 /// foo: 195 /// 196 /// @param Symbol - The symbol to emit. A given symbol should only be 197 /// emitted as a label once, and symbols emitted as a label should never be 198 /// used in an assignment. 199 virtual void EmitLabel(MCSymbol *Symbol); 200 201 virtual void EmitEHSymAttributes(const MCSymbol *Symbol, 202 MCSymbol *EHSymbol); 203 204 /// EmitAssemblerFlag - Note in the output the specified @p Flag 205 virtual void EmitAssemblerFlag(MCAssemblerFlag Flag) = 0; 206 207 /// EmitThumbFunc - Note in the output that the specified @p Func is 208 /// a Thumb mode function (ARM target only). 209 virtual void EmitThumbFunc(MCSymbol *Func) = 0; 210 211 /// EmitAssignment - Emit an assignment of @p Value to @p Symbol. 212 /// 213 /// This corresponds to an assembler statement such as: 214 /// symbol = value 215 /// 216 /// The assignment generates no code, but has the side effect of binding the 217 /// value in the current context. For the assembly streamer, this prints the 218 /// binding into the .s file. 219 /// 220 /// @param Symbol - The symbol being assigned to. 221 /// @param Value - The value for the symbol. 222 virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) = 0; 223 224 /// EmitWeakReference - Emit an weak reference from @p Alias to @p Symbol. 225 /// 226 /// This corresponds to an assembler statement such as: 227 /// .weakref alias, symbol 228 /// 229 /// @param Alias - The alias that is being created. 230 /// @param Symbol - The symbol being aliased. 231 virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) = 0; 232 233 /// EmitSymbolAttribute - Add the given @p Attribute to @p Symbol. 234 virtual void EmitSymbolAttribute(MCSymbol *Symbol, 235 MCSymbolAttr Attribute) = 0; 236 237 /// EmitSymbolDesc - Set the @p DescValue for the @p Symbol. 238 /// 239 /// @param Symbol - The symbol to have its n_desc field set. 240 /// @param DescValue - The value to set into the n_desc field. 241 virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) = 0; 242 243 /// BeginCOFFSymbolDef - Start emitting COFF symbol definition 244 /// 245 /// @param Symbol - The symbol to have its External & Type fields set. 246 virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) = 0; 247 248 /// EmitCOFFSymbolStorageClass - Emit the storage class of the symbol. 249 /// 250 /// @param StorageClass - The storage class the symbol should have. 251 virtual void EmitCOFFSymbolStorageClass(int StorageClass) = 0; 252 253 /// EmitCOFFSymbolType - Emit the type of the symbol. 254 /// 255 /// @param Type - A COFF type identifier (see COFF::SymbolType in X86COFF.h) 256 virtual void EmitCOFFSymbolType(int Type) = 0; 257 258 /// EndCOFFSymbolDef - Marks the end of the symbol definition. 259 virtual void EndCOFFSymbolDef() = 0; 260 261 /// EmitELFSize - Emit an ELF .size directive. 262 /// 263 /// This corresponds to an assembler statement such as: 264 /// .size symbol, expression 265 /// 266 virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) = 0; 267 268 /// EmitCommonSymbol - Emit a common symbol. 269 /// 270 /// @param Symbol - The common symbol to emit. 271 /// @param Size - The size of the common symbol. 272 /// @param ByteAlignment - The alignment of the symbol if 273 /// non-zero. This must be a power of 2. 274 virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size, 275 unsigned ByteAlignment) = 0; 276 277 /// EmitLocalCommonSymbol - Emit a local common (.lcomm) symbol. 278 /// 279 /// @param Symbol - The common symbol to emit. 280 /// @param Size - The size of the common symbol. 281 virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) = 0; 282 283 /// EmitZerofill - Emit the zerofill section and an optional symbol. 284 /// 285 /// @param Section - The zerofill section to create and or to put the symbol 286 /// @param Symbol - The zerofill symbol to emit, if non-NULL. 287 /// @param Size - The size of the zerofill symbol. 288 /// @param ByteAlignment - The alignment of the zerofill symbol if 289 /// non-zero. This must be a power of 2 on some targets. 290 virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0, 291 unsigned Size = 0,unsigned ByteAlignment = 0) = 0; 292 293 /// EmitTBSSSymbol - Emit a thread local bss (.tbss) symbol. 294 /// 295 /// @param Section - The thread local common section. 296 /// @param Symbol - The thread local common symbol to emit. 297 /// @param Size - The size of the symbol. 298 /// @param ByteAlignment - The alignment of the thread local common symbol 299 /// if non-zero. This must be a power of 2 on some targets. 300 virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol, 301 uint64_t Size, unsigned ByteAlignment = 0) = 0; 302 303 /// @} 304 /// @name Generating Data 305 /// @{ 306 307 /// EmitBytes - Emit the bytes in \arg Data into the output. 308 /// 309 /// This is used to implement assembler directives such as .byte, .ascii, 310 /// etc. 311 virtual void EmitBytes(StringRef Data, unsigned AddrSpace) = 0; 312 313 /// EmitValue - Emit the expression @p Value into the output as a native 314 /// integer of the given @p Size bytes. 315 /// 316 /// This is used to implement assembler directives such as .word, .quad, 317 /// etc. 318 /// 319 /// @param Value - The value to emit. 320 /// @param Size - The size of the integer (in bytes) to emit. This must 321 /// match a native machine width. 322 virtual void EmitValueImpl(const MCExpr *Value, unsigned Size, 323 unsigned AddrSpace) = 0; 324 325 void EmitValue(const MCExpr *Value, unsigned Size, unsigned AddrSpace = 0); 326 327 /// EmitIntValue - Special case of EmitValue that avoids the client having 328 /// to pass in a MCExpr for constant integers. 329 virtual void EmitIntValue(uint64_t Value, unsigned Size, 330 unsigned AddrSpace = 0); 331 332 /// EmitAbsValue - Emit the Value, but try to avoid relocations. On MachO 333 /// this is done by producing 334 /// foo = value 335 /// .long foo 336 void EmitAbsValue(const MCExpr *Value, unsigned Size, 337 unsigned AddrSpace = 0); 338 339 virtual void EmitULEB128Value(const MCExpr *Value) = 0; 340 341 virtual void EmitSLEB128Value(const MCExpr *Value) = 0; 342 343 /// EmitULEB128Value - Special case of EmitULEB128Value that avoids the 344 /// client having to pass in a MCExpr for constant integers. 345 void EmitULEB128IntValue(uint64_t Value, unsigned AddrSpace = 0); 346 347 /// EmitSLEB128Value - Special case of EmitSLEB128Value that avoids the 348 /// client having to pass in a MCExpr for constant integers. 349 void EmitSLEB128IntValue(int64_t Value, unsigned AddrSpace = 0); 350 351 /// EmitSymbolValue - Special case of EmitValue that avoids the client 352 /// having to pass in a MCExpr for MCSymbols. 353 void EmitSymbolValue(const MCSymbol *Sym, unsigned Size, 354 unsigned AddrSpace = 0); 355 356 /// EmitGPRel32Value - Emit the expression @p Value into the output as a 357 /// gprel32 (32-bit GP relative) value. 358 /// 359 /// This is used to implement assembler directives such as .gprel32 on 360 /// targets that support them. 361 virtual void EmitGPRel32Value(const MCExpr *Value); 362 363 /// EmitFill - Emit NumBytes bytes worth of the value specified by 364 /// FillValue. This implements directives such as '.space'. 365 virtual void EmitFill(uint64_t NumBytes, uint8_t FillValue, 366 unsigned AddrSpace); 367 368 /// EmitZeros - Emit NumBytes worth of zeros. This is a convenience 369 /// function that just wraps EmitFill. 370 void EmitZeros(uint64_t NumBytes, unsigned AddrSpace) { 371 EmitFill(NumBytes, 0, AddrSpace); 372 } 373 374 375 /// EmitValueToAlignment - Emit some number of copies of @p Value until 376 /// the byte alignment @p ByteAlignment is reached. 377 /// 378 /// If the number of bytes need to emit for the alignment is not a multiple 379 /// of @p ValueSize, then the contents of the emitted fill bytes is 380 /// undefined. 381 /// 382 /// This used to implement the .align assembler directive. 383 /// 384 /// @param ByteAlignment - The alignment to reach. This must be a power of 385 /// two on some targets. 386 /// @param Value - The value to use when filling bytes. 387 /// @param ValueSize - The size of the integer (in bytes) to emit for 388 /// @p Value. This must match a native machine width. 389 /// @param MaxBytesToEmit - The maximum numbers of bytes to emit, or 0. If 390 /// the alignment cannot be reached in this many bytes, no bytes are 391 /// emitted. 392 virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0, 393 unsigned ValueSize = 1, 394 unsigned MaxBytesToEmit = 0) = 0; 395 396 /// EmitCodeAlignment - Emit nops until the byte alignment @p ByteAlignment 397 /// is reached. 398 /// 399 /// This used to align code where the alignment bytes may be executed. This 400 /// can emit different bytes for different sizes to optimize execution. 401 /// 402 /// @param ByteAlignment - The alignment to reach. This must be a power of 403 /// two on some targets. 404 /// @param MaxBytesToEmit - The maximum numbers of bytes to emit, or 0. If 405 /// the alignment cannot be reached in this many bytes, no bytes are 406 /// emitted. 407 virtual void EmitCodeAlignment(unsigned ByteAlignment, 408 unsigned MaxBytesToEmit = 0) = 0; 409 410 /// EmitValueToOffset - Emit some number of copies of @p Value until the 411 /// byte offset @p Offset is reached. 412 /// 413 /// This is used to implement assembler directives such as .org. 414 /// 415 /// @param Offset - The offset to reach. This may be an expression, but the 416 /// expression must be associated with the current section. 417 /// @param Value - The value to use when filling bytes. 418 virtual void EmitValueToOffset(const MCExpr *Offset, 419 unsigned char Value = 0) = 0; 420 421 /// @} 422 423 /// EmitFileDirective - Switch to a new logical file. This is used to 424 /// implement the '.file "foo.c"' assembler directive. 425 virtual void EmitFileDirective(StringRef Filename) = 0; 426 427 /// EmitDwarfFileDirective - Associate a filename with a specified logical 428 /// file number. This implements the DWARF2 '.file 4 "foo.c"' assembler 429 /// directive. 430 virtual bool EmitDwarfFileDirective(unsigned FileNo,StringRef Filename); 431 432 /// EmitDwarfLocDirective - This implements the DWARF2 433 // '.loc fileno lineno ...' assembler directive. 434 virtual void EmitDwarfLocDirective(unsigned FileNo, unsigned Line, 435 unsigned Column, unsigned Flags, 436 unsigned Isa, 437 unsigned Discriminator, 438 StringRef FileName); 439 440 virtual void EmitDwarfAdvanceLineAddr(int64_t LineDelta, 441 const MCSymbol *LastLabel, 442 const MCSymbol *Label) = 0; 443 444 virtual void EmitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel, 445 const MCSymbol *Label) { 446 } 447 448 void EmitDwarfSetLineAddr(int64_t LineDelta, const MCSymbol *Label, 449 int PointerSize); 450 451 virtual void EmitCFISections(bool EH, bool Debug); 452 virtual void EmitCFIStartProc(); 453 virtual void EmitCFIEndProc(); 454 virtual void EmitCFIDefCfa(int64_t Register, int64_t Offset); 455 virtual void EmitCFIDefCfaOffset(int64_t Offset); 456 virtual void EmitCFIDefCfaRegister(int64_t Register); 457 virtual void EmitCFIOffset(int64_t Register, int64_t Offset); 458 virtual void EmitCFIPersonality(const MCSymbol *Sym, unsigned Encoding); 459 virtual void EmitCFILsda(const MCSymbol *Sym, unsigned Encoding); 460 virtual void EmitCFIRememberState(); 461 virtual void EmitCFIRestoreState(); 462 virtual void EmitCFISameValue(int64_t Register); 463 virtual void EmitCFIRelOffset(int64_t Register, int64_t Offset); 464 virtual void EmitCFIAdjustCfaOffset(int64_t Adjustment); 465 466 virtual void EmitWin64EHStartProc(MCSymbol *Symbol); 467 virtual void EmitWin64EHEndProc(); 468 virtual void EmitWin64EHStartChained(); 469 virtual void EmitWin64EHEndChained(); 470 virtual void EmitWin64EHHandler(const MCSymbol *Sym, bool Unwind, 471 bool Except); 472 virtual void EmitWin64EHHandlerData(); 473 virtual void EmitWin64EHPushReg(int64_t Register); 474 virtual void EmitWin64EHSetFrame(int64_t Register, int64_t Offset); 475 virtual void EmitWin64EHAllocStack(int64_t Size); 476 virtual void EmitWin64EHSaveReg(int64_t Register, int64_t Offset); 477 virtual void EmitWin64EHSaveXMM(int64_t Register, int64_t Offset); 478 virtual void EmitWin64EHPushFrame(bool Code); 479 virtual void EmitWin64EHEndProlog(); 480 481 /// EmitInstruction - Emit the given @p Instruction into the current 482 /// section. 483 virtual void EmitInstruction(const MCInst &Inst) = 0; 484 485 /// EmitRawText - If this file is backed by a assembly streamer, this dumps 486 /// the specified string in the output .s file. This capability is 487 /// indicated by the hasRawTextSupport() predicate. By default this aborts. 488 virtual void EmitRawText(StringRef String); 489 void EmitRawText(const Twine &String); 490 491 /// ARM-related methods. 492 /// FIXME: Eventually we should have some "target MC streamer" and move 493 /// these methods there. 494 virtual void EmitFnStart(); 495 virtual void EmitFnEnd(); 496 virtual void EmitCantUnwind(); 497 virtual void EmitPersonality(const MCSymbol *Personality); 498 virtual void EmitHandlerData(); 499 virtual void EmitSetFP(unsigned FpReg, unsigned SpReg, int64_t Offset = 0); 500 virtual void EmitPad(int64_t Offset); 501 virtual void EmitRegSave(const SmallVectorImpl<unsigned> &RegList, 502 bool isVector); 503 504 /// Finish - Finish emission of machine code. 505 virtual void Finish() = 0; 506 }; 507 508 /// createNullStreamer - Create a dummy machine code streamer, which does 509 /// nothing. This is useful for timing the assembler front end. 510 MCStreamer *createNullStreamer(MCContext &Ctx); 511 512 /// createAsmStreamer - Create a machine code streamer which will print out 513 /// assembly for the native target, suitable for compiling with a native 514 /// assembler. 515 /// 516 /// \param InstPrint - If given, the instruction printer to use. If not given 517 /// the MCInst representation will be printed. This method takes ownership of 518 /// InstPrint. 519 /// 520 /// \param CE - If given, a code emitter to use to show the instruction 521 /// encoding inline with the assembly. This method takes ownership of \arg CE. 522 /// 523 /// \param TAB - If given, a target asm backend to use to show the fixup 524 /// information in conjunction with encoding information. This method takes 525 /// ownership of \arg TAB. 526 /// 527 /// \param ShowInst - Whether to show the MCInst representation inline with 528 /// the assembly. 529 MCStreamer *createAsmStreamer(MCContext &Ctx, formatted_raw_ostream &OS, 530 bool isVerboseAsm, 531 bool useLoc, 532 bool useCFI, 533 MCInstPrinter *InstPrint = 0, 534 MCCodeEmitter *CE = 0, 535 TargetAsmBackend *TAB = 0, 536 bool ShowInst = false); 537 538 /// createMachOStreamer - Create a machine code streamer which will generate 539 /// Mach-O format object files. 540 /// 541 /// Takes ownership of \arg TAB and \arg CE. 542 MCStreamer *createMachOStreamer(MCContext &Ctx, TargetAsmBackend &TAB, 543 raw_ostream &OS, MCCodeEmitter *CE, 544 bool RelaxAll = false); 545 546 /// createWinCOFFStreamer - Create a machine code streamer which will 547 /// generate Microsoft COFF format object files. 548 /// 549 /// Takes ownership of \arg TAB and \arg CE. 550 MCStreamer *createWinCOFFStreamer(MCContext &Ctx, 551 TargetAsmBackend &TAB, 552 MCCodeEmitter &CE, raw_ostream &OS, 553 bool RelaxAll = false); 554 555 /// createELFStreamer - Create a machine code streamer which will generate 556 /// ELF format object files. 557 MCStreamer *createELFStreamer(MCContext &Ctx, TargetAsmBackend &TAB, 558 raw_ostream &OS, MCCodeEmitter *CE, 559 bool RelaxAll, bool NoExecStack); 560 561 /// createLoggingStreamer - Create a machine code streamer which just logs the 562 /// API calls and then dispatches to another streamer. 563 /// 564 /// The new streamer takes ownership of the \arg Child. 565 MCStreamer *createLoggingStreamer(MCStreamer *Child, raw_ostream &OS); 566 567 /// createPureStreamer - Create a machine code streamer which will generate 568 /// "pure" MC object files, for use with MC-JIT and testing tools. 569 /// 570 /// Takes ownership of \arg TAB and \arg CE. 571 MCStreamer *createPureStreamer(MCContext &Ctx, TargetAsmBackend &TAB, 572 raw_ostream &OS, MCCodeEmitter *CE); 573 574} // end namespace llvm 575 576#endif 577