llvm/lib/Support/MemoryBuffer.cpp

   1 //===--- MemoryBuffer.cpp - Memory Buffer implementation ------------------===//
   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 //
   9 //  This file implements the MemoryBuffer interface.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/Support/MemoryBuffer.h"
  14 #include "llvm/ADT/STLExtras.h"
  15 #include "llvm/ADT/SmallString.h"
  16 #include "llvm/Config/config.h"
  17 #include "llvm/Support/Alignment.h"
  18 #include "llvm/Support/Errc.h"
  19 #include "llvm/Support/Error.h"
  20 #include "llvm/Support/ErrorHandling.h"
  21 #include "llvm/Support/FileSystem.h"
  22 #include "llvm/Support/MathExtras.h"
  23 #include "llvm/Support/Process.h"
  24 #include "llvm/Support/Program.h"
  25 #include "llvm/Support/SmallVectorMemoryBuffer.h"
  26 #include <algorithm>
  27 #include <cassert>
  28 #include <cstring>
  29 #include <new>
  30 #include <sys/types.h>
  31 #include <system_error>
  32 #if !defined(_MSC_VER) && !defined(__MINGW32__)
  33 #include <unistd.h>
  34 #else
  35 #include <io.h>
  36 #endif
  37
  38 #ifdef __MVS__
  39 #include "llvm/Support/AutoConvert.h"
  40 #endif
  41 using namespace llvm;
  42
  43 //===----------------------------------------------------------------------===//
  44 // MemoryBuffer implementation itself.
  45 //===----------------------------------------------------------------------===//
  46
  47 MemoryBuffer::~MemoryBuffer() = default;
  48
  49 /// init - Initialize this MemoryBuffer as a reference to externally allocated
  50 /// memory, memory that we know is already null terminated.
  51 void MemoryBuffer::init(const char *BufStart, const char *BufEnd,
  52                         bool RequiresNullTerminator) {
  53   assert((!RequiresNullTerminator || BufEnd[0] == 0) &&
  54          "Buffer is not null terminated!");
  55   BufferStart = BufStart;
  56   BufferEnd = BufEnd;
  57 }
  58
  59 //===----------------------------------------------------------------------===//
  60 // MemoryBufferMem implementation.
  61 //===----------------------------------------------------------------------===//
  62
  63 /// CopyStringRef - Copies contents of a StringRef into a block of memory and
  64 /// null-terminates it.
  65 static void CopyStringRef(char *Memory, StringRef Data) {
  66   if (!Data.empty())
  67     memcpy(Memory, Data.data(), Data.size());
  68   Memory[Data.size()] = 0; // Null terminate string.
  69 }
  70
  71 namespace {
  72 struct NamedBufferAlloc {
  73   const Twine &Name;
  74   NamedBufferAlloc(const Twine &Name) : Name(Name) {}
  75 };
  76 } // namespace
  77
  78 void *operator new(size_t N, const NamedBufferAlloc &Alloc) {
  79   SmallString<256> NameBuf;
  80   StringRef NameRef = Alloc.Name.toStringRef(NameBuf);
  81
  82   char *Mem = static_cast<char *>(operator new(N + sizeof(size_t) +
  83                                                NameRef.size() + 1));
  84   *reinterpret_cast<size_t *>(Mem + N) = NameRef.size();
  85   CopyStringRef(Mem + N + sizeof(size_t), NameRef);
  86   return Mem;
  87 }
  88
  89 namespace {
  90 /// MemoryBufferMem - Named MemoryBuffer pointing to a block of memory.
  91 template<typename MB>
  92 class MemoryBufferMem : public MB {
  93 public:
  94   MemoryBufferMem(StringRef InputData, bool RequiresNullTerminator) {
  95     MemoryBuffer::init(InputData.begin(), InputData.end(),
  96                        RequiresNullTerminator);
  97   }
  98
  99   /// Disable sized deallocation for MemoryBufferMem, because it has
 100   /// tail-allocated data.
 101   void operator delete(void *p) { ::operator delete(p); }
 102
 103   StringRef getBufferIdentifier() const override {
 104     // The name is stored after the class itself.
 105     return StringRef(reinterpret_cast<const char *>(this + 1) + sizeof(size_t),
 106                      *reinterpret_cast<const size_t *>(this + 1));
 107   }
 108
 109   MemoryBuffer::BufferKind getBufferKind() const override {
 110     return MemoryBuffer::MemoryBuffer_Malloc;
 111   }
 112 };
 113 } // namespace
 114
 115 template <typename MB>
 116 static ErrorOr<std::unique_ptr<MB>>
 117 getFileAux(const Twine &Filename, uint64_t MapSize, uint64_t Offset,
 118            bool IsText, bool RequiresNullTerminator, bool IsVolatile,
 119            std::optional<Align> Alignment);
 120
 121 std::unique_ptr<MemoryBuffer>
 122 MemoryBuffer::getMemBuffer(StringRef InputData, StringRef BufferName,
 123                            bool RequiresNullTerminator) {
 124   auto *Ret = new (NamedBufferAlloc(BufferName))
 125       MemoryBufferMem<MemoryBuffer>(InputData, RequiresNullTerminator);
 126   return std::unique_ptr<MemoryBuffer>(Ret);
 127 }
 128
 129 std::unique_ptr<MemoryBuffer>
 130 MemoryBuffer::getMemBuffer(MemoryBufferRef Ref, bool RequiresNullTerminator) {
 131   return std::unique_ptr<MemoryBuffer>(getMemBuffer(
 132       Ref.getBuffer(), Ref.getBufferIdentifier(), RequiresNullTerminator));
 133 }
 134
 135 static ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
 136 getMemBufferCopyImpl(StringRef InputData, const Twine &BufferName) {
 137   auto Buf =
 138       WritableMemoryBuffer::getNewUninitMemBuffer(InputData.size(), BufferName);
 139   if (!Buf)
 140     return make_error_code(errc::not_enough_memory);
 141   // Calling memcpy with null src/dst is UB, and an empty StringRef is
 142   // represented with {nullptr, 0}.
 143   llvm::copy(InputData, Buf->getBufferStart());
 144   return std::move(Buf);
 145 }
 146
 147 std::unique_ptr<MemoryBuffer>
 148 MemoryBuffer::getMemBufferCopy(StringRef InputData, const Twine &BufferName) {
 149   auto Buf = getMemBufferCopyImpl(InputData, BufferName);
 150   if (Buf)
 151     return std::move(*Buf);
 152   return nullptr;
 153 }
 154
 155 ErrorOr<std::unique_ptr<MemoryBuffer>>
 156 MemoryBuffer::getFileOrSTDIN(const Twine &Filename, bool IsText,
 157                              bool RequiresNullTerminator,
 158                              std::optional<Align> Alignment) {
 159   SmallString<256> NameBuf;
 160   StringRef NameRef = Filename.toStringRef(NameBuf);
 161
 162   if (NameRef == "-")
 163     return getSTDIN();
 164   return getFile(Filename, IsText, RequiresNullTerminator,
 165                  /*IsVolatile=*/false, Alignment);
 166 }
 167
 168 ErrorOr<std::unique_ptr<MemoryBuffer>>
 169 MemoryBuffer::getFileSlice(const Twine &FilePath, uint64_t MapSize,
 170                            uint64_t Offset, bool IsVolatile,
 171                            std::optional<Align> Alignment) {
 172   return getFileAux<MemoryBuffer>(FilePath, MapSize, Offset, /*IsText=*/false,
 173                                   /*RequiresNullTerminator=*/false, IsVolatile,
 174                                   Alignment);
 175 }
 176
 177 //===----------------------------------------------------------------------===//
 178 // MemoryBuffer::getFile implementation.
 179 //===----------------------------------------------------------------------===//
 180
 181 namespace {
 182
 183 template <typename MB>
 184 constexpr sys::fs::mapped_file_region::mapmode Mapmode =
 185     sys::fs::mapped_file_region::readonly;
 186 template <>
 187 constexpr sys::fs::mapped_file_region::mapmode Mapmode<MemoryBuffer> =
 188     sys::fs::mapped_file_region::readonly;
 189 template <>
 190 constexpr sys::fs::mapped_file_region::mapmode Mapmode<WritableMemoryBuffer> =
 191     sys::fs::mapped_file_region::priv;
 192 template <>
 193 constexpr sys::fs::mapped_file_region::mapmode
 194     Mapmode<WriteThroughMemoryBuffer> = sys::fs::mapped_file_region::readwrite;
 195
 196 /// Memory maps a file descriptor using sys::fs::mapped_file_region.
 197 ///
 198 /// This handles converting the offset into a legal offset on the platform.
 199 template<typename MB>
 200 class MemoryBufferMMapFile : public MB {
 201   sys::fs::mapped_file_region MFR;
 202
 203   static uint64_t getLegalMapOffset(uint64_t Offset) {
 204     return Offset & ~(sys::fs::mapped_file_region::alignment() - 1);
 205   }
 206
 207   static uint64_t getLegalMapSize(uint64_t Len, uint64_t Offset) {
 208     return Len + (Offset - getLegalMapOffset(Offset));
 209   }
 210
 211   const char *getStart(uint64_t Len, uint64_t Offset) {
 212     return MFR.const_data() + (Offset - getLegalMapOffset(Offset));
 213   }
 214
 215 public:
 216   MemoryBufferMMapFile(bool RequiresNullTerminator, sys::fs::file_t FD, uint64_t Len,
 217                        uint64_t Offset, std::error_code &EC)
 218       : MFR(FD, Mapmode<MB>, getLegalMapSize(Len, Offset),
 219             getLegalMapOffset(Offset), EC) {
 220     if (!EC) {
 221       const char *Start = getStart(Len, Offset);
 222       MemoryBuffer::init(Start, Start + Len, RequiresNullTerminator);
 223     }
 224   }
 225
 226   /// Disable sized deallocation for MemoryBufferMMapFile, because it has
 227   /// tail-allocated data.
 228   void operator delete(void *p) { ::operator delete(p); }
 229
 230   StringRef getBufferIdentifier() const override {
 231     // The name is stored after the class itself.
 232     return StringRef(reinterpret_cast<const char *>(this + 1) + sizeof(size_t),
 233                      *reinterpret_cast<const size_t *>(this + 1));
 234   }
 235
 236   MemoryBuffer::BufferKind getBufferKind() const override {
 237     return MemoryBuffer::MemoryBuffer_MMap;
 238   }
 239
 240   void dontNeedIfMmap() override { MFR.dontNeed(); }
 241 };
 242 } // namespace
 243
 244 static ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
 245 getMemoryBufferForStream(sys::fs::file_t FD, const Twine &BufferName) {
 246   SmallString<sys::fs::DefaultReadChunkSize> Buffer;
 247   if (Error E = sys::fs::readNativeFileToEOF(FD, Buffer))
 248     return errorToErrorCode(std::move(E));
 249   return getMemBufferCopyImpl(Buffer, BufferName);
 250 }
 251
 252 ErrorOr<std::unique_ptr<MemoryBuffer>>
 253 MemoryBuffer::getFile(const Twine &Filename, bool IsText,
 254                       bool RequiresNullTerminator, bool IsVolatile,
 255                       std::optional<Align> Alignment) {
 256   return getFileAux<MemoryBuffer>(Filename, /*MapSize=*/-1, /*Offset=*/0,
 257                                   IsText, RequiresNullTerminator, IsVolatile,
 258                                   Alignment);
 259 }
 260
 261 template <typename MB>
 262 static ErrorOr<std::unique_ptr<MB>>
 263 getOpenFileImpl(sys::fs::file_t FD, const Twine &Filename, uint64_t FileSize,
 264                 uint64_t MapSize, int64_t Offset, bool RequiresNullTerminator,
 265                 bool IsVolatile, std::optional<Align> Alignment);
 266
 267 template <typename MB>
 268 static ErrorOr<std::unique_ptr<MB>>
 269 getFileAux(const Twine &Filename, uint64_t MapSize, uint64_t Offset,
 270            bool IsText, bool RequiresNullTerminator, bool IsVolatile,
 271            std::optional<Align> Alignment) {
 272   Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(
 273       Filename, IsText ? sys::fs::OF_TextWithCRLF : sys::fs::OF_None);
 274   if (!FDOrErr)
 275     return errorToErrorCode(FDOrErr.takeError());
 276   sys::fs::file_t FD = *FDOrErr;
 277   auto Ret = getOpenFileImpl<MB>(FD, Filename, /*FileSize=*/-1, MapSize, Offset,
 278                                  RequiresNullTerminator, IsVolatile, Alignment);
 279   sys::fs::closeFile(FD);
 280   return Ret;
 281 }
 282
 283 ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
 284 WritableMemoryBuffer::getFile(const Twine &Filename, bool IsVolatile,
 285                               std::optional<Align> Alignment) {
 286   return getFileAux<WritableMemoryBuffer>(
 287       Filename, /*MapSize=*/-1, /*Offset=*/0, /*IsText=*/false,
 288       /*RequiresNullTerminator=*/false, IsVolatile, Alignment);
 289 }
 290
 291 ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
 292 WritableMemoryBuffer::getFileSlice(const Twine &Filename, uint64_t MapSize,
 293                                    uint64_t Offset, bool IsVolatile,
 294                                    std::optional<Align> Alignment) {
 295   return getFileAux<WritableMemoryBuffer>(
 296       Filename, MapSize, Offset, /*IsText=*/false,
 297       /*RequiresNullTerminator=*/false, IsVolatile, Alignment);
 298 }
 299
 300 std::unique_ptr<WritableMemoryBuffer>
 301 WritableMemoryBuffer::getNewUninitMemBuffer(size_t Size,
 302                                             const Twine &BufferName,
 303                                             std::optional<Align> Alignment) {
 304   using MemBuffer = MemoryBufferMem<WritableMemoryBuffer>;
 305
 306   // Use 16-byte alignment if no alignment is specified.
 307   Align BufAlign = Alignment.value_or(Align(16));
 308
 309   // Allocate space for the MemoryBuffer, the data and the name. It is important
 310   // that MemoryBuffer and data are aligned so PointerIntPair works with them.
 311   SmallString<256> NameBuf;
 312   StringRef NameRef = BufferName.toStringRef(NameBuf);
 313
 314   size_t StringLen = sizeof(MemBuffer) + sizeof(size_t) + NameRef.size() + 1;
 315   size_t RealLen = StringLen + Size + 1 + BufAlign.value();
 316   if (RealLen <= Size) // Check for rollover.
 317     return nullptr;
 318   char *Mem = static_cast<char*>(operator new(RealLen, std::nothrow));
 319   if (!Mem)
 320     return nullptr;
 321
 322   // The name is stored after the class itself.
 323   *reinterpret_cast<size_t *>(Mem + sizeof(MemBuffer)) = NameRef.size();
 324   CopyStringRef(Mem + sizeof(MemBuffer) + sizeof(size_t), NameRef);
 325
 326   // The buffer begins after the name and must be aligned.
 327   char *Buf = (char *)alignAddr(Mem + StringLen, BufAlign);
 328   Buf[Size] = 0; // Null terminate buffer.
 329
 330   auto *Ret = new (Mem) MemBuffer(StringRef(Buf, Size), true);
 331   return std::unique_ptr<WritableMemoryBuffer>(Ret);
 332 }
 333
 334 std::unique_ptr<WritableMemoryBuffer>
 335 WritableMemoryBuffer::getNewMemBuffer(size_t Size, const Twine &BufferName) {
 336   auto SB = WritableMemoryBuffer::getNewUninitMemBuffer(Size, BufferName);
 337   if (!SB)
 338     return nullptr;
 339   memset(SB->getBufferStart(), 0, Size);
 340   return SB;
 341 }
 342
 343 static bool shouldUseMmap(sys::fs::file_t FD,
 344                           size_t FileSize,
 345                           size_t MapSize,
 346                           off_t Offset,
 347                           bool RequiresNullTerminator,
 348                           int PageSize,
 349                           bool IsVolatile) {
 350   // mmap may leave the buffer without null terminator if the file size changed
 351   // by the time the last page is mapped in, so avoid it if the file size is
 352   // likely to change.
 353   if (IsVolatile && RequiresNullTerminator)
 354     return false;
 355
 356   // We don't use mmap for small files because this can severely fragment our
 357   // address space.
 358   if (MapSize < 4 * 4096 || MapSize < (unsigned)PageSize)
 359     return false;
 360
 361   if (!RequiresNullTerminator)
 362     return true;
 363
 364   // If we don't know the file size, use fstat to find out.  fstat on an open
 365   // file descriptor is cheaper than stat on a random path.
 366   // FIXME: this chunk of code is duplicated, but it avoids a fstat when
 367   // RequiresNullTerminator = false and MapSize != -1.
 368   if (FileSize == size_t(-1)) {
 369     sys::fs::file_status Status;
 370     if (sys::fs::status(FD, Status))
 371       return false;
 372     FileSize = Status.getSize();
 373   }
 374
 375   // If we need a null terminator and the end of the map is inside the file,
 376   // we cannot use mmap.
 377   size_t End = Offset + MapSize;
 378   assert(End <= FileSize);
 379   if (End != FileSize)
 380     return false;
 381
 382   // Don't try to map files that are exactly a multiple of the system page size
 383   // if we need a null terminator.
 384   if ((FileSize & (PageSize -1)) == 0)
 385     return false;
 386
 387 #if defined(__CYGWIN__)
 388   // Don't try to map files that are exactly a multiple of the physical page size
 389   // if we need a null terminator.
 390   // FIXME: We should reorganize again getPageSize() on Win32.
 391   if ((FileSize & (4096 - 1)) == 0)
 392     return false;
 393 #endif
 394
 395   return true;
 396 }
 397
 398 static ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
 399 getReadWriteFile(const Twine &Filename, uint64_t FileSize, uint64_t MapSize,
 400                  uint64_t Offset) {
 401   Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForReadWrite(
 402       Filename, sys::fs::CD_OpenExisting, sys::fs::OF_None);
 403   if (!FDOrErr)
 404     return errorToErrorCode(FDOrErr.takeError());
 405   sys::fs::file_t FD = *FDOrErr;
 406
 407   // Default is to map the full file.
 408   if (MapSize == uint64_t(-1)) {
 409     // If we don't know the file size, use fstat to find out.  fstat on an open
 410     // file descriptor is cheaper than stat on a random path.
 411     if (FileSize == uint64_t(-1)) {
 412       sys::fs::file_status Status;
 413       std::error_code EC = sys::fs::status(FD, Status);
 414       if (EC)
 415         return EC;
 416
 417       // If this not a file or a block device (e.g. it's a named pipe
 418       // or character device), we can't mmap it, so error out.
 419       sys::fs::file_type Type = Status.type();
 420       if (Type != sys::fs::file_type::regular_file &&
 421           Type != sys::fs::file_type::block_file)
 422         return make_error_code(errc::invalid_argument);
 423
 424       FileSize = Status.getSize();
 425     }
 426     MapSize = FileSize;
 427   }
 428
 429   std::error_code EC;
 430   std::unique_ptr<WriteThroughMemoryBuffer> Result(
 431       new (NamedBufferAlloc(Filename))
 432           MemoryBufferMMapFile<WriteThroughMemoryBuffer>(false, FD, MapSize,
 433                                                          Offset, EC));
 434   if (EC)
 435     return EC;
 436   return std::move(Result);
 437 }
 438
 439 ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
 440 WriteThroughMemoryBuffer::getFile(const Twine &Filename, int64_t FileSize) {
 441   return getReadWriteFile(Filename, FileSize, FileSize, 0);
 442 }
 443
 444 /// Map a subrange of the specified file as a WritableMemoryBuffer.
 445 ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
 446 WriteThroughMemoryBuffer::getFileSlice(const Twine &Filename, uint64_t MapSize,
 447                                        uint64_t Offset) {
 448   return getReadWriteFile(Filename, -1, MapSize, Offset);
 449 }
 450
 451 template <typename MB>
 452 static ErrorOr<std::unique_ptr<MB>>
 453 getOpenFileImpl(sys::fs::file_t FD, const Twine &Filename, uint64_t FileSize,
 454                 uint64_t MapSize, int64_t Offset, bool RequiresNullTerminator,
 455                 bool IsVolatile, std::optional<Align> Alignment) {
 456   static int PageSize = sys::Process::getPageSizeEstimate();
 457
 458   // Default is to map the full file.
 459   if (MapSize == uint64_t(-1)) {
 460     // If we don't know the file size, use fstat to find out.  fstat on an open
 461     // file descriptor is cheaper than stat on a random path.
 462     if (FileSize == uint64_t(-1)) {
 463       sys::fs::file_status Status;
 464       std::error_code EC = sys::fs::status(FD, Status);
 465       if (EC)
 466         return EC;
 467
 468       // If this not a file or a block device (e.g. it's a named pipe
 469       // or character device), we can't trust the size. Create the memory
 470       // buffer by copying off the stream.
 471       sys::fs::file_type Type = Status.type();
 472       if (Type != sys::fs::file_type::regular_file &&
 473           Type != sys::fs::file_type::block_file)
 474         return getMemoryBufferForStream(FD, Filename);
 475
 476       FileSize = Status.getSize();
 477     }
 478     MapSize = FileSize;
 479   }
 480
 481   if (shouldUseMmap(FD, FileSize, MapSize, Offset, RequiresNullTerminator,
 482                     PageSize, IsVolatile)) {
 483     std::error_code EC;
 484     std::unique_ptr<MB> Result(
 485         new (NamedBufferAlloc(Filename)) MemoryBufferMMapFile<MB>(
 486             RequiresNullTerminator, FD, MapSize, Offset, EC));
 487     if (!EC)
 488       return std::move(Result);
 489   }
 490
 491 #ifdef __MVS__
 492   // Set codepage auto-conversion for z/OS.
 493   if (auto EC = llvm::enableAutoConversion(FD))
 494     return EC;
 495 #endif
 496
 497   auto Buf =
 498       WritableMemoryBuffer::getNewUninitMemBuffer(MapSize, Filename, Alignment);
 499   if (!Buf) {
 500     // Failed to create a buffer. The only way it can fail is if
 501     // new(std::nothrow) returns 0.
 502     return make_error_code(errc::not_enough_memory);
 503   }
 504
 505   // Read until EOF, zero-initialize the rest.
 506   MutableArrayRef<char> ToRead = Buf->getBuffer();
 507   while (!ToRead.empty()) {
 508     Expected<size_t> ReadBytes =
 509         sys::fs::readNativeFileSlice(FD, ToRead, Offset);
 510     if (!ReadBytes)
 511       return errorToErrorCode(ReadBytes.takeError());
 512     if (*ReadBytes == 0) {
 513       std::memset(ToRead.data(), 0, ToRead.size());
 514       break;
 515     }
 516     ToRead = ToRead.drop_front(*ReadBytes);
 517     Offset += *ReadBytes;
 518   }
 519
 520   return std::move(Buf);
 521 }
 522
 523 ErrorOr<std::unique_ptr<MemoryBuffer>>
 524 MemoryBuffer::getOpenFile(sys::fs::file_t FD, const Twine &Filename,
 525                           uint64_t FileSize, bool RequiresNullTerminator,
 526                           bool IsVolatile, std::optional<Align> Alignment) {
 527   return getOpenFileImpl<MemoryBuffer>(FD, Filename, FileSize, FileSize, 0,
 528                                        RequiresNullTerminator, IsVolatile,
 529                                        Alignment);
 530 }
 531
 532 ErrorOr<std::unique_ptr<MemoryBuffer>> MemoryBuffer::getOpenFileSlice(
 533     sys::fs::file_t FD, const Twine &Filename, uint64_t MapSize, int64_t Offset,
 534     bool IsVolatile, std::optional<Align> Alignment) {
 535   assert(MapSize != uint64_t(-1));
 536   return getOpenFileImpl<MemoryBuffer>(FD, Filename, -1, MapSize, Offset, false,
 537                                        IsVolatile, Alignment);
 538 }
 539
 540 ErrorOr<std::unique_ptr<MemoryBuffer>> MemoryBuffer::getSTDIN() {
 541   // Read in all of the data from stdin, we cannot mmap stdin.
 542   //
 543   // FIXME: That isn't necessarily true, we should try to mmap stdin and
 544   // fallback if it fails.
 545   sys::ChangeStdinMode(sys::fs::OF_Text);
 546
 547   return getMemoryBufferForStream(sys::fs::getStdinHandle(), "<stdin>");
 548 }
 549
 550 ErrorOr<std::unique_ptr<MemoryBuffer>>
 551 MemoryBuffer::getFileAsStream(const Twine &Filename) {
 552   Expected<sys::fs::file_t> FDOrErr =
 553       sys::fs::openNativeFileForRead(Filename, sys::fs::OF_None);
 554   if (!FDOrErr)
 555     return errorToErrorCode(FDOrErr.takeError());
 556   sys::fs::file_t FD = *FDOrErr;
 557   ErrorOr<std::unique_ptr<MemoryBuffer>> Ret =
 558       getMemoryBufferForStream(FD, Filename);
 559   sys::fs::closeFile(FD);
 560   return Ret;
 561 }
 562
 563 MemoryBufferRef MemoryBuffer::getMemBufferRef() const {
 564   StringRef Data = getBuffer();
 565   StringRef Identifier = getBufferIdentifier();
 566   return MemoryBufferRef(Data, Identifier);
 567 }
 568
 569 SmallVectorMemoryBuffer::~SmallVectorMemoryBuffer() = default;