llvm/lib/Support/MemoryBuffer.cpp - toolchain/llvm-project - Gitiles

 //===--- MemoryBuffer.cpp - Memory Buffer implementation ------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 //  This file implements the MemoryBuffer interface.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Config/config.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/Errno.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/SmallVectorMemoryBuffer.h"
 #include <cassert>
 #include <cerrno>
 #include <cstring>
 #include <new>
 #include <sys/types.h>
 #include <system_error>
 #if !defined(_MSC_VER) && !defined(__MINGW32__)
 #include <unistd.h>
 #else
 #include <io.h>
 #endif
 using namespace llvm;

 //===----------------------------------------------------------------------===//
 // MemoryBuffer implementation itself.
 //===----------------------------------------------------------------------===//

 MemoryBuffer::~MemoryBuffer() { }

 /// init - Initialize this MemoryBuffer as a reference to externally allocated
 /// memory, memory that we know is already null terminated.
 void MemoryBuffer::init(const char *BufStart, const char *BufEnd,
                         bool RequiresNullTerminator) {
   assert((!RequiresNullTerminator || BufEnd[0] == 0) &&
          "Buffer is not null terminated!");
   BufferStart = BufStart;
   BufferEnd = BufEnd;
 }

 //===----------------------------------------------------------------------===//
 // MemoryBufferMem implementation.
 //===----------------------------------------------------------------------===//

 /// CopyStringRef - Copies contents of a StringRef into a block of memory and
 /// null-terminates it.
 static void CopyStringRef(char *Memory, StringRef Data) {
   if (!Data.empty())
     memcpy(Memory, Data.data(), Data.size());
   Memory[Data.size()] = 0; // Null terminate string.
 }

 namespace {
 struct NamedBufferAlloc {
   const Twine &Name;
   NamedBufferAlloc(const Twine &Name) : Name(Name) {}
 };
 }

 void *operator new(size_t N, const NamedBufferAlloc &Alloc) {
   SmallString<256> NameBuf;
   StringRef NameRef = Alloc.Name.toStringRef(NameBuf);

   char *Mem = static_cast<char *>(operator new(N + NameRef.size() + 1));
   CopyStringRef(Mem + N, NameRef);
   return Mem;
 }

 namespace {
 /// MemoryBufferMem - Named MemoryBuffer pointing to a block of memory.
 template<typename MB>
 class MemoryBufferMem : public MB {
 public:
   MemoryBufferMem(StringRef InputData, bool RequiresNullTerminator) {
     MemoryBuffer::init(InputData.begin(), InputData.end(),
                        RequiresNullTerminator);
   }

   /// Disable sized deallocation for MemoryBufferMem, because it has
   /// tail-allocated data.
   void operator delete(void *p) { ::operator delete(p); }

   StringRef getBufferIdentifier() const override {
     // The name is stored after the class itself.
     return StringRef(reinterpret_cast<const char *>(this + 1));
   }

   MemoryBuffer::BufferKind getBufferKind() const override {
     return MemoryBuffer::MemoryBuffer_Malloc;
   }
 };
 }

 template <typename MB>
 static ErrorOr<std::unique_ptr<MB>>
 getFileAux(const Twine &Filename, int64_t FileSize, uint64_t MapSize,
            uint64_t Offset, bool RequiresNullTerminator, bool IsVolatile);

 std::unique_ptr<MemoryBuffer>
 MemoryBuffer::getMemBuffer(StringRef InputData, StringRef BufferName,
                            bool RequiresNullTerminator) {
   auto *Ret = new (NamedBufferAlloc(BufferName))
       MemoryBufferMem<MemoryBuffer>(InputData, RequiresNullTerminator);
   return std::unique_ptr<MemoryBuffer>(Ret);
 }

 std::unique_ptr<MemoryBuffer>
 MemoryBuffer::getMemBuffer(MemoryBufferRef Ref, bool RequiresNullTerminator) {
   return std::unique_ptr<MemoryBuffer>(getMemBuffer(
       Ref.getBuffer(), Ref.getBufferIdentifier(), RequiresNullTerminator));
 }

 static ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
 getMemBufferCopyImpl(StringRef InputData, const Twine &BufferName) {
   auto Buf = WritableMemoryBuffer::getNewUninitMemBuffer(InputData.size(), BufferName);
   if (!Buf)
     return make_error_code(errc::not_enough_memory);
   memcpy(Buf->getBufferStart(), InputData.data(), InputData.size());
   return std::move(Buf);
 }

 std::unique_ptr<MemoryBuffer>
 MemoryBuffer::getMemBufferCopy(StringRef InputData, const Twine &BufferName) {
   auto Buf = getMemBufferCopyImpl(InputData, BufferName);
   if (Buf)
     return std::move(*Buf);
   return nullptr;
 }

 ErrorOr<std::unique_ptr<MemoryBuffer>>
 MemoryBuffer::getFileOrSTDIN(const Twine &Filename, int64_t FileSize,
                              bool RequiresNullTerminator) {
   SmallString<256> NameBuf;
   StringRef NameRef = Filename.toStringRef(NameBuf);

   if (NameRef == "-")
     return getSTDIN();
   return getFile(Filename, FileSize, RequiresNullTerminator);
 }

 ErrorOr<std::unique_ptr<MemoryBuffer>>
 MemoryBuffer::getFileSlice(const Twine &FilePath, uint64_t MapSize,
                            uint64_t Offset, bool IsVolatile) {
   return getFileAux<MemoryBuffer>(FilePath, -1, MapSize, Offset, false,
                                   IsVolatile);
 }

 //===----------------------------------------------------------------------===//
 // MemoryBuffer::getFile implementation.
 //===----------------------------------------------------------------------===//

 namespace {
 /// Memory maps a file descriptor using sys::fs::mapped_file_region.
 ///
 /// This handles converting the offset into a legal offset on the platform.
 template<typename MB>
 class MemoryBufferMMapFile : public MB {
   sys::fs::mapped_file_region MFR;

   static uint64_t getLegalMapOffset(uint64_t Offset) {
     return Offset & ~(sys::fs::mapped_file_region::alignment() - 1);
   }

   static uint64_t getLegalMapSize(uint64_t Len, uint64_t Offset) {
     return Len + (Offset - getLegalMapOffset(Offset));
   }

   const char *getStart(uint64_t Len, uint64_t Offset) {
     return MFR.const_data() + (Offset - getLegalMapOffset(Offset));
   }

 public:
   MemoryBufferMMapFile(bool RequiresNullTerminator, int FD, uint64_t Len,
                        uint64_t Offset, std::error_code &EC)
       : MFR(FD, MB::Mapmode, getLegalMapSize(Len, Offset),
             getLegalMapOffset(Offset), EC) {
     if (!EC) {
       const char *Start = getStart(Len, Offset);
       MemoryBuffer::init(Start, Start + Len, RequiresNullTerminator);
     }
   }

   /// Disable sized deallocation for MemoryBufferMMapFile, because it has
   /// tail-allocated data.
   void operator delete(void *p) { ::operator delete(p); }

   StringRef getBufferIdentifier() const override {
     // The name is stored after the class itself.
     return StringRef(reinterpret_cast<const char *>(this + 1));
   }

   MemoryBuffer::BufferKind getBufferKind() const override {
     return MemoryBuffer::MemoryBuffer_MMap;
   }
 };
 }

 static ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
 getMemoryBufferForStream(int FD, const Twine &BufferName) {
   const ssize_t ChunkSize = 4096*4;
   SmallString<ChunkSize> Buffer;
   ssize_t ReadBytes;
   // Read into Buffer until we hit EOF.
   do {
     Buffer.reserve(Buffer.size() + ChunkSize);
     ReadBytes = sys::RetryAfterSignal(-1, ::read, FD, Buffer.end(), ChunkSize);
     if (ReadBytes == -1)
       return std::error_code(errno, std::generic_category());
     Buffer.set_size(Buffer.size() + ReadBytes);
   } while (ReadBytes != 0);

   return getMemBufferCopyImpl(Buffer, BufferName);
 }


 ErrorOr<std::unique_ptr<MemoryBuffer>>
 MemoryBuffer::getFile(const Twine &Filename, int64_t FileSize,
                       bool RequiresNullTerminator, bool IsVolatile) {
   return getFileAux<MemoryBuffer>(Filename, FileSize, FileSize, 0,
                                   RequiresNullTerminator, IsVolatile);
 }

 template <typename MB>
 static ErrorOr<std::unique_ptr<MB>>
 getOpenFileImpl(int FD, const Twine &Filename, uint64_t FileSize,
                 uint64_t MapSize, int64_t Offset, bool RequiresNullTerminator,
                 bool IsVolatile);

 template <typename MB>
 static ErrorOr<std::unique_ptr<MB>>
 getFileAux(const Twine &Filename, int64_t FileSize, uint64_t MapSize,
            uint64_t Offset, bool RequiresNullTerminator, bool IsVolatile) {
   int FD;
   std::error_code EC = sys::fs::openFileForRead(Filename, FD, sys::fs::OF_None);

   if (EC)
     return EC;

   auto Ret = getOpenFileImpl<MB>(FD, Filename, FileSize, MapSize, Offset,
                                  RequiresNullTerminator, IsVolatile);
   close(FD);
   return Ret;
 }

 ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
 WritableMemoryBuffer::getFile(const Twine &Filename, int64_t FileSize,
                               bool IsVolatile) {
   return getFileAux<WritableMemoryBuffer>(Filename, FileSize, FileSize, 0,
                                           /*RequiresNullTerminator*/ false,
                                           IsVolatile);
 }

 ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
 WritableMemoryBuffer::getFileSlice(const Twine &Filename, uint64_t MapSize,
                                    uint64_t Offset, bool IsVolatile) {
   return getFileAux<WritableMemoryBuffer>(Filename, -1, MapSize, Offset, false,
                                           IsVolatile);
 }

 std::unique_ptr<WritableMemoryBuffer>
 WritableMemoryBuffer::getNewUninitMemBuffer(size_t Size, const Twine &BufferName) {
   using MemBuffer = MemoryBufferMem<WritableMemoryBuffer>;
   // Allocate space for the MemoryBuffer, the data and the name. It is important
   // that MemoryBuffer and data are aligned so PointerIntPair works with them.
   // TODO: Is 16-byte alignment enough?  We copy small object files with large
   // alignment expectations into this buffer.
   SmallString<256> NameBuf;
   StringRef NameRef = BufferName.toStringRef(NameBuf);
   size_t AlignedStringLen = alignTo(sizeof(MemBuffer) + NameRef.size() + 1, 16);
   size_t RealLen = AlignedStringLen + Size + 1;
   char *Mem = static_cast<char*>(operator new(RealLen, std::nothrow));
   if (!Mem)
     return nullptr;

   // The name is stored after the class itself.
   CopyStringRef(Mem + sizeof(MemBuffer), NameRef);

   // The buffer begins after the name and must be aligned.
   char *Buf = Mem + AlignedStringLen;
   Buf[Size] = 0; // Null terminate buffer.

   auto *Ret = new (Mem) MemBuffer(StringRef(Buf, Size), true);
   return std::unique_ptr<WritableMemoryBuffer>(Ret);
 }

 std::unique_ptr<WritableMemoryBuffer>
 WritableMemoryBuffer::getNewMemBuffer(size_t Size, const Twine &BufferName) {
   auto SB = WritableMemoryBuffer::getNewUninitMemBuffer(Size, BufferName);
   if (!SB)
     return nullptr;
   memset(SB->getBufferStart(), 0, Size);
   return SB;
 }

 static bool shouldUseMmap(int FD,
                           size_t FileSize,
                           size_t MapSize,
                           off_t Offset,
                           bool RequiresNullTerminator,
                           int PageSize,
                           bool IsVolatile) {
   // mmap may leave the buffer without null terminator if the file size changed
   // by the time the last page is mapped in, so avoid it if the file size is
   // likely to change.
   if (IsVolatile)
     return false;

   // We don't use mmap for small files because this can severely fragment our
   // address space.
   if (MapSize < 4 * 4096 || MapSize < (unsigned)PageSize)
     return false;

   if (!RequiresNullTerminator)
     return true;

   // If we don't know the file size, use fstat to find out.  fstat on an open
   // file descriptor is cheaper than stat on a random path.
   // FIXME: this chunk of code is duplicated, but it avoids a fstat when
   // RequiresNullTerminator = false and MapSize != -1.
   if (FileSize == size_t(-1)) {
     sys::fs::file_status Status;
     if (sys::fs::status(FD, Status))
       return false;
     FileSize = Status.getSize();
   }

   // If we need a null terminator and the end of the map is inside the file,
   // we cannot use mmap.
   size_t End = Offset + MapSize;
   assert(End <= FileSize);
   if (End != FileSize)
     return false;

   // Don't try to map files that are exactly a multiple of the system page size
   // if we need a null terminator.
   if ((FileSize & (PageSize -1)) == 0)
     return false;

 #if defined(__CYGWIN__)
   // Don't try to map files that are exactly a multiple of the physical page size
   // if we need a null terminator.
   // FIXME: We should reorganize again getPageSize() on Win32.
   if ((FileSize & (4096 - 1)) == 0)
     return false;
 #endif

   return true;
 }

 static ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
 getReadWriteFile(const Twine &Filename, uint64_t FileSize, uint64_t MapSize,
                  uint64_t Offset) {
   int FD;
   std::error_code EC = sys::fs::openFileForReadWrite(
       Filename, FD, sys::fs::CD_OpenExisting, sys::fs::OF_None);

   if (EC)
     return EC;

   // Default is to map the full file.
   if (MapSize == uint64_t(-1)) {
     // If we don't know the file size, use fstat to find out.  fstat on an open
     // file descriptor is cheaper than stat on a random path.
     if (FileSize == uint64_t(-1)) {
       sys::fs::file_status Status;
       std::error_code EC = sys::fs::status(FD, Status);
       if (EC)
         return EC;

       // If this not a file or a block device (e.g. it's a named pipe
       // or character device), we can't mmap it, so error out.
       sys::fs::file_type Type = Status.type();
       if (Type != sys::fs::file_type::regular_file &&
           Type != sys::fs::file_type::block_file)
         return make_error_code(errc::invalid_argument);

       FileSize = Status.getSize();
     }
     MapSize = FileSize;
   }

   std::unique_ptr<WriteThroughMemoryBuffer> Result(
       new (NamedBufferAlloc(Filename))
           MemoryBufferMMapFile<WriteThroughMemoryBuffer>(false, FD, MapSize,
                                                          Offset, EC));
   if (EC)
     return EC;
   return std::move(Result);
 }

 ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
 WriteThroughMemoryBuffer::getFile(const Twine &Filename, int64_t FileSize) {
   return getReadWriteFile(Filename, FileSize, FileSize, 0);
 }

 /// Map a subrange of the specified file as a WritableMemoryBuffer.
 ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
 WriteThroughMemoryBuffer::getFileSlice(const Twine &Filename, uint64_t MapSize,
                                        uint64_t Offset) {
   return getReadWriteFile(Filename, -1, MapSize, Offset);
 }

 template <typename MB>
 static ErrorOr<std::unique_ptr<MB>>
 getOpenFileImpl(int FD, const Twine &Filename, uint64_t FileSize,
                 uint64_t MapSize, int64_t Offset, bool RequiresNullTerminator,
                 bool IsVolatile) {
   static int PageSize = sys::Process::getPageSize();

   // Default is to map the full file.
   if (MapSize == uint64_t(-1)) {
     // If we don't know the file size, use fstat to find out.  fstat on an open
     // file descriptor is cheaper than stat on a random path.
     if (FileSize == uint64_t(-1)) {
       sys::fs::file_status Status;
       std::error_code EC = sys::fs::status(FD, Status);
       if (EC)
         return EC;

       // If this not a file or a block device (e.g. it's a named pipe
       // or character device), we can't trust the size. Create the memory
       // buffer by copying off the stream.
       sys::fs::file_type Type = Status.type();
       if (Type != sys::fs::file_type::regular_file &&
           Type != sys::fs::file_type::block_file)
         return getMemoryBufferForStream(FD, Filename);

       FileSize = Status.getSize();
     }
     MapSize = FileSize;
   }

   if (shouldUseMmap(FD, FileSize, MapSize, Offset, RequiresNullTerminator,
                     PageSize, IsVolatile)) {
     std::error_code EC;
     std::unique_ptr<MB> Result(
         new (NamedBufferAlloc(Filename)) MemoryBufferMMapFile<MB>(
             RequiresNullTerminator, FD, MapSize, Offset, EC));
     if (!EC)
       return std::move(Result);
   }

   auto Buf = WritableMemoryBuffer::getNewUninitMemBuffer(MapSize, Filename);
   if (!Buf) {
     // Failed to create a buffer. The only way it can fail is if
     // new(std::nothrow) returns 0.
     return make_error_code(errc::not_enough_memory);
   }

   char *BufPtr = Buf.get()->getBufferStart();

   size_t BytesLeft = MapSize;
 #ifndef HAVE_PREAD
   if (lseek(FD, Offset, SEEK_SET) == -1)
     return std::error_code(errno, std::generic_category());
 #endif

   while (BytesLeft) {
 #ifdef HAVE_PREAD
     ssize_t NumRead = sys::RetryAfterSignal(-1, ::pread, FD, BufPtr, BytesLeft,
                                             MapSize - BytesLeft + Offset);
 #else
     ssize_t NumRead = sys::RetryAfterSignal(-1, ::read, FD, BufPtr, BytesLeft);
 #endif
     if (NumRead == -1) {
       // Error while reading.
       return std::error_code(errno, std::generic_category());
     }
     if (NumRead == 0) {
       memset(BufPtr, 0, BytesLeft); // zero-initialize rest of the buffer.
       break;
     }
     BytesLeft -= NumRead;
     BufPtr += NumRead;
   }

   return std::move(Buf);
 }

 ErrorOr<std::unique_ptr<MemoryBuffer>>
 MemoryBuffer::getOpenFile(int FD, const Twine &Filename, uint64_t FileSize,
                           bool RequiresNullTerminator, bool IsVolatile) {
   return getOpenFileImpl<MemoryBuffer>(FD, Filename, FileSize, FileSize, 0,
                          RequiresNullTerminator, IsVolatile);
 }

 ErrorOr<std::unique_ptr<MemoryBuffer>>
 MemoryBuffer::getOpenFileSlice(int FD, const Twine &Filename, uint64_t MapSize,
                                int64_t Offset, bool IsVolatile) {
   assert(MapSize != uint64_t(-1));
   return getOpenFileImpl<MemoryBuffer>(FD, Filename, -1, MapSize, Offset, false,
                                        IsVolatile);
 }

 ErrorOr<std::unique_ptr<MemoryBuffer>> MemoryBuffer::getSTDIN() {
   // Read in all of the data from stdin, we cannot mmap stdin.
   //
   // FIXME: That isn't necessarily true, we should try to mmap stdin and
   // fallback if it fails.
   sys::ChangeStdinToBinary();

   return getMemoryBufferForStream(0, "<stdin>");
 }

 ErrorOr<std::unique_ptr<MemoryBuffer>>
 MemoryBuffer::getFileAsStream(const Twine &Filename) {
   int FD;
   std::error_code EC = sys::fs::openFileForRead(Filename, FD, sys::fs::OF_None);
   if (EC)
     return EC;
   ErrorOr<std::unique_ptr<MemoryBuffer>> Ret =
       getMemoryBufferForStream(FD, Filename);
   close(FD);
   return Ret;
 }

 MemoryBufferRef MemoryBuffer::getMemBufferRef() const {
   StringRef Data = getBuffer();
   StringRef Identifier = getBufferIdentifier();
   return MemoryBufferRef(Data, Identifier);
 }

 SmallVectorMemoryBuffer::~SmallVectorMemoryBuffer() {}
	//===--- MemoryBuffer.cpp - Memory Buffer implementation ------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This file implements the MemoryBuffer interface.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/Support/MemoryBuffer.h"
	#include "llvm/ADT/SmallString.h"
	#include "llvm/Config/config.h"
	#include "llvm/Support/Errc.h"
	#include "llvm/Support/Errno.h"
	#include "llvm/Support/FileSystem.h"
	#include "llvm/Support/MathExtras.h"
	#include "llvm/Support/Path.h"
	#include "llvm/Support/Process.h"
	#include "llvm/Support/Program.h"
	#include "llvm/Support/SmallVectorMemoryBuffer.h"
	#include <cassert>
	#include <cerrno>
	#include <cstring>
	#include <new>
	#include <sys/types.h>
	#include <system_error>
	#if !defined(_MSC_VER) && !defined(__MINGW32__)
	#include <unistd.h>
	#else
	#include <io.h>
	#endif
	using namespace llvm;

	//===----------------------------------------------------------------------===//
	// MemoryBuffer implementation itself.
	//===----------------------------------------------------------------------===//

	MemoryBuffer::~MemoryBuffer() { }

	/// init - Initialize this MemoryBuffer as a reference to externally allocated
	/// memory, memory that we know is already null terminated.
	void MemoryBuffer::init(const char BufStart, const char BufEnd,
	bool RequiresNullTerminator) {
	assert((!RequiresNullTerminator \|\| BufEnd[0] == 0) &&
	"Buffer is not null terminated!");
	BufferStart = BufStart;
	BufferEnd = BufEnd;
	}

	//===----------------------------------------------------------------------===//
	// MemoryBufferMem implementation.
	//===----------------------------------------------------------------------===//

	/// CopyStringRef - Copies contents of a StringRef into a block of memory and
	/// null-terminates it.
	static void CopyStringRef(char *Memory, StringRef Data) {
	if (!Data.empty())
	memcpy(Memory, Data.data(), Data.size());
	Memory[Data.size()] = 0; // Null terminate string.
	}

	namespace {
	struct NamedBufferAlloc {
	const Twine &Name;
	NamedBufferAlloc(const Twine &Name) : Name(Name) {}
	};
	}

	void *operator new(size_t N, const NamedBufferAlloc &Alloc) {
	SmallString<256> NameBuf;
	StringRef NameRef = Alloc.Name.toStringRef(NameBuf);

	char Mem = static_cast<char >(operator new(N + NameRef.size() + 1));
	CopyStringRef(Mem + N, NameRef);
	return Mem;
	}

	namespace {
	/// MemoryBufferMem - Named MemoryBuffer pointing to a block of memory.
	template<typename MB>
	class MemoryBufferMem : public MB {
	public:
	MemoryBufferMem(StringRef InputData, bool RequiresNullTerminator) {
	MemoryBuffer::init(InputData.begin(), InputData.end(),
	RequiresNullTerminator);
	}

	/// Disable sized deallocation for MemoryBufferMem, because it has
	/// tail-allocated data.
	void operator delete(void *p) { ::operator delete(p); }

	StringRef getBufferIdentifier() const override {
	// The name is stored after the class itself.
	return StringRef(reinterpret_cast<const char *>(this + 1));
	}

	MemoryBuffer::BufferKind getBufferKind() const override {
	return MemoryBuffer::MemoryBuffer_Malloc;
	}
	};
	}

	template <typename MB>
	static ErrorOr<std::unique_ptr<MB>>
	getFileAux(const Twine &Filename, int64_t FileSize, uint64_t MapSize,
	uint64_t Offset, bool RequiresNullTerminator, bool IsVolatile);

	std::unique_ptr<MemoryBuffer>
	MemoryBuffer::getMemBuffer(StringRef InputData, StringRef BufferName,
	bool RequiresNullTerminator) {
	auto *Ret = new (NamedBufferAlloc(BufferName))
	MemoryBufferMem<MemoryBuffer>(InputData, RequiresNullTerminator);
	return std::unique_ptr<MemoryBuffer>(Ret);
	}

	std::unique_ptr<MemoryBuffer>
	MemoryBuffer::getMemBuffer(MemoryBufferRef Ref, bool RequiresNullTerminator) {
	return std::unique_ptr<MemoryBuffer>(getMemBuffer(
	Ref.getBuffer(), Ref.getBufferIdentifier(), RequiresNullTerminator));
	}

	static ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
	getMemBufferCopyImpl(StringRef InputData, const Twine &BufferName) {
	auto Buf = WritableMemoryBuffer::getNewUninitMemBuffer(InputData.size(), BufferName);
	if (!Buf)
	return make_error_code(errc::not_enough_memory);
	memcpy(Buf->getBufferStart(), InputData.data(), InputData.size());
	return std::move(Buf);
	}

	std::unique_ptr<MemoryBuffer>
	MemoryBuffer::getMemBufferCopy(StringRef InputData, const Twine &BufferName) {
	auto Buf = getMemBufferCopyImpl(InputData, BufferName);
	if (Buf)
	return std::move(*Buf);
	return nullptr;
	}

	ErrorOr<std::unique_ptr<MemoryBuffer>>
	MemoryBuffer::getFileOrSTDIN(const Twine &Filename, int64_t FileSize,
	bool RequiresNullTerminator) {
	SmallString<256> NameBuf;
	StringRef NameRef = Filename.toStringRef(NameBuf);

	if (NameRef == "-")
	return getSTDIN();
	return getFile(Filename, FileSize, RequiresNullTerminator);
	}

	ErrorOr<std::unique_ptr<MemoryBuffer>>
	MemoryBuffer::getFileSlice(const Twine &FilePath, uint64_t MapSize,
	uint64_t Offset, bool IsVolatile) {
	return getFileAux<MemoryBuffer>(FilePath, -1, MapSize, Offset, false,
	IsVolatile);
	}

	//===----------------------------------------------------------------------===//
	// MemoryBuffer::getFile implementation.
	//===----------------------------------------------------------------------===//

	namespace {
	/// Memory maps a file descriptor using sys::fs::mapped_file_region.
	///
	/// This handles converting the offset into a legal offset on the platform.
	template<typename MB>
	class MemoryBufferMMapFile : public MB {
	sys::fs::mapped_file_region MFR;

	static uint64_t getLegalMapOffset(uint64_t Offset) {
	return Offset & ~(sys::fs::mapped_file_region::alignment() - 1);
	}

	static uint64_t getLegalMapSize(uint64_t Len, uint64_t Offset) {
	return Len + (Offset - getLegalMapOffset(Offset));
	}

	const char *getStart(uint64_t Len, uint64_t Offset) {
	return MFR.const_data() + (Offset - getLegalMapOffset(Offset));
	}

	public:
	MemoryBufferMMapFile(bool RequiresNullTerminator, int FD, uint64_t Len,
	uint64_t Offset, std::error_code &EC)
	: MFR(FD, MB::Mapmode, getLegalMapSize(Len, Offset),
	getLegalMapOffset(Offset), EC) {
	if (!EC) {
	const char *Start = getStart(Len, Offset);
	MemoryBuffer::init(Start, Start + Len, RequiresNullTerminator);
	}
	}

	/// Disable sized deallocation for MemoryBufferMMapFile, because it has
	/// tail-allocated data.
	void operator delete(void *p) { ::operator delete(p); }

	StringRef getBufferIdentifier() const override {
	// The name is stored after the class itself.
	return StringRef(reinterpret_cast<const char *>(this + 1));
	}

	MemoryBuffer::BufferKind getBufferKind() const override {
	return MemoryBuffer::MemoryBuffer_MMap;
	}
	};
	}

	static ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
	getMemoryBufferForStream(int FD, const Twine &BufferName) {
	const ssize_t ChunkSize = 4096*4;
	SmallString<ChunkSize> Buffer;
	ssize_t ReadBytes;
	// Read into Buffer until we hit EOF.
	do {
	Buffer.reserve(Buffer.size() + ChunkSize);
	ReadBytes = sys::RetryAfterSignal(-1, ::read, FD, Buffer.end(), ChunkSize);
	if (ReadBytes == -1)
	return std::error_code(errno, std::generic_category());
	Buffer.set_size(Buffer.size() + ReadBytes);
	} while (ReadBytes != 0);

	return getMemBufferCopyImpl(Buffer, BufferName);
	}


	ErrorOr<std::unique_ptr<MemoryBuffer>>
	MemoryBuffer::getFile(const Twine &Filename, int64_t FileSize,
	bool RequiresNullTerminator, bool IsVolatile) {
	return getFileAux<MemoryBuffer>(Filename, FileSize, FileSize, 0,
	RequiresNullTerminator, IsVolatile);
	}

	template <typename MB>
	static ErrorOr<std::unique_ptr<MB>>
	getOpenFileImpl(int FD, const Twine &Filename, uint64_t FileSize,
	uint64_t MapSize, int64_t Offset, bool RequiresNullTerminator,
	bool IsVolatile);

	template <typename MB>
	static ErrorOr<std::unique_ptr<MB>>
	getFileAux(const Twine &Filename, int64_t FileSize, uint64_t MapSize,
	uint64_t Offset, bool RequiresNullTerminator, bool IsVolatile) {
	int FD;
	std::error_code EC = sys::fs::openFileForRead(Filename, FD, sys::fs::OF_None);

	if (EC)
	return EC;

	auto Ret = getOpenFileImpl<MB>(FD, Filename, FileSize, MapSize, Offset,
	RequiresNullTerminator, IsVolatile);
	close(FD);
	return Ret;
	}

	ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
	WritableMemoryBuffer::getFile(const Twine &Filename, int64_t FileSize,
	bool IsVolatile) {
	return getFileAux<WritableMemoryBuffer>(Filename, FileSize, FileSize, 0,
	/RequiresNullTerminator/ false,
	IsVolatile);
	}

	ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
	WritableMemoryBuffer::getFileSlice(const Twine &Filename, uint64_t MapSize,
	uint64_t Offset, bool IsVolatile) {
	return getFileAux<WritableMemoryBuffer>(Filename, -1, MapSize, Offset, false,
	IsVolatile);
	}

	std::unique_ptr<WritableMemoryBuffer>
	WritableMemoryBuffer::getNewUninitMemBuffer(size_t Size, const Twine &BufferName) {
	using MemBuffer = MemoryBufferMem<WritableMemoryBuffer>;
	// Allocate space for the MemoryBuffer, the data and the name. It is important
	// that MemoryBuffer and data are aligned so PointerIntPair works with them.
	// TODO: Is 16-byte alignment enough? We copy small object files with large
	// alignment expectations into this buffer.
	SmallString<256> NameBuf;
	StringRef NameRef = BufferName.toStringRef(NameBuf);
	size_t AlignedStringLen = alignTo(sizeof(MemBuffer) + NameRef.size() + 1, 16);
	size_t RealLen = AlignedStringLen + Size + 1;
	char Mem = static_cast<char>(operator new(RealLen, std::nothrow));
	if (!Mem)
	return nullptr;

	// The name is stored after the class itself.
	CopyStringRef(Mem + sizeof(MemBuffer), NameRef);

	// The buffer begins after the name and must be aligned.
	char *Buf = Mem + AlignedStringLen;
	Buf[Size] = 0; // Null terminate buffer.

	auto *Ret = new (Mem) MemBuffer(StringRef(Buf, Size), true);
	return std::unique_ptr<WritableMemoryBuffer>(Ret);
	}

	std::unique_ptr<WritableMemoryBuffer>
	WritableMemoryBuffer::getNewMemBuffer(size_t Size, const Twine &BufferName) {
	auto SB = WritableMemoryBuffer::getNewUninitMemBuffer(Size, BufferName);
	if (!SB)
	return nullptr;
	memset(SB->getBufferStart(), 0, Size);
	return SB;
	}

	static bool shouldUseMmap(int FD,
	size_t FileSize,
	size_t MapSize,
	off_t Offset,
	bool RequiresNullTerminator,
	int PageSize,
	bool IsVolatile) {
	// mmap may leave the buffer without null terminator if the file size changed
	// by the time the last page is mapped in, so avoid it if the file size is
	// likely to change.
	if (IsVolatile)
	return false;

	// We don't use mmap for small files because this can severely fragment our
	// address space.
	if (MapSize < 4 * 4096 \|\| MapSize < (unsigned)PageSize)
	return false;

	if (!RequiresNullTerminator)
	return true;

	// If we don't know the file size, use fstat to find out. fstat on an open
	// file descriptor is cheaper than stat on a random path.
	// FIXME: this chunk of code is duplicated, but it avoids a fstat when
	// RequiresNullTerminator = false and MapSize != -1.
	if (FileSize == size_t(-1)) {
	sys::fs::file_status Status;
	if (sys::fs::status(FD, Status))
	return false;
	FileSize = Status.getSize();
	}

	// If we need a null terminator and the end of the map is inside the file,
	// we cannot use mmap.
	size_t End = Offset + MapSize;
	assert(End <= FileSize);
	if (End != FileSize)
	return false;

	// Don't try to map files that are exactly a multiple of the system page size
	// if we need a null terminator.
	if ((FileSize & (PageSize -1)) == 0)
	return false;

	#if defined(__CYGWIN__)
	// Don't try to map files that are exactly a multiple of the physical page size
	// if we need a null terminator.
	// FIXME: We should reorganize again getPageSize() on Win32.
	if ((FileSize & (4096 - 1)) == 0)
	return false;
	#endif

	return true;
	}

	static ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
	getReadWriteFile(const Twine &Filename, uint64_t FileSize, uint64_t MapSize,
	uint64_t Offset) {
	int FD;
	std::error_code EC = sys::fs::openFileForReadWrite(
	Filename, FD, sys::fs::CD_OpenExisting, sys::fs::OF_None);

	if (EC)
	return EC;

	// Default is to map the full file.
	if (MapSize == uint64_t(-1)) {
	// If we don't know the file size, use fstat to find out. fstat on an open
	// file descriptor is cheaper than stat on a random path.
	if (FileSize == uint64_t(-1)) {
	sys::fs::file_status Status;
	std::error_code EC = sys::fs::status(FD, Status);
	if (EC)
	return EC;

	// If this not a file or a block device (e.g. it's a named pipe
	// or character device), we can't mmap it, so error out.
	sys::fs::file_type Type = Status.type();
	if (Type != sys::fs::file_type::regular_file &&
	Type != sys::fs::file_type::block_file)
	return make_error_code(errc::invalid_argument);

	FileSize = Status.getSize();
	}
	MapSize = FileSize;
	}

	std::unique_ptr<WriteThroughMemoryBuffer> Result(
	new (NamedBufferAlloc(Filename))
	MemoryBufferMMapFile<WriteThroughMemoryBuffer>(false, FD, MapSize,
	Offset, EC));
	if (EC)
	return EC;
	return std::move(Result);
	}

	ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
	WriteThroughMemoryBuffer::getFile(const Twine &Filename, int64_t FileSize) {
	return getReadWriteFile(Filename, FileSize, FileSize, 0);
	}

	/// Map a subrange of the specified file as a WritableMemoryBuffer.
	ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
	WriteThroughMemoryBuffer::getFileSlice(const Twine &Filename, uint64_t MapSize,
	uint64_t Offset) {
	return getReadWriteFile(Filename, -1, MapSize, Offset);
	}

	template <typename MB>
	static ErrorOr<std::unique_ptr<MB>>
	getOpenFileImpl(int FD, const Twine &Filename, uint64_t FileSize,
	uint64_t MapSize, int64_t Offset, bool RequiresNullTerminator,
	bool IsVolatile) {
	static int PageSize = sys::Process::getPageSize();

	// Default is to map the full file.
	if (MapSize == uint64_t(-1)) {
	// If we don't know the file size, use fstat to find out. fstat on an open
	// file descriptor is cheaper than stat on a random path.
	if (FileSize == uint64_t(-1)) {
	sys::fs::file_status Status;
	std::error_code EC = sys::fs::status(FD, Status);
	if (EC)
	return EC;

	// If this not a file or a block device (e.g. it's a named pipe
	// or character device), we can't trust the size. Create the memory
	// buffer by copying off the stream.
	sys::fs::file_type Type = Status.type();
	if (Type != sys::fs::file_type::regular_file &&
	Type != sys::fs::file_type::block_file)
	return getMemoryBufferForStream(FD, Filename);

	FileSize = Status.getSize();
	}
	MapSize = FileSize;
	}

	if (shouldUseMmap(FD, FileSize, MapSize, Offset, RequiresNullTerminator,
	PageSize, IsVolatile)) {
	std::error_code EC;
	std::unique_ptr<MB> Result(
	new (NamedBufferAlloc(Filename)) MemoryBufferMMapFile<MB>(
	RequiresNullTerminator, FD, MapSize, Offset, EC));
	if (!EC)
	return std::move(Result);
	}

	auto Buf = WritableMemoryBuffer::getNewUninitMemBuffer(MapSize, Filename);
	if (!Buf) {
	// Failed to create a buffer. The only way it can fail is if
	// new(std::nothrow) returns 0.
	return make_error_code(errc::not_enough_memory);
	}

	char *BufPtr = Buf.get()->getBufferStart();

	size_t BytesLeft = MapSize;
	#ifndef HAVE_PREAD
	if (lseek(FD, Offset, SEEK_SET) == -1)
	return std::error_code(errno, std::generic_category());
	#endif

	while (BytesLeft) {
	#ifdef HAVE_PREAD
	ssize_t NumRead = sys::RetryAfterSignal(-1, ::pread, FD, BufPtr, BytesLeft,
	MapSize - BytesLeft + Offset);
	#else
	ssize_t NumRead = sys::RetryAfterSignal(-1, ::read, FD, BufPtr, BytesLeft);
	#endif
	if (NumRead == -1) {
	// Error while reading.
	return std::error_code(errno, std::generic_category());
	}
	if (NumRead == 0) {
	memset(BufPtr, 0, BytesLeft); // zero-initialize rest of the buffer.
	break;
	}
	BytesLeft -= NumRead;
	BufPtr += NumRead;
	}

	return std::move(Buf);
	}

	ErrorOr<std::unique_ptr<MemoryBuffer>>
	MemoryBuffer::getOpenFile(int FD, const Twine &Filename, uint64_t FileSize,
	bool RequiresNullTerminator, bool IsVolatile) {
	return getOpenFileImpl<MemoryBuffer>(FD, Filename, FileSize, FileSize, 0,
	RequiresNullTerminator, IsVolatile);
	}

	ErrorOr<std::unique_ptr<MemoryBuffer>>
	MemoryBuffer::getOpenFileSlice(int FD, const Twine &Filename, uint64_t MapSize,
	int64_t Offset, bool IsVolatile) {
	assert(MapSize != uint64_t(-1));
	return getOpenFileImpl<MemoryBuffer>(FD, Filename, -1, MapSize, Offset, false,
	IsVolatile);
	}

	ErrorOr<std::unique_ptr<MemoryBuffer>> MemoryBuffer::getSTDIN() {
	// Read in all of the data from stdin, we cannot mmap stdin.
	//
	// FIXME: That isn't necessarily true, we should try to mmap stdin and
	// fallback if it fails.
	sys::ChangeStdinToBinary();

	return getMemoryBufferForStream(0, "<stdin>");
	}

	ErrorOr<std::unique_ptr<MemoryBuffer>>
	MemoryBuffer::getFileAsStream(const Twine &Filename) {
	int FD;
	std::error_code EC = sys::fs::openFileForRead(Filename, FD, sys::fs::OF_None);
	if (EC)
	return EC;
	ErrorOr<std::unique_ptr<MemoryBuffer>> Ret =
	getMemoryBufferForStream(FD, Filename);
	close(FD);
	return Ret;
	}

	MemoryBufferRef MemoryBuffer::getMemBufferRef() const {
	StringRef Data = getBuffer();
	StringRef Identifier = getBufferIdentifier();
	return MemoryBufferRef(Data, Identifier);
	}

	SmallVectorMemoryBuffer::~SmallVectorMemoryBuffer() {}