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/SmallString.h"
15 #include "llvm/Config/config.h"
16 #include "llvm/Support/Errc.h"
17 #include "llvm/Support/Errno.h"
18 #include "llvm/Support/FileSystem.h"
19 #include "llvm/Support/MathExtras.h"
20 #include "llvm/Support/Path.h"
21 #include "llvm/Support/Process.h"
22 #include "llvm/Support/Program.h"
23 #include "llvm/Support/SmallVectorMemoryBuffer.h"
24 #include <cassert>
25 #include <cerrno>
26 #include <cstring>
27 #include <new>
28 #include <sys/types.h>
29 #include <system_error>
30 #if !defined(_MSC_VER) && !defined(__MINGW32__)
31 #include <unistd.h>
32 #else
33 #include <io.h>
34 #endif
35 using namespace llvm;
36
37 //===----------------------------------------------------------------------===//
38 // MemoryBuffer implementation itself.
39 //===----------------------------------------------------------------------===//
40
~MemoryBuffer()41 MemoryBuffer::~MemoryBuffer() { }
42
43 /// init - Initialize this MemoryBuffer as a reference to externally allocated
44 /// memory, memory that we know is already null terminated.
init(const char * BufStart,const char * BufEnd,bool RequiresNullTerminator)45 void MemoryBuffer::init(const char *BufStart, const char *BufEnd,
46 bool RequiresNullTerminator) {
47 assert((!RequiresNullTerminator || BufEnd[0] == 0) &&
48 "Buffer is not null terminated!");
49 BufferStart = BufStart;
50 BufferEnd = BufEnd;
51 }
52
53 //===----------------------------------------------------------------------===//
54 // MemoryBufferMem implementation.
55 //===----------------------------------------------------------------------===//
56
57 /// CopyStringRef - Copies contents of a StringRef into a block of memory and
58 /// null-terminates it.
CopyStringRef(char * Memory,StringRef Data)59 static void CopyStringRef(char *Memory, StringRef Data) {
60 if (!Data.empty())
61 memcpy(Memory, Data.data(), Data.size());
62 Memory[Data.size()] = 0; // Null terminate string.
63 }
64
65 namespace {
66 struct NamedBufferAlloc {
67 const Twine &Name;
NamedBufferAlloc__anone85bf1750111::NamedBufferAlloc68 NamedBufferAlloc(const Twine &Name) : Name(Name) {}
69 };
70 }
71
operator new(size_t N,const NamedBufferAlloc & Alloc)72 void *operator new(size_t N, const NamedBufferAlloc &Alloc) {
73 SmallString<256> NameBuf;
74 StringRef NameRef = Alloc.Name.toStringRef(NameBuf);
75
76 char *Mem = static_cast<char *>(operator new(N + NameRef.size() + 1));
77 CopyStringRef(Mem + N, NameRef);
78 return Mem;
79 }
80
81 namespace {
82 /// MemoryBufferMem - Named MemoryBuffer pointing to a block of memory.
83 template<typename MB>
84 class MemoryBufferMem : public MB {
85 public:
MemoryBufferMem(StringRef InputData,bool RequiresNullTerminator)86 MemoryBufferMem(StringRef InputData, bool RequiresNullTerminator) {
87 MemoryBuffer::init(InputData.begin(), InputData.end(),
88 RequiresNullTerminator);
89 }
90
91 /// Disable sized deallocation for MemoryBufferMem, because it has
92 /// tail-allocated data.
operator delete(void * p)93 void operator delete(void *p) { ::operator delete(p); }
94
getBufferIdentifier() const95 StringRef getBufferIdentifier() const override {
96 // The name is stored after the class itself.
97 return StringRef(reinterpret_cast<const char *>(this + 1));
98 }
99
getBufferKind() const100 MemoryBuffer::BufferKind getBufferKind() const override {
101 return MemoryBuffer::MemoryBuffer_Malloc;
102 }
103 };
104 }
105
106 template <typename MB>
107 static ErrorOr<std::unique_ptr<MB>>
108 getFileAux(const Twine &Filename, int64_t FileSize, uint64_t MapSize,
109 uint64_t Offset, bool RequiresNullTerminator, bool IsVolatile);
110
111 std::unique_ptr<MemoryBuffer>
getMemBuffer(StringRef InputData,StringRef BufferName,bool RequiresNullTerminator)112 MemoryBuffer::getMemBuffer(StringRef InputData, StringRef BufferName,
113 bool RequiresNullTerminator) {
114 auto *Ret = new (NamedBufferAlloc(BufferName))
115 MemoryBufferMem<MemoryBuffer>(InputData, RequiresNullTerminator);
116 return std::unique_ptr<MemoryBuffer>(Ret);
117 }
118
119 std::unique_ptr<MemoryBuffer>
getMemBuffer(MemoryBufferRef Ref,bool RequiresNullTerminator)120 MemoryBuffer::getMemBuffer(MemoryBufferRef Ref, bool RequiresNullTerminator) {
121 return std::unique_ptr<MemoryBuffer>(getMemBuffer(
122 Ref.getBuffer(), Ref.getBufferIdentifier(), RequiresNullTerminator));
123 }
124
125 static ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
getMemBufferCopyImpl(StringRef InputData,const Twine & BufferName)126 getMemBufferCopyImpl(StringRef InputData, const Twine &BufferName) {
127 auto Buf = WritableMemoryBuffer::getNewUninitMemBuffer(InputData.size(), BufferName);
128 if (!Buf)
129 return make_error_code(errc::not_enough_memory);
130 memcpy(Buf->getBufferStart(), InputData.data(), InputData.size());
131 return std::move(Buf);
132 }
133
134 std::unique_ptr<MemoryBuffer>
getMemBufferCopy(StringRef InputData,const Twine & BufferName)135 MemoryBuffer::getMemBufferCopy(StringRef InputData, const Twine &BufferName) {
136 auto Buf = getMemBufferCopyImpl(InputData, BufferName);
137 if (Buf)
138 return std::move(*Buf);
139 return nullptr;
140 }
141
142 ErrorOr<std::unique_ptr<MemoryBuffer>>
getFileOrSTDIN(const Twine & Filename,int64_t FileSize,bool RequiresNullTerminator)143 MemoryBuffer::getFileOrSTDIN(const Twine &Filename, int64_t FileSize,
144 bool RequiresNullTerminator) {
145 SmallString<256> NameBuf;
146 StringRef NameRef = Filename.toStringRef(NameBuf);
147
148 if (NameRef == "-")
149 return getSTDIN();
150 return getFile(Filename, FileSize, RequiresNullTerminator);
151 }
152
153 ErrorOr<std::unique_ptr<MemoryBuffer>>
getFileSlice(const Twine & FilePath,uint64_t MapSize,uint64_t Offset,bool IsVolatile)154 MemoryBuffer::getFileSlice(const Twine &FilePath, uint64_t MapSize,
155 uint64_t Offset, bool IsVolatile) {
156 return getFileAux<MemoryBuffer>(FilePath, -1, MapSize, Offset, false,
157 IsVolatile);
158 }
159
160 //===----------------------------------------------------------------------===//
161 // MemoryBuffer::getFile implementation.
162 //===----------------------------------------------------------------------===//
163
164 namespace {
165 /// Memory maps a file descriptor using sys::fs::mapped_file_region.
166 ///
167 /// This handles converting the offset into a legal offset on the platform.
168 template<typename MB>
169 class MemoryBufferMMapFile : public MB {
170 sys::fs::mapped_file_region MFR;
171
getLegalMapOffset(uint64_t Offset)172 static uint64_t getLegalMapOffset(uint64_t Offset) {
173 return Offset & ~(sys::fs::mapped_file_region::alignment() - 1);
174 }
175
getLegalMapSize(uint64_t Len,uint64_t Offset)176 static uint64_t getLegalMapSize(uint64_t Len, uint64_t Offset) {
177 return Len + (Offset - getLegalMapOffset(Offset));
178 }
179
getStart(uint64_t Len,uint64_t Offset)180 const char *getStart(uint64_t Len, uint64_t Offset) {
181 return MFR.const_data() + (Offset - getLegalMapOffset(Offset));
182 }
183
184 public:
MemoryBufferMMapFile(bool RequiresNullTerminator,sys::fs::file_t FD,uint64_t Len,uint64_t Offset,std::error_code & EC)185 MemoryBufferMMapFile(bool RequiresNullTerminator, sys::fs::file_t FD, uint64_t Len,
186 uint64_t Offset, std::error_code &EC)
187 : MFR(FD, MB::Mapmode, getLegalMapSize(Len, Offset),
188 getLegalMapOffset(Offset), EC) {
189 if (!EC) {
190 const char *Start = getStart(Len, Offset);
191 MemoryBuffer::init(Start, Start + Len, RequiresNullTerminator);
192 }
193 }
194
195 /// Disable sized deallocation for MemoryBufferMMapFile, because it has
196 /// tail-allocated data.
operator delete(void * p)197 void operator delete(void *p) { ::operator delete(p); }
198
getBufferIdentifier() const199 StringRef getBufferIdentifier() const override {
200 // The name is stored after the class itself.
201 return StringRef(reinterpret_cast<const char *>(this + 1));
202 }
203
getBufferKind() const204 MemoryBuffer::BufferKind getBufferKind() const override {
205 return MemoryBuffer::MemoryBuffer_MMap;
206 }
207 };
208 }
209
210 static ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
getMemoryBufferForStream(sys::fs::file_t FD,const Twine & BufferName)211 getMemoryBufferForStream(sys::fs::file_t FD, const Twine &BufferName) {
212 const ssize_t ChunkSize = 4096*4;
213 SmallString<ChunkSize> Buffer;
214 size_t ReadBytes;
215 // Read into Buffer until we hit EOF.
216 do {
217 Buffer.reserve(Buffer.size() + ChunkSize);
218 if (auto EC = sys::fs::readNativeFile(
219 FD, makeMutableArrayRef(Buffer.end(), ChunkSize), &ReadBytes))
220 return EC;
221 Buffer.set_size(Buffer.size() + ReadBytes);
222 } while (ReadBytes != 0);
223
224 return getMemBufferCopyImpl(Buffer, BufferName);
225 }
226
227
228 ErrorOr<std::unique_ptr<MemoryBuffer>>
getFile(const Twine & Filename,int64_t FileSize,bool RequiresNullTerminator,bool IsVolatile)229 MemoryBuffer::getFile(const Twine &Filename, int64_t FileSize,
230 bool RequiresNullTerminator, bool IsVolatile) {
231 return getFileAux<MemoryBuffer>(Filename, FileSize, FileSize, 0,
232 RequiresNullTerminator, IsVolatile);
233 }
234
235 template <typename MB>
236 static ErrorOr<std::unique_ptr<MB>>
237 getOpenFileImpl(sys::fs::file_t FD, const Twine &Filename, uint64_t FileSize,
238 uint64_t MapSize, int64_t Offset, bool RequiresNullTerminator,
239 bool IsVolatile);
240
241 template <typename MB>
242 static ErrorOr<std::unique_ptr<MB>>
getFileAux(const Twine & Filename,int64_t FileSize,uint64_t MapSize,uint64_t Offset,bool RequiresNullTerminator,bool IsVolatile)243 getFileAux(const Twine &Filename, int64_t FileSize, uint64_t MapSize,
244 uint64_t Offset, bool RequiresNullTerminator, bool IsVolatile) {
245 Expected<sys::fs::file_t> FDOrErr =
246 sys::fs::openNativeFileForRead(Filename, sys::fs::OF_None);
247 if (!FDOrErr)
248 return errorToErrorCode(FDOrErr.takeError());
249 sys::fs::file_t FD = *FDOrErr;
250 auto Ret = getOpenFileImpl<MB>(FD, Filename, FileSize, MapSize, Offset,
251 RequiresNullTerminator, IsVolatile);
252 sys::fs::closeFile(FD);
253 return Ret;
254 }
255
256 ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
getFile(const Twine & Filename,int64_t FileSize,bool IsVolatile)257 WritableMemoryBuffer::getFile(const Twine &Filename, int64_t FileSize,
258 bool IsVolatile) {
259 return getFileAux<WritableMemoryBuffer>(Filename, FileSize, FileSize, 0,
260 /*RequiresNullTerminator*/ false,
261 IsVolatile);
262 }
263
264 ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
getFileSlice(const Twine & Filename,uint64_t MapSize,uint64_t Offset,bool IsVolatile)265 WritableMemoryBuffer::getFileSlice(const Twine &Filename, uint64_t MapSize,
266 uint64_t Offset, bool IsVolatile) {
267 return getFileAux<WritableMemoryBuffer>(Filename, -1, MapSize, Offset, false,
268 IsVolatile);
269 }
270
271 std::unique_ptr<WritableMemoryBuffer>
getNewUninitMemBuffer(size_t Size,const Twine & BufferName)272 WritableMemoryBuffer::getNewUninitMemBuffer(size_t Size, const Twine &BufferName) {
273 using MemBuffer = MemoryBufferMem<WritableMemoryBuffer>;
274 // Allocate space for the MemoryBuffer, the data and the name. It is important
275 // that MemoryBuffer and data are aligned so PointerIntPair works with them.
276 // TODO: Is 16-byte alignment enough? We copy small object files with large
277 // alignment expectations into this buffer.
278 SmallString<256> NameBuf;
279 StringRef NameRef = BufferName.toStringRef(NameBuf);
280 size_t AlignedStringLen = alignTo(sizeof(MemBuffer) + NameRef.size() + 1, 16);
281 size_t RealLen = AlignedStringLen + Size + 1;
282 char *Mem = static_cast<char*>(operator new(RealLen, std::nothrow));
283 if (!Mem)
284 return nullptr;
285
286 // The name is stored after the class itself.
287 CopyStringRef(Mem + sizeof(MemBuffer), NameRef);
288
289 // The buffer begins after the name and must be aligned.
290 char *Buf = Mem + AlignedStringLen;
291 Buf[Size] = 0; // Null terminate buffer.
292
293 auto *Ret = new (Mem) MemBuffer(StringRef(Buf, Size), true);
294 return std::unique_ptr<WritableMemoryBuffer>(Ret);
295 }
296
297 std::unique_ptr<WritableMemoryBuffer>
getNewMemBuffer(size_t Size,const Twine & BufferName)298 WritableMemoryBuffer::getNewMemBuffer(size_t Size, const Twine &BufferName) {
299 auto SB = WritableMemoryBuffer::getNewUninitMemBuffer(Size, BufferName);
300 if (!SB)
301 return nullptr;
302 memset(SB->getBufferStart(), 0, Size);
303 return SB;
304 }
305
shouldUseMmap(sys::fs::file_t FD,size_t FileSize,size_t MapSize,off_t Offset,bool RequiresNullTerminator,int PageSize,bool IsVolatile)306 static bool shouldUseMmap(sys::fs::file_t FD,
307 size_t FileSize,
308 size_t MapSize,
309 off_t Offset,
310 bool RequiresNullTerminator,
311 int PageSize,
312 bool IsVolatile) {
313 // mmap may leave the buffer without null terminator if the file size changed
314 // by the time the last page is mapped in, so avoid it if the file size is
315 // likely to change.
316 if (IsVolatile)
317 return false;
318
319 // We don't use mmap for small files because this can severely fragment our
320 // address space.
321 if (MapSize < 4 * 4096 || MapSize < (unsigned)PageSize)
322 return false;
323
324 if (!RequiresNullTerminator)
325 return true;
326
327 // If we don't know the file size, use fstat to find out. fstat on an open
328 // file descriptor is cheaper than stat on a random path.
329 // FIXME: this chunk of code is duplicated, but it avoids a fstat when
330 // RequiresNullTerminator = false and MapSize != -1.
331 if (FileSize == size_t(-1)) {
332 sys::fs::file_status Status;
333 if (sys::fs::status(FD, Status))
334 return false;
335 FileSize = Status.getSize();
336 }
337
338 // If we need a null terminator and the end of the map is inside the file,
339 // we cannot use mmap.
340 size_t End = Offset + MapSize;
341 assert(End <= FileSize);
342 if (End != FileSize)
343 return false;
344
345 // Don't try to map files that are exactly a multiple of the system page size
346 // if we need a null terminator.
347 if ((FileSize & (PageSize -1)) == 0)
348 return false;
349
350 #if defined(__CYGWIN__)
351 // Don't try to map files that are exactly a multiple of the physical page size
352 // if we need a null terminator.
353 // FIXME: We should reorganize again getPageSize() on Win32.
354 if ((FileSize & (4096 - 1)) == 0)
355 return false;
356 #endif
357
358 return true;
359 }
360
361 static ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
getReadWriteFile(const Twine & Filename,uint64_t FileSize,uint64_t MapSize,uint64_t Offset)362 getReadWriteFile(const Twine &Filename, uint64_t FileSize, uint64_t MapSize,
363 uint64_t Offset) {
364 Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForReadWrite(
365 Filename, sys::fs::CD_OpenExisting, sys::fs::OF_None);
366 if (!FDOrErr)
367 return errorToErrorCode(FDOrErr.takeError());
368 sys::fs::file_t FD = *FDOrErr;
369
370 // Default is to map the full file.
371 if (MapSize == uint64_t(-1)) {
372 // If we don't know the file size, use fstat to find out. fstat on an open
373 // file descriptor is cheaper than stat on a random path.
374 if (FileSize == uint64_t(-1)) {
375 sys::fs::file_status Status;
376 std::error_code EC = sys::fs::status(FD, Status);
377 if (EC)
378 return EC;
379
380 // If this not a file or a block device (e.g. it's a named pipe
381 // or character device), we can't mmap it, so error out.
382 sys::fs::file_type Type = Status.type();
383 if (Type != sys::fs::file_type::regular_file &&
384 Type != sys::fs::file_type::block_file)
385 return make_error_code(errc::invalid_argument);
386
387 FileSize = Status.getSize();
388 }
389 MapSize = FileSize;
390 }
391
392 std::error_code EC;
393 std::unique_ptr<WriteThroughMemoryBuffer> Result(
394 new (NamedBufferAlloc(Filename))
395 MemoryBufferMMapFile<WriteThroughMemoryBuffer>(false, FD, MapSize,
396 Offset, EC));
397 if (EC)
398 return EC;
399 return std::move(Result);
400 }
401
402 ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
getFile(const Twine & Filename,int64_t FileSize)403 WriteThroughMemoryBuffer::getFile(const Twine &Filename, int64_t FileSize) {
404 return getReadWriteFile(Filename, FileSize, FileSize, 0);
405 }
406
407 /// Map a subrange of the specified file as a WritableMemoryBuffer.
408 ErrorOr<std::unique_ptr<WriteThroughMemoryBuffer>>
getFileSlice(const Twine & Filename,uint64_t MapSize,uint64_t Offset)409 WriteThroughMemoryBuffer::getFileSlice(const Twine &Filename, uint64_t MapSize,
410 uint64_t Offset) {
411 return getReadWriteFile(Filename, -1, MapSize, Offset);
412 }
413
414 template <typename MB>
415 static ErrorOr<std::unique_ptr<MB>>
getOpenFileImpl(sys::fs::file_t FD,const Twine & Filename,uint64_t FileSize,uint64_t MapSize,int64_t Offset,bool RequiresNullTerminator,bool IsVolatile)416 getOpenFileImpl(sys::fs::file_t FD, const Twine &Filename, uint64_t FileSize,
417 uint64_t MapSize, int64_t Offset, bool RequiresNullTerminator,
418 bool IsVolatile) {
419 static int PageSize = sys::Process::getPageSizeEstimate();
420
421 // Default is to map the full file.
422 if (MapSize == uint64_t(-1)) {
423 // If we don't know the file size, use fstat to find out. fstat on an open
424 // file descriptor is cheaper than stat on a random path.
425 if (FileSize == uint64_t(-1)) {
426 sys::fs::file_status Status;
427 std::error_code EC = sys::fs::status(FD, Status);
428 if (EC)
429 return EC;
430
431 // If this not a file or a block device (e.g. it's a named pipe
432 // or character device), we can't trust the size. Create the memory
433 // buffer by copying off the stream.
434 sys::fs::file_type Type = Status.type();
435 if (Type != sys::fs::file_type::regular_file &&
436 Type != sys::fs::file_type::block_file)
437 return getMemoryBufferForStream(FD, Filename);
438
439 FileSize = Status.getSize();
440 }
441 MapSize = FileSize;
442 }
443
444 if (shouldUseMmap(FD, FileSize, MapSize, Offset, RequiresNullTerminator,
445 PageSize, IsVolatile)) {
446 std::error_code EC;
447 std::unique_ptr<MB> Result(
448 new (NamedBufferAlloc(Filename)) MemoryBufferMMapFile<MB>(
449 RequiresNullTerminator, FD, MapSize, Offset, EC));
450 if (!EC)
451 return std::move(Result);
452 }
453
454 auto Buf = WritableMemoryBuffer::getNewUninitMemBuffer(MapSize, Filename);
455 if (!Buf) {
456 // Failed to create a buffer. The only way it can fail is if
457 // new(std::nothrow) returns 0.
458 return make_error_code(errc::not_enough_memory);
459 }
460
461 sys::fs::readNativeFileSlice(FD, Buf->getBuffer(), Offset);
462
463 return std::move(Buf);
464 }
465
466 ErrorOr<std::unique_ptr<MemoryBuffer>>
getOpenFile(sys::fs::file_t FD,const Twine & Filename,uint64_t FileSize,bool RequiresNullTerminator,bool IsVolatile)467 MemoryBuffer::getOpenFile(sys::fs::file_t FD, const Twine &Filename, uint64_t FileSize,
468 bool RequiresNullTerminator, bool IsVolatile) {
469 return getOpenFileImpl<MemoryBuffer>(FD, Filename, FileSize, FileSize, 0,
470 RequiresNullTerminator, IsVolatile);
471 }
472
473 ErrorOr<std::unique_ptr<MemoryBuffer>>
getOpenFileSlice(sys::fs::file_t FD,const Twine & Filename,uint64_t MapSize,int64_t Offset,bool IsVolatile)474 MemoryBuffer::getOpenFileSlice(sys::fs::file_t FD, const Twine &Filename, uint64_t MapSize,
475 int64_t Offset, bool IsVolatile) {
476 assert(MapSize != uint64_t(-1));
477 return getOpenFileImpl<MemoryBuffer>(FD, Filename, -1, MapSize, Offset, false,
478 IsVolatile);
479 }
480
getSTDIN()481 ErrorOr<std::unique_ptr<MemoryBuffer>> MemoryBuffer::getSTDIN() {
482 // Read in all of the data from stdin, we cannot mmap stdin.
483 //
484 // FIXME: That isn't necessarily true, we should try to mmap stdin and
485 // fallback if it fails.
486 sys::ChangeStdinToBinary();
487
488 return getMemoryBufferForStream(sys::fs::getStdinHandle(), "<stdin>");
489 }
490
491 ErrorOr<std::unique_ptr<MemoryBuffer>>
getFileAsStream(const Twine & Filename)492 MemoryBuffer::getFileAsStream(const Twine &Filename) {
493 Expected<sys::fs::file_t> FDOrErr =
494 sys::fs::openNativeFileForRead(Filename, sys::fs::OF_None);
495 if (!FDOrErr)
496 return errorToErrorCode(FDOrErr.takeError());
497 sys::fs::file_t FD = *FDOrErr;
498 ErrorOr<std::unique_ptr<MemoryBuffer>> Ret =
499 getMemoryBufferForStream(FD, Filename);
500 sys::fs::closeFile(FD);
501 return Ret;
502 }
503
getMemBufferRef() const504 MemoryBufferRef MemoryBuffer::getMemBufferRef() const {
505 StringRef Data = getBuffer();
506 StringRef Identifier = getBufferIdentifier();
507 return MemoryBufferRef(Data, Identifier);
508 }
509
~SmallVectorMemoryBuffer()510 SmallVectorMemoryBuffer::~SmallVectorMemoryBuffer() {}
511