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8dbe3629a0
PDBs can be extremely large. We're already mapping the entire PDB into the process's address space, but to make matters worse the blocks of the PDB are not arranged contiguously. So, when we have something like an array or a string embedded into the stream, we have to make a copy. Since it's convenient to use traditional data structures to iterate and manipulate these records, we need the memory to be contiguous. As a result of this, we were using roughly twice as much memory as the file size of the PDB, because every stream was copied out and re-stitched together contiguously. This patch addresses this by improving the MappedBlockStream to allocate from a BumpPtrAllocator only when a read requires a discontiguous read. Furthermore, it introduces some data structures backed by a stream which can iterate over both fixed and variable length records of a PDB. Since everything is backed by a stream and not a buffer, we can read almost everything from the PDB with zero copies. Differential Revision: http://reviews.llvm.org/D20654 Reviewed By: ruiu llvm-svn: 270951
94 lines
2.7 KiB
C++
94 lines
2.7 KiB
C++
//===- StreamReader.cpp - Reads bytes and objects from a stream -----------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/DebugInfo/CodeView/StreamReader.h"
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#include "llvm/DebugInfo/CodeView/CodeViewError.h"
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#include "llvm/DebugInfo/CodeView/StreamRef.h"
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using namespace llvm;
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using namespace llvm::codeview;
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StreamReader::StreamReader(const StreamInterface &S) : Stream(S), Offset(0) {}
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Error StreamReader::readBytes(uint32_t Size, ArrayRef<uint8_t> &Buffer) {
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if (auto EC = Stream.readBytes(Offset, Size, Buffer))
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return EC;
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Offset += Size;
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return Error::success();
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}
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Error StreamReader::readBytes(MutableArrayRef<uint8_t> Buffer) {
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if (auto EC = Stream.readBytes(Offset, Buffer))
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return EC;
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Offset += Buffer.size();
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return Error::success();
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}
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Error StreamReader::readInteger(uint16_t &Dest) {
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const support::ulittle16_t *P;
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if (auto EC = readObject(P))
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return EC;
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Dest = *P;
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return Error::success();
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}
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Error StreamReader::readInteger(uint32_t &Dest) {
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const support::ulittle32_t *P;
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if (auto EC = readObject(P))
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return EC;
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Dest = *P;
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return Error::success();
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}
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Error StreamReader::readZeroString(StringRef &Dest) {
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uint32_t Length = 0;
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// First compute the length of the string by reading 1 byte at a time.
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uint32_t OriginalOffset = getOffset();
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const char *C;
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do {
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if (auto EC = readObject(C))
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return EC;
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if (*C != '\0')
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++Length;
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} while (*C != '\0');
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// Now go back and request a reference for that many bytes.
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uint32_t NewOffset = getOffset();
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setOffset(OriginalOffset);
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ArrayRef<uint8_t> Data;
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if (auto EC = readBytes(Length, Data))
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return EC;
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Dest = StringRef(reinterpret_cast<const char *>(Data.begin()), Data.size());
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// Now set the offset back to where it was after we calculated the length.
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setOffset(NewOffset);
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return Error::success();
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}
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Error StreamReader::readFixedString(StringRef &Dest, uint32_t Length) {
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ArrayRef<uint8_t> Bytes;
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if (auto EC = readBytes(Length, Bytes))
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return EC;
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Dest = StringRef(reinterpret_cast<const char *>(Bytes.begin()), Bytes.size());
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return Error::success();
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}
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Error StreamReader::readStreamRef(StreamRef &Ref) {
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return readStreamRef(Ref, bytesRemaining());
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}
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Error StreamReader::readStreamRef(StreamRef &Ref, uint32_t Length) {
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if (bytesRemaining() < Length)
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return make_error<CodeViewError>(cv_error_code::insufficient_buffer);
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Ref = StreamRef(Stream, Offset, Length);
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Offset += Length;
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return Error::success();
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}
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