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llvm-mirror/tools/llvm-objcopy/COFF/Writer.h
Alexey Lapshin c75c8e75b3 [llvm-objcopy][NFC] replace class Buffer/MemBuffer/FileBuffer with streams.
During D88827 it was requested to remove the local implementation
of Memory/File Buffers:

// TODO: refactor the buffer classes in LLVM to enable us to use them here
// directly.

This patch uses raw_ostream instead of Buffers. Generally, using streams
could allow us to reduce memory usages. No need to load all data into the
memory - the data could be streamed through a smaller buffer.
Thus, this patch uses raw_ostream as an interface for output data:

Error executeObjcopyOnBinary(CopyConfig &Config,
                             object::Binary &In,
                             raw_ostream &Out);

Note 1. This patch does not change the implementation of Writers
so that data would be directly stored into raw_ostream.
This is assumed to be done later.

Note 2. It would be better if Writers would be implemented in a such way
that data could be streamed without seeking/updating. If that would be
inconvenient then raw_ostream could be replaced with raw_pwrite_stream
to have a possibility to seek back and update file headers.
This is assumed to be done later if necessary.

Note 3. Current FileOutputBuffer allows using a memory-mapped file.
The raw_fd_ostream (which could be used if data should be stored in the file)
does not allow us to use a memory-mapped file. Memory map functionality
could be implemented for raw_fd_ostream:

It is possible to add resize() method into raw_ostream.

class raw_ostream {
  void resize(uint64_t size);
}

That method, implemented for raw_fd_ostream, could create a memory-mapped file.
The streamed data would be written into that memory file then.
Thus we would be able to use memory-mapped files with raw_fd_ostream.
This is assumed to be done later if necessary.

Differential Revision: https://reviews.llvm.org/D91028
2021-03-10 23:50:04 +03:00

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//===- Writer.h -------------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_TOOLS_OBJCOPY_COFF_WRITER_H
#define LLVM_TOOLS_OBJCOPY_COFF_WRITER_H
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/MemoryBuffer.h"
#include <cstddef>
#include <utility>
namespace llvm {
namespace objcopy {
namespace coff {
struct Object;
class COFFWriter {
Object &Obj;
std::unique_ptr<WritableMemoryBuffer> Buf;
raw_ostream &Out;
size_t FileSize;
size_t FileAlignment;
size_t SizeOfInitializedData;
StringTableBuilder StrTabBuilder;
template <class SymbolTy> std::pair<size_t, size_t> finalizeSymbolTable();
Error finalizeRelocTargets();
Error finalizeSymbolContents();
void layoutSections();
size_t finalizeStringTable();
Error finalize(bool IsBigObj);
void writeHeaders(bool IsBigObj);
void writeSections();
template <class SymbolTy> void writeSymbolStringTables();
Error write(bool IsBigObj);
Error patchDebugDirectory();
Expected<uint32_t> virtualAddressToFileAddress(uint32_t RVA);
public:
virtual ~COFFWriter() {}
Error write();
COFFWriter(Object &Obj, raw_ostream &Out)
: Obj(Obj), Out(Out), StrTabBuilder(StringTableBuilder::WinCOFF) {}
};
} // end namespace coff
} // end namespace objcopy
} // end namespace llvm
#endif // LLVM_TOOLS_OBJCOPY_COFF_WRITER_H