4f16e177e1
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
50 lines
1.6 KiB
C++
50 lines
1.6 KiB
C++
//===- Writer.h -------------------------------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TOOLS_LLVM_OBJCOPY_WASM_WRITER_H
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#define LLVM_TOOLS_LLVM_OBJCOPY_WASM_WRITER_H
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#include "Object.h"
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#include <cstdint>
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#include <vector>
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namespace llvm {
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namespace objcopy {
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namespace wasm {
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class Writer {
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public:
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Writer(Object &Obj, raw_ostream &Out) : Obj(Obj), Out(Out) {}
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Error write();
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private:
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using SectionHeader = SmallVector<char, 8>;
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Object &Obj;
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raw_ostream &Out;
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std::vector<SectionHeader> SectionHeaders;
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/// Generate a wasm section section header for S.
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/// The header consists of
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/// * A one-byte section ID (aka the section type).
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/// * The size of the section contents, encoded as ULEB128.
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/// * If the section is a custom section (type 0) it also has a name, which is
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/// encoded as a length-prefixed string. The encoded section size *includes*
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/// this string.
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/// See https://webassembly.github.io/spec/core/binary/modules.html#sections
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/// Return the header and store the total size in SectionSize.
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static SectionHeader createSectionHeader(const Section &S,
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size_t &SectionSize);
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size_t finalize();
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};
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} // end namespace wasm
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} // end namespace objcopy
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} // end namespace llvm
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#endif // LLVM_TOOLS_LLVM_OBJCOPY_WASM_WRITER_H
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