162 lines
4.4 KiB
C++
162 lines
4.4 KiB
C++
//===- Core/NativeFileFormat.h - Describes native object file -------------===//
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//
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// The LLVM Linker
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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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#ifndef LLD_CORE_NATIVE_FILE_FORMAT_H_
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#define LLD_CORE_NATIVE_FILE_FORMAT_H_
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#include <stdint.h>
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namespace lld {
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//
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// Overview:
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//
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// The number one design goal of this file format is enable the linker to
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// read object files into in-memory Atom objects extremely quickly.
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// The second design goal is to enable future modifications to the
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// Atom attribute model.
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//
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// The llvm native object file format is not like traditional object file
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// formats (e.g. ELF, COFF, mach-o). There is no symbol table and no
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// sections. Instead the file is essentially an array of archived Atoms.
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// It is *not* serialized Atoms which would require deserialization into
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// in memory objects. Instead it is an array of read-only info about each
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// Atom. The NativeReader bulk creates in-memory Atoms which just have
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// an ivar which points to the read-only info for that Atom. No additional
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// processing is done to construct the in-memory Atoms. All Atom attribute
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// getter methods are virtual calls which dig up the info they need from the
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// ivar data.
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//
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// To support the gradual evolution of Atom attributes, the Atom read-only
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// data is versioned. The NativeReader chooses which in-memory Atom class
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// to use based on the version. What this means is that if new attributes
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// are added (or changed) in the Atom model, a new native atom class and
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// read-only atom info struct needs to be defined. Then, all the existing
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// native reader atom classes need to be modified to do their best effort
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// to map their old style read-only data to the new Atom model. At some point
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// some classes to support old versions may be dropped.
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//
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//
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// Details:
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//
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// The native object file format consists of a header that specifies the
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// endianness of the file and the architecture along with a list of "chunks"
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// in the file. A Chunk is simply a tagged range of the file. There is
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// one chunk for the array of atom infos. There is another chunk for the
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// string pool, and another for the content pool.
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//
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// It turns out there most atoms have very similar sets of attributes, only
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// the name and content attribute vary. To exploit this fact to reduce the file
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// size, the atom read-only info contains just the name and content info plus
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// a reference to which attribute set it uses. The attribute sets are stored
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// in another chunk.
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//
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//
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// An entry in the NativeFileHeader that describes one chunk of the file.
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//
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struct NativeChunk {
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uint32_t signature;
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uint32_t fileOffset;
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uint32_t fileSize;
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uint32_t elementCount;
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};
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//
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// The header in a native object file
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//
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struct NativeFileHeader {
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uint8_t magic[16];
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uint32_t endian;
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uint32_t architecture;
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uint32_t fileSize;
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uint32_t chunkCount;
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NativeChunk chunks[];
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};
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//
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// Possible values for NativeChunk.signature field
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//
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enum NativeChunkSignatures {
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NCS_DefinedAtomsV1 = 1,
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NCS_AttributesArrayV1 = 2,
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NCS_Content = 3,
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NCS_Strings = 4,
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NCS_ReferencesArray = 5,
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};
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//
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// The 16-bytes at the start of a native object file
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//
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#define NATIVE_FILE_HEADER_MAGIC "llvm nat obj v1 "
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//
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// Possible values for the NativeFileHeader.endian field
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//
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enum {
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NFH_BigEndian = 0x42696745,
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NFH_LittleEndian = 0x4574696c
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};
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//
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// Possible values for the NativeFileHeader.architecture field
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//
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enum {
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NFA_x86 = 1,
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NFA_x86_64 = 2,
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NFA_armv6 = 3,
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NFA_armv7 = 4,
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};
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//
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// The NCS_DefinedAtomsV1 chunk contains an array of these structs
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//
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struct NativeDefinedAtomIvarsV1 {
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uint32_t nameOffset;
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uint32_t attributesOffset;
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uint32_t contentOffset;
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uint32_t contentSize;
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};
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//
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// The NCS_AttributesArrayV1 chunk contains an array of these structs
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//
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struct NativeAtomAttributesV1 {
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uint32_t sectionNameOffset;
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uint16_t align2;
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uint16_t alignModulus;
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uint8_t internalName;
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uint8_t scope;
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uint8_t interposable;
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uint8_t merge;
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uint8_t contentType;
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uint8_t sectionChoice;
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uint8_t deadStrip;
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uint8_t permissions;
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uint8_t thumb;
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uint8_t alias;
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uint8_t pad1;
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uint8_t pad2;
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};
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} // namespace lld
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#endif // LLD_CORE_NATIVE_FILE_FORMAT_H_
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