1//===-- Decompressor.cpp --------------------------------------------------===//
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#include "llvm/Object/Decompressor.h"
10#include "llvm/BinaryFormat/ELF.h"
11#include "llvm/Object/ELFObjectFile.h"
12#include "llvm/Support/Compression.h"
13#include "llvm/Support/DataExtractor.h"
14#include "llvm/Support/Endian.h"
15
16using namespace llvm;
17using namespace llvm::support::endian;
18using namespace object;
19
20Expected<Decompressor> Decompressor::create(StringRef Name, StringRef Data,
21                                            bool IsLE, bool Is64Bit) {
22  if (!zlib::isAvailable())
23    return createError("zlib is not available");
24
25  Decompressor D(Data);
26  Error Err = isGnuStyle(Name) ? D.consumeCompressedGnuHeader()
27                               : D.consumeCompressedZLibHeader(Is64Bit, IsLE);
28  if (Err)
29    return std::move(Err);
30  return D;
31}
32
33Decompressor::Decompressor(StringRef Data)
34    : SectionData(Data), DecompressedSize(0) {}
35
36Error Decompressor::consumeCompressedGnuHeader() {
37  if (!SectionData.startswith("ZLIB"))
38    return createError("corrupted compressed section header");
39
40  SectionData = SectionData.substr(4);
41
42  // Consume uncompressed section size (big-endian 8 bytes).
43  if (SectionData.size() < 8)
44    return createError("corrupted uncompressed section size");
45  DecompressedSize = read64be(SectionData.data());
46  SectionData = SectionData.substr(8);
47
48  return Error::success();
49}
50
51Error Decompressor::consumeCompressedZLibHeader(bool Is64Bit,
52                                                bool IsLittleEndian) {
53  using namespace ELF;
54  uint64_t HdrSize = Is64Bit ? sizeof(Elf64_Chdr) : sizeof(Elf32_Chdr);
55  if (SectionData.size() < HdrSize)
56    return createError("corrupted compressed section header");
57
58  DataExtractor Extractor(SectionData, IsLittleEndian, 0);
59  uint64_t Offset = 0;
60  if (Extractor.getUnsigned(&Offset, Is64Bit ? sizeof(Elf64_Word)
61                                             : sizeof(Elf32_Word)) !=
62      ELFCOMPRESS_ZLIB)
63    return createError("unsupported compression type");
64
65  // Skip Elf64_Chdr::ch_reserved field.
66  if (Is64Bit)
67    Offset += sizeof(Elf64_Word);
68
69  DecompressedSize = Extractor.getUnsigned(
70      &Offset, Is64Bit ? sizeof(Elf64_Xword) : sizeof(Elf32_Word));
71  SectionData = SectionData.substr(HdrSize);
72  return Error::success();
73}
74
75bool Decompressor::isGnuStyle(StringRef Name) {
76  return Name.startswith(".zdebug");
77}
78
79bool Decompressor::isCompressed(const object::SectionRef &Section) {
80  if (Section.isCompressed())
81    return true;
82
83  Expected<StringRef> SecNameOrErr = Section.getName();
84  if (SecNameOrErr)
85    return isGnuStyle(*SecNameOrErr);
86
87  consumeError(SecNameOrErr.takeError());
88  return false;
89}
90
91bool Decompressor::isCompressedELFSection(uint64_t Flags, StringRef Name) {
92  return (Flags & ELF::SHF_COMPRESSED) || isGnuStyle(Name);
93}
94
95Error Decompressor::decompress(MutableArrayRef<char> Buffer) {
96  size_t Size = Buffer.size();
97  return zlib::uncompress(SectionData, Buffer.data(), Size);
98}
99