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 
16 using namespace llvm;
17 using namespace llvm::support::endian;
18 using namespace object;
19 
20 Expected<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 
33 Decompressor::Decompressor(StringRef Data)
34     : SectionData(Data), DecompressedSize(0) {}
35 
36 Error 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 
51 Error 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   uint32_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 
75 bool Decompressor::isGnuStyle(StringRef Name) {
76   return Name.startswith(".zdebug");
77 }
78 
79 bool Decompressor::isCompressed(const object::SectionRef &Section) {
80   StringRef Name;
81   if (Section.getName(Name))
82     return false;
83   return Section.isCompressed() || isGnuStyle(Name);
84 }
85 
86 bool Decompressor::isCompressedELFSection(uint64_t Flags, StringRef Name) {
87   return (Flags & ELF::SHF_COMPRESSED) || isGnuStyle(Name);
88 }
89 
90 Error Decompressor::decompress(MutableArrayRef<char> Buffer) {
91   size_t Size = Buffer.size();
92   return zlib::uncompress(SectionData, Buffer.data(), Size);
93 }
94