lib/Object/Decompressor.cpp

   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   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
  75 bool Decompressor::isGnuStyle(StringRef Name) {
  76   return Name.startswith(".zdebug");
  77 }
  78
  79 bool 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
  91 bool Decompressor::isCompressedELFSection(uint64_t Flags, StringRef Name) {
  92   return (Flags & ELF::SHF_COMPRESSED) || isGnuStyle(Name);
  93 }
  94
  95 Error Decompressor::decompress(MutableArrayRef<char> Buffer) {
  96   size_t Size = Buffer.size();
  97   return zlib::uncompress(SectionData, Buffer.data(), Size);
  98 }