elf_writer_quick.cc revision ad5fa8c5b26a325dc2a9521b87188755046c17f3 
1/*
2 * Copyright (C) 2012 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include "elf_writer_quick.h"
18
19#include <unordered_map>
20#include <unordered_set>
21
22#include "base/logging.h"
23#include "base/unix_file/fd_file.h"
24#include "compiled_method.h"
25#include "dex_file-inl.h"
26#include "driver/compiler_driver.h"
27#include "driver/compiler_options.h"
28#include "elf_builder.h"
29#include "elf_file.h"
30#include "elf_utils.h"
31#include "elf_writer_debug.h"
32#include "globals.h"
33#include "leb128.h"
34#include "oat.h"
35#include "oat_writer.h"
36#include "utils.h"
37
38namespace art {
39
40// .eh_frame and .debug_frame are almost identical.
41// Except for some minor formatting differences, the main difference
42// is that .eh_frame is allocated within the running program because
43// it is used by C++ exception handling (which we do not use so we
44// can choose either).  C++ compilers generally tend to use .eh_frame
45// because if they need it sometimes, they might as well always use it.
46constexpr dwarf::CFIFormat kCFIFormat = dwarf::DW_EH_FRAME_FORMAT;
47
48template <typename ElfTypes>
49bool ElfWriterQuick<ElfTypes>::Create(File* elf_file,
50                                      OatWriter* oat_writer,
51                                      const std::vector<const DexFile*>& dex_files,
52                                      const std::string& android_root,
53                                      bool is_host,
54                                      const CompilerDriver& driver) {
55  ElfWriterQuick elf_writer(driver, elf_file);
56  return elf_writer.Write(oat_writer, dex_files, android_root, is_host);
57}
58
59template <typename ElfTypes>
60static void WriteDebugSymbols(ElfBuilder<ElfTypes>* builder, OatWriter* oat_writer);
61
62// Encode patch locations in .oat_patches format.
63template <typename ElfTypes>
64void ElfWriterQuick<ElfTypes>::EncodeOatPatches(
65    const OatWriter::PatchLocationsMap& sections,
66    std::vector<uint8_t>* buffer) {
67  for (const auto& section : sections) {
68    const std::string& name = section.first;
69    std::vector<uintptr_t>* locations = section.second.get();
70    DCHECK(!name.empty());
71    std::sort(locations->begin(), locations->end());
72    // Reserve buffer space - guess 2 bytes per ULEB128.
73    buffer->reserve(buffer->size() + name.size() + locations->size() * 2);
74    // Write null-terminated section name.
75    const uint8_t* name_data = reinterpret_cast<const uint8_t*>(name.c_str());
76    buffer->insert(buffer->end(), name_data, name_data + name.size() + 1);
77    // Write placeholder for data length.
78    size_t length_pos = buffer->size();
79    EncodeUnsignedLeb128(buffer, UINT32_MAX);
80    // Write LEB128 encoded list of advances (deltas between consequtive addresses).
81    size_t data_pos = buffer->size();
82    uintptr_t address = 0;  // relative to start of section.
83    for (uintptr_t location : *locations) {
84      DCHECK_LT(location - address, UINT32_MAX) << "Large gap between patch locations";
85      EncodeUnsignedLeb128(buffer, location - address);
86      address = location;
87    }
88    // Update length.
89    UpdateUnsignedLeb128(buffer->data() + length_pos, buffer->size() - data_pos);
90  }
91  buffer->push_back(0);  // End of sections.
92}
93
94class RodataWriter FINAL : public CodeOutput {
95 public:
96  explicit RodataWriter(OatWriter* oat_writer) : oat_writer_(oat_writer) {}
97
98  bool Write(OutputStream* out) OVERRIDE {
99    return oat_writer_->WriteRodata(out);
100  }
101
102 private:
103  OatWriter* oat_writer_;
104};
105
106class TextWriter FINAL : public CodeOutput {
107 public:
108  explicit TextWriter(OatWriter* oat_writer) : oat_writer_(oat_writer) {}
109
110  bool Write(OutputStream* out) OVERRIDE {
111    return oat_writer_->WriteCode(out);
112  }
113
114 private:
115  OatWriter* oat_writer_;
116};
117
118enum PatchResult {
119  kAbsoluteAddress,  // Absolute memory location.
120  kPointerRelativeAddress,  // Offset relative to the location of the pointer.
121  kSectionRelativeAddress,  // Offset relative to start of containing section.
122};
123
124// Patch memory addresses within a buffer.
125// It assumes that the unpatched addresses are offsets relative to base_address.
126// (which generally means method's low_pc relative to the start of .text)
127template <typename Elf_Addr, typename Address, PatchResult kPatchResult>
128static void Patch(const std::vector<uintptr_t>& patch_locations,
129                  Elf_Addr buffer_address, Elf_Addr base_address,
130                  std::vector<uint8_t>* buffer) {
131  for (uintptr_t location : patch_locations) {
132    typedef __attribute__((__aligned__(1))) Address UnalignedAddress;
133    auto* to_patch = reinterpret_cast<UnalignedAddress*>(buffer->data() + location);
134    switch (kPatchResult) {
135      case kAbsoluteAddress:
136        *to_patch = (base_address + *to_patch);
137        break;
138      case kPointerRelativeAddress:
139        *to_patch = (base_address + *to_patch) - (buffer_address + location);
140        break;
141      case kSectionRelativeAddress:
142        *to_patch = (base_address + *to_patch) - buffer_address;
143        break;
144    }
145  }
146}
147
148template <typename ElfTypes>
149bool ElfWriterQuick<ElfTypes>::Write(
150    OatWriter* oat_writer,
151    const std::vector<const DexFile*>& dex_files_unused ATTRIBUTE_UNUSED,
152    const std::string& android_root_unused ATTRIBUTE_UNUSED,
153    bool is_host_unused ATTRIBUTE_UNUSED) {
154  using Elf_Addr = typename ElfTypes::Addr;
155  const InstructionSet isa = compiler_driver_->GetInstructionSet();
156
157  // Setup the builder with the main OAT sections (.rodata .text .bss).
158  const size_t rodata_size = oat_writer->GetOatHeader().GetExecutableOffset();
159  const size_t text_size = oat_writer->GetSize() - rodata_size;
160  const size_t bss_size = oat_writer->GetBssSize();
161  RodataWriter rodata_writer(oat_writer);
162  TextWriter text_writer(oat_writer);
163  std::unique_ptr<ElfBuilder<ElfTypes>> builder(new ElfBuilder<ElfTypes>(
164      isa, rodata_size, &rodata_writer, text_size, &text_writer, bss_size));
165
166  // Add debug sections.
167  // They are stack allocated here (in the same scope as the builder),
168  // but they are registred with the builder only if they are used.
169  using RawSection = typename ElfBuilder<ElfTypes>::RawSection;
170  const auto* text = builder->GetText();
171  const bool is64bit = Is64BitInstructionSet(isa);
172  const int pointer_size = GetInstructionSetPointerSize(isa);
173  RawSection eh_frame(".eh_frame", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0,
174                      is64bit ? Patch<Elf_Addr, uint64_t, kPointerRelativeAddress> :
175                                Patch<Elf_Addr, uint32_t, kPointerRelativeAddress>,
176                      text);
177  RawSection eh_frame_hdr(".eh_frame_hdr", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, 4, 0,
178                          Patch<Elf_Addr, uint32_t, kSectionRelativeAddress>, text);
179  RawSection debug_frame(".debug_frame", SHT_PROGBITS, 0, nullptr, 0, pointer_size, 0,
180                         is64bit ? Patch<Elf_Addr, uint64_t, kAbsoluteAddress> :
181                                   Patch<Elf_Addr, uint32_t, kAbsoluteAddress>,
182                         text);
183  RawSection debug_info(".debug_info", SHT_PROGBITS, 0, nullptr, 0, 1, 0,
184                        Patch<Elf_Addr, uint32_t, kAbsoluteAddress>, text);
185  RawSection debug_abbrev(".debug_abbrev", SHT_PROGBITS, 0, nullptr, 0, 1, 0);
186  RawSection debug_str(".debug_str", SHT_PROGBITS, 0, nullptr, 0, 1, 0);
187  RawSection debug_line(".debug_line", SHT_PROGBITS, 0, nullptr, 0, 1, 0,
188                        Patch<Elf_Addr, uint32_t, kAbsoluteAddress>, text);
189  if (!oat_writer->GetMethodDebugInfo().empty()) {
190    if (compiler_driver_->GetCompilerOptions().GetIncludeCFI()) {
191      if (kCFIFormat == dwarf::DW_EH_FRAME_FORMAT) {
192        dwarf::WriteCFISection(
193            compiler_driver_, oat_writer,
194            dwarf::DW_EH_PE_pcrel, kCFIFormat,
195            eh_frame.GetBuffer(), eh_frame.GetPatchLocations(),
196            eh_frame_hdr.GetBuffer(), eh_frame_hdr.GetPatchLocations());
197        builder->RegisterSection(&eh_frame);
198        builder->RegisterSection(&eh_frame_hdr);
199      } else {
200        DCHECK(kCFIFormat == dwarf::DW_DEBUG_FRAME_FORMAT);
201        dwarf::WriteCFISection(
202            compiler_driver_, oat_writer,
203            dwarf::DW_EH_PE_absptr, kCFIFormat,
204            debug_frame.GetBuffer(), debug_frame.GetPatchLocations(),
205            nullptr, nullptr);
206        builder->RegisterSection(&debug_frame);
207        *oat_writer->GetAbsolutePatchLocationsFor(".debug_frame") =
208            *debug_frame.GetPatchLocations();
209      }
210    }
211    if (compiler_driver_->GetCompilerOptions().GetIncludeDebugSymbols()) {
212      // Add methods to .symtab.
213      WriteDebugSymbols(builder.get(), oat_writer);
214      // Generate DWARF .debug_* sections.
215      dwarf::WriteDebugSections(
216          compiler_driver_, oat_writer,
217          debug_info.GetBuffer(), debug_info.GetPatchLocations(),
218          debug_abbrev.GetBuffer(),
219          debug_str.GetBuffer(),
220          debug_line.GetBuffer(), debug_line.GetPatchLocations());
221      builder->RegisterSection(&debug_info);
222      builder->RegisterSection(&debug_abbrev);
223      builder->RegisterSection(&debug_str);
224      builder->RegisterSection(&debug_line);
225      *oat_writer->GetAbsolutePatchLocationsFor(".debug_info") =
226          *debug_info.GetPatchLocations();
227      *oat_writer->GetAbsolutePatchLocationsFor(".debug_line") =
228          *debug_line.GetPatchLocations();
229    }
230  }
231
232  // Add relocation section.
233  RawSection oat_patches(".oat_patches", SHT_OAT_PATCH, 0, nullptr, 0, 1, 0);
234  if (compiler_driver_->GetCompilerOptions().GetIncludePatchInformation() ||
235      // ElfWriter::Fixup will be called regardless and it needs to be able
236      // to patch debug sections so we have to include patches for them.
237      compiler_driver_->GetCompilerOptions().GetIncludeDebugSymbols()) {
238    EncodeOatPatches(oat_writer->GetAbsolutePatchLocations(), oat_patches.GetBuffer());
239    builder->RegisterSection(&oat_patches);
240  }
241
242  return builder->Write(elf_file_);
243}
244
245template <typename ElfTypes>
246static void WriteDebugSymbols(ElfBuilder<ElfTypes>* builder, OatWriter* oat_writer) {
247  const std::vector<OatWriter::DebugInfo>& method_info = oat_writer->GetMethodDebugInfo();
248
249  // Find all addresses (low_pc) which contain deduped methods.
250  // The first instance of method is not marked deduped_, but the rest is.
251  std::unordered_set<uint32_t> deduped_addresses;
252  for (auto it = method_info.begin(); it != method_info.end(); ++it) {
253    if (it->deduped_) {
254      deduped_addresses.insert(it->low_pc_);
255    }
256  }
257
258  auto* symtab = builder->GetSymtab();
259  for (auto it = method_info.begin(); it != method_info.end(); ++it) {
260    if (it->deduped_) {
261      continue;  // Add symbol only for the first instance.
262    }
263    std::string name = PrettyMethod(it->dex_method_index_, *it->dex_file_, true);
264    if (deduped_addresses.find(it->low_pc_) != deduped_addresses.end()) {
265      name += " [DEDUPED]";
266    }
267
268    uint32_t low_pc = it->low_pc_;
269    // Add in code delta, e.g., thumb bit 0 for Thumb2 code.
270    low_pc += it->compiled_method_->CodeDelta();
271    symtab->AddSymbol(name, builder->GetText(), low_pc,
272                      true, it->high_pc_ - it->low_pc_, STB_GLOBAL, STT_FUNC);
273
274    // Conforming to aaelf, add $t mapping symbol to indicate start of a sequence of thumb2
275    // instructions, so that disassembler tools can correctly disassemble.
276    if (it->compiled_method_->GetInstructionSet() == kThumb2) {
277      symtab->AddSymbol("$t", builder->GetText(), it->low_pc_ & ~1, true,
278                        0, STB_LOCAL, STT_NOTYPE);
279    }
280  }
281}
282
283// Explicit instantiations
284template class ElfWriterQuick<ElfTypes32>;
285template class ElfWriterQuick<ElfTypes64>;
286
287}  // namespace art
288