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Commit 1a141a09 authored by Christopher Ferris's avatar Christopher Ferris
Browse files

Small behavioral changes to the unwinder. 

- Be a little more lenient when reading the cies/fdes. If next entry data
  winds up incorrect, don't fail, simply stop processing the entries. This
  only applies when reading all of the cies/fdes at once.
- Fail to init an eh_frame with no entries and fallback to assuming the
  eh_frame has no header instead.
- Change the step to always try debug_frame first which has the most
  accurate information.
- Add small unit tests and a couple of offline unit tests to verify
  this behavior.

These changes are needed to support offline unwinding since it depends
on this new behavior.

Bug: 65682279

Test: Ran new unit tests.
Change-Id: I3529f1b0c8e14cd7409494e5de2f3c9e78d0855e
parent 0ad42435

libunwindstack/Android.bp

+2 −0
Original line number Diff line number Diff line
@@ -170,6 +170,8 @@ cc_test { 
    data: [

        "tests/files/elf32.xz",

        "tests/files/elf64.xz",

        "tests/files/offline/bad_eh_frame_hdr_arm64/*",

        "tests/files/offline/debug_frame_first_x86/*",

        "tests/files/offline/jit_debug_arm32/*",

        "tests/files/offline/jit_debug_x86_32/*",

        "tests/files/offline/gnu_debugdata_arm32/*",

libunwindstack/DwarfEhFrameWithHdr.cpp

+5 −0
Original line number Diff line number Diff line
@@ -64,6 +64,11 @@ bool DwarfEhFrameWithHdr<AddressType>::Init(uint64_t offset, uint64_t size) { 
    return false;

  }



  if (fde_count_ == 0) {

    last_error_ = DWARF_ERROR_NO_FDES;

    return false;

  }



  entries_offset_ = memory_.cur_offset();

  entries_end_ = offset + size;

  entries_data_offset_ = offset;

libunwindstack/DwarfError.h

+1 −0
Original line number Diff line number Diff line
@@ -31,6 +31,7 @@ enum DwarfError : uint8_t { 
  DWARF_ERROR_TOO_MANY_ITERATIONS,

  DWARF_ERROR_CFA_NOT_DEFINED,

  DWARF_ERROR_UNSUPPORTED_VERSION,

  DWARF_ERROR_NO_FDES,

};



}  // namespace unwindstack

libunwindstack/DwarfSection.cpp

+2 −3
Original line number Diff line number Diff line
@@ -835,9 +835,8 @@ bool DwarfSectionImpl<AddressType>::CreateSortedFdeList() { 
    }



    if (next_entry_offset < memory_.cur_offset()) {

      // This indicates some kind of corruption, or malformed section data.

      last_error_ = DWARF_ERROR_ILLEGAL_VALUE;

      return false;

      // Simply consider the processing done in this case.

      break;

    }

    memory_.set_cur_offset(next_entry_offset);

  }

libunwindstack/ElfInterface.cpp

+19 −14
Original line number Diff line number Diff line
@@ -126,21 +126,25 @@ void ElfInterface::InitHeadersWithTemplate() { 
  if (eh_frame_hdr_offset_ != 0) {

    eh_frame_.reset(new DwarfEhFrameWithHdr<AddressType>(memory_));

    if (!eh_frame_->Init(eh_frame_hdr_offset_, eh_frame_hdr_size_)) {

      // Even if the eh_frame_offset_ is non-zero, do not bother

      // trying to read that since something has gone wrong.

      eh_frame_.reset(nullptr);

      eh_frame_hdr_offset_ = 0;

      eh_frame_hdr_size_ = static_cast<uint64_t>(-1);

    }

  } else if (eh_frame_offset_ != 0) {

    // If there is a eh_frame section without a eh_frame_hdr section.

  }



  if (eh_frame_.get() == nullptr && eh_frame_offset_ != 0) {

    // If there is an eh_frame section without an eh_frame_hdr section,

    // or using the frame hdr object failed to init.

    eh_frame_.reset(new DwarfEhFrame<AddressType>(memory_));

    if (!eh_frame_->Init(eh_frame_offset_, eh_frame_size_)) {

      eh_frame_.reset(nullptr);

    }

  }



  if (eh_frame_.get() == nullptr) {

    eh_frame_hdr_offset_ = 0;

    eh_frame_hdr_size_ = static_cast<uint64_t>(-1);

    eh_frame_offset_ = 0;

    eh_frame_size_ = static_cast<uint64_t>(-1);

  }

  }



  if (debug_frame_offset_ != 0) {

    debug_frame_.reset(new DwarfDebugFrame<AddressType>(memory_));
@@ -436,15 +440,16 @@ bool ElfInterface::Step(uint64_t pc, uint64_t load_bias, Regs* regs, Memory* pro 
  }

  uint64_t adjusted_pc = pc - load_bias;



  // Try the eh_frame first.

  DwarfSection* eh_frame = eh_frame_.get();

  if (eh_frame != nullptr && eh_frame->Step(adjusted_pc, regs, process_memory, finished)) {

  // Try the debug_frame first since it contains the most specific unwind

  // information.

  DwarfSection* debug_frame = debug_frame_.get();

  if (debug_frame != nullptr && debug_frame->Step(adjusted_pc, regs, process_memory, finished)) {

    return true;

  }



  // Try the debug_frame next.

  DwarfSection* debug_frame = debug_frame_.get();

  if (debug_frame != nullptr && debug_frame->Step(adjusted_pc, regs, process_memory, finished)) {

  // Try the eh_frame next.

  DwarfSection* eh_frame = eh_frame_.get();

  if (eh_frame != nullptr && eh_frame->Step(adjusted_pc, regs, process_memory, finished)) {

    return true;

  }