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// ehframe.cc -- handle exception frame sections for gold

// Copyright 2006, 2007, 2008 Free Software Foundation, Inc.

// Written by Ian Lance Taylor <iant@google.com>.

// This file is part of gold.

// This program is free software; you can redistribute it and/or modify

// it under the terms of the GNU General Public License as published by

// the Free Software Foundation; either version 3 of the License, or

// (at your option) any later version.

// This program is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License

// along with this program; if not, write to the Free Software

// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,

// MA 02110-1301, USA.

#include "gold.h"

#include <cstring>

#include <algorithm>

#include "elfcpp.h"

#include "dwarf.h"

#include "symtab.h"

#include "reloc.h"

#include "ehframe.h"

namespace gold

{

// This file handles generation of the exception frame header that

// gcc's runtime support libraries use to find unwind information at

// runtime.  This file also handles discarding duplicate exception

// frame information.

// The exception frame header starts with four bytes:

// 0: The version number, currently 1.

// 1: The encoding of the pointer to the exception frames.  This can

//    be any DWARF unwind encoding (DW_EH_PE_*).  It is normally a 4

//    byte PC relative offset (DW_EH_PE_pcrel | DW_EH_PE_sdata4).

// 2: The encoding of the count of the number of FDE pointers in the

//    lookup table.  This can be any DWARF unwind encoding, and in

//    particular can be DW_EH_PE_omit if the count is omitted.  It is

//    normally a 4 byte unsigned count (DW_EH_PE_udata4).

// 3: The encoding of the lookup table entries.  Currently gcc's

//    libraries will only support DW_EH_PE_datarel | DW_EH_PE_sdata4,

//    which means that the values are 4 byte offsets from the start of

//    the table.

// The exception frame header is followed by a pointer to the contents

// of the exception frame section (.eh_frame).  This pointer is

// encoded as specified in the byte at offset 1 of the header (i.e.,

// it is normally a 4 byte PC relative offset).

// If there is a lookup table, this is followed by the count of the

// number of FDE pointers, encoded as specified in the byte at offset

// 2 of the header (i.e., normally a 4 byte unsigned integer).

// This is followed by the table, which should start at an 4-byte

// aligned address in memory.  Each entry in the table is 8 bytes.

// Each entry represents an FDE.  The first four bytes of each entry

// are an offset to the starting PC for the FDE.  The last four bytes

// of each entry are an offset to the FDE data.  The offsets are from

// the start of the exception frame header information.  The entries

// are in sorted order by starting PC.

const int eh_frame_hdr_size = 4;

// Construct the exception frame header.

Eh_frame_hdr::Eh_frame_hdr(Output_section* eh_frame_section,

                           const Eh_frame* eh_frame_data)

  : Output_section_data(4),

    eh_frame_section_(eh_frame_section),

    eh_frame_data_(eh_frame_data),

    fde_offsets_(),

    any_unrecognized_eh_frame_sections_(false)

{

}

// Set the size of the exception frame header.

void

Eh_frame_hdr::set_final_data_size()

{

  unsigned int data_size = eh_frame_hdr_size + 4;

  if (!this->any_unrecognized_eh_frame_sections_)

    {

      unsigned int fde_count = this->eh_frame_data_->fde_count();

      if (fde_count != 0)

        data_size += 4 + 8 * fde_count;

      this->fde_offsets_.reserve(fde_count);

    }

  this->set_data_size(data_size);

}

// Write the data to the flie.

void

Eh_frame_hdr::do_write(Output_file* of)

{

  switch (parameters->size_and_endianness())

    {

#ifdef HAVE_TARGET_32_LITTLE

    case Parameters::TARGET_32_LITTLE:

      this->do_sized_write<32, false>(of);

      break;

#endif

#ifdef HAVE_TARGET_32_BIG

    case Parameters::TARGET_32_BIG:

      this->do_sized_write<32, true>(of);

      break;

#endif

#ifdef HAVE_TARGET_64_LITTLE

    case Parameters::TARGET_64_LITTLE:

      this->do_sized_write<64, false>(of);

      break;

#endif

#ifdef HAVE_TARGET_64_BIG

    case Parameters::TARGET_64_BIG:

      this->do_sized_write<64, true>(of);

      break;

#endif

    default:

      gold_unreachable();

    }

}

// Write the data to the file with the right endianness.

template<int size, bool big_endian>

void

Eh_frame_hdr::do_sized_write(Output_file* of)

{

  const off_t off = this->offset();

  const off_t oview_size = this->data_size();

  unsigned char* const oview = of->get_output_view(off, oview_size);

  // Version number.

  oview[0] = 1;

  // Write out a 4 byte PC relative offset to the address of the

  // .eh_frame section.

  oview[1] = elfcpp::DW_EH_PE_pcrel | elfcpp::DW_EH_PE_sdata4;

  uint64_t eh_frame_address = this->eh_frame_section_->address();

  uint64_t eh_frame_hdr_address = this->address();

  uint64_t eh_frame_offset = (eh_frame_address -

                              (eh_frame_hdr_address + 4));

  elfcpp::Swap<32, big_endian>::writeval(oview + 4, eh_frame_offset);

  if (this->any_unrecognized_eh_frame_sections_

      || this->fde_offsets_.empty())

    {

      // There are no FDEs, or we didn't recognize the format of the

      // some of the .eh_frame sections, so we can't write out the

      // sorted table.

      oview[2] = elfcpp::DW_EH_PE_omit;

      oview[3] = elfcpp::DW_EH_PE_omit;

      gold_assert(oview_size == 8);

    }

  else

    {

      oview[2] = elfcpp::DW_EH_PE_udata4;

      oview[3] = elfcpp::DW_EH_PE_datarel | elfcpp::DW_EH_PE_sdata4;

      elfcpp::Swap<32, big_endian>::writeval(oview + 8,

                                             this->fde_offsets_.size());

      // We have the offsets of the FDEs in the .eh_frame section.  We

      // couldn't easily get the PC values before, as they depend on

      // relocations which are, of course, target specific.  This code

      // is run after all those relocations have been applied to the

      // output file.  Here we read the output file again to find the

      // PC values.  Then we sort the list and write it out.

      Fde_addresses<size> fde_addresses(this->fde_offsets_.size());

      this->get_fde_addresses<size, big_endian>(of, &this->fde_offsets_,

                                                &fde_addresses);

      std::sort(fde_addresses.begin(), fde_addresses.end(),

                Fde_address_compare<size>());

      typename elfcpp::Elf_types<size>::Elf_Addr output_address;

      output_address = this->address();

      unsigned char* pfde = oview + 12;

      for (typename Fde_addresses<size>::iterator p = fde_addresses.begin();

           p != fde_addresses.end();

           ++p)

        {

          elfcpp::Swap<32, big_endian>::writeval(pfde,

                                                 p->first - output_address);

          elfcpp::Swap<32, big_endian>::writeval(pfde + 4,

                                                 p->second - output_address);

          pfde += 8;

        }

      gold_assert(pfde - oview == oview_size);

    }

  of->write_output_view(off, oview_size, oview);

}

// Given the offset FDE_OFFSET of an FDE in the .eh_frame section, and

// the contents of the .eh_frame section EH_FRAME_CONTENTS, where the

// FDE's encoding is FDE_ENCODING, return the output address of the

// FDE's PC.

template<int size, bool big_endian>

typename elfcpp::Elf_types<size>::Elf_Addr

Eh_frame_hdr::get_fde_pc(

    typename elfcpp::Elf_types<size>::Elf_Addr eh_frame_address,

    const unsigned char* eh_frame_contents,

    section_offset_type fde_offset,

    unsigned char fde_encoding)

{

  // The FDE starts with a 4 byte length and a 4 byte offset to the

  // CIE.  The PC follows.

  const unsigned char* p = eh_frame_contents + fde_offset + 8;

  typename elfcpp::Elf_types<size>::Elf_Addr pc;

  bool is_signed = (fde_encoding & elfcpp::DW_EH_PE_signed) != 0;

  int pc_size = fde_encoding & 7;

  if (pc_size == elfcpp::DW_EH_PE_absptr)

    {

      if (size == 32)

        pc_size = elfcpp::DW_EH_PE_udata4;

      else if (size == 64)

        pc_size = elfcpp::DW_EH_PE_udata8;

      else

        gold_unreachable();

    }

  switch (pc_size)

    {

    case elfcpp::DW_EH_PE_udata2:

      pc = elfcpp::Swap<16, big_endian>::readval(p);

      if (is_signed)

        pc = (pc ^ 0x8000) - 0x8000;

      break;

    case elfcpp::DW_EH_PE_udata4:

      pc = elfcpp::Swap<32, big_endian>::readval(p);

      if (size > 32 && is_signed)

        pc = (pc ^ 0x80000000) - 0x80000000;

      break;

    case elfcpp::DW_EH_PE_udata8:

      gold_assert(size == 64);

      pc = elfcpp::Swap_unaligned<64, big_endian>::readval(p);

      break;

    default:

      // All other cases were rejected in Eh_frame::read_cie.

      gold_unreachable();

    }

  switch (fde_encoding & 0xf0)

    {

    case 0:

      break;

    case elfcpp::DW_EH_PE_pcrel:

      pc += eh_frame_address + fde_offset + 8;

      break;

    default:

      // If other cases arise, then we have to handle them, or we have

      // to reject them by returning false in Eh_frame::read_cie.

      gold_unreachable();

    }

  return pc;

}

// Given an array of FDE offsets in the .eh_frame section, return an

// array of offsets from the exception frame header to the FDE's

// output PC and to the output address of the FDE itself.  We get the

// FDE's PC by actually looking in the .eh_frame section we just wrote

// to the output file.

template<int size, bool big_endian>

void

Eh_frame_hdr::get_fde_addresses(Output_file* of,

                                const Fde_offsets* fde_offsets,

                                Fde_addresses<size>* fde_addresses)

{

  typename elfcpp::Elf_types<size>::Elf_Addr eh_frame_address;

  eh_frame_address = this->eh_frame_section_->address();

  off_t eh_frame_offset = this->eh_frame_section_->offset();

  off_t eh_frame_size = this->eh_frame_section_->data_size();

  const unsigned char* eh_frame_contents = of->get_input_view(eh_frame_offset,

                                                              eh_frame_size);

  for (Fde_offsets::const_iterator p = fde_offsets->begin();

       p != fde_offsets->end();

       ++p)

    {

      typename elfcpp::Elf_types<size>::Elf_Addr fde_pc;

      fde_pc = this->get_fde_pc<size, big_endian>(eh_frame_address,

                                                  eh_frame_contents,

                                                  p->first, p->second);

      fde_addresses->push_back(fde_pc, eh_frame_address + p->first);

    }

  of->free_input_view(eh_frame_offset, eh_frame_size, eh_frame_contents);

}

// Class Fde.

// Write the FDE to OVIEW starting at OFFSET.  CIE_OFFSET is the

// offset of the CIE in OVIEW.  FDE_ENCODING is the encoding, from the

// CIE.  ADDRALIGN is the required alignment.  Record the FDE pc for

// EH_FRAME_HDR.  Return the new offset.

template<int size, bool big_endian>

section_offset_type

Fde::write(unsigned char* oview, section_offset_type offset,

           unsigned int addralign, section_offset_type cie_offset,

           unsigned char fde_encoding, Eh_frame_hdr* eh_frame_hdr)

{

  gold_assert((offset & (addralign - 1)) == 0);

  size_t length = this->contents_.length();

  // We add 8 when getting the aligned length to account for the

  // length word and the CIE offset.

  size_t aligned_full_length = align_address(length + 8, addralign);

  // Write the length of the FDE as a 32-bit word.  The length word

  // does not include the four bytes of the length word itself, but it

  // does include the offset to the CIE.

  elfcpp::Swap<32, big_endian>::writeval(oview + offset,

                                         aligned_full_length - 4);

  // Write the offset to the CIE as a 32-bit word.  This is the

  // difference between the address of the offset word itself and the

  // CIE address.

  elfcpp::Swap<32, big_endian>::writeval(oview + offset + 4,

                                         offset + 4 - cie_offset);

  // Copy the rest of the FDE.  Note that this is run before

  // relocation processing is done on this section, so the relocations

  // will later be applied to the FDE data.

  memcpy(oview + offset + 8, this->contents_.data(), length);

  if (aligned_full_length > length + 8)

    memset(oview + offset + length + 8, 0, aligned_full_length - (length + 8));

  // Tell the exception frame header about this FDE.

  if (eh_frame_hdr != NULL)

    eh_frame_hdr->record_fde(offset, fde_encoding);

  return offset + aligned_full_length;

}

// Class Cie.

// Destructor.

Cie::~Cie()

{

  for (std::vector<Fde*>::iterator p = this->fdes_.begin();

       p != this->fdes_.end();

       ++p)

    delete *p;

}

// Set the output offset of a CIE.  Return the new output offset.

section_offset_type

Cie::set_output_offset(section_offset_type output_offset,

                       unsigned int addralign,

                       Merge_map* merge_map)

{

  size_t length = this->contents_.length();

  // Add 4 for length and 4 for zero CIE identifier tag.

  length += 8;

  merge_map->add_mapping(this->object_, this->shndx_, this->input_offset_,

                         length, output_offset);

  length = align_address(length, addralign);

  for (std::vector<Fde*>::const_iterator p = this->fdes_.begin();

       p != this->fdes_.end();

       ++p)

    {

      (*p)->add_mapping(output_offset + length, merge_map);

      size_t fde_length = (*p)->length();

      fde_length = align_address(fde_length, addralign);

      length += fde_length;

    }

  return output_offset + length;

}

// Write the CIE to OVIEW starting at OFFSET.  EH_FRAME_HDR is for FDE

// recording.  Round up the bytes to ADDRALIGN.  Return the new

// offset.

template<int size, bool big_endian>

section_offset_type

Cie::write(unsigned char* oview, section_offset_type offset,

           unsigned int addralign, Eh_frame_hdr* eh_frame_hdr)

{

  gold_assert((offset & (addralign - 1)) == 0);

  section_offset_type cie_offset = offset;

  size_t length = this->contents_.length();

  // We add 8 when getting the aligned length to account for the

  // length word and the CIE tag.

  size_t aligned_full_length = align_address(length + 8, addralign);

  // Write the length of the CIE as a 32-bit word.  The length word

  // does not include the four bytes of the length word itself.

  elfcpp::Swap<32, big_endian>::writeval(oview + offset,

                                         aligned_full_length - 4);

  // Write the tag which marks this as a CIE: a 32-bit zero.

  elfcpp::Swap<32, big_endian>::writeval(oview + offset + 4, 0);

  // Write out the CIE data.

  memcpy(oview + offset + 8, this->contents_.data(), length);

  if (aligned_full_length > length + 8)

    memset(oview + offset + length + 8, 0, aligned_full_length - (length + 8));

  offset += aligned_full_length;

  // Write out the associated FDEs.

  unsigned char fde_encoding = this->fde_encoding_;

  for (std::vector<Fde*>::const_iterator p = this->fdes_.begin();

       p != this->fdes_.end();

       ++p)

    offset = (*p)->write<size, big_endian>(oview, offset, addralign,

                                           cie_offset, fde_encoding,

                                           eh_frame_hdr);

  return offset;

}

// We track all the CIEs we see, and merge them when possible.  This

// works because each FDE holds an offset to the relevant CIE: we

// rewrite the FDEs to point to the merged CIE.  This is worthwhile

// because in a typical C++ program many FDEs in many different object

// files will use the same CIE.

// An equality operator for Cie.

bool

operator==(const Cie& cie1, const Cie& cie2)

{

  return (cie1.personality_name_ == cie2.personality_name_

          && cie1.contents_ == cie2.contents_);

}

// A less-than operator for Cie.

bool

operator<(const Cie& cie1, const Cie& cie2)

{

  if (cie1.personality_name_ != cie2.personality_name_)

    return cie1.personality_name_ < cie2.personality_name_;

  return cie1.contents_ < cie2.contents_;

}

// Class Eh_frame.

Eh_frame::Eh_frame()

  : Output_section_data(Output_data::default_alignment()),

    eh_frame_hdr_(NULL),

    cie_offsets_(),

    unmergeable_cie_offsets_(),

    merge_map_(),

    mappings_are_done_(false),

    final_data_size_(0)

{

}

// Skip an LEB128, updating *PP to point to the next character.

// Return false if we ran off the end of the string.

bool

Eh_frame::skip_leb128(const unsigned char** pp, const unsigned char* pend)

{

  const unsigned char* p;

  for (p = *pp; p < pend; ++p)

    {

      if ((*p & 0x80) == 0)

        {

          *pp = p + 1;

          return true;

        }

    }

  return false;

}

// Add input section SHNDX in OBJECT to an exception frame section.

// SYMBOLS is the contents of the symbol table section (size

// SYMBOLS_SIZE), SYMBOL_NAMES is the symbol names section (size

// SYMBOL_NAMES_SIZE).  RELOC_SHNDX is the index of a relocation

// section applying to SHNDX, or 0 if none, or -1U if more than one.

// RELOC_TYPE is the type of the reloc section if there is one, either

// SHT_REL or SHT_RELA.  We try to parse the input exception frame

// data into our data structures.  If we can't do it, we return false

// to mean that the section should be handled as a normal input

// section.

template<int size, bool big_endian>

bool

Eh_frame::add_ehframe_input_section(

    Sized_relobj<size, big_endian>* object,

    const unsigned char* symbols,

    section_size_type symbols_size,

    const unsigned char* symbol_names,

    section_size_type symbol_names_size,

    unsigned int shndx,

    unsigned int reloc_shndx,

    unsigned int reloc_type)

{

  // Get the section contents.

  section_size_type contents_len;

  const unsigned char* pcontents = object->section_contents(shndx,

                                                            &contents_len,

                                                            false);

  if (contents_len == 0)

    return false;

  // If this is the marker section for the end of the data, then

  // return false to force it to be handled as an ordinary input

  // section.  If we don't do this, we won't correctly handle the case

  // of unrecognized .eh_frame sections.

  if (contents_len == 4

      && elfcpp::Swap<32, big_endian>::readval(pcontents) == 0)

    return false;

  New_cies new_cies;

  if (!this->do_add_ehframe_input_section(object, symbols, symbols_size,

                                          symbol_names, symbol_names_size,

                                          shndx, reloc_shndx,

                                          reloc_type, pcontents,

                                          contents_len, &new_cies))

    {

      if (this->eh_frame_hdr_ != NULL)

        this->eh_frame_hdr_->found_unrecognized_eh_frame_section();

      for (New_cies::iterator p = new_cies.begin();

           p != new_cies.end();

           ++p)

        delete p->first;

      return false;

    }

  // Now that we know we are using this section, record any new CIEs

  // that we found.

  for (New_cies::const_iterator p = new_cies.begin();

       p != new_cies.end();

       ++p)

    {

      if (p->second)

        this->cie_offsets_.insert(p->first);

      else

        this->unmergeable_cie_offsets_.push_back(p->first);

    }

  return true;

}

// The bulk of the implementation of add_ehframe_input_section.

template<int size, bool big_endian>

bool

Eh_frame::do_add_ehframe_input_section(

    Sized_relobj<size, big_endian>* object,

    const unsigned char* symbols,

    section_size_type symbols_size,

    const unsigned char* symbol_names,

    section_size_type symbol_names_size,

    unsigned int shndx,

    unsigned int reloc_shndx,

    unsigned int reloc_type,

    const unsigned char* pcontents,

    section_size_type contents_len,

    New_cies* new_cies)

{

  typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;

  Track_relocs<size, big_endian> relocs;

  const unsigned char* p = pcontents;

  const unsigned char* pend = p + contents_len;

  // Get the contents of the reloc section if any.

  if (!relocs.initialize(object, reloc_shndx, reloc_type))

    return false;

  // Keep track of which CIEs are at which offsets.

  Offsets_to_cie cies;

  while (p < pend)

    {

      if (pend - p < 4)

        return false;

      // There shouldn't be any relocations here.

      if (relocs.advance(p + 4 - pcontents) > 0)

        return false;

      unsigned int len = elfcpp::Swap<32, big_endian>::readval(p);

      p += 4;

      if (len == 0)

        {

          // We should only find a zero-length entry at the end of the

          // section.

          if (p < pend)

            return false;

          break;

        }

      // We don't support a 64-bit .eh_frame.

      if (len == 0xffffffff)

        return false;

      if (static_cast<unsigned int>(pend - p) < len)

        return false;

      const unsigned char* const pentend = p + len;

      if (pend - p < 4)

        return false;

      if (relocs.advance(p + 4 - pcontents) > 0)

        return false;

      unsigned int id = elfcpp::Swap<32, big_endian>::readval(p);

      p += 4;

      if (id == 0)

        {

          // CIE.

          if (!this->read_cie(object, shndx, symbols, symbols_size,

                              symbol_names, symbol_names_size,

                              pcontents, p, pentend, &relocs, &cies,

                              new_cies))

            return false;

        }

      else

        {

          // FDE.

          if (!this->read_fde(object, shndx, symbols, symbols_size,

                              pcontents, id, p, pentend, &relocs, &cies))

            return false;

        }

      p = pentend;

    }

  return true;