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//===----------------------------------------------------------------------===//
// 
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// 
// 
//  Parses ELF .eh_frame_hdr sections. 
// 
//===----------------------------------------------------------------------===// 
 
#ifndef __EHHEADERPARSER_HPP__ 
#define __EHHEADERPARSER_HPP__ 
 
#include "libunwind.h" 
 
#include "DwarfParser.hpp" 
 
namespace libunwind { 
 
/// \brief EHHeaderParser does basic parsing of an ELF .eh_frame_hdr section. 
/// 
/// See DWARF spec for details: 
///    http://refspecs.linuxbase.org/LSB_3.1.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html 
/// 
template <typename A> class EHHeaderParser { 
public: 
  typedef typename A::pint_t pint_t; 
 
  /// Information encoded in the EH frame header. 
  struct EHHeaderInfo { 
    pint_t eh_frame_ptr; 
    size_t fde_count; 
    pint_t table; 
    uint8_t table_enc; 
  }; 
 
  static bool decodeEHHdr(A &addressSpace, pint_t ehHdrStart, pint_t ehHdrEnd,
                          EHHeaderInfo &ehHdrInfo); 
  static bool findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart, 
                      uint32_t sectionLength, 
                      typename CFI_Parser<A>::FDE_Info *fdeInfo, 
                      typename CFI_Parser<A>::CIE_Info *cieInfo); 
 
private: 
  static bool decodeTableEntry(A &addressSpace, pint_t &tableEntry, 
                               pint_t ehHdrStart, pint_t ehHdrEnd, 
                               uint8_t tableEnc, 
                               typename CFI_Parser<A>::FDE_Info *fdeInfo, 
                               typename CFI_Parser<A>::CIE_Info *cieInfo); 
  static size_t getTableEntrySize(uint8_t tableEnc); 
}; 
 
template <typename A> 
bool EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
                                    pint_t ehHdrEnd, EHHeaderInfo &ehHdrInfo) { 
  pint_t p = ehHdrStart; 
  uint8_t version = addressSpace.get8(p++); 
  if (version != 1) {
    _LIBUNWIND_LOG0("Unsupported .eh_frame_hdr version");
    return false;
  }
 
  uint8_t eh_frame_ptr_enc = addressSpace.get8(p++); 
  uint8_t fde_count_enc = addressSpace.get8(p++); 
  ehHdrInfo.table_enc = addressSpace.get8(p++); 
 
  ehHdrInfo.eh_frame_ptr = 
      addressSpace.getEncodedP(p, ehHdrEnd, eh_frame_ptr_enc, ehHdrStart); 
  ehHdrInfo.fde_count = 
      fde_count_enc == DW_EH_PE_omit
          ? 0
          : addressSpace.getEncodedP(p, ehHdrEnd, fde_count_enc, ehHdrStart);
  ehHdrInfo.table = p; 

  return true;
} 
 
template <typename A> 
bool EHHeaderParser<A>::decodeTableEntry( 
    A &addressSpace, pint_t &tableEntry, pint_t ehHdrStart, pint_t ehHdrEnd, 
    uint8_t tableEnc, typename CFI_Parser<A>::FDE_Info *fdeInfo, 
    typename CFI_Parser<A>::CIE_Info *cieInfo) { 
  // Have to decode the whole FDE for the PC range anyway, so just throw away 
  // the PC start. 
  addressSpace.getEncodedP(tableEntry, ehHdrEnd, tableEnc, ehHdrStart); 
  pint_t fde = 
      addressSpace.getEncodedP(tableEntry, ehHdrEnd, tableEnc, ehHdrStart); 
  const char *message = 
      CFI_Parser<A>::decodeFDE(addressSpace, fde, fdeInfo, cieInfo); 
  if (message != NULL) { 
    _LIBUNWIND_DEBUG_LOG("EHHeaderParser::decodeTableEntry: bad fde: %s",
                         message); 
    return false; 
  } 
 
  return true; 
} 
 
template <typename A> 
bool EHHeaderParser<A>::findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart, 
                                uint32_t sectionLength, 
                                typename CFI_Parser<A>::FDE_Info *fdeInfo, 
                                typename CFI_Parser<A>::CIE_Info *cieInfo) { 
  pint_t ehHdrEnd = ehHdrStart + sectionLength; 
 
  EHHeaderParser<A>::EHHeaderInfo hdrInfo; 
  if (!EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd,
                                      hdrInfo))
    return false;
 
  if (hdrInfo.fde_count == 0) return false;

  size_t tableEntrySize = getTableEntrySize(hdrInfo.table_enc); 
  pint_t tableEntry; 
 
  size_t low = 0; 
  for (size_t len = hdrInfo.fde_count; len > 1;) { 
    size_t mid = low + (len / 2); 
    tableEntry = hdrInfo.table + mid * tableEntrySize; 
    pint_t start = addressSpace.getEncodedP(tableEntry, ehHdrEnd, 
                                            hdrInfo.table_enc, ehHdrStart); 
 
    if (start == pc) { 
      low = mid; 
      break; 
    } else if (start < pc) { 
      low = mid; 
      len -= (len / 2); 
    } else { 
      len /= 2; 
    } 
  } 
 
  tableEntry = hdrInfo.table + low * tableEntrySize; 
  if (decodeTableEntry(addressSpace, tableEntry, ehHdrStart, ehHdrEnd, 
                       hdrInfo.table_enc, fdeInfo, cieInfo)) { 
    if (pc >= fdeInfo->pcStart && pc < fdeInfo->pcEnd) 
      return true; 
  } 
 
  return false; 
} 
 
template <typename A> 
size_t EHHeaderParser<A>::getTableEntrySize(uint8_t tableEnc) { 
  switch (tableEnc & 0x0f) { 
  case DW_EH_PE_sdata2: 
  case DW_EH_PE_udata2: 
    return 4; 
  case DW_EH_PE_sdata4: 
  case DW_EH_PE_udata4: 
    return 8; 
  case DW_EH_PE_sdata8: 
  case DW_EH_PE_udata8: 
    return 16; 
  case DW_EH_PE_sleb128: 
  case DW_EH_PE_uleb128: 
    _LIBUNWIND_ABORT("Can't binary search on variable length encoded data."); 
  case DW_EH_PE_omit: 
    return 0; 
  default: 
    _LIBUNWIND_ABORT("Unknown DWARF encoding for search table."); 
  } 
} 
 
} 
 
#endif