libunwind/src/EHHeaderParser.hpp

   1 //===----------------------------------------------------------------------===//
   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 //  Parses ELF .eh_frame_hdr sections.
   9 //
  10 //===----------------------------------------------------------------------===//
  11
  12 #ifndef __EHHEADERPARSER_HPP__
  13 #define __EHHEADERPARSER_HPP__
  14
  15 #include "libunwind.h"
  16
  17 #include "DwarfParser.hpp"
  18
  19 namespace libunwind {
  20
  21 /// \brief EHHeaderParser does basic parsing of an ELF .eh_frame_hdr section.
  22 ///
  23 /// See DWARF spec for details:
  24 ///    http://refspecs.linuxbase.org/LSB_3.1.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html
  25 ///
  26 template <typename A> class EHHeaderParser {
  27 public:
  28   typedef typename A::pint_t pint_t;
  29
  30   /// Information encoded in the EH frame header.
  31   struct EHHeaderInfo {
  32     pint_t eh_frame_ptr;
  33     size_t fde_count;
  34     pint_t table;
  35     uint8_t table_enc;
  36   };
  37
  38   static bool decodeEHHdr(A &addressSpace, pint_t ehHdrStart, pint_t ehHdrEnd,
  39                           EHHeaderInfo &ehHdrInfo);
  40   static bool findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
  41                       uint32_t sectionLength,
  42                       typename CFI_Parser<A>::FDE_Info *fdeInfo,
  43                       typename CFI_Parser<A>::CIE_Info *cieInfo);
  44
  45 private:
  46   static bool decodeTableEntry(A &addressSpace, pint_t &tableEntry,
  47                                pint_t ehHdrStart, pint_t ehHdrEnd,
  48                                uint8_t tableEnc,
  49                                typename CFI_Parser<A>::FDE_Info *fdeInfo,
  50                                typename CFI_Parser<A>::CIE_Info *cieInfo);
  51   static size_t getTableEntrySize(uint8_t tableEnc);
  52 };
  53
  54 template <typename A>
  55 bool EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
  56                                     pint_t ehHdrEnd, EHHeaderInfo &ehHdrInfo) {
  57   pint_t p = ehHdrStart;
  58   uint8_t version = addressSpace.get8(p++);
  59   if (version != 1) {
  60     _LIBUNWIND_LOG("unsupported .eh_frame_hdr version: %" PRIu8 " at %" PRIx64,
  61                    version, static_cast<uint64_t>(ehHdrStart));
  62     return false;
  63   }
  64
  65   uint8_t eh_frame_ptr_enc = addressSpace.get8(p++);
  66   uint8_t fde_count_enc = addressSpace.get8(p++);
  67   ehHdrInfo.table_enc = addressSpace.get8(p++);
  68
  69   ehHdrInfo.eh_frame_ptr =
  70       addressSpace.getEncodedP(p, ehHdrEnd, eh_frame_ptr_enc, ehHdrStart);
  71   ehHdrInfo.fde_count =
  72       fde_count_enc == DW_EH_PE_omit
  73           ? 0
  74           : addressSpace.getEncodedP(p, ehHdrEnd, fde_count_enc, ehHdrStart);
  75   ehHdrInfo.table = p;
  76
  77   return true;
  78 }
  79
  80 template <typename A>
  81 bool EHHeaderParser<A>::decodeTableEntry(
  82     A &addressSpace, pint_t &tableEntry, pint_t ehHdrStart, pint_t ehHdrEnd,
  83     uint8_t tableEnc, typename CFI_Parser<A>::FDE_Info *fdeInfo,
  84     typename CFI_Parser<A>::CIE_Info *cieInfo) {
  85   // Have to decode the whole FDE for the PC range anyway, so just throw away
  86   // the PC start.
  87   addressSpace.getEncodedP(tableEntry, ehHdrEnd, tableEnc, ehHdrStart);
  88   pint_t fde =
  89       addressSpace.getEncodedP(tableEntry, ehHdrEnd, tableEnc, ehHdrStart);
  90   const char *message =
  91       CFI_Parser<A>::decodeFDE(addressSpace, fde, fdeInfo, cieInfo);
  92   if (message != NULL) {
  93     _LIBUNWIND_DEBUG_LOG("EHHeaderParser::decodeTableEntry: bad fde: %s",
  94                          message);
  95     return false;
  96   }
  97
  98   return true;
  99 }
 100
 101 template <typename A>
 102 bool EHHeaderParser<A>::findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
 103                                 uint32_t sectionLength,
 104                                 typename CFI_Parser<A>::FDE_Info *fdeInfo,
 105                                 typename CFI_Parser<A>::CIE_Info *cieInfo) {
 106   pint_t ehHdrEnd = ehHdrStart + sectionLength;
 107
 108   EHHeaderParser<A>::EHHeaderInfo hdrInfo;
 109   if (!EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd,
 110                                       hdrInfo))
 111     return false;
 112
 113   if (hdrInfo.fde_count == 0) return false;
 114
 115   size_t tableEntrySize = getTableEntrySize(hdrInfo.table_enc);
 116   pint_t tableEntry;
 117
 118   size_t low = 0;
 119   for (size_t len = hdrInfo.fde_count; len > 1;) {
 120     size_t mid = low + (len / 2);
 121     tableEntry = hdrInfo.table + mid * tableEntrySize;
 122     pint_t start = addressSpace.getEncodedP(tableEntry, ehHdrEnd,
 123                                             hdrInfo.table_enc, ehHdrStart);
 124
 125     if (start == pc) {
 126       low = mid;
 127       break;
 128     } else if (start < pc) {
 129       low = mid;
 130       len -= (len / 2);
 131     } else {
 132       len /= 2;
 133     }
 134   }
 135
 136   tableEntry = hdrInfo.table + low * tableEntrySize;
 137   if (decodeTableEntry(addressSpace, tableEntry, ehHdrStart, ehHdrEnd,
 138                        hdrInfo.table_enc, fdeInfo, cieInfo)) {
 139     if (pc >= fdeInfo->pcStart && pc < fdeInfo->pcEnd)
 140       return true;
 141   }
 142
 143   return false;
 144 }
 145
 146 template <typename A>
 147 size_t EHHeaderParser<A>::getTableEntrySize(uint8_t tableEnc) {
 148   switch (tableEnc & 0x0f) {
 149   case DW_EH_PE_sdata2:
 150   case DW_EH_PE_udata2:
 151     return 4;
 152   case DW_EH_PE_sdata4:
 153   case DW_EH_PE_udata4:
 154     return 8;
 155   case DW_EH_PE_sdata8:
 156   case DW_EH_PE_udata8:
 157     return 16;
 158   case DW_EH_PE_sleb128:
 159   case DW_EH_PE_uleb128:
 160     _LIBUNWIND_ABORT("Can't binary search on variable length encoded data.");
 161   case DW_EH_PE_omit:
 162     return 0;
 163   default:
 164     _LIBUNWIND_ABORT("Unknown DWARF encoding for search table.");
 165   }
 166 }
 167
 168 }
 169
 170 #endif