1 //===------------------------- EHHeaderParser.hpp -------------------------===// 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_LOG0("Unsupported .eh_frame_hdr version"); 61 return false; 62 } 63 64 uint8_t eh_frame_ptr_enc = addressSpace.get8(p++); 65 uint8_t fde_count_enc = addressSpace.get8(p++); 66 ehHdrInfo.table_enc = addressSpace.get8(p++); 67 68 ehHdrInfo.eh_frame_ptr = 69 addressSpace.getEncodedP(p, ehHdrEnd, eh_frame_ptr_enc, ehHdrStart); 70 ehHdrInfo.fde_count = 71 fde_count_enc == DW_EH_PE_omit 72 ? 0 73 : addressSpace.getEncodedP(p, ehHdrEnd, fde_count_enc, ehHdrStart); 74 ehHdrInfo.table = p; 75 76 return true; 77 } 78 79 template <typename A> 80 bool EHHeaderParser<A>::decodeTableEntry( 81 A &addressSpace, pint_t &tableEntry, pint_t ehHdrStart, pint_t ehHdrEnd, 82 uint8_t tableEnc, typename CFI_Parser<A>::FDE_Info *fdeInfo, 83 typename CFI_Parser<A>::CIE_Info *cieInfo) { 84 // Have to decode the whole FDE for the PC range anyway, so just throw away 85 // the PC start. 86 addressSpace.getEncodedP(tableEntry, ehHdrEnd, tableEnc, ehHdrStart); 87 pint_t fde = 88 addressSpace.getEncodedP(tableEntry, ehHdrEnd, tableEnc, ehHdrStart); 89 const char *message = 90 CFI_Parser<A>::decodeFDE(addressSpace, fde, fdeInfo, cieInfo); 91 if (message != NULL) { 92 _LIBUNWIND_DEBUG_LOG("EHHeaderParser::decodeTableEntry: bad fde: %s", 93 message); 94 return false; 95 } 96 97 return true; 98 } 99 100 template <typename A> 101 bool EHHeaderParser<A>::findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart, 102 uint32_t sectionLength, 103 typename CFI_Parser<A>::FDE_Info *fdeInfo, 104 typename CFI_Parser<A>::CIE_Info *cieInfo) { 105 pint_t ehHdrEnd = ehHdrStart + sectionLength; 106 107 EHHeaderParser<A>::EHHeaderInfo hdrInfo; 108 if (!EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd, 109 hdrInfo)) 110 return false; 111 112 size_t tableEntrySize = getTableEntrySize(hdrInfo.table_enc); 113 pint_t tableEntry; 114 115 size_t low = 0; 116 for (size_t len = hdrInfo.fde_count; len > 1;) { 117 size_t mid = low + (len / 2); 118 tableEntry = hdrInfo.table + mid * tableEntrySize; 119 pint_t start = addressSpace.getEncodedP(tableEntry, ehHdrEnd, 120 hdrInfo.table_enc, ehHdrStart); 121 122 if (start == pc) { 123 low = mid; 124 break; 125 } else if (start < pc) { 126 low = mid; 127 len -= (len / 2); 128 } else { 129 len /= 2; 130 } 131 } 132 133 tableEntry = hdrInfo.table + low * tableEntrySize; 134 if (decodeTableEntry(addressSpace, tableEntry, ehHdrStart, ehHdrEnd, 135 hdrInfo.table_enc, fdeInfo, cieInfo)) { 136 if (pc >= fdeInfo->pcStart && pc < fdeInfo->pcEnd) 137 return true; 138 } 139 140 return false; 141 } 142 143 template <typename A> 144 size_t EHHeaderParser<A>::getTableEntrySize(uint8_t tableEnc) { 145 switch (tableEnc & 0x0f) { 146 case DW_EH_PE_sdata2: 147 case DW_EH_PE_udata2: 148 return 4; 149 case DW_EH_PE_sdata4: 150 case DW_EH_PE_udata4: 151 return 8; 152 case DW_EH_PE_sdata8: 153 case DW_EH_PE_udata8: 154 return 16; 155 case DW_EH_PE_sleb128: 156 case DW_EH_PE_uleb128: 157 _LIBUNWIND_ABORT("Can't binary search on variable length encoded data."); 158 case DW_EH_PE_omit: 159 return 0; 160 default: 161 _LIBUNWIND_ABORT("Unknown DWARF encoding for search table."); 162 } 163 } 164 165 } 166 167 #endif 168
