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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-exception6//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 19namespace 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.html25///26template <typename A> class EHHeaderParser {27public: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 45private: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 54template <typename A>55bool EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,56 pint_t ehHdrEnd, EHHeaderInfo &ehHdrInfo) {57 pint_t p = ehHdrStart;58 59 // Ensure that we don't read data beyond the end of .eh_frame_hdr60 if (ehHdrEnd - ehHdrStart < 4) {61 // Don't print a message for an empty .eh_frame_hdr (this can happen if62 // the linker script defines symbols for it even in the empty case).63 if (ehHdrEnd == ehHdrStart)64 return false;65 _LIBUNWIND_LOG("unsupported .eh_frame_hdr at %" PRIx6466 ": need at least 4 bytes of data but only got %zd",67 static_cast<uint64_t>(ehHdrStart),68 static_cast<size_t>(ehHdrEnd - ehHdrStart));69 return false;70 }71 uint8_t version = addressSpace.get8(p++);72 if (version != 1) {73 _LIBUNWIND_LOG("unsupported .eh_frame_hdr version: %" PRIu8 " at %" PRIx64,74 version, static_cast<uint64_t>(ehHdrStart));75 return false;76 }77 78 uint8_t eh_frame_ptr_enc = addressSpace.get8(p++);79 uint8_t fde_count_enc = addressSpace.get8(p++);80 ehHdrInfo.table_enc = addressSpace.get8(p++);81 82 ehHdrInfo.eh_frame_ptr =83 addressSpace.getEncodedP(p, ehHdrEnd, eh_frame_ptr_enc, ehHdrStart);84 ehHdrInfo.fde_count =85 fde_count_enc == DW_EH_PE_omit86 ? 087 : addressSpace.getEncodedP(p, ehHdrEnd, fde_count_enc, ehHdrStart);88 ehHdrInfo.table = p;89 90 return true;91}92 93template <typename A>94bool EHHeaderParser<A>::decodeTableEntry(95 A &addressSpace, pint_t &tableEntry, pint_t ehHdrStart, pint_t ehHdrEnd,96 uint8_t tableEnc, typename CFI_Parser<A>::FDE_Info *fdeInfo,97 typename CFI_Parser<A>::CIE_Info *cieInfo) {98 // Have to decode the whole FDE for the PC range anyway, so just throw away99 // the PC start.100 addressSpace.getEncodedP(tableEntry, ehHdrEnd, tableEnc, ehHdrStart);101 pint_t fde =102 addressSpace.getEncodedP(tableEntry, ehHdrEnd, tableEnc, ehHdrStart);103 const char *message =104 CFI_Parser<A>::decodeFDE(addressSpace, fde, fdeInfo, cieInfo);105 if (message != NULL) {106 _LIBUNWIND_DEBUG_LOG("EHHeaderParser::decodeTableEntry: bad fde: %s",107 message);108 return false;109 }110 111 return true;112}113 114template <typename A>115bool EHHeaderParser<A>::findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,116 uint32_t sectionLength,117 typename CFI_Parser<A>::FDE_Info *fdeInfo,118 typename CFI_Parser<A>::CIE_Info *cieInfo) {119 pint_t ehHdrEnd = ehHdrStart + sectionLength;120 121 EHHeaderParser<A>::EHHeaderInfo hdrInfo;122 if (!EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd,123 hdrInfo))124 return false;125 126 if (hdrInfo.fde_count == 0) return false;127 128 size_t tableEntrySize = getTableEntrySize(hdrInfo.table_enc);129 pint_t tableEntry;130 131 size_t low = 0;132 for (size_t len = hdrInfo.fde_count; len > 1;) {133 size_t mid = low + (len / 2);134 tableEntry = hdrInfo.table + mid * tableEntrySize;135 pint_t start = addressSpace.getEncodedP(tableEntry, ehHdrEnd,136 hdrInfo.table_enc, ehHdrStart);137 138 if (start == pc) {139 low = mid;140 break;141 } else if (start < pc) {142 low = mid;143 len -= (len / 2);144 } else {145 len /= 2;146 }147 }148 149 tableEntry = hdrInfo.table + low * tableEntrySize;150 if (decodeTableEntry(addressSpace, tableEntry, ehHdrStart, ehHdrEnd,151 hdrInfo.table_enc, fdeInfo, cieInfo)) {152 if (pc >= fdeInfo->pcStart && pc < fdeInfo->pcEnd)153 return true;154 }155 156 return false;157}158 159template <typename A>160size_t EHHeaderParser<A>::getTableEntrySize(uint8_t tableEnc) {161 switch (tableEnc & 0x0f) {162 case DW_EH_PE_sdata2:163 case DW_EH_PE_udata2:164 return 4;165 case DW_EH_PE_sdata4:166 case DW_EH_PE_udata4:167 return 8;168 case DW_EH_PE_sdata8:169 case DW_EH_PE_udata8:170 return 16;171 case DW_EH_PE_sleb128:172 case DW_EH_PE_uleb128:173 _LIBUNWIND_ABORT("Can't binary search on variable length encoded data.");174 case DW_EH_PE_omit:175 return 0;176 default:177 _LIBUNWIND_ABORT("Unknown DWARF encoding for search table.");178 }179}180 181}182 183#endif184