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>
decodeEHHdr(A & addressSpace,pint_t ehHdrStart,pint_t ehHdrEnd,EHHeaderInfo & ehHdrInfo)55 bool 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_hdr
60 if (ehHdrEnd - ehHdrStart < 4) {
61 // Don't print a message for an empty .eh_frame_hdr (this can happen if
62 // 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 %" PRIx64
66 ": 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_omit
86 ? 0
87 : addressSpace.getEncodedP(p, ehHdrEnd, fde_count_enc, ehHdrStart);
88 ehHdrInfo.table = p;
89
90 return true;
91 }
92
93 template <typename 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)94 bool 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 away
99 // 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
114 template <typename 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)115 bool 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
159 template <typename A>
getTableEntrySize(uint8_t tableEnc)160 size_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 #endif
184