1 //===------------------------- EHHeaderParser.hpp -------------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is dual licensed under the MIT and the University of Illinois Open
6 // Source Licenses. See LICENSE.TXT for details.
7 //
8 //
9 // Parses ELF .eh_frame_hdr sections.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #ifndef __EHHEADERPARSER_HPP__
14 #define __EHHEADERPARSER_HPP__
15
16 #include "libunwind.h"
17
18 #include "DwarfParser.hpp"
19
20 namespace libunwind {
21
22 /// \brief EHHeaderParser does basic parsing of an ELF .eh_frame_hdr section.
23 ///
24 /// See DWARF spec for details:
25 /// http://refspecs.linuxbase.org/LSB_3.1.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html
26 ///
27 template <typename A> class EHHeaderParser {
28 public:
29 typedef typename A::pint_t pint_t;
30
31 /// Information encoded in the EH frame header.
32 struct EHHeaderInfo {
33 pint_t eh_frame_ptr;
34 size_t fde_count;
35 pint_t table;
36 uint8_t table_enc;
37 };
38
39 static bool decodeEHHdr(A &addressSpace, pint_t ehHdrStart, pint_t ehHdrEnd,
40 EHHeaderInfo &ehHdrInfo);
41 static bool findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
42 uint32_t sectionLength,
43 typename CFI_Parser<A>::FDE_Info *fdeInfo,
44 typename CFI_Parser<A>::CIE_Info *cieInfo);
45
46 private:
47 static bool decodeTableEntry(A &addressSpace, pint_t &tableEntry,
48 pint_t ehHdrStart, pint_t ehHdrEnd,
49 uint8_t tableEnc,
50 typename CFI_Parser<A>::FDE_Info *fdeInfo,
51 typename CFI_Parser<A>::CIE_Info *cieInfo);
52 static size_t getTableEntrySize(uint8_t tableEnc);
53 };
54
55 template <typename A>
decodeEHHdr(A & addressSpace,pint_t ehHdrStart,pint_t ehHdrEnd,EHHeaderInfo & ehHdrInfo)56 bool EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
57 pint_t ehHdrEnd, EHHeaderInfo &ehHdrInfo) {
58 pint_t p = ehHdrStart;
59 uint8_t version = addressSpace.get8(p++);
60 if (version != 1) {
61 _LIBUNWIND_LOG0("Unsupported .eh_frame_hdr version");
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>
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)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>
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)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 size_t tableEntrySize = getTableEntrySize(hdrInfo.table_enc);
114 pint_t tableEntry;
115
116 size_t low = 0;
117 for (size_t len = hdrInfo.fde_count; len > 1;) {
118 size_t mid = low + (len / 2);
119 tableEntry = hdrInfo.table + mid * tableEntrySize;
120 pint_t start = addressSpace.getEncodedP(tableEntry, ehHdrEnd,
121 hdrInfo.table_enc, ehHdrStart);
122
123 if (start == pc) {
124 low = mid;
125 break;
126 } else if (start < pc) {
127 low = mid;
128 len -= (len / 2);
129 } else {
130 len /= 2;
131 }
132 }
133
134 tableEntry = hdrInfo.table + low * tableEntrySize;
135 if (decodeTableEntry(addressSpace, tableEntry, ehHdrStart, ehHdrEnd,
136 hdrInfo.table_enc, fdeInfo, cieInfo)) {
137 if (pc >= fdeInfo->pcStart && pc < fdeInfo->pcEnd)
138 return true;
139 }
140
141 return false;
142 }
143
144 template <typename A>
getTableEntrySize(uint8_t tableEnc)145 size_t EHHeaderParser<A>::getTableEntrySize(uint8_t tableEnc) {
146 switch (tableEnc & 0x0f) {
147 case DW_EH_PE_sdata2:
148 case DW_EH_PE_udata2:
149 return 4;
150 case DW_EH_PE_sdata4:
151 case DW_EH_PE_udata4:
152 return 8;
153 case DW_EH_PE_sdata8:
154 case DW_EH_PE_udata8:
155 return 16;
156 case DW_EH_PE_sleb128:
157 case DW_EH_PE_uleb128:
158 _LIBUNWIND_ABORT("Can't binary search on variable length encoded data.");
159 case DW_EH_PE_omit:
160 return 0;
161 default:
162 _LIBUNWIND_ABORT("Unknown DWARF encoding for search table.");
163 }
164 }
165
166 }
167
168 #endif
169