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