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