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 "AddressSpace.hpp"
19 #include "DwarfParser.hpp"
20
21 namespace libunwind {
22
23 /// \brief EHHeaderParser does basic parsing of an ELF .eh_frame_hdr section.
24 ///
25 /// See DWARF spec for details:
26 /// http://refspecs.linuxbase.org/LSB_3.1.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html
27 ///
28 template <typename A> class EHHeaderParser {
29 public:
30 typedef typename A::pint_t pint_t;
31
32 /// Information encoded in the EH frame header.
33 struct EHHeaderInfo {
34 pint_t eh_frame_ptr;
35 size_t fde_count;
36 pint_t table;
37 uint8_t table_enc;
38 };
39
40 static void decodeEHHdr(A &addressSpace, pint_t ehHdrStart, pint_t ehHdrEnd,
41 EHHeaderInfo &ehHdrInfo);
42 static bool findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
43 uint32_t sectionLength,
44 typename CFI_Parser<A>::FDE_Info *fdeInfo,
45 typename CFI_Parser<A>::CIE_Info *cieInfo);
46
47 private:
48 static bool decodeTableEntry(A &addressSpace, pint_t &tableEntry,
49 pint_t ehHdrStart, pint_t ehHdrEnd,
50 uint8_t tableEnc,
51 typename CFI_Parser<A>::FDE_Info *fdeInfo,
52 typename CFI_Parser<A>::CIE_Info *cieInfo);
53 static size_t getTableEntrySize(uint8_t tableEnc);
54 };
55
56 template <typename A>
decodeEHHdr(A & addressSpace,pint_t ehHdrStart,pint_t ehHdrEnd,EHHeaderInfo & ehHdrInfo)57 void EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
58 pint_t ehHdrEnd, EHHeaderInfo &ehHdrInfo) {
59 pint_t p = ehHdrStart;
60 uint8_t version = addressSpace.get8(p++);
61 if (version != 1)
62 _LIBUNWIND_ABORT("Unsupported .eh_frame_hdr version");
63
64 uint8_t eh_frame_ptr_enc = addressSpace.get8(p++);
65 uint8_t fde_count_enc = addressSpace.get8(p++);
66 ehHdrInfo.table_enc = addressSpace.get8(p++);
67
68 ehHdrInfo.eh_frame_ptr =
69 addressSpace.getEncodedP(p, ehHdrEnd, eh_frame_ptr_enc, ehHdrStart);
70 ehHdrInfo.fde_count =
71 addressSpace.getEncodedP(p, ehHdrEnd, fde_count_enc, ehHdrStart);
72 ehHdrInfo.table = p;
73 }
74
75 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)76 bool EHHeaderParser<A>::decodeTableEntry(
77 A &addressSpace, pint_t &tableEntry, pint_t ehHdrStart, pint_t ehHdrEnd,
78 uint8_t tableEnc, typename CFI_Parser<A>::FDE_Info *fdeInfo,
79 typename CFI_Parser<A>::CIE_Info *cieInfo) {
80 // Have to decode the whole FDE for the PC range anyway, so just throw away
81 // the PC start.
82 addressSpace.getEncodedP(tableEntry, ehHdrEnd, tableEnc, ehHdrStart);
83 pint_t fde =
84 addressSpace.getEncodedP(tableEntry, ehHdrEnd, tableEnc, ehHdrStart);
85 const char *message =
86 CFI_Parser<A>::decodeFDE(addressSpace, fde, fdeInfo, cieInfo);
87 if (message != NULL) {
88 _LIBUNWIND_DEBUG_LOG("EHHeaderParser::decodeTableEntry: bad fde: %s\n",
89 message);
90 return false;
91 }
92
93 return true;
94 }
95
96 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)97 bool EHHeaderParser<A>::findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
98 uint32_t sectionLength,
99 typename CFI_Parser<A>::FDE_Info *fdeInfo,
100 typename CFI_Parser<A>::CIE_Info *cieInfo) {
101 pint_t ehHdrEnd = ehHdrStart + sectionLength;
102
103 EHHeaderParser<A>::EHHeaderInfo hdrInfo;
104 EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd, hdrInfo);
105
106 size_t tableEntrySize = getTableEntrySize(hdrInfo.table_enc);
107 pint_t tableEntry;
108
109 size_t low = 0;
110 for (size_t len = hdrInfo.fde_count; len > 1;) {
111 size_t mid = low + (len / 2);
112 tableEntry = hdrInfo.table + mid * tableEntrySize;
113 pint_t start = addressSpace.getEncodedP(tableEntry, ehHdrEnd,
114 hdrInfo.table_enc, ehHdrStart);
115
116 if (start == pc) {
117 low = mid;
118 break;
119 } else if (start < pc) {
120 low = mid;
121 len -= (len / 2);
122 } else {
123 len /= 2;
124 }
125 }
126
127 tableEntry = hdrInfo.table + low * tableEntrySize;
128 if (decodeTableEntry(addressSpace, tableEntry, ehHdrStart, ehHdrEnd,
129 hdrInfo.table_enc, fdeInfo, cieInfo)) {
130 if (pc >= fdeInfo->pcStart && pc < fdeInfo->pcEnd)
131 return true;
132 }
133
134 return false;
135 }
136
137 template <typename A>
getTableEntrySize(uint8_t tableEnc)138 size_t EHHeaderParser<A>::getTableEntrySize(uint8_t tableEnc) {
139 switch (tableEnc & 0x0f) {
140 case DW_EH_PE_sdata2:
141 case DW_EH_PE_udata2:
142 return 4;
143 case DW_EH_PE_sdata4:
144 case DW_EH_PE_udata4:
145 return 8;
146 case DW_EH_PE_sdata8:
147 case DW_EH_PE_udata8:
148 return 16;
149 case DW_EH_PE_sleb128:
150 case DW_EH_PE_uleb128:
151 _LIBUNWIND_ABORT("Can't binary search on variable length encoded data.");
152 case DW_EH_PE_omit:
153 return 0;
154 default:
155 _LIBUNWIND_ABORT("Unknown DWARF encoding for search table.");
156 }
157 }
158
159 }
160
161 #endif
162