1 //===- EhFrame.cpp --------------------------------------------------------===//
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
9 #include "EhFrame.h"
10 #include "InputFiles.h"
11
12 #include "lld/Common/ErrorHandler.h"
13 #include "llvm/BinaryFormat/Dwarf.h"
14 #include "llvm/Support/Endian.h"
15
16 using namespace llvm;
17 using namespace lld;
18 using namespace lld::macho;
19 using namespace llvm::support::endian;
20
readLength(size_t * off) const21 uint64_t EhReader::readLength(size_t *off) const {
22 const size_t errOff = *off;
23 if (*off + 4 > data.size())
24 failOn(errOff, "CIE/FDE too small");
25 uint64_t len = read32le(data.data() + *off);
26 *off += 4;
27 if (len == dwarf::DW_LENGTH_DWARF64) {
28 // FIXME: test this DWARF64 code path
29 if (*off + 8 > data.size())
30 failOn(errOff, "CIE/FDE too small");
31 len = read64le(data.data() + *off);
32 *off += 8;
33 }
34 if (*off + len > data.size())
35 failOn(errOff, "CIE/FDE extends past the end of the section");
36 return len;
37 }
38
skipValidLength(size_t * off) const39 void EhReader::skipValidLength(size_t *off) const {
40 uint32_t len = read32le(data.data() + *off);
41 *off += 4;
42 if (len == dwarf::DW_LENGTH_DWARF64)
43 *off += 8;
44 }
45
46 // Read a byte and advance off by one byte.
readByte(size_t * off) const47 uint8_t EhReader::readByte(size_t *off) const {
48 if (*off + 1 > data.size())
49 failOn(*off, "unexpected end of CIE/FDE");
50 return data[(*off)++];
51 }
52
readU32(size_t * off) const53 uint32_t EhReader::readU32(size_t *off) const {
54 if (*off + 4 > data.size())
55 failOn(*off, "unexpected end of CIE/FDE");
56 uint32_t v = read32le(data.data() + *off);
57 *off += 4;
58 return v;
59 }
60
readPointer(size_t * off,uint8_t size) const61 uint64_t EhReader::readPointer(size_t *off, uint8_t size) const {
62 if (*off + size > data.size())
63 failOn(*off, "unexpected end of CIE/FDE");
64 uint64_t v;
65 if (size == 8)
66 v = read64le(data.data() + *off);
67 else {
68 assert(size == 4);
69 v = read32le(data.data() + *off);
70 }
71 *off += size;
72 return v;
73 }
74
75 // Read a null-terminated string.
readString(size_t * off) const76 StringRef EhReader::readString(size_t *off) const {
77 if (*off > data.size())
78 failOn(*off, "corrupted CIE (failed to read string)");
79 const size_t maxlen = data.size() - *off;
80 auto *c = reinterpret_cast<const char *>(data.data() + *off);
81 size_t len = strnlen(c, maxlen);
82 if (len == maxlen) // we failed to find the null terminator
83 failOn(*off, "corrupted CIE (failed to read string)");
84 *off += len + 1; // skip the null byte too
85 return StringRef(c, len);
86 }
87
skipLeb128(size_t * off) const88 void EhReader::skipLeb128(size_t *off) const {
89 const size_t errOff = *off;
90 while (*off < data.size()) {
91 uint8_t val = data[(*off)++];
92 if ((val & 0x80) == 0)
93 return;
94 }
95 failOn(errOff, "corrupted CIE (failed to read LEB128)");
96 }
97
failOn(size_t errOff,const Twine & msg) const98 void EhReader::failOn(size_t errOff, const Twine &msg) const {
99 fatal(toString(file) + ":(__eh_frame+0x" +
100 Twine::utohexstr(dataOff + errOff) + "): " + msg);
101 }
102
103 /*
104 * Create a pair of relocs to write the value of:
105 * `b - (offset + a)` if Invert == false
106 * `(a + offset) - b` if Invert == true
107 */
108 template <bool Invert = false>
createSubtraction(PointerUnion<Symbol *,InputSection * > a,PointerUnion<Symbol *,InputSection * > b,uint64_t off,uint8_t length,SmallVectorImpl<Reloc> * newRelocs)109 static void createSubtraction(PointerUnion<Symbol *, InputSection *> a,
110 PointerUnion<Symbol *, InputSection *> b,
111 uint64_t off, uint8_t length,
112 SmallVectorImpl<Reloc> *newRelocs) {
113 auto subtrahend = a;
114 auto minuend = b;
115 if (Invert)
116 std::swap(subtrahend, minuend);
117 assert(subtrahend.is<Symbol *>());
118 Reloc subtrahendReloc(target->subtractorRelocType, /*pcrel=*/false, length,
119 off, /*addend=*/0, subtrahend);
120 Reloc minuendReloc(target->unsignedRelocType, /*pcrel=*/false, length, off,
121 (Invert ? 1 : -1) * off, minuend);
122 newRelocs->push_back(subtrahendReloc);
123 newRelocs->push_back(minuendReloc);
124 }
125
makePcRel(uint64_t off,PointerUnion<Symbol *,InputSection * > target,uint8_t length)126 void EhRelocator::makePcRel(uint64_t off,
127 PointerUnion<Symbol *, InputSection *> target,
128 uint8_t length) {
129 createSubtraction(isec->symbols[0], target, off, length, &newRelocs);
130 }
131
makeNegativePcRel(uint64_t off,PointerUnion<Symbol *,InputSection * > target,uint8_t length)132 void EhRelocator::makeNegativePcRel(
133 uint64_t off, PointerUnion<Symbol *, InputSection *> target,
134 uint8_t length) {
135 createSubtraction</*Invert=*/true>(isec, target, off, length, &newRelocs);
136 }
137
commit()138 void EhRelocator::commit() {
139 isec->relocs.insert(isec->relocs.end(), newRelocs.begin(), newRelocs.end());
140 }
141