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
16using namespace llvm;
17using namespace lld;
18using namespace lld::macho;
19using namespace llvm::support::endian;
20
21uint64_t EhReader::readLength(size_t *off) const {
22 const size_t errOff = *off;
23 if (*off + 4 > data.size())
24 failOn(errOff, msg: "CIE/FDE too small");
25 uint64_t len = read32le(P: 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, msg: "CIE/FDE too small");
31 len = read64le(P: data.data() + *off);
32 *off += 8;
33 }
34 if (*off + len > data.size())
35 failOn(errOff, msg: "CIE/FDE extends past the end of the section");
36 return len;
37}
38
39void EhReader::skipValidLength(size_t *off) const {
40 uint32_t len = read32le(P: 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.
47uint8_t EhReader::readByte(size_t *off) const {
48 if (*off + 1 > data.size())
49 failOn(errOff: *off, msg: "unexpected end of CIE/FDE");
50 return data[(*off)++];
51}
52
53uint32_t EhReader::readU32(size_t *off) const {
54 if (*off + 4 > data.size())
55 failOn(errOff: *off, msg: "unexpected end of CIE/FDE");
56 uint32_t v = read32le(P: data.data() + *off);
57 *off += 4;
58 return v;
59}
60
61uint64_t EhReader::readPointer(size_t *off, uint8_t size) const {
62 if (*off + size > data.size())
63 failOn(errOff: *off, msg: "unexpected end of CIE/FDE");
64 uint64_t v;
65 if (size == 8)
66 v = read64le(P: data.data() + *off);
67 else {
68 assert(size == 4);
69 v = read32le(P: data.data() + *off);
70 }
71 *off += size;
72 return v;
73}
74
75// Read a null-terminated string.
76StringRef EhReader::readString(size_t *off) const {
77 if (*off > data.size())
78 failOn(errOff: *off, msg: "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(string: c, maxlen: maxlen);
82 if (len == maxlen) // we failed to find the null terminator
83 failOn(errOff: *off, msg: "corrupted CIE (failed to read string)");
84 *off += len + 1; // skip the null byte too
85 return StringRef(c, len);
86}
87
88void 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, msg: "corrupted CIE (failed to read LEB128)");
96}
97
98void EhReader::failOn(size_t errOff, const Twine &msg) const {
99 fatal(msg: toString(file) + ":(__eh_frame+0x" +
100 Twine::utohexstr(Val: 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 */
108template <bool Invert = false>
109static 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(a&: subtrahend, b&: minuend);
117 assert(isa<Symbol *>(subtrahend));
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(Elt: subtrahendReloc);
123 newRelocs->push_back(Elt: minuendReloc);
124}
125
126void EhRelocator::makePcRel(uint64_t off,
127 PointerUnion<Symbol *, InputSection *> target,
128 uint8_t length) {
129 createSubtraction(a: isec->symbols[0], b: target, off, length, newRelocs: &newRelocs);
130}
131
132void EhRelocator::makeNegativePcRel(
133 uint64_t off, PointerUnion<Symbol *, InputSection *> target,
134 uint8_t length) {
135 createSubtraction</*Invert=*/true>(a: isec, b: target, off, length, newRelocs: &newRelocs);
136}
137
138void EhRelocator::commit() {
139 isec->relocs.insert(position: isec->relocs.end(), first: newRelocs.begin(), last: newRelocs.end());
140}
141