1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
|
//===- EhFrame.h ------------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef LLD_MACHO_EH_FRAME_H
#define LLD_MACHO_EH_FRAME_H
#include "InputSection.h"
#include "Relocations.h"
#include "lld/Common/LLVM.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/ADT/SmallVector.h"
/*
* NOTE: The main bulk of the EH frame parsing logic is in InputFiles.cpp as it
* is closely coupled with other file parsing logic; EhFrame.h just contains a
* few helpers.
*/
/*
* === The EH frame format ===
*
* EH frames can either be Common Information Entries (CIEs) or Frame
* Description Entries (FDEs). CIEs contain information that is common amongst
* several FDEs. Each FDE contains a pointer to its CIE. Thus all the EH frame
* entries together form a forest of two-level trees, with CIEs as the roots
* and FDEs as the leaves. Note that a CIE must precede the FDEs which point
* to it.
*
* A CIE comprises the following fields in order:
* 1. Length of the entry (4 or 12 bytes)
* 2. CIE offset (4 bytes; always 0 for CIEs)
* 3. CIE version (byte)
* 4. Null-terminated augmentation string
* 5-8. LEB128 values that we don't care about
* 9. Augmentation data, to be interpreted using the aug string
* 10. DWARF instructions (ignored by LLD)
*
* An FDE comprises of the following:
* 1. Length of the entry (4 or 12 bytes)
* 2. CIE offset (4 bytes pcrel offset that points backwards to this FDE's CIE)
* 3. Function address (pointer-sized pcrel offset)
* 4. (Optional) Augmentation data length
* 5. (Optional) LSDA address (pointer-sized pcrel offset)
* 6. DWARF instructions (ignored by LLD)
*/
namespace lld {
namespace macho {
class EhReader {
public:
EhReader(const ObjFile *file, ArrayRef<uint8_t> data, size_t dataOff)
: file(file), data(data), dataOff(dataOff) {}
size_t size() const { return data.size(); }
// Read and validate the length field.
uint64_t readLength(size_t *off) const;
// Skip the length field without doing validation.
void skipValidLength(size_t *off) const;
uint8_t readByte(size_t *off) const;
uint32_t readU32(size_t *off) const;
uint64_t readPointer(size_t *off, uint8_t size) const;
StringRef readString(size_t *off) const;
void skipLeb128(size_t *off) const;
void failOn(size_t errOff, const Twine &msg) const;
private:
const ObjFile *file;
ArrayRef<uint8_t> data;
// The offset of the data array within its section. Used only for error
// reporting.
const size_t dataOff;
};
// The EH frame format, when emitted by llvm-mc, consists of a number of
// "abs-ified" relocations, i.e. relocations that are implicitly encoded as
// pcrel offsets in the section data. The offsets refer to the locations of
// symbols in the input object file. When we ingest these EH frames, we convert
// these implicit relocations into explicit Relocs.
//
// These pcrel relocations are semantically similar to X86_64_RELOC_SIGNED_4.
// However, we need this operation to be cross-platform, and ARM does not have a
// similar relocation that is applicable. We therefore use the more verbose (but
// more generic) subtractor relocation to encode these pcrel values. ld64
// appears to do something similar -- its `-r` output contains these explicit
// subtractor relocations.
class EhRelocator {
public:
EhRelocator(InputSection *isec) : isec(isec) {}
// For the next two methods, let `PC` denote `isec address + off`.
// Create relocs writing the value of target - PC to PC.
void makePcRel(uint64_t off,
llvm::PointerUnion<Symbol *, InputSection *> target,
uint8_t length);
// Create relocs writing the value of PC - target to PC.
void makeNegativePcRel(uint64_t off,
llvm::PointerUnion<Symbol *, InputSection *> target,
uint8_t length);
// Insert the new relocations into isec->relocs.
void commit();
private:
InputSection *isec;
// Insert new relocs here so that we don't invalidate iterators into the
// existing relocs vector.
SmallVector<Reloc, 6> newRelocs;
};
} // namespace macho
} // namespace lld
#endif
|
