1//===- Target.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// Machine-specific things, such as applying relocations, creation of
10// GOT or PLT entries, etc., are handled in this file.
11//
12// Refer the ELF spec for the single letter variables, S, A or P, used
13// in this file.
14//
15// Some functions defined in this file has "relaxTls" as part of their names.
16// They do peephole optimization for TLS variables by rewriting instructions.
17// They are not part of the ABI but optional optimization, so you can skip
18// them if you are not interested in how TLS variables are optimized.
19// See the following paper for the details.
20//
21// Ulrich Drepper, ELF Handling For Thread-Local Storage
22// http://www.akkadia.org/drepper/tls.pdf
23//
24//===----------------------------------------------------------------------===//
25
26#include "Target.h"
27#include "InputFiles.h"
28#include "OutputSections.h"
29#include "SymbolTable.h"
30#include "Symbols.h"
31#include "SyntheticSections.h"
32#include "lld/Common/ErrorHandler.h"
33#include "llvm/Object/ELF.h"
34
35using namespace llvm;
36using namespace llvm::object;
37using namespace llvm::ELF;
38using namespace lld;
39using namespace lld::elf;
40
41const TargetInfo *elf::target;
42
43std::string lld::toString(RelType type) {
44 StringRef s = getELFRelocationTypeName(Machine: elf::config->emachine, Type: type);
45 if (s == "Unknown")
46 return ("Unknown (" + Twine(type) + ")").str();
47 return std::string(s);
48}
49
50TargetInfo *elf::getTarget() {
51 switch (config->emachine) {
52 case EM_386:
53 case EM_IAMCU:
54 return getX86TargetInfo();
55 case EM_AARCH64:
56 return getAArch64TargetInfo();
57 case EM_AMDGPU:
58 return getAMDGPUTargetInfo();
59 case EM_ARM:
60 return getARMTargetInfo();
61 case EM_AVR:
62 return getAVRTargetInfo();
63 case EM_HEXAGON:
64 return getHexagonTargetInfo();
65 case EM_LOONGARCH:
66 return getLoongArchTargetInfo();
67 case EM_MIPS:
68 switch (config->ekind) {
69 case ELF32LEKind:
70 return getMipsTargetInfo<ELF32LE>();
71 case ELF32BEKind:
72 return getMipsTargetInfo<ELF32BE>();
73 case ELF64LEKind:
74 return getMipsTargetInfo<ELF64LE>();
75 case ELF64BEKind:
76 return getMipsTargetInfo<ELF64BE>();
77 default:
78 llvm_unreachable("unsupported MIPS target");
79 }
80 case EM_MSP430:
81 return getMSP430TargetInfo();
82 case EM_PPC:
83 return getPPCTargetInfo();
84 case EM_PPC64:
85 return getPPC64TargetInfo();
86 case EM_RISCV:
87 return getRISCVTargetInfo();
88 case EM_SPARCV9:
89 return getSPARCV9TargetInfo();
90 case EM_S390:
91 return getSystemZTargetInfo();
92 case EM_X86_64:
93 return getX86_64TargetInfo();
94 default:
95 fatal(msg: "unsupported e_machine value: " + Twine(config->emachine));
96 }
97}
98
99ErrorPlace elf::getErrorPlace(const uint8_t *loc) {
100 assert(loc != nullptr);
101 for (InputSectionBase *d : ctx.inputSections) {
102 auto *isec = dyn_cast<InputSection>(Val: d);
103 if (!isec || !isec->getParent() || (isec->type & SHT_NOBITS))
104 continue;
105
106 const uint8_t *isecLoc =
107 Out::bufferStart
108 ? (Out::bufferStart + isec->getParent()->offset + isec->outSecOff)
109 : isec->contentMaybeDecompress().data();
110 if (isecLoc == nullptr) {
111 assert(isa<SyntheticSection>(isec) && "No data but not synthetic?");
112 continue;
113 }
114 if (isecLoc <= loc && loc < isecLoc + isec->getSize()) {
115 std::string objLoc = isec->getLocation(offset: loc - isecLoc);
116 // Return object file location and source file location.
117 // TODO: Refactor getSrcMsg not to take a variable.
118 Undefined dummy(ctx.internalFile, "", STB_LOCAL, 0, 0);
119 return {.isec: isec, .loc: objLoc + ": ",
120 .srcLoc: isec->file ? isec->getSrcMsg(sym: dummy, offset: loc - isecLoc) : ""};
121 }
122 }
123 return {};
124}
125
126TargetInfo::~TargetInfo() {}
127
128int64_t TargetInfo::getImplicitAddend(const uint8_t *buf, RelType type) const {
129 internalLinkerError(loc: getErrorLocation(loc: buf),
130 msg: "cannot read addend for relocation " + toString(type));
131 return 0;
132}
133
134bool TargetInfo::usesOnlyLowPageBits(RelType type) const { return false; }
135
136bool TargetInfo::needsThunk(RelExpr expr, RelType type, const InputFile *file,
137 uint64_t branchAddr, const Symbol &s,
138 int64_t a) const {
139 return false;
140}
141
142bool TargetInfo::adjustPrologueForCrossSplitStack(uint8_t *loc, uint8_t *end,
143 uint8_t stOther) const {
144 llvm_unreachable("Target doesn't support split stacks.");
145}
146
147bool TargetInfo::inBranchRange(RelType type, uint64_t src, uint64_t dst) const {
148 return true;
149}
150
151RelExpr TargetInfo::adjustTlsExpr(RelType type, RelExpr expr) const {
152 return expr;
153}
154
155RelExpr TargetInfo::adjustGotPcExpr(RelType type, int64_t addend,
156 const uint8_t *data) const {
157 return R_GOT_PC;
158}
159
160void TargetInfo::relocateAlloc(InputSectionBase &sec, uint8_t *buf) const {
161 const unsigned bits = config->is64 ? 64 : 32;
162 uint64_t secAddr = sec.getOutputSection()->addr;
163 if (auto *s = dyn_cast<InputSection>(Val: &sec))
164 secAddr += s->outSecOff;
165 else if (auto *ehIn = dyn_cast<EhInputSection>(Val: &sec))
166 secAddr += ehIn->getParent()->outSecOff;
167 for (const Relocation &rel : sec.relocs()) {
168 uint8_t *loc = buf + rel.offset;
169 const uint64_t val = SignExtend64(
170 X: sec.getRelocTargetVA(File: sec.file, Type: rel.type, A: rel.addend,
171 P: secAddr + rel.offset, Sym: *rel.sym, Expr: rel.expr),
172 B: bits);
173 if (rel.expr != R_RELAX_HINT)
174 relocate(loc, rel, val);
175 }
176}
177
178uint64_t TargetInfo::getImageBase() const {
179 // Use --image-base if set. Fall back to the target default if not.
180 if (config->imageBase)
181 return *config->imageBase;
182 return config->isPic ? 0 : defaultImageBase;
183}
184

source code of lld/ELF/Target.cpp