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 
35 using namespace llvm;
36 using namespace llvm::object;
37 using namespace llvm::ELF;
38 using namespace lld;
39 using namespace lld::elf;
40 
41 const TargetInfo *elf::target;
42 
43 std::string lld::toString(RelType type) {
44   StringRef s = getELFRelocationTypeName(elf::config->emachine, type);
45   if (s == "Unknown")
46     return ("Unknown (" + Twine(type) + ")").str();
47   return std::string(s);
48 }
49 
50 TargetInfo *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_MIPS:
66     switch (config->ekind) {
67     case ELF32LEKind:
68       return getMipsTargetInfo<ELF32LE>();
69     case ELF32BEKind:
70       return getMipsTargetInfo<ELF32BE>();
71     case ELF64LEKind:
72       return getMipsTargetInfo<ELF64LE>();
73     case ELF64BEKind:
74       return getMipsTargetInfo<ELF64BE>();
75     default:
76       llvm_unreachable("unsupported MIPS target");
77     }
78   case EM_MSP430:
79     return getMSP430TargetInfo();
80   case EM_PPC:
81     return getPPCTargetInfo();
82   case EM_PPC64:
83     return getPPC64TargetInfo();
84   case EM_RISCV:
85     return getRISCVTargetInfo();
86   case EM_SPARCV9:
87     return getSPARCV9TargetInfo();
88   case EM_X86_64:
89     return getX86_64TargetInfo();
90   }
91   llvm_unreachable("unknown target machine");
92 }
93 
94 ErrorPlace elf::getErrorPlace(const uint8_t *loc) {
95   assert(loc != nullptr);
96   for (InputSectionBase *d : ctx.inputSections) {
97     auto *isec = dyn_cast<InputSection>(d);
98     if (!isec || !isec->getParent() || (isec->type & SHT_NOBITS))
99       continue;
100 
101     const uint8_t *isecLoc =
102         Out::bufferStart
103             ? (Out::bufferStart + isec->getParent()->offset + isec->outSecOff)
104             : isec->contentMaybeDecompress().data();
105     if (isecLoc == nullptr) {
106       assert(isa<SyntheticSection>(isec) && "No data but not synthetic?");
107       continue;
108     }
109     if (isecLoc <= loc && loc < isecLoc + isec->getSize()) {
110       std::string objLoc = isec->getLocation(loc - isecLoc);
111       // Return object file location and source file location.
112       // TODO: Refactor getSrcMsg not to take a variable.
113       Undefined dummy(nullptr, "", STB_LOCAL, 0, 0);
114       return {isec, objLoc + ": ",
115               isec->file ? isec->getSrcMsg(dummy, loc - isecLoc) : ""};
116     }
117   }
118   return {};
119 }
120 
121 TargetInfo::~TargetInfo() {}
122 
123 int64_t TargetInfo::getImplicitAddend(const uint8_t *buf, RelType type) const {
124   internalLinkerError(getErrorLocation(buf),
125                       "cannot read addend for relocation " + toString(type));
126   return 0;
127 }
128 
129 bool TargetInfo::usesOnlyLowPageBits(RelType type) const { return false; }
130 
131 bool TargetInfo::needsThunk(RelExpr expr, RelType type, const InputFile *file,
132                             uint64_t branchAddr, const Symbol &s,
133                             int64_t a) const {
134   return false;
135 }
136 
137 bool TargetInfo::adjustPrologueForCrossSplitStack(uint8_t *loc, uint8_t *end,
138                                                   uint8_t stOther) const {
139   llvm_unreachable("Target doesn't support split stacks.");
140 }
141 
142 bool TargetInfo::inBranchRange(RelType type, uint64_t src, uint64_t dst) const {
143   return true;
144 }
145 
146 RelExpr TargetInfo::adjustTlsExpr(RelType type, RelExpr expr) const {
147   return expr;
148 }
149 
150 RelExpr TargetInfo::adjustGotPcExpr(RelType type, int64_t addend,
151                                     const uint8_t *data) const {
152   return R_GOT_PC;
153 }
154 
155 void TargetInfo::relocateAlloc(InputSectionBase &sec, uint8_t *buf) const {
156   const unsigned bits = config->is64 ? 64 : 32;
157   uint64_t secAddr = sec.getOutputSection()->addr;
158   if (auto *s = dyn_cast<InputSection>(&sec))
159     secAddr += s->outSecOff;
160   for (const Relocation &rel : sec.relocs()) {
161     uint8_t *loc = buf + rel.offset;
162     const uint64_t val = SignExtend64(
163         sec.getRelocTargetVA(sec.file, rel.type, rel.addend,
164                              secAddr + rel.offset, *rel.sym, rel.expr),
165         bits);
166     if (rel.expr != R_RELAX_HINT)
167       relocate(loc, rel, val);
168   }
169 }
170 
171 uint64_t TargetInfo::getImageBase() const {
172   // Use --image-base if set. Fall back to the target default if not.
173   if (config->imageBase)
174     return *config->imageBase;
175   return config->isPic ? 0 : defaultImageBase;
176 }
177