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1 //===- Thunks.h --------------------------------------------------------===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8
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9 #ifndef LLD_ELF_THUNKS_H
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10 #define LLD_ELF_THUNKS_H
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11
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221
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12 #include "llvm/ADT/SmallVector.h"
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150
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13 #include "Relocations.h"
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14
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236
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15 namespace lld::elf {
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16 class Defined;
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17 class InputFile;
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18 class Symbol;
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19 class ThunkSection;
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20 // Class to describe an instance of a Thunk.
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21 // A Thunk is a code-sequence inserted by the linker in between a caller and
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22 // the callee. The relocation to the callee is redirected to the Thunk, which
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23 // after executing transfers control to the callee. Typical uses of Thunks
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24 // include transferring control from non-pi to pi and changing state on
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25 // targets like ARM.
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26 //
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27 // Thunks can be created for Defined, Shared and Undefined Symbols.
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28 // Thunks are assigned to synthetic ThunkSections
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29 class Thunk {
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30 public:
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31 Thunk(Symbol &destination, int64_t addend);
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32 virtual ~Thunk();
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33
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34 virtual uint32_t size() = 0;
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35 virtual void writeTo(uint8_t *buf) = 0;
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36
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37 // All Thunks must define at least one symbol, known as the thunk target
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38 // symbol, so that we can redirect relocations to it. The thunk may define
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39 // additional symbols, but these are never targets for relocations.
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40 virtual void addSymbols(ThunkSection &isec) = 0;
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41
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42 void setOffset(uint64_t offset);
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43 Defined *addSymbol(StringRef name, uint8_t type, uint64_t value,
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44 InputSectionBase §ion);
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45
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46 // Some Thunks must be placed immediately before their Target as they elide
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47 // a branch and fall through to the first Symbol in the Target.
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48 virtual InputSection *getTargetInputSection() const { return nullptr; }
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49
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50 // To reuse a Thunk the InputSection and the relocation must be compatible
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51 // with it.
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52 virtual bool isCompatibleWith(const InputSection &,
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53 const Relocation &) const {
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54 return true;
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55 }
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56
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57 Defined *getThunkTargetSym() const { return syms[0]; }
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58
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59 Symbol &destination;
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60 int64_t addend;
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61 llvm::SmallVector<Defined *, 3> syms;
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62 uint64_t offset = 0;
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63 // The alignment requirement for this Thunk, defaults to the size of the
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64 // typical code section alignment.
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65 uint32_t alignment = 4;
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66 };
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67
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68 // For a Relocation to symbol S create a Thunk to be added to a synthetic
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69 // ThunkSection.
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70 Thunk *addThunk(const InputSection &isec, Relocation &rel);
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71
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72 void writePPC32PltCallStub(uint8_t *buf, uint64_t gotPltVA,
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73 const InputFile *file, int64_t addend);
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74 void writePPC64LoadAndBranch(uint8_t *buf, int64_t offset);
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75
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236
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76 } // namespace lld::elf
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150
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77
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78 #endif
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