1 //===- Thunks.h --------------------------------------------------------===// 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 #ifndef LLD_ELF_THUNKS_H 10 #define LLD_ELF_THUNKS_H 11 12 #include "llvm/ADT/SmallVector.h" 13 #include "Relocations.h" 14 15 namespace lld::elf { 16 class Defined; 17 class InputFile; 18 class Symbol; 19 class ThunkSection; 20 // Class to describe an instance of a Thunk. 21 // A Thunk is a code-sequence inserted by the linker in between a caller and 22 // the callee. The relocation to the callee is redirected to the Thunk, which 23 // after executing transfers control to the callee. Typical uses of Thunks 24 // include transferring control from non-pi to pi and changing state on 25 // targets like ARM. 26 // 27 // Thunks can be created for Defined, Shared and Undefined Symbols. 28 // Thunks are assigned to synthetic ThunkSections 29 class Thunk { 30 public: 31 Thunk(Symbol &destination, int64_t addend); 32 virtual ~Thunk(); 33 34 virtual uint32_t size() = 0; 35 virtual void writeTo(uint8_t *buf) = 0; 36 37 // All Thunks must define at least one symbol, known as the thunk target 38 // symbol, so that we can redirect relocations to it. The thunk may define 39 // additional symbols, but these are never targets for relocations. 40 virtual void addSymbols(ThunkSection &isec) = 0; 41 42 void setOffset(uint64_t offset); 43 Defined *addSymbol(StringRef name, uint8_t type, uint64_t value, 44 InputSectionBase §ion); 45 46 // Some Thunks must be placed immediately before their Target as they elide 47 // a branch and fall through to the first Symbol in the Target. 48 virtual InputSection *getTargetInputSection() const { return nullptr; } 49 50 // To reuse a Thunk the InputSection and the relocation must be compatible 51 // with it. 52 virtual bool isCompatibleWith(const InputSection &, 53 const Relocation &) const { 54 return true; 55 } 56 57 Defined *getThunkTargetSym() const { return syms[0]; } 58 59 Symbol &destination; 60 int64_t addend; 61 llvm::SmallVector<Defined *, 3> syms; 62 uint64_t offset = 0; 63 // The alignment requirement for this Thunk, defaults to the size of the 64 // typical code section alignment. 65 uint32_t alignment = 4; 66 }; 67 68 // For a Relocation to symbol S create a Thunk to be added to a synthetic 69 // ThunkSection. 70 Thunk *addThunk(const InputSection &isec, Relocation &rel); 71 72 void writePPC32PltCallStub(uint8_t *buf, uint64_t gotPltVA, 73 const InputFile *file, int64_t addend); 74 void writePPC64LoadAndBranch(uint8_t *buf, int64_t offset); 75 76 static inline uint16_t computeHiBits(uint32_t toCompute) { 77 return (toCompute + 0x8000) >> 16; 78 } 79 80 } // namespace lld::elf 81 82 #endif 83