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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-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef LLD_ELF_THUNKS_H10#define LLD_ELF_THUNKS_H11 12#include "llvm/ADT/SmallVector.h"13#include "Relocations.h"14 15namespace lld::elf {16struct Ctx;17class Defined;18class InputFile;19class Symbol;20class ThunkSection;21// Class to describe an instance of a Thunk.22// A Thunk is a code-sequence inserted by the linker in between a caller and23// the callee. The relocation to the callee is redirected to the Thunk, which24// after executing transfers control to the callee. Typical uses of Thunks25// include transferring control from non-pi to pi and changing state on26// targets like ARM.27//28// Thunks can be created for Defined, Shared and Undefined Symbols.29// Thunks are assigned to synthetic ThunkSections30class Thunk {31public:32 Thunk(Ctx &, Symbol &destination, int64_t addend);33 virtual ~Thunk();34 35 virtual uint32_t size() = 0;36 virtual void writeTo(uint8_t *buf) = 0;37 38 // All Thunks must define at least one symbol, known as the thunk target39 // symbol, so that we can redirect relocations to it. The thunk may define40 // additional symbols, but these are never targets for relocations.41 virtual void addSymbols(ThunkSection &isec) = 0;42 43 void setOffset(uint64_t offset);44 Defined *addSymbol(StringRef name, uint8_t type, uint64_t value,45 InputSectionBase §ion);46 47 // Some Thunks must be placed immediately before their Target as they elide48 // a branch and fall through to the first Symbol in the Target.49 virtual InputSection *getTargetInputSection() const { return nullptr; }50 51 // To reuse a Thunk the InputSection and the relocation must be compatible52 // with it.53 virtual bool isCompatibleWith(const InputSection &,54 const Relocation &) const {55 return true;56 }57 58 // Thunks that indirectly branch to targets may need a synthetic landing59 // pad generated close to the target. For example AArch64 when BTI is60 // enabled.61 virtual bool needsSyntheticLandingPad() { return false; }62 63 Defined *getThunkTargetSym() const { return syms[0]; }64 65 Ctx &ctx;66 Symbol &destination;67 int64_t addend;68 // Alternative target when indirect branch to destination can't be used.69 Symbol *landingPad = nullptr;70 llvm::SmallVector<Defined *, 3> syms;71 uint64_t offset = 0;72 // The alignment requirement for this Thunk, defaults to the size of the73 // typical code section alignment.74 uint32_t alignment = 4;75};76 77// For a Relocation to symbol S create a Thunk to be added to a synthetic78// ThunkSection.79std::unique_ptr<Thunk> addThunk(Ctx &, const InputSection &isec,80 Relocation &rel);81 82// Create a landing pad Thunk for use when indirect branches from Thunks83// are restricted.84std::unique_ptr<Thunk> addLandingPadThunk(Ctx &, Symbol &s, int64_t a);85 86void writePPC32PltCallStub(Ctx &, uint8_t *buf, uint64_t gotPltVA,87 const InputFile *file, int64_t addend);88void writePPC64LoadAndBranch(Ctx &, uint8_t *buf, int64_t offset);89 90} // namespace lld::elf91 92#endif93