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//===- Thunks.h --------------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef LLD_ELF_THUNKS_H
#define LLD_ELF_THUNKS_H
#include "Relocations.h"
namespace lld {
namespace elf {
class SymbolBody;
class ThunkSection;
// Class to describe an instance of a Thunk.
// A Thunk is a code-sequence inserted by the linker in between a caller and
// the callee. The relocation to the callee is redirected to the Thunk, which
// after executing transfers control to the callee. Typical uses of Thunks
// include transferring control from non-pi to pi and changing state on
// targets like ARM.
//
// Thunks can be created for DefinedRegular, Shared and Undefined Symbols.
// Thunks are assigned to synthetic ThunkSections
class Thunk {
public:
Thunk(const SymbolBody &Destination);
virtual ~Thunk();
virtual uint32_t size() const { return 0; }
virtual void writeTo(uint8_t *Buf, ThunkSection &IS) const {}
// All Thunks must define at least one symbol ThunkSym so that we can
// redirect relocations to it.
virtual void addSymbols(ThunkSection &IS) {}
// Some Thunks must be placed immediately before their Target as they elide
// a branch and fall through to the first Symbol in the Target.
virtual InputSection *getTargetInputSection() const { return nullptr; }
// To reuse a Thunk the caller as identified by the RelocType must be
// compatible with it.
virtual bool isCompatibleWith(uint32_t RelocType) const { return true; }
// The alignment requirement for this Thunk, defaults to the size of the
// typical code section alignment.
const SymbolBody &Destination;
SymbolBody *ThunkSym;
uint64_t Offset;
uint32_t Alignment = 4;
};
// For a Relocation to symbol S create a Thunk to be added to a synthetic
// ThunkSection. At present there are implementations for ARM and Mips Thunks.
Thunk *addThunk(uint32_t RelocType, SymbolBody &S);
} // namespace elf
} // namespace lld
#endif
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