1 //===- Thunks.h --------------------------------------------------------===//
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
7 //===----------------------------------------------------------------------===//
9 #ifndef LLD_ELF_THUNKS_H
10 #define LLD_ELF_THUNKS_H
12 #include "Relocations.h"
19 // Class to describe an instance of a Thunk.
20 // A Thunk is a code-sequence inserted by the linker in between a caller and
21 // the callee. The relocation to the callee is redirected to the Thunk, which
22 // after executing transfers control to the callee. Typical uses of Thunks
23 // include transferring control from non-pi to pi and changing state on
26 // Thunks can be created for Defined, Shared and Undefined Symbols.
27 // Thunks are assigned to synthetic ThunkSections
30 Thunk(Symbol &destination);
33 virtual uint32_t size() = 0;
34 virtual void writeTo(uint8_t *buf) = 0;
36 // All Thunks must define at least one symbol, known as the thunk target
37 // symbol, so that we can redirect relocations to it. The thunk may define
38 // additional symbols, but these are never targets for relocations.
39 virtual void addSymbols(ThunkSection &isec) = 0;
41 void setOffset(uint64_t offset);
42 Defined *addSymbol(StringRef name, uint8_t type, uint64_t value,
43 InputSectionBase §ion);
45 // Some Thunks must be placed immediately before their Target as they elide
46 // a branch and fall through to the first Symbol in the Target.
47 virtual InputSection *getTargetInputSection() const { return nullptr; }
49 // To reuse a Thunk the InputSection and the relocation must be compatible
51 virtual bool isCompatibleWith(const InputSection &,
52 const Relocation &) const {
56 Defined *getThunkTargetSym() const { return syms[0]; }
58 // The alignment requirement for this Thunk, defaults to the size of the
59 // typical code section alignment.
61 llvm::SmallVector<Defined *, 3> syms;
63 uint32_t alignment = 4;
66 // For a Relocation to symbol S create a Thunk to be added to a synthetic
68 Thunk *addThunk(const InputSection &isec, Relocation &rel);