1 //===- Thunks.h --------------------------------------------------------===//
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #ifndef LLD_ELF_THUNKS_H
11 #define LLD_ELF_THUNKS_H
13 #include "Relocations.h"
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
27 // Thunks can be created for Defined, Shared and Undefined Symbols.
28 // Thunks are assigned to synthetic ThunkSections
31 Thunk(Symbol &Destination);
34 virtual uint32_t size() = 0;
35 virtual void writeTo(uint8_t *Buf) = 0;
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 &IS) = 0;
42 void setOffset(uint64_t Offset);
43 Defined *addSymbol(StringRef Name, uint8_t Type, uint64_t Value,
44 InputSectionBase &Section);
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; }
50 // To reuse a Thunk the caller as identified by the Type must be
51 // compatible with it.
52 virtual bool isCompatibleWith(RelType Type) const { return true; }
54 Defined *getThunkTargetSym() const { return Syms[0]; }
56 // The alignment requirement for this Thunk, defaults to the size of the
57 // typical code section alignment.
59 llvm::SmallVector<Defined *, 3> Syms;
61 uint32_t Alignment = 4;
64 // For a Relocation to symbol S create a Thunk to be added to a synthetic
65 // ThunkSection. At present there are implementations for ARM and Mips Thunks.
66 Thunk *addThunk(RelType Type, Symbol &S);