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 {
16 namespace elf {
17 class Defined;
18 class InputFile;
19 class Symbol;
20 class 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 and
23 // the callee. The relocation to the callee is redirected to the Thunk, which
24 // after executing transfers control to the callee. Typical uses of Thunks
25 // include transferring control from non-pi to pi and changing state on
26 // targets like ARM.
27 //
28 // Thunks can be created for Defined, Shared and Undefined Symbols.
29 // Thunks are assigned to synthetic ThunkSections
30 class Thunk {
31 public:
32 Thunk(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 target
39 // symbol, so that we can redirect relocations to it. The thunk may define
40 // 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 elide
48 // a branch and fall through to the first Symbol in the Target.
getTargetInputSection()49 virtual InputSection *getTargetInputSection() const { return nullptr; }
50
51 // To reuse a Thunk the InputSection and the relocation must be compatible
52 // with it.
isCompatibleWith(const InputSection &,const Relocation &)53 virtual bool isCompatibleWith(const InputSection &,
54 const Relocation &) const {
55 return true;
56 }
57
getThunkTargetSym()58 Defined *getThunkTargetSym() const { return syms[0]; }
59
60 Symbol &destination;
61 int64_t addend;
62 llvm::SmallVector<Defined *, 3> syms;
63 uint64_t offset = 0;
64 // The alignment requirement for this Thunk, defaults to the size of the
65 // typical code section alignment.
66 uint32_t alignment = 4;
67 };
68
69 // For a Relocation to symbol S create a Thunk to be added to a synthetic
70 // ThunkSection.
71 Thunk *addThunk(const InputSection &isec, Relocation &rel);
72
73 void writePPC32PltCallStub(uint8_t *buf, uint64_t gotPltVA,
74 const InputFile *file, int64_t addend);
75 void writePPC64LoadAndBranch(uint8_t *buf, int64_t offset);
76
computeHiBits(uint32_t toCompute)77 static inline uint16_t computeHiBits(uint32_t toCompute) {
78 return (toCompute + 0x8000) >> 16;
79 }
80
81 } // namespace elf
82 } // namespace lld
83
84 #endif
85