1 //===- Relocations.h -------------------------------------------*- C++ -*-===//
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_RELOCATIONS_H
10 #define LLD_ELF_RELOCATIONS_H
11 
12 #include "lld/Common/LLVM.h"
13 #include "llvm/ADT/DenseMap.h"
14 #include <map>
15 #include <vector>
16 
17 namespace lld {
18 namespace elf {
19 class Symbol;
20 class InputSection;
21 class InputSectionBase;
22 class OutputSection;
23 class SectionBase;
24 
25 // Represents a relocation type, such as R_X86_64_PC32 or R_ARM_THM_CALL.
26 using RelType = uint32_t;
27 using JumpModType = uint32_t;
28 
29 // List of target-independent relocation types. Relocations read
30 // from files are converted to these types so that the main code
31 // doesn't have to know about architecture-specific details.
32 enum RelExpr {
33   R_ABS,
34   R_ADDEND,
35   R_DTPREL,
36   R_GOT,
37   R_GOT_OFF,
38   R_GOT_PC,
39   R_GOTONLY_PC,
40   R_GOTPLTONLY_PC,
41   R_GOTPLT,
42   R_GOTPLTREL,
43   R_GOTREL,
44   R_NONE,
45   R_PC,
46   R_PLT,
47   R_PLT_PC,
48   R_RELAX_GOT_PC,
49   R_RELAX_GOT_PC_NOPIC,
50   R_RELAX_TLS_GD_TO_IE,
51   R_RELAX_TLS_GD_TO_IE_ABS,
52   R_RELAX_TLS_GD_TO_IE_GOT_OFF,
53   R_RELAX_TLS_GD_TO_IE_GOTPLT,
54   R_RELAX_TLS_GD_TO_LE,
55   R_RELAX_TLS_GD_TO_LE_NEG,
56   R_RELAX_TLS_IE_TO_LE,
57   R_RELAX_TLS_LD_TO_LE,
58   R_RELAX_TLS_LD_TO_LE_ABS,
59   R_SIZE,
60   R_TPREL,
61   R_TPREL_NEG,
62   R_TLSDESC,
63   R_TLSDESC_CALL,
64   R_TLSDESC_PC,
65   R_TLSGD_GOT,
66   R_TLSGD_GOTPLT,
67   R_TLSGD_PC,
68   R_TLSIE_HINT,
69   R_TLSLD_GOT,
70   R_TLSLD_GOTPLT,
71   R_TLSLD_GOT_OFF,
72   R_TLSLD_HINT,
73   R_TLSLD_PC,
74 
75   // The following is abstract relocation types used for only one target.
76   //
77   // Even though RelExpr is intended to be a target-neutral representation
78   // of a relocation type, there are some relocations whose semantics are
79   // unique to a target. Such relocation are marked with R_<TARGET_NAME>.
80   R_AARCH64_GOT_PAGE_PC,
81   R_AARCH64_GOT_PAGE,
82   R_AARCH64_PAGE_PC,
83   R_AARCH64_RELAX_TLS_GD_TO_IE_PAGE_PC,
84   R_AARCH64_TLSDESC_PAGE,
85   R_ARM_PCA,
86   R_ARM_SBREL,
87   R_MIPS_GOTREL,
88   R_MIPS_GOT_GP,
89   R_MIPS_GOT_GP_PC,
90   R_MIPS_GOT_LOCAL_PAGE,
91   R_MIPS_GOT_OFF,
92   R_MIPS_GOT_OFF32,
93   R_MIPS_TLSGD,
94   R_MIPS_TLSLD,
95   R_PPC32_PLTREL,
96   R_PPC64_CALL,
97   R_PPC64_CALL_PLT,
98   R_PPC64_RELAX_TOC,
99   R_PPC64_TOCBASE,
100   R_PPC64_RELAX_GOT_PC,
101   R_RISCV_ADD,
102   R_RISCV_PC_INDIRECT,
103 };
104 
105 // Architecture-neutral representation of relocation.
106 struct Relocation {
107   RelExpr expr;
108   RelType type;
109   uint64_t offset;
110   int64_t addend;
111   Symbol *sym;
112 };
113 
114 // Manipulate jump instructions with these modifiers.  These are used to relax
115 // jump instruction opcodes at basic block boundaries and are particularly
116 // useful when basic block sections are enabled.
117 struct JumpInstrMod {
118   JumpModType original;
119   uint64_t offset;
120   unsigned size;
121 };
122 
123 // This function writes undefined symbol diagnostics to an internal buffer.
124 // Call reportUndefinedSymbols() after calling scanRelocations() to emit
125 // the diagnostics.
126 template <class ELFT> void scanRelocations(InputSectionBase &);
127 
128 template <class ELFT> void reportUndefinedSymbols();
129 
130 void hexagonTLSSymbolUpdate(ArrayRef<OutputSection *> outputSections);
131 bool hexagonNeedsTLSSymbol(ArrayRef<OutputSection *> outputSections);
132 
133 class ThunkSection;
134 class Thunk;
135 class InputSectionDescription;
136 
137 class ThunkCreator {
138 public:
139   // Return true if Thunks have been added to OutputSections
140   bool createThunks(ArrayRef<OutputSection *> outputSections);
141 
142   // The number of completed passes of createThunks this permits us
143   // to do one time initialization on Pass 0 and put a limit on the
144   // number of times it can be called to prevent infinite loops.
145   uint32_t pass = 0;
146 
147 private:
148   void mergeThunks(ArrayRef<OutputSection *> outputSections);
149 
150   ThunkSection *getISDThunkSec(OutputSection *os, InputSection *isec,
151                                InputSectionDescription *isd,
152                                const Relocation &rel, uint64_t src);
153 
154   ThunkSection *getISThunkSec(InputSection *isec);
155 
156   void createInitialThunkSections(ArrayRef<OutputSection *> outputSections);
157 
158   std::pair<Thunk *, bool> getThunk(InputSection *isec, Relocation &rel,
159                                     uint64_t src);
160 
161   ThunkSection *addThunkSection(OutputSection *os, InputSectionDescription *,
162                                 uint64_t off);
163 
164   bool normalizeExistingThunk(Relocation &rel, uint64_t src);
165 
166   // Record all the available Thunks for a (Symbol, addend) pair, where Symbol
167   // is represented as a (section, offset) pair. There may be multiple
168   // relocations sharing the same (section, offset + addend) pair. We may revert
169   // a relocation back to its original non-Thunk target, and restore the
170   // original addend, so we cannot fold offset + addend. A nested pair is used
171   // because DenseMapInfo is not specialized for std::tuple.
172   llvm::DenseMap<std::pair<std::pair<SectionBase *, uint64_t>, int64_t>,
173                  std::vector<Thunk *>>
174       thunkedSymbolsBySectionAndAddend;
175   llvm::DenseMap<std::pair<Symbol *, int64_t>, std::vector<Thunk *>>
176       thunkedSymbols;
177 
178   // Find a Thunk from the Thunks symbol definition, we can use this to find
179   // the Thunk from a relocation to the Thunks symbol definition.
180   llvm::DenseMap<Symbol *, Thunk *> thunks;
181 
182   // Track InputSections that have an inline ThunkSection placed in front
183   // an inline ThunkSection may have control fall through to the section below
184   // so we need to make sure that there is only one of them.
185   // The Mips LA25 Thunk is an example of an inline ThunkSection.
186   llvm::DenseMap<InputSection *, ThunkSection *> thunkedSections;
187 };
188 
189 // Return a int64_t to make sure we get the sign extension out of the way as
190 // early as possible.
191 template <class ELFT>
getAddend(const typename ELFT::Rel & rel)192 static inline int64_t getAddend(const typename ELFT::Rel &rel) {
193   return 0;
194 }
195 template <class ELFT>
getAddend(const typename ELFT::Rela & rel)196 static inline int64_t getAddend(const typename ELFT::Rela &rel) {
197   return rel.r_addend;
198 }
199 
200 template <typename RelTy>
sortRels(ArrayRef<RelTy> rels,SmallVector<RelTy,0> & storage)201 ArrayRef<RelTy> sortRels(ArrayRef<RelTy> rels, SmallVector<RelTy, 0> &storage) {
202   auto cmp = [](const RelTy &a, const RelTy &b) {
203     return a.r_offset < b.r_offset;
204   };
205   if (!llvm::is_sorted(rels, cmp)) {
206     storage.assign(rels.begin(), rels.end());
207     llvm::stable_sort(storage, cmp);
208     rels = storage;
209   }
210   return rels;
211 }
212 } // namespace elf
213 } // namespace lld
214 
215 #endif
216