1 //===- llvm/MC/MCELFObjectWriter.h - ELF Object Writer ----------*- 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 LLVM_MC_MCELFOBJECTWRITER_H
10 #define LLVM_MC_MCELFOBJECTWRITER_H
11 
12 #include "llvm/BinaryFormat/ELF.h"
13 #include "llvm/MC/MCObjectWriter.h"
14 #include "llvm/MC/MCSectionELF.h"
15 #include "llvm/Support/Casting.h"
16 #include "llvm/Support/raw_ostream.h"
17 #include "llvm/TargetParser/Triple.h"
18 #include <cstdint>
19 #include <vector>
20 
21 namespace llvm {
22 
23 class MCAssembler;
24 class MCContext;
25 class MCFixup;
26 class MCSymbol;
27 class MCSymbolELF;
28 class MCValue;
29 
30 struct ELFRelocationEntry {
31   uint64_t Offset; // Where is the relocation.
32   const MCSymbolELF *Symbol; // The symbol to relocate with.
33   unsigned Type;   // The type of the relocation.
34   uint64_t Addend; // The addend to use.
35   const MCSymbolELF *OriginalSymbol; // The original value of Symbol if we changed it.
36   uint64_t OriginalAddend; // The original value of addend.
37 
38   ELFRelocationEntry(uint64_t Offset, const MCSymbolELF *Symbol, unsigned Type,
39                      uint64_t Addend, const MCSymbolELF *OriginalSymbol,
40                      uint64_t OriginalAddend)
41       : Offset(Offset), Symbol(Symbol), Type(Type), Addend(Addend),
42         OriginalSymbol(OriginalSymbol), OriginalAddend(OriginalAddend) {}
43 
44   void print(raw_ostream &Out) const {
45     Out << "Off=" << Offset << ", Sym=" << Symbol << ", Type=" << Type
46         << ", Addend=" << Addend << ", OriginalSymbol=" << OriginalSymbol
47         << ", OriginalAddend=" << OriginalAddend;
48   }
49 
50   LLVM_DUMP_METHOD void dump() const { print(errs()); }
51 };
52 
53 class MCELFObjectTargetWriter : public MCObjectTargetWriter {
54   const uint8_t OSABI;
55   const uint8_t ABIVersion;
56   const uint16_t EMachine;
57   const unsigned HasRelocationAddend : 1;
58   const unsigned Is64Bit : 1;
59 
60 protected:
61   MCELFObjectTargetWriter(bool Is64Bit_, uint8_t OSABI_, uint16_t EMachine_,
62                           bool HasRelocationAddend_, uint8_t ABIVersion_ = 0);
63 
64 public:
65   virtual ~MCELFObjectTargetWriter() = default;
66 
67   Triple::ObjectFormatType getFormat() const override { return Triple::ELF; }
68   static bool classof(const MCObjectTargetWriter *W) {
69     return W->getFormat() == Triple::ELF;
70   }
71 
72   static uint8_t getOSABI(Triple::OSType OSType) {
73     switch (OSType) {
74       case Triple::CloudABI:
75         return ELF::ELFOSABI_CLOUDABI;
76       case Triple::HermitCore:
77         return ELF::ELFOSABI_STANDALONE;
78       case Triple::PS4:
79       case Triple::FreeBSD:
80         return ELF::ELFOSABI_FREEBSD;
81       case Triple::Solaris:
82         return ELF::ELFOSABI_SOLARIS;
83       default:
84         return ELF::ELFOSABI_NONE;
85     }
86   }
87 
88   virtual unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
89                                 const MCFixup &Fixup, bool IsPCRel) const = 0;
90 
91   virtual bool needsRelocateWithSymbol(const MCSymbol &Sym,
92                                        unsigned Type) const;
93 
94   virtual void sortRelocs(const MCAssembler &Asm,
95                           std::vector<ELFRelocationEntry> &Relocs);
96 
97   virtual void addTargetSectionFlags(MCContext &Ctx, MCSectionELF &Sec);
98 
99   /// \name Accessors
100   /// @{
101   uint8_t getOSABI() const { return OSABI; }
102   uint8_t getABIVersion() const { return ABIVersion; }
103   uint16_t getEMachine() const { return EMachine; }
104   bool hasRelocationAddend() const { return HasRelocationAddend; }
105   bool is64Bit() const { return Is64Bit; }
106   /// @}
107 
108   // Instead of changing everyone's API we pack the N64 Type fields
109   // into the existing 32 bit data unsigned.
110 #define R_TYPE_SHIFT 0
111 #define R_TYPE_MASK 0xffffff00
112 #define R_TYPE2_SHIFT 8
113 #define R_TYPE2_MASK 0xffff00ff
114 #define R_TYPE3_SHIFT 16
115 #define R_TYPE3_MASK 0xff00ffff
116 #define R_SSYM_SHIFT 24
117 #define R_SSYM_MASK 0x00ffffff
118 
119   // N64 relocation type accessors
120   uint8_t getRType(uint32_t Type) const {
121     return (unsigned)((Type >> R_TYPE_SHIFT) & 0xff);
122   }
123   uint8_t getRType2(uint32_t Type) const {
124     return (unsigned)((Type >> R_TYPE2_SHIFT) & 0xff);
125   }
126   uint8_t getRType3(uint32_t Type) const {
127     return (unsigned)((Type >> R_TYPE3_SHIFT) & 0xff);
128   }
129   uint8_t getRSsym(uint32_t Type) const {
130     return (unsigned)((Type >> R_SSYM_SHIFT) & 0xff);
131   }
132 
133   // N64 relocation type setting
134   static unsigned setRTypes(unsigned Value1, unsigned Value2, unsigned Value3) {
135     return ((Value1 & 0xff) << R_TYPE_SHIFT) |
136            ((Value2 & 0xff) << R_TYPE2_SHIFT) |
137            ((Value3 & 0xff) << R_TYPE3_SHIFT);
138   }
139   unsigned setRSsym(unsigned Value, unsigned Type) const {
140     return (Type & R_SSYM_MASK) | ((Value & 0xff) << R_SSYM_SHIFT);
141   }
142 
143   // On AArch64, return a new section to be added to the ELF object that
144   // contains relocations used to describe every symbol that should have memory
145   // tags applied. Returns nullptr if no such section is necessary (i.e. there's
146   // no tagged globals).
147   virtual MCSectionELF *getMemtagRelocsSection(MCContext &Ctx) const {
148     return nullptr;
149   }
150 };
151 
152 /// Construct a new ELF writer instance.
153 ///
154 /// \param MOTW - The target specific ELF writer subclass.
155 /// \param OS - The stream to write to.
156 /// \returns The constructed object writer.
157 std::unique_ptr<MCObjectWriter>
158 createELFObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
159                       raw_pwrite_stream &OS, bool IsLittleEndian);
160 
161 std::unique_ptr<MCObjectWriter>
162 createELFDwoObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
163                          raw_pwrite_stream &OS, raw_pwrite_stream &DwoOS,
164                          bool IsLittleEndian);
165 
166 } // end namespace llvm
167 
168 #endif // LLVM_MC_MCELFOBJECTWRITER_H
169