1 //===-- BPFMCCodeEmitter.cpp - Convert BPF code to machine code -----------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the BPFMCCodeEmitter class.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "MCTargetDesc/BPFMCTargetDesc.h"
15 #include "llvm/MC/MCCodeEmitter.h"
16 #include "llvm/MC/MCFixup.h"
17 #include "llvm/MC/MCInst.h"
18 #include "llvm/MC/MCInstrInfo.h"
19 #include "llvm/MC/MCRegisterInfo.h"
20 #include "llvm/MC/MCSubtargetInfo.h"
21 #include "llvm/MC/MCSymbol.h"
22 #include "llvm/ADT/Statistic.h"
23 #include "llvm/Support/raw_ostream.h"
24 using namespace llvm;
25 
26 #define DEBUG_TYPE "mccodeemitter"
27 
28 namespace {
29 class BPFMCCodeEmitter : public MCCodeEmitter {
30   BPFMCCodeEmitter(const BPFMCCodeEmitter &) = delete;
31   void operator=(const BPFMCCodeEmitter &) = delete;
32   const MCRegisterInfo &MRI;
33 
34 public:
35   BPFMCCodeEmitter(const MCRegisterInfo &mri) : MRI(mri) {}
36 
37   ~BPFMCCodeEmitter() {}
38 
39   // getBinaryCodeForInstr - TableGen'erated function for getting the
40   // binary encoding for an instruction.
41   uint64_t getBinaryCodeForInstr(const MCInst &MI,
42                                  SmallVectorImpl<MCFixup> &Fixups,
43                                  const MCSubtargetInfo &STI) const;
44 
45   // getMachineOpValue - Return binary encoding of operand. If the machin
46   // operand requires relocation, record the relocation and return zero.
47   unsigned getMachineOpValue(const MCInst &MI, const MCOperand &MO,
48                              SmallVectorImpl<MCFixup> &Fixups,
49                              const MCSubtargetInfo &STI) const;
50 
51   uint64_t getMemoryOpValue(const MCInst &MI, unsigned Op,
52                             SmallVectorImpl<MCFixup> &Fixups,
53                             const MCSubtargetInfo &STI) const;
54 
55   void EncodeInstruction(const MCInst &MI, raw_ostream &OS,
56                          SmallVectorImpl<MCFixup> &Fixups,
57                          const MCSubtargetInfo &STI) const override;
58 };
59 }
60 
61 MCCodeEmitter *llvm::createBPFMCCodeEmitter(const MCInstrInfo &MCII,
62                                             const MCRegisterInfo &MRI,
63                                             MCContext &Ctx) {
64   return new BPFMCCodeEmitter(MRI);
65 }
66 
67 unsigned BPFMCCodeEmitter::getMachineOpValue(const MCInst &MI,
68                                              const MCOperand &MO,
69                                              SmallVectorImpl<MCFixup> &Fixups,
70                                              const MCSubtargetInfo &STI) const {
71   if (MO.isReg())
72     return MRI.getEncodingValue(MO.getReg());
73   if (MO.isImm())
74     return static_cast<unsigned>(MO.getImm());
75 
76   assert(MO.isExpr());
77 
78   const MCExpr *Expr = MO.getExpr();
79 
80   assert(Expr->getKind() == MCExpr::SymbolRef);
81 
82   if (MI.getOpcode() == BPF::JAL)
83     // func call name
84     Fixups.push_back(MCFixup::Create(0, Expr, FK_SecRel_4));
85   else if (MI.getOpcode() == BPF::LD_imm64)
86     Fixups.push_back(MCFixup::Create(0, Expr, FK_SecRel_8));
87   else
88     // bb label
89     Fixups.push_back(MCFixup::Create(0, Expr, FK_PCRel_2));
90 
91   return 0;
92 }
93 
94 // Emit one byte through output stream
95 void EmitByte(unsigned char C, unsigned &CurByte, raw_ostream &OS) {
96   OS << (char)C;
97   ++CurByte;
98 }
99 
100 // Emit a series of bytes (little endian)
101 void EmitLEConstant(uint64_t Val, unsigned Size, unsigned &CurByte,
102                     raw_ostream &OS) {
103   assert(Size <= 8 && "size too big in emit constant");
104 
105   for (unsigned i = 0; i != Size; ++i) {
106     EmitByte(Val & 255, CurByte, OS);
107     Val >>= 8;
108   }
109 }
110 
111 // Emit a series of bytes (big endian)
112 void EmitBEConstant(uint64_t Val, unsigned Size, unsigned &CurByte,
113                     raw_ostream &OS) {
114   assert(Size <= 8 && "size too big in emit constant");
115 
116   for (int i = (Size - 1) * 8; i >= 0; i -= 8)
117     EmitByte((Val >> i) & 255, CurByte, OS);
118 }
119 
120 void BPFMCCodeEmitter::EncodeInstruction(const MCInst &MI, raw_ostream &OS,
121                                          SmallVectorImpl<MCFixup> &Fixups,
122                                          const MCSubtargetInfo &STI) const {
123   unsigned Opcode = MI.getOpcode();
124   // Keep track of the current byte being emitted
125   unsigned CurByte = 0;
126 
127   if (Opcode == BPF::LD_imm64 || Opcode == BPF::LD_pseudo) {
128     uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
129     EmitByte(Value >> 56, CurByte, OS);
130     EmitByte(((Value >> 48) & 0xff), CurByte, OS);
131     EmitLEConstant(0, 2, CurByte, OS);
132     EmitLEConstant(Value & 0xffffFFFF, 4, CurByte, OS);
133 
134     const MCOperand &MO = MI.getOperand(1);
135     uint64_t Imm = MO.isImm() ? MO.getImm() : 0;
136     EmitByte(0, CurByte, OS);
137     EmitByte(0, CurByte, OS);
138     EmitLEConstant(0, 2, CurByte, OS);
139     EmitLEConstant(Imm >> 32, 4, CurByte, OS);
140   } else {
141     // Get instruction encoding and emit it
142     uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
143     EmitByte(Value >> 56, CurByte, OS);
144     EmitByte((Value >> 48) & 0xff, CurByte, OS);
145     EmitLEConstant((Value >> 32) & 0xffff, 2, CurByte, OS);
146     EmitLEConstant(Value & 0xffffFFFF, 4, CurByte, OS);
147   }
148 }
149 
150 // Encode BPF Memory Operand
151 uint64_t BPFMCCodeEmitter::getMemoryOpValue(const MCInst &MI, unsigned Op,
152                                             SmallVectorImpl<MCFixup> &Fixups,
153                                             const MCSubtargetInfo &STI) const {
154   uint64_t Encoding;
155   const MCOperand Op1 = MI.getOperand(1);
156   assert(Op1.isReg() && "First operand is not register.");
157   Encoding = MRI.getEncodingValue(Op1.getReg());
158   Encoding <<= 16;
159   MCOperand Op2 = MI.getOperand(2);
160   assert(Op2.isImm() && "Second operand is not immediate.");
161   Encoding |= Op2.getImm() & 0xffff;
162   return Encoding;
163 }
164 
165 #include "BPFGenMCCodeEmitter.inc"
166