BPFMCCodeEmitter.cpp revision 314564 
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/ADT/SmallVector.h"
16#include "llvm/MC/MCCodeEmitter.h"
17#include "llvm/MC/MCFixup.h"
18#include "llvm/MC/MCInst.h"
19#include "llvm/MC/MCInstrInfo.h"
20#include "llvm/MC/MCRegisterInfo.h"
21#include "llvm/MC/MCSubtargetInfo.h"
22#include "llvm/Support/Endian.h"
23#include "llvm/Support/EndianStream.h"
24#include <cassert>
25#include <cstdint>
26
27using namespace llvm;
28
29#define DEBUG_TYPE "mccodeemitter"
30
31namespace {
32
33class BPFMCCodeEmitter : public MCCodeEmitter {
34  const MCInstrInfo &MCII;
35  const MCRegisterInfo &MRI;
36  bool IsLittleEndian;
37
38public:
39  BPFMCCodeEmitter(const MCInstrInfo &mcii, const MCRegisterInfo &mri,
40                   bool IsLittleEndian)
41      : MCII(mcii), MRI(mri), IsLittleEndian(IsLittleEndian) {}
42  BPFMCCodeEmitter(const BPFMCCodeEmitter &) = delete;
43  void operator=(const BPFMCCodeEmitter &) = delete;
44  ~BPFMCCodeEmitter() override = default;
45
46  // getBinaryCodeForInstr - TableGen'erated function for getting the
47  // binary encoding for an instruction.
48  uint64_t getBinaryCodeForInstr(const MCInst &MI,
49                                 SmallVectorImpl<MCFixup> &Fixups,
50                                 const MCSubtargetInfo &STI) const;
51
52  // getMachineOpValue - Return binary encoding of operand. If the machin
53  // operand requires relocation, record the relocation and return zero.
54  unsigned getMachineOpValue(const MCInst &MI, const MCOperand &MO,
55                             SmallVectorImpl<MCFixup> &Fixups,
56                             const MCSubtargetInfo &STI) const;
57
58  uint64_t getMemoryOpValue(const MCInst &MI, unsigned Op,
59                            SmallVectorImpl<MCFixup> &Fixups,
60                            const MCSubtargetInfo &STI) const;
61
62  void encodeInstruction(const MCInst &MI, raw_ostream &OS,
63                         SmallVectorImpl<MCFixup> &Fixups,
64                         const MCSubtargetInfo &STI) const override;
65
66private:
67  uint64_t computeAvailableFeatures(const FeatureBitset &FB) const;
68  void verifyInstructionPredicates(const MCInst &MI,
69                                   uint64_t AvailableFeatures) const;
70};
71
72} // end anonymous namespace
73
74MCCodeEmitter *llvm::createBPFMCCodeEmitter(const MCInstrInfo &MCII,
75                                            const MCRegisterInfo &MRI,
76                                            MCContext &Ctx) {
77  return new BPFMCCodeEmitter(MCII, MRI, true);
78}
79
80MCCodeEmitter *llvm::createBPFbeMCCodeEmitter(const MCInstrInfo &MCII,
81                                              const MCRegisterInfo &MRI,
82                                              MCContext &Ctx) {
83  return new BPFMCCodeEmitter(MCII, MRI, false);
84}
85
86unsigned BPFMCCodeEmitter::getMachineOpValue(const MCInst &MI,
87                                             const MCOperand &MO,
88                                             SmallVectorImpl<MCFixup> &Fixups,
89                                             const MCSubtargetInfo &STI) const {
90  if (MO.isReg())
91    return MRI.getEncodingValue(MO.getReg());
92  if (MO.isImm())
93    return static_cast<unsigned>(MO.getImm());
94
95  assert(MO.isExpr());
96
97  const MCExpr *Expr = MO.getExpr();
98
99  assert(Expr->getKind() == MCExpr::SymbolRef);
100
101  if (MI.getOpcode() == BPF::JAL)
102    // func call name
103    Fixups.push_back(MCFixup::create(0, Expr, FK_SecRel_4));
104  else if (MI.getOpcode() == BPF::LD_imm64)
105    Fixups.push_back(MCFixup::create(0, Expr, FK_SecRel_8));
106  else
107    // bb label
108    Fixups.push_back(MCFixup::create(0, Expr, FK_PCRel_2));
109
110  return 0;
111}
112
113static uint8_t SwapBits(uint8_t Val)
114{
115  return (Val & 0x0F) << 4 | (Val & 0xF0) >> 4;
116}
117
118void BPFMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
119                                         SmallVectorImpl<MCFixup> &Fixups,
120                                         const MCSubtargetInfo &STI) const {
121  verifyInstructionPredicates(MI,
122                              computeAvailableFeatures(STI.getFeatureBits()));
123
124  unsigned Opcode = MI.getOpcode();
125  support::endian::Writer<support::little> LE(OS);
126  support::endian::Writer<support::big> BE(OS);
127
128  if (Opcode == BPF::LD_imm64 || Opcode == BPF::LD_pseudo) {
129    uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
130    LE.write<uint8_t>(Value >> 56);
131    if (IsLittleEndian)
132      LE.write<uint8_t>((Value >> 48) & 0xff);
133    else
134      LE.write<uint8_t>(SwapBits((Value >> 48) & 0xff));
135    LE.write<uint16_t>(0);
136    if (IsLittleEndian)
137      LE.write<uint32_t>(Value & 0xffffFFFF);
138    else
139      BE.write<uint32_t>(Value & 0xffffFFFF);
140
141    const MCOperand &MO = MI.getOperand(1);
142    uint64_t Imm = MO.isImm() ? MO.getImm() : 0;
143    LE.write<uint8_t>(0);
144    LE.write<uint8_t>(0);
145    LE.write<uint16_t>(0);
146    if (IsLittleEndian)
147      LE.write<uint32_t>(Imm >> 32);
148    else
149      BE.write<uint32_t>(Imm >> 32);
150  } else {
151    // Get instruction encoding and emit it
152    uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
153    LE.write<uint8_t>(Value >> 56);
154    if (IsLittleEndian) {
155      LE.write<uint8_t>((Value >> 48) & 0xff);
156      LE.write<uint16_t>((Value >> 32) & 0xffff);
157      LE.write<uint32_t>(Value & 0xffffFFFF);
158    } else {
159      LE.write<uint8_t>(SwapBits((Value >> 48) & 0xff));
160      BE.write<uint16_t>((Value >> 32) & 0xffff);
161      BE.write<uint32_t>(Value & 0xffffFFFF);
162    }
163  }
164}
165
166// Encode BPF Memory Operand
167uint64_t BPFMCCodeEmitter::getMemoryOpValue(const MCInst &MI, unsigned Op,
168                                            SmallVectorImpl<MCFixup> &Fixups,
169                                            const MCSubtargetInfo &STI) const {
170  uint64_t Encoding;
171  const MCOperand Op1 = MI.getOperand(1);
172  assert(Op1.isReg() && "First operand is not register.");
173  Encoding = MRI.getEncodingValue(Op1.getReg());
174  Encoding <<= 16;
175  MCOperand Op2 = MI.getOperand(2);
176  assert(Op2.isImm() && "Second operand is not immediate.");
177  Encoding |= Op2.getImm() & 0xffff;
178  return Encoding;
179}
180
181#define ENABLE_INSTR_PREDICATE_VERIFIER
182#include "BPFGenMCCodeEmitter.inc"
183