1//===-- SystemZMCAsmBackend.cpp - SystemZ assembler backend ---------------===//
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#include "MCTargetDesc/SystemZMCTargetDesc.h"
11#include "MCTargetDesc/SystemZMCFixups.h"
12#include "llvm/MC/MCAsmBackend.h"
13#include "llvm/MC/MCELFObjectWriter.h"
14#include "llvm/MC/MCFixupKindInfo.h"
15#include "llvm/MC/MCInst.h"
16#include "llvm/MC/MCObjectWriter.h"
17
18using namespace llvm;
19
20// Value is a fully-resolved relocation value: Symbol + Addend [- Pivot].
21// Return the bits that should be installed in a relocation field for
22// fixup kind Kind.
23static uint64_t extractBitsForFixup(MCFixupKind Kind, uint64_t Value) {
24  if (Kind < FirstTargetFixupKind)
25    return Value;
26
27  switch (unsigned(Kind)) {
28  case SystemZ::FK_390_PC16DBL:
29  case SystemZ::FK_390_PC32DBL:
30  case SystemZ::FK_390_PLT16DBL:
31  case SystemZ::FK_390_PLT32DBL:
32    return (int64_t)Value / 2;
33  }
34
35  llvm_unreachable("Unknown fixup kind!");
36}
37
38// If Opcode can be relaxed, return the relaxed form, otherwise return 0.
39static unsigned getRelaxedOpcode(unsigned Opcode) {
40  switch (Opcode) {
41  case SystemZ::BRC:  return SystemZ::BRCL;
42  case SystemZ::J:    return SystemZ::JG;
43  case SystemZ::BRAS: return SystemZ::BRASL;
44  }
45  return 0;
46}
47
48namespace {
49class SystemZMCAsmBackend : public MCAsmBackend {
50  uint8_t OSABI;
51public:
52  SystemZMCAsmBackend(uint8_t osABI)
53    : OSABI(osABI) {}
54
55  // Override MCAsmBackend
56  virtual unsigned getNumFixupKinds() const LLVM_OVERRIDE {
57    return SystemZ::NumTargetFixupKinds;
58  }
59  virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const
60    LLVM_OVERRIDE;
61  virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
62                          uint64_t Value) const LLVM_OVERRIDE;
63  virtual bool mayNeedRelaxation(const MCInst &Inst) const LLVM_OVERRIDE;
64  virtual bool fixupNeedsRelaxation(const MCFixup &Fixup,
65                                    uint64_t Value,
66                                    const MCRelaxableFragment *Fragment,
67                                    const MCAsmLayout &Layout) const
68    LLVM_OVERRIDE;
69  virtual void relaxInstruction(const MCInst &Inst,
70                                MCInst &Res) const LLVM_OVERRIDE;
71  virtual bool writeNopData(uint64_t Count,
72                            MCObjectWriter *OW) const LLVM_OVERRIDE;
73  virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const
74    LLVM_OVERRIDE {
75    return createSystemZObjectWriter(OS, OSABI);
76  }
77  virtual bool doesSectionRequireSymbols(const MCSection &Section) const
78    LLVM_OVERRIDE {
79    return false;
80  }
81};
82} // end anonymous namespace
83
84const MCFixupKindInfo &
85SystemZMCAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
86  const static MCFixupKindInfo Infos[SystemZ::NumTargetFixupKinds] = {
87    { "FK_390_PC16DBL",  0, 16, MCFixupKindInfo::FKF_IsPCRel },
88    { "FK_390_PC32DBL",  0, 32, MCFixupKindInfo::FKF_IsPCRel },
89    { "FK_390_PLT16DBL", 0, 16, MCFixupKindInfo::FKF_IsPCRel },
90    { "FK_390_PLT32DBL", 0, 32, MCFixupKindInfo::FKF_IsPCRel }
91  };
92
93  if (Kind < FirstTargetFixupKind)
94    return MCAsmBackend::getFixupKindInfo(Kind);
95
96  assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
97         "Invalid kind!");
98  return Infos[Kind - FirstTargetFixupKind];
99}
100
101void SystemZMCAsmBackend::applyFixup(const MCFixup &Fixup, char *Data,
102                                     unsigned DataSize, uint64_t Value) const {
103  MCFixupKind Kind = Fixup.getKind();
104  unsigned Offset = Fixup.getOffset();
105  unsigned Size = (getFixupKindInfo(Kind).TargetSize + 7) / 8;
106
107  assert(Offset + Size <= DataSize && "Invalid fixup offset!");
108
109  // Big-endian insertion of Size bytes.
110  Value = extractBitsForFixup(Kind, Value);
111  unsigned ShiftValue = (Size * 8) - 8;
112  for (unsigned I = 0; I != Size; ++I) {
113    Data[Offset + I] |= uint8_t(Value >> ShiftValue);
114    ShiftValue -= 8;
115  }
116}
117
118bool SystemZMCAsmBackend::mayNeedRelaxation(const MCInst &Inst) const {
119  return getRelaxedOpcode(Inst.getOpcode()) != 0;
120}
121
122bool
123SystemZMCAsmBackend::fixupNeedsRelaxation(const MCFixup &Fixup,
124                                          uint64_t Value,
125                                          const MCRelaxableFragment *Fragment,
126                                          const MCAsmLayout &Layout) const {
127  // At the moment we just need to relax 16-bit fields to wider fields.
128  Value = extractBitsForFixup(Fixup.getKind(), Value);
129  return (int16_t)Value != (int64_t)Value;
130}
131
132void SystemZMCAsmBackend::relaxInstruction(const MCInst &Inst,
133                                           MCInst &Res) const {
134  unsigned Opcode = getRelaxedOpcode(Inst.getOpcode());
135  assert(Opcode && "Unexpected insn to relax");
136  Res = Inst;
137  Res.setOpcode(Opcode);
138}
139
140bool SystemZMCAsmBackend::writeNopData(uint64_t Count,
141                                       MCObjectWriter *OW) const {
142  for (uint64_t I = 0; I != Count; ++I)
143    OW->Write8(7);
144  return true;
145}
146
147MCAsmBackend *llvm::createSystemZMCAsmBackend(const Target &T, StringRef TT,
148                                              StringRef CPU) {
149  uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(Triple(TT).getOS());
150  return new SystemZMCAsmBackend(OSABI);
151}
152