SystemZMCAsmBackend.cpp revision 44b486ed78c60b50aa14d4eed92ee828d4d44293 
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 is a relaxable interprocedural reference, return the relaxed form,
39// otherwise return 0.
40static unsigned getRelaxedOpcode(unsigned Opcode) {
41  switch (Opcode) {
42  case SystemZ::BRAS: return SystemZ::BRASL;
43  }
44  return 0;
45}
46
47namespace {
48class SystemZMCAsmBackend : public MCAsmBackend {
49  uint8_t OSABI;
50public:
51  SystemZMCAsmBackend(uint8_t osABI)
52    : OSABI(osABI) {}
53
54  // Override MCAsmBackend
55  virtual unsigned getNumFixupKinds() const LLVM_OVERRIDE {
56    return SystemZ::NumTargetFixupKinds;
57  }
58  virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const
59    LLVM_OVERRIDE;
60  virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
61                          uint64_t Value) const LLVM_OVERRIDE;
62  virtual bool mayNeedRelaxation(const MCInst &Inst) const LLVM_OVERRIDE;
63  virtual bool fixupNeedsRelaxation(const MCFixup &Fixup,
64                                    uint64_t Value,
65                                    const MCRelaxableFragment *Fragment,
66                                    const MCAsmLayout &Layout) const
67    LLVM_OVERRIDE;
68  virtual void relaxInstruction(const MCInst &Inst,
69                                MCInst &Res) const LLVM_OVERRIDE;
70  virtual bool writeNopData(uint64_t Count,
71                            MCObjectWriter *OW) const LLVM_OVERRIDE;
72  virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const
73    LLVM_OVERRIDE {
74    return createSystemZObjectWriter(OS, OSABI);
75  }
76  virtual bool doesSectionRequireSymbols(const MCSection &Section) const
77    LLVM_OVERRIDE {
78    return false;
79  }
80};
81} // end anonymous namespace
82
83const MCFixupKindInfo &
84SystemZMCAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
85  const static MCFixupKindInfo Infos[SystemZ::NumTargetFixupKinds] = {
86    { "FK_390_PC16DBL",  0, 16, MCFixupKindInfo::FKF_IsPCRel },
87    { "FK_390_PC32DBL",  0, 32, MCFixupKindInfo::FKF_IsPCRel },
88    { "FK_390_PLT16DBL", 0, 16, MCFixupKindInfo::FKF_IsPCRel },
89    { "FK_390_PLT32DBL", 0, 32, MCFixupKindInfo::FKF_IsPCRel }
90  };
91
92  if (Kind < FirstTargetFixupKind)
93    return MCAsmBackend::getFixupKindInfo(Kind);
94
95  assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
96         "Invalid kind!");
97  return Infos[Kind - FirstTargetFixupKind];
98}
99
100void SystemZMCAsmBackend::applyFixup(const MCFixup &Fixup, char *Data,
101                                     unsigned DataSize, uint64_t Value) const {
102  MCFixupKind Kind = Fixup.getKind();
103  unsigned Offset = Fixup.getOffset();
104  unsigned Size = (getFixupKindInfo(Kind).TargetSize + 7) / 8;
105
106  assert(Offset + Size <= DataSize && "Invalid fixup offset!");
107
108  // Big-endian insertion of Size bytes.
109  Value = extractBitsForFixup(Kind, Value);
110  unsigned ShiftValue = (Size * 8) - 8;
111  for (unsigned I = 0; I != Size; ++I) {
112    Data[Offset + I] |= uint8_t(Value >> ShiftValue);
113    ShiftValue -= 8;
114  }
115}
116
117bool SystemZMCAsmBackend::mayNeedRelaxation(const MCInst &Inst) const {
118  return getRelaxedOpcode(Inst.getOpcode()) != 0;
119}
120
121bool
122SystemZMCAsmBackend::fixupNeedsRelaxation(const MCFixup &Fixup,
123                                          uint64_t Value,
124                                          const MCRelaxableFragment *Fragment,
125                                          const MCAsmLayout &Layout) const {
126  // At the moment we just need to relax 16-bit fields to wider fields.
127  Value = extractBitsForFixup(Fixup.getKind(), Value);
128  return (int16_t)Value != (int64_t)Value;
129}
130
131void SystemZMCAsmBackend::relaxInstruction(const MCInst &Inst,
132                                           MCInst &Res) const {
133  unsigned Opcode = getRelaxedOpcode(Inst.getOpcode());
134  assert(Opcode && "Unexpected insn to relax");
135  Res = Inst;
136  Res.setOpcode(Opcode);
137}
138
139bool SystemZMCAsmBackend::writeNopData(uint64_t Count,
140                                       MCObjectWriter *OW) const {
141  for (uint64_t I = 0; I != Count; ++I)
142    OW->Write8(7);
143  return true;
144}
145
146MCAsmBackend *llvm::createSystemZMCAsmBackend(const Target &T, StringRef TT,
147                                              StringRef CPU) {
148  uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(Triple(TT).getOS());
149  return new SystemZMCAsmBackend(OSABI);
150}
151