MipsELFObjectWriter.cpp revision 93ee286e8d949147f8df7f093c9bd8529a99102d 
1//===-- MipsELFObjectWriter.cpp - Mips ELF Writer -------------------------===//
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/MipsBaseInfo.h"
11#include "MCTargetDesc/MipsFixupKinds.h"
12#include "MCTargetDesc/MipsMCTargetDesc.h"
13#include "llvm/MC/MCAssembler.h"
14#include "llvm/MC/MCELFObjectWriter.h"
15#include "llvm/MC/MCExpr.h"
16#include "llvm/MC/MCSection.h"
17#include "llvm/MC/MCValue.h"
18#include "llvm/Support/ErrorHandling.h"
19#include <list>
20
21using namespace llvm;
22
23namespace {
24  struct RelEntry {
25    RelEntry(const ELFRelocationEntry &R, const MCSymbol *S, int64_t O) :
26      Reloc(R), Sym(S), Offset(O) {}
27    ELFRelocationEntry Reloc;
28    const MCSymbol *Sym;
29    int64_t Offset;
30  };
31
32  typedef std::list<RelEntry> RelLs;
33  typedef RelLs::iterator RelLsIter;
34
35  class MipsELFObjectWriter : public MCELFObjectTargetWriter {
36  public:
37    MipsELFObjectWriter(bool _is64Bit, uint8_t OSABI, bool _isN64);
38
39    virtual ~MipsELFObjectWriter();
40
41    virtual unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
42                                  bool IsPCRel, bool IsRelocWithSymbol,
43                                  int64_t Addend) const;
44    virtual unsigned getEFlags() const;
45    virtual const MCSymbol *ExplicitRelSym(const MCAssembler &Asm,
46                                           const MCValue &Target,
47                                           const MCFragment &F,
48                                           const MCFixup &Fixup,
49                                           bool IsPCRel) const;
50    virtual void sortRelocs(const MCAssembler &Asm,
51                            std::vector<ELFRelocationEntry> &Relocs);
52  };
53}
54
55MipsELFObjectWriter::MipsELFObjectWriter(bool _is64Bit, uint8_t OSABI,
56                                         bool _isN64)
57  : MCELFObjectTargetWriter(_is64Bit, OSABI, ELF::EM_MIPS,
58                            /*HasRelocationAddend*/ false,
59                            /*IsN64*/ _isN64) {}
60
61MipsELFObjectWriter::~MipsELFObjectWriter() {}
62
63// FIXME: get the real EABI Version from the Subtarget class.
64unsigned MipsELFObjectWriter::getEFlags() const {
65
66  // FIXME: We can't tell if we are PIC (dynamic) or CPIC (static)
67  unsigned Flag = ELF::EF_MIPS_NOREORDER;
68
69  if (is64Bit())
70    Flag |= ELF::EF_MIPS_ARCH_64R2;
71  else
72    Flag |= ELF::EF_MIPS_ARCH_32R2;
73  return Flag;
74}
75
76const MCSymbol *MipsELFObjectWriter::ExplicitRelSym(const MCAssembler &Asm,
77                                                    const MCValue &Target,
78                                                    const MCFragment &F,
79                                                    const MCFixup &Fixup,
80                                                    bool IsPCRel) const {
81  assert(Target.getSymA() && "SymA cannot be 0.");
82  const MCSymbol &Sym = Target.getSymA()->getSymbol().AliasedSymbol();
83
84  if (Sym.getSection().getKind().isMergeableCString() ||
85      Sym.getSection().getKind().isMergeableConst())
86    return &Sym;
87
88  return NULL;
89}
90
91unsigned MipsELFObjectWriter::GetRelocType(const MCValue &Target,
92                                           const MCFixup &Fixup,
93                                           bool IsPCRel,
94                                           bool IsRelocWithSymbol,
95                                           int64_t Addend) const {
96  // determine the type of the relocation
97  unsigned Type = (unsigned)ELF::R_MIPS_NONE;
98  unsigned Kind = (unsigned)Fixup.getKind();
99
100  switch (Kind) {
101  default:
102    llvm_unreachable("invalid fixup kind!");
103  case FK_Data_4:
104    Type = ELF::R_MIPS_32;
105    break;
106  case FK_GPRel_4:
107    Type = ELF::R_MIPS_GPREL32;
108    break;
109  case Mips::fixup_Mips_GPREL16:
110    Type = ELF::R_MIPS_GPREL16;
111    break;
112  case Mips::fixup_Mips_26:
113    Type = ELF::R_MIPS_26;
114    break;
115  case Mips::fixup_Mips_CALL16:
116    Type = ELF::R_MIPS_CALL16;
117    break;
118  case Mips::fixup_Mips_GOT_Global:
119  case Mips::fixup_Mips_GOT_Local:
120    Type = ELF::R_MIPS_GOT16;
121    break;
122  case Mips::fixup_Mips_HI16:
123    Type = ELF::R_MIPS_HI16;
124    break;
125  case Mips::fixup_Mips_LO16:
126    Type = ELF::R_MIPS_LO16;
127    break;
128  case Mips::fixup_Mips_TLSGD:
129    Type = ELF::R_MIPS_TLS_GD;
130    break;
131  case Mips::fixup_Mips_GOTTPREL:
132    Type = ELF::R_MIPS_TLS_GOTTPREL;
133    break;
134  case Mips::fixup_Mips_TPREL_HI:
135    Type = ELF::R_MIPS_TLS_TPREL_HI16;
136    break;
137  case Mips::fixup_Mips_TPREL_LO:
138    Type = ELF::R_MIPS_TLS_TPREL_LO16;
139    break;
140  case Mips::fixup_Mips_TLSLDM:
141    Type = ELF::R_MIPS_TLS_LDM;
142    break;
143  case Mips::fixup_Mips_DTPREL_HI:
144    Type = ELF::R_MIPS_TLS_DTPREL_HI16;
145    break;
146  case Mips::fixup_Mips_DTPREL_LO:
147    Type = ELF::R_MIPS_TLS_DTPREL_LO16;
148    break;
149  case Mips::fixup_Mips_Branch_PCRel:
150  case Mips::fixup_Mips_PC16:
151    Type = ELF::R_MIPS_PC16;
152    break;
153  }
154  return Type;
155}
156
157// Return true if R is either a GOT16 against a local symbol or HI16.
158static bool NeedsMatchingLo(const MCAssembler &Asm, const RelEntry &R) {
159  if (!R.Sym)
160    return false;
161
162  MCSymbolData &SD = Asm.getSymbolData(R.Sym->AliasedSymbol());
163
164  return ((R.Reloc.Type == ELF::R_MIPS_GOT16) && !SD.isExternal()) ||
165    (R.Reloc.Type == ELF::R_MIPS_HI16);
166}
167
168static bool HasMatchingLo(const MCAssembler &Asm, RelLsIter I, RelLsIter Last) {
169  if (I == Last)
170    return false;
171
172  RelLsIter Hi = I++;
173
174  return (I->Reloc.Type == ELF::R_MIPS_LO16) && (Hi->Sym == I->Sym) &&
175    (Hi->Offset == I->Offset);
176}
177
178static bool HasSameSymbol(const RelEntry &R0, const RelEntry &R1) {
179  return R0.Sym == R1.Sym;
180}
181
182static int CompareOffset(const RelEntry &R0, const RelEntry &R1) {
183  return (R0.Offset > R1.Offset) ? 1 : ((R0.Offset == R1.Offset) ? 0 : -1);
184}
185
186void MipsELFObjectWriter::sortRelocs(const MCAssembler &Asm,
187                                     std::vector<ELFRelocationEntry> &Relocs) {
188  // Call the default function first. Relocations are sorted in descending
189  // order of r_offset.
190  MCELFObjectTargetWriter::sortRelocs(Asm, Relocs);
191
192  RelLs RelocLs;
193  std::vector<RelLsIter> Unmatched;
194
195  // Fill RelocLs. Traverse Relocs backwards so that relocations in RelocLs
196  // are in ascending order of r_offset.
197  for (std::vector<ELFRelocationEntry>::reverse_iterator R = Relocs.rbegin();
198       R != Relocs.rend(); ++R) {
199     std::pair<const MCSymbolRefExpr*, int64_t> P =
200       MipsGetSymAndOffset(*R->Fixup);
201     RelocLs.push_back(RelEntry(*R, P.first ? &P.first->getSymbol() : 0,
202                                P.second));
203  }
204
205  // Get list of unmatched HI16 and GOT16.
206  for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R)
207    if (NeedsMatchingLo(Asm, *R) && !HasMatchingLo(Asm, R, --RelocLs.end()))
208      Unmatched.push_back(R);
209
210  // Insert unmatched HI16 and GOT16 immediately before their matching LO16.
211  for (std::vector<RelLsIter>::iterator U = Unmatched.begin();
212       U != Unmatched.end(); ++U) {
213    RelLsIter LoPos = RelocLs.end(), HiPos = *U;
214    bool MatchedLo = false;
215
216    for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R) {
217      if ((R->Reloc.Type == ELF::R_MIPS_LO16) && HasSameSymbol(*HiPos, *R) &&
218          (CompareOffset(*R, *HiPos) >= 0) &&
219          ((LoPos == RelocLs.end()) || ((CompareOffset(*R, *LoPos) < 0)) ||
220           (!MatchedLo && !CompareOffset(*R, *LoPos))))
221        LoPos = R;
222
223      MatchedLo = NeedsMatchingLo(Asm, *R) &&
224        HasMatchingLo(Asm, R, --RelocLs.end());
225    }
226
227    // If a matching LoPos was found, move HiPos and insert it before LoPos.
228    // Make the offsets of HiPos and LoPos match.
229    if (LoPos != RelocLs.end()) {
230      HiPos->Offset = LoPos->Offset;
231      RelocLs.insert(LoPos, *HiPos);
232      RelocLs.erase(HiPos);
233    }
234  }
235
236  // Put the sorted list back in reverse order.
237  assert(Relocs.size() == RelocLs.size());
238  unsigned I = RelocLs.size();
239
240  for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R)
241    Relocs[--I] = R->Reloc;
242}
243
244MCObjectWriter *llvm::createMipsELFObjectWriter(raw_ostream &OS,
245                                                uint8_t OSABI,
246                                                bool IsLittleEndian,
247                                                bool Is64Bit) {
248  MCELFObjectTargetWriter *MOTW = new MipsELFObjectWriter(Is64Bit, OSABI,
249                                                (Is64Bit) ? true : false);
250  return createELFObjectWriter(MOTW, OS, IsLittleEndian);
251}
252