MipsELFObjectWriter.cpp revision 864f66085cd9543070ef01b9f7371c110ecd7898 
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);
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  : MCELFObjectTargetWriter(_is64Bit, OSABI, ELF::EM_MIPS,
57                            /*HasRelocationAddend*/ false) {}
58
59MipsELFObjectWriter::~MipsELFObjectWriter() {}
60
61// FIXME: get the real EABI Version from the Subtarget class.
62unsigned MipsELFObjectWriter::getEFlags() const {
63
64  // FIXME: We can't tell if we are PIC (dynamic) or CPIC (static)
65  unsigned Flag = ELF::EF_MIPS_NOREORDER;
66
67  if (is64Bit())
68    Flag |= ELF::EF_MIPS_ARCH_64R2;
69  else
70    Flag |= ELF::EF_MIPS_ARCH_32R2;
71  return Flag;
72}
73
74const MCSymbol *MipsELFObjectWriter::ExplicitRelSym(const MCAssembler &Asm,
75                                                    const MCValue &Target,
76                                                    const MCFragment &F,
77                                                    const MCFixup &Fixup,
78                                                    bool IsPCRel) const {
79  assert(Target.getSymA() && "SymA cannot be 0.");
80  const MCSymbol &Sym = Target.getSymA()->getSymbol().AliasedSymbol();
81
82  if (Sym.getSection().getKind().isMergeableCString() ||
83      Sym.getSection().getKind().isMergeableConst())
84    return &Sym;
85
86  return NULL;
87}
88
89unsigned MipsELFObjectWriter::GetRelocType(const MCValue &Target,
90                                           const MCFixup &Fixup,
91                                           bool IsPCRel,
92                                           bool IsRelocWithSymbol,
93                                           int64_t Addend) const {
94  // determine the type of the relocation
95  unsigned Type = (unsigned)ELF::R_MIPS_NONE;
96  unsigned Kind = (unsigned)Fixup.getKind();
97
98  switch (Kind) {
99  default:
100    llvm_unreachable("invalid fixup kind!");
101  case FK_Data_4:
102    Type = ELF::R_MIPS_32;
103    break;
104  case FK_GPRel_4:
105    Type = ELF::R_MIPS_GPREL32;
106    break;
107  case Mips::fixup_Mips_GPREL16:
108    Type = ELF::R_MIPS_GPREL16;
109    break;
110  case Mips::fixup_Mips_26:
111    Type = ELF::R_MIPS_26;
112    break;
113  case Mips::fixup_Mips_CALL16:
114    Type = ELF::R_MIPS_CALL16;
115    break;
116  case Mips::fixup_Mips_GOT_Global:
117  case Mips::fixup_Mips_GOT_Local:
118    Type = ELF::R_MIPS_GOT16;
119    break;
120  case Mips::fixup_Mips_HI16:
121    Type = ELF::R_MIPS_HI16;
122    break;
123  case Mips::fixup_Mips_LO16:
124    Type = ELF::R_MIPS_LO16;
125    break;
126  case Mips::fixup_Mips_TLSGD:
127    Type = ELF::R_MIPS_TLS_GD;
128    break;
129  case Mips::fixup_Mips_GOTTPREL:
130    Type = ELF::R_MIPS_TLS_GOTTPREL;
131    break;
132  case Mips::fixup_Mips_TPREL_HI:
133    Type = ELF::R_MIPS_TLS_TPREL_HI16;
134    break;
135  case Mips::fixup_Mips_TPREL_LO:
136    Type = ELF::R_MIPS_TLS_TPREL_LO16;
137    break;
138  case Mips::fixup_Mips_TLSLDM:
139    Type = ELF::R_MIPS_TLS_LDM;
140    break;
141  case Mips::fixup_Mips_DTPREL_HI:
142    Type = ELF::R_MIPS_TLS_DTPREL_HI16;
143    break;
144  case Mips::fixup_Mips_DTPREL_LO:
145    Type = ELF::R_MIPS_TLS_DTPREL_LO16;
146    break;
147  case Mips::fixup_Mips_Branch_PCRel:
148  case Mips::fixup_Mips_PC16:
149    Type = ELF::R_MIPS_PC16;
150    break;
151  }
152
153  return Type;
154}
155
156// Return true if R is either a GOT16 against a local symbol or HI16.
157static bool NeedsMatchingLo(const MCAssembler &Asm, const RelEntry &R) {
158  if (!R.Sym)
159    return false;
160
161  MCSymbolData &SD = Asm.getSymbolData(R.Sym->AliasedSymbol());
162
163  return ((R.Reloc.Type == ELF::R_MIPS_GOT16) && !SD.isExternal()) ||
164    (R.Reloc.Type == ELF::R_MIPS_HI16);
165}
166
167static bool HasMatchingLo(const MCAssembler &Asm, RelLsIter I, RelLsIter Last) {
168  if (I == Last)
169    return false;
170
171  RelLsIter Hi = I++;
172
173  return (I->Reloc.Type == ELF::R_MIPS_LO16) && (Hi->Sym == I->Sym) &&
174    (Hi->Offset == I->Offset);
175}
176
177static bool HasSameSymbol(const RelEntry &R0, const RelEntry &R1) {
178  return R0.Sym == R1.Sym;
179}
180
181static int CompareOffset(const RelEntry &R0, const RelEntry &R1) {
182  return (R0.Offset > R1.Offset) ? 1 : ((R0.Offset == R1.Offset) ? 0 : -1);
183}
184
185void MipsELFObjectWriter::sortRelocs(const MCAssembler &Asm,
186                                     std::vector<ELFRelocationEntry> &Relocs) {
187  // Call the defualt function first. Relocations are sorted in descending
188  // order of r_offset.
189  MCELFObjectTargetWriter::sortRelocs(Asm, Relocs);
190
191  RelLs RelocLs;
192  std::vector<RelLsIter> Unmatched;
193
194  // Fill RelocLs. Traverse Relocs backwards so that relocations in RelocLs
195  // are in ascending order of r_offset.
196  for (std::vector<ELFRelocationEntry>::reverse_iterator R = Relocs.rbegin();
197       R != Relocs.rend(); ++R) {
198     std::pair<const MCSymbolRefExpr*, int64_t> P =
199       MipsGetSymAndOffset(*R->Fixup);
200     RelocLs.push_back(RelEntry(*R, P.first ? &P.first->getSymbol() : 0,
201                                P.second));
202  }
203
204  // Get list of unmatched HI16 and GOT16.
205  for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R)
206    if (NeedsMatchingLo(Asm, *R) && !HasMatchingLo(Asm, R, --RelocLs.end()))
207      Unmatched.push_back(R);
208
209  // Insert unmatched HI16 and GOT16 immediately before their matching LO16.
210  for (std::vector<RelLsIter>::iterator U = Unmatched.begin();
211       U != Unmatched.end(); ++U) {
212    RelLsIter LoPos = RelocLs.end(), HiPos = *U;
213    bool MatchedLo = false;
214
215    for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R) {
216      if ((R->Reloc.Type == ELF::R_MIPS_LO16) && HasSameSymbol(*HiPos, *R) &&
217          (CompareOffset(*R, *HiPos) >= 0) &&
218          ((LoPos == RelocLs.end()) || ((CompareOffset(*R, *LoPos) < 0)) ||
219           (!MatchedLo && !CompareOffset(*R, *LoPos))))
220        LoPos = R;
221
222      MatchedLo = NeedsMatchingLo(Asm, *R) &&
223        HasMatchingLo(Asm, R, --RelocLs.end());
224    }
225
226    // If a matching LoPos was found, move HiPos and insert it before LoPos.
227    // Make the offsets of HiPos and LoPos match.
228    if (LoPos != RelocLs.end()) {
229      HiPos->Offset = LoPos->Offset;
230      RelocLs.insert(LoPos, *HiPos);
231      RelocLs.erase(HiPos);
232    }
233  }
234
235  // Put the sorted list back in reverse order.
236  assert(Relocs.size() == RelocLs.size());
237  unsigned I = RelocLs.size();
238
239  for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R)
240    Relocs[--I] = R->Reloc;
241}
242
243MCObjectWriter *llvm::createMipsELFObjectWriter(raw_ostream &OS,
244                                                uint8_t OSABI,
245                                                bool IsLittleEndian,
246                                                bool Is64Bit) {
247  MCELFObjectTargetWriter *MOTW = new MipsELFObjectWriter(Is64Bit, OSABI);
248  return createELFObjectWriter(MOTW, OS, IsLittleEndian);
249}
250