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      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 
     21 using namespace llvm;
     22 
     23 namespace {
     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                         bool _isN64, bool IsLittleEndian);
     39 
     40     virtual ~MipsELFObjectWriter();
     41 
     42     virtual unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
     43                                   bool IsPCRel, bool IsRelocWithSymbol,
     44                                   int64_t Addend) 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 
     55 MipsELFObjectWriter::MipsELFObjectWriter(bool _is64Bit, uint8_t OSABI,
     56                                          bool _isN64, bool IsLittleEndian)
     57   : MCELFObjectTargetWriter(_is64Bit, OSABI, ELF::EM_MIPS,
     58                             /*HasRelocationAddend*/ (_isN64) ? true : false,
     59                             /*IsN64*/ _isN64) {}
     60 
     61 MipsELFObjectWriter::~MipsELFObjectWriter() {}
     62 
     63 const MCSymbol *MipsELFObjectWriter::ExplicitRelSym(const MCAssembler &Asm,
     64                                                     const MCValue &Target,
     65                                                     const MCFragment &F,
     66                                                     const MCFixup &Fixup,
     67                                                     bool IsPCRel) const {
     68   assert(Target.getSymA() && "SymA cannot be 0.");
     69   const MCSymbol &Sym = Target.getSymA()->getSymbol().AliasedSymbol();
     70 
     71   if (Sym.getSection().getKind().isMergeableCString() ||
     72       Sym.getSection().getKind().isMergeableConst())
     73     return &Sym;
     74 
     75   return NULL;
     76 }
     77 
     78 unsigned MipsELFObjectWriter::GetRelocType(const MCValue &Target,
     79                                            const MCFixup &Fixup,
     80                                            bool IsPCRel,
     81                                            bool IsRelocWithSymbol,
     82                                            int64_t Addend) const {
     83   // determine the type of the relocation
     84   unsigned Type = (unsigned)ELF::R_MIPS_NONE;
     85   unsigned Kind = (unsigned)Fixup.getKind();
     86 
     87   switch (Kind) {
     88   default:
     89     llvm_unreachable("invalid fixup kind!");
     90   case FK_Data_4:
     91     Type = ELF::R_MIPS_32;
     92     break;
     93   case FK_Data_8:
     94     Type = ELF::R_MIPS_64;
     95     break;
     96   case FK_GPRel_4:
     97     if (isN64()) {
     98       Type = setRType((unsigned)ELF::R_MIPS_GPREL32, Type);
     99       Type = setRType2((unsigned)ELF::R_MIPS_64, Type);
    100       Type = setRType3((unsigned)ELF::R_MIPS_NONE, Type);
    101     }
    102     else
    103       Type = ELF::R_MIPS_GPREL32;
    104     break;
    105   case Mips::fixup_Mips_GPREL16:
    106     Type = ELF::R_MIPS_GPREL16;
    107     break;
    108   case Mips::fixup_Mips_26:
    109     Type = ELF::R_MIPS_26;
    110     break;
    111   case Mips::fixup_Mips_CALL16:
    112     Type = ELF::R_MIPS_CALL16;
    113     break;
    114   case Mips::fixup_Mips_GOT_Global:
    115   case Mips::fixup_Mips_GOT_Local:
    116     Type = ELF::R_MIPS_GOT16;
    117     break;
    118   case Mips::fixup_Mips_HI16:
    119     Type = ELF::R_MIPS_HI16;
    120     break;
    121   case Mips::fixup_Mips_LO16:
    122     Type = ELF::R_MIPS_LO16;
    123     break;
    124   case Mips::fixup_Mips_TLSGD:
    125     Type = ELF::R_MIPS_TLS_GD;
    126     break;
    127   case Mips::fixup_Mips_GOTTPREL:
    128     Type = ELF::R_MIPS_TLS_GOTTPREL;
    129     break;
    130   case Mips::fixup_Mips_TPREL_HI:
    131     Type = ELF::R_MIPS_TLS_TPREL_HI16;
    132     break;
    133   case Mips::fixup_Mips_TPREL_LO:
    134     Type = ELF::R_MIPS_TLS_TPREL_LO16;
    135     break;
    136   case Mips::fixup_Mips_TLSLDM:
    137     Type = ELF::R_MIPS_TLS_LDM;
    138     break;
    139   case Mips::fixup_Mips_DTPREL_HI:
    140     Type = ELF::R_MIPS_TLS_DTPREL_HI16;
    141     break;
    142   case Mips::fixup_Mips_DTPREL_LO:
    143     Type = ELF::R_MIPS_TLS_DTPREL_LO16;
    144     break;
    145   case Mips::fixup_Mips_Branch_PCRel:
    146   case Mips::fixup_Mips_PC16:
    147     Type = ELF::R_MIPS_PC16;
    148     break;
    149   case Mips::fixup_Mips_GOT_PAGE:
    150     Type = ELF::R_MIPS_GOT_PAGE;
    151     break;
    152   case Mips::fixup_Mips_GOT_OFST:
    153     Type = ELF::R_MIPS_GOT_OFST;
    154     break;
    155   case Mips::fixup_Mips_GOT_DISP:
    156     Type = ELF::R_MIPS_GOT_DISP;
    157     break;
    158   case Mips::fixup_Mips_GPOFF_HI:
    159     Type = setRType((unsigned)ELF::R_MIPS_GPREL16, Type);
    160     Type = setRType2((unsigned)ELF::R_MIPS_SUB, Type);
    161     Type = setRType3((unsigned)ELF::R_MIPS_HI16, Type);
    162     break;
    163   case Mips::fixup_Mips_GPOFF_LO:
    164     Type = setRType((unsigned)ELF::R_MIPS_GPREL16, Type);
    165     Type = setRType2((unsigned)ELF::R_MIPS_SUB, Type);
    166     Type = setRType3((unsigned)ELF::R_MIPS_LO16, Type);
    167     break;
    168   case Mips::fixup_Mips_HIGHER:
    169     Type = ELF::R_MIPS_HIGHER;
    170     break;
    171   case Mips::fixup_Mips_HIGHEST:
    172     Type = ELF::R_MIPS_HIGHEST;
    173     break;
    174   case Mips::fixup_Mips_GOT_HI16:
    175     Type = ELF::R_MIPS_GOT_HI16;
    176     break;
    177   case Mips::fixup_Mips_GOT_LO16:
    178     Type = ELF::R_MIPS_GOT_LO16;
    179     break;
    180   case Mips::fixup_Mips_CALL_HI16:
    181     Type = ELF::R_MIPS_CALL_HI16;
    182     break;
    183   case Mips::fixup_Mips_CALL_LO16:
    184     Type = ELF::R_MIPS_CALL_LO16;
    185     break;
    186   }
    187   return Type;
    188 }
    189 
    190 // Return true if R is either a GOT16 against a local symbol or HI16.
    191 static bool NeedsMatchingLo(const MCAssembler &Asm, const RelEntry &R) {
    192   if (!R.Sym)
    193     return false;
    194 
    195   MCSymbolData &SD = Asm.getSymbolData(R.Sym->AliasedSymbol());
    196 
    197   return ((R.Reloc.Type == ELF::R_MIPS_GOT16) && !SD.isExternal()) ||
    198     (R.Reloc.Type == ELF::R_MIPS_HI16);
    199 }
    200 
    201 static bool HasMatchingLo(const MCAssembler &Asm, RelLsIter I, RelLsIter Last) {
    202   if (I == Last)
    203     return false;
    204 
    205   RelLsIter Hi = I++;
    206 
    207   return (I->Reloc.Type == ELF::R_MIPS_LO16) && (Hi->Sym == I->Sym) &&
    208     (Hi->Offset == I->Offset);
    209 }
    210 
    211 static bool HasSameSymbol(const RelEntry &R0, const RelEntry &R1) {
    212   return R0.Sym == R1.Sym;
    213 }
    214 
    215 static int CompareOffset(const RelEntry &R0, const RelEntry &R1) {
    216   return (R0.Offset > R1.Offset) ? 1 : ((R0.Offset == R1.Offset) ? 0 : -1);
    217 }
    218 
    219 void MipsELFObjectWriter::sortRelocs(const MCAssembler &Asm,
    220                                      std::vector<ELFRelocationEntry> &Relocs) {
    221   // Call the default function first. Relocations are sorted in descending
    222   // order of r_offset.
    223   MCELFObjectTargetWriter::sortRelocs(Asm, Relocs);
    224 
    225   RelLs RelocLs;
    226   std::vector<RelLsIter> Unmatched;
    227 
    228   // Fill RelocLs. Traverse Relocs backwards so that relocations in RelocLs
    229   // are in ascending order of r_offset.
    230   for (std::vector<ELFRelocationEntry>::reverse_iterator R = Relocs.rbegin();
    231        R != Relocs.rend(); ++R) {
    232      std::pair<const MCSymbolRefExpr*, int64_t> P =
    233        MipsGetSymAndOffset(*R->Fixup);
    234      RelocLs.push_back(RelEntry(*R, P.first ? &P.first->getSymbol() : 0,
    235                                 P.second));
    236   }
    237 
    238   // Get list of unmatched HI16 and GOT16.
    239   for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R)
    240     if (NeedsMatchingLo(Asm, *R) && !HasMatchingLo(Asm, R, --RelocLs.end()))
    241       Unmatched.push_back(R);
    242 
    243   // Insert unmatched HI16 and GOT16 immediately before their matching LO16.
    244   for (std::vector<RelLsIter>::iterator U = Unmatched.begin();
    245        U != Unmatched.end(); ++U) {
    246     RelLsIter LoPos = RelocLs.end(), HiPos = *U;
    247     bool MatchedLo = false;
    248 
    249     for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R) {
    250       if ((R->Reloc.Type == ELF::R_MIPS_LO16) && HasSameSymbol(*HiPos, *R) &&
    251           (CompareOffset(*R, *HiPos) >= 0) &&
    252           ((LoPos == RelocLs.end()) || ((CompareOffset(*R, *LoPos) < 0)) ||
    253            (!MatchedLo && !CompareOffset(*R, *LoPos))))
    254         LoPos = R;
    255 
    256       MatchedLo = NeedsMatchingLo(Asm, *R) &&
    257         HasMatchingLo(Asm, R, --RelocLs.end());
    258     }
    259 
    260     // If a matching LoPos was found, move HiPos and insert it before LoPos.
    261     // Make the offsets of HiPos and LoPos match.
    262     if (LoPos != RelocLs.end()) {
    263       HiPos->Offset = LoPos->Offset;
    264       RelocLs.insert(LoPos, *HiPos);
    265       RelocLs.erase(HiPos);
    266     }
    267   }
    268 
    269   // Put the sorted list back in reverse order.
    270   assert(Relocs.size() == RelocLs.size());
    271   unsigned I = RelocLs.size();
    272 
    273   for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R)
    274     Relocs[--I] = R->Reloc;
    275 }
    276 
    277 MCObjectWriter *llvm::createMipsELFObjectWriter(raw_ostream &OS,
    278                                                 uint8_t OSABI,
    279                                                 bool IsLittleEndian,
    280                                                 bool Is64Bit) {
    281   MCELFObjectTargetWriter *MOTW = new MipsELFObjectWriter(Is64Bit, OSABI,
    282                                                 (Is64Bit) ? true : false,
    283                                                 IsLittleEndian);
    284   return createELFObjectWriter(MOTW, OS, IsLittleEndian);
    285 }
    286