lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp

   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/MipsFixupKinds.h"
  11 #include "MCTargetDesc/MipsMCTargetDesc.h"
  12 #include "llvm/ADT/STLExtras.h"
  13 #include "llvm/BinaryFormat/ELF.h"
  14 #include "llvm/MC/MCContext.h"
  15 #include "llvm/MC/MCELFObjectWriter.h"
  16 #include "llvm/MC/MCFixup.h"
  17 #include "llvm/MC/MCObjectWriter.h"
  18 #include "llvm/MC/MCSymbolELF.h"
  19 #include "llvm/Support/Casting.h"
  20 #include "llvm/Support/Compiler.h"
  21 #include "llvm/Support/Debug.h"
  22 #include "llvm/Support/ErrorHandling.h"
  23 #include "llvm/Support/MathExtras.h"
  24 #include "llvm/Support/raw_ostream.h"
  25 #include <algorithm>
  26 #include <cassert>
  27 #include <cstdint>
  28 #include <iterator>
  29 #include <list>
  30 #include <utility>
  31
  32 #define DEBUG_TYPE "mips-elf-object-writer"
  33
  34 using namespace llvm;
  35
  36 namespace {
  37
  38 /// Holds additional information needed by the relocation ordering algorithm.
  39 struct MipsRelocationEntry {
  40   const ELFRelocationEntry R; ///< The relocation.
  41   bool Matched = false;       ///< Is this relocation part of a match.
  42
  43   MipsRelocationEntry(const ELFRelocationEntry &R) : R(R) {}
  44
  45   void print(raw_ostream &Out) const {
  46     R.print(Out);
  47     Out << ", Matched=" << Matched;
  48   }
  49 };
  50
  51 #ifndef NDEBUG
  52 raw_ostream &operator<<(raw_ostream &OS, const MipsRelocationEntry &RHS) {
  53   RHS.print(OS);
  54   return OS;
  55 }
  56 #endif
  57
  58 class MipsELFObjectWriter : public MCELFObjectTargetWriter {
  59 public:
  60   MipsELFObjectWriter(uint8_t OSABI, bool HasRelocationAddend, bool Is64);
  61
  62   ~MipsELFObjectWriter() override = default;
  63
  64   unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
  65                         const MCFixup &Fixup, bool IsPCRel) const override;
  66   bool needsRelocateWithSymbol(const MCSymbol &Sym,
  67                                unsigned Type) const override;
  68   void sortRelocs(const MCAssembler &Asm,
  69                   std::vector<ELFRelocationEntry> &Relocs) override;
  70 };
  71
  72 /// The possible results of the Predicate function used by find_best.
  73 enum FindBestPredicateResult {
  74   FindBest_NoMatch = 0,  ///< The current element is not a match.
  75   FindBest_Match,        ///< The current element is a match but better ones are
  76                          ///  possible.
  77   FindBest_PerfectMatch, ///< The current element is an unbeatable match.
  78 };
  79
  80 } // end anonymous namespace
  81
  82 /// Copy elements in the range [First, Last) to d1 when the predicate is true or
  83 /// d2 when the predicate is false. This is essentially both std::copy_if and
  84 /// std::remove_copy_if combined into a single pass.
  85 template <class InputIt, class OutputIt1, class OutputIt2, class UnaryPredicate>
  86 static std::pair<OutputIt1, OutputIt2> copy_if_else(InputIt First, InputIt Last,
  87                                                     OutputIt1 d1, OutputIt2 d2,
  88                                                     UnaryPredicate Predicate) {
  89   for (InputIt I = First; I != Last; ++I) {
  90     if (Predicate(*I)) {
  91       *d1 = *I;
  92       d1++;
  93     } else {
  94       *d2 = *I;
  95       d2++;
  96     }
  97   }
  98
  99   return std::make_pair(d1, d2);
 100 }
 101
 102 /// Find the best match in the range [First, Last).
 103 ///
 104 /// An element matches when Predicate(X) returns FindBest_Match or
 105 /// FindBest_PerfectMatch. A value of FindBest_PerfectMatch also terminates
 106 /// the search. BetterThan(A, B) is a comparator that returns true when A is a
 107 /// better match than B. The return value is the position of the best match.
 108 ///
 109 /// This is similar to std::find_if but finds the best of multiple possible
 110 /// matches.
 111 template <class InputIt, class UnaryPredicate, class Comparator>
 112 static InputIt find_best(InputIt First, InputIt Last, UnaryPredicate Predicate,
 113                          Comparator BetterThan) {
 114   InputIt Best = Last;
 115
 116   for (InputIt I = First; I != Last; ++I) {
 117     unsigned Matched = Predicate(*I);
 118     if (Matched != FindBest_NoMatch) {
 119       LLVM_DEBUG(dbgs() << std::distance(First, I) << " is a match (";
 120                  I->print(dbgs()); dbgs() << ")\n");
 121       if (Best == Last || BetterThan(*I, *Best)) {
 122         LLVM_DEBUG(dbgs() << ".. and it beats the last one\n");
 123         Best = I;
 124       }
 125     }
 126     if (Matched == FindBest_PerfectMatch) {
 127       LLVM_DEBUG(dbgs() << ".. and it is unbeatable\n");
 128       break;
 129     }
 130   }
 131
 132   return Best;
 133 }
 134
 135 /// Determine the low relocation that matches the given relocation.
 136 /// If the relocation does not need a low relocation then the return value
 137 /// is ELF::R_MIPS_NONE.
 138 ///
 139 /// The relocations that need a matching low part are
 140 /// R_(MIPS|MICROMIPS|MIPS16)_HI16 for all symbols and
 141 /// R_(MIPS|MICROMIPS|MIPS16)_GOT16 for local symbols only.
 142 static unsigned getMatchingLoType(const ELFRelocationEntry &Reloc) {
 143   unsigned Type = Reloc.Type;
 144   if (Type == ELF::R_MIPS_HI16)
 145     return ELF::R_MIPS_LO16;
 146   if (Type == ELF::R_MICROMIPS_HI16)
 147     return ELF::R_MICROMIPS_LO16;
 148   if (Type == ELF::R_MIPS16_HI16)
 149     return ELF::R_MIPS16_LO16;
 150
 151   if (Reloc.OriginalSymbol &&
 152       Reloc.OriginalSymbol->getBinding() != ELF::STB_LOCAL)
 153     return ELF::R_MIPS_NONE;
 154
 155   if (Type == ELF::R_MIPS_GOT16)
 156     return ELF::R_MIPS_LO16;
 157   if (Type == ELF::R_MICROMIPS_GOT16)
 158     return ELF::R_MICROMIPS_LO16;
 159   if (Type == ELF::R_MIPS16_GOT16)
 160     return ELF::R_MIPS16_LO16;
 161
 162   return ELF::R_MIPS_NONE;
 163 }
 164
 165 /// Determine whether a relocation (X) matches the one given in R.
 166 ///
 167 /// A relocation matches if:
 168 /// - It's type matches that of a corresponding low part. This is provided in
 169 ///   MatchingType for efficiency.
 170 /// - It's based on the same symbol.
 171 /// - It's offset of greater or equal to that of the one given in R.
 172 ///   It should be noted that this rule assumes the programmer does not use
 173 ///   offsets that exceed the alignment of the symbol. The carry-bit will be
 174 ///   incorrect if this is not true.
 175 ///
 176 /// A matching relocation is unbeatable if:
 177 /// - It is not already involved in a match.
 178 /// - It's offset is exactly that of the one given in R.
 179 static FindBestPredicateResult isMatchingReloc(const MipsRelocationEntry &X,
 180                                                const ELFRelocationEntry &R,
 181                                                unsigned MatchingType) {
 182   if (X.R.Type == MatchingType && X.R.OriginalSymbol == R.OriginalSymbol) {
 183     if (!X.Matched &&
 184         X.R.OriginalAddend == R.OriginalAddend)
 185       return FindBest_PerfectMatch;
 186     else if (X.R.OriginalAddend >= R.OriginalAddend)
 187       return FindBest_Match;
 188   }
 189   return FindBest_NoMatch;
 190 }
 191
 192 /// Determine whether Candidate or PreviousBest is the better match.
 193 /// The return value is true if Candidate is the better match.
 194 ///
 195 /// A matching relocation is a better match if:
 196 /// - It has a smaller addend.
 197 /// - It is not already involved in a match.
 198 static bool compareMatchingRelocs(const MipsRelocationEntry &Candidate,
 199                                   const MipsRelocationEntry &PreviousBest) {
 200   if (Candidate.R.OriginalAddend != PreviousBest.R.OriginalAddend)
 201     return Candidate.R.OriginalAddend < PreviousBest.R.OriginalAddend;
 202   return PreviousBest.Matched && !Candidate.Matched;
 203 }
 204
 205 #ifndef NDEBUG
 206 /// Print all the relocations.
 207 template <class Container>
 208 static void dumpRelocs(const char *Prefix, const Container &Relocs) {
 209   for (const auto &R : Relocs)
 210     dbgs() << Prefix << R << "\n";
 211 }
 212 #endif
 213
 214 MipsELFObjectWriter::MipsELFObjectWriter(uint8_t OSABI,
 215                                          bool HasRelocationAddend, bool Is64)
 216     : MCELFObjectTargetWriter(Is64, OSABI, ELF::EM_MIPS, HasRelocationAddend) {}
 217
 218 unsigned MipsELFObjectWriter::getRelocType(MCContext &Ctx,
 219                                            const MCValue &Target,
 220                                            const MCFixup &Fixup,
 221                                            bool IsPCRel) const {
 222   // Determine the type of the relocation.
 223   unsigned Kind = (unsigned)Fixup.getKind();
 224
 225   switch (Kind) {
 226   case Mips::fixup_Mips_NONE:
 227     return ELF::R_MIPS_NONE;
 228   case FK_Data_1:
 229     Ctx.reportError(Fixup.getLoc(),
 230                     "MIPS does not support one byte relocations");
 231     return ELF::R_MIPS_NONE;
 232   case Mips::fixup_Mips_16:
 233   case FK_Data_2:
 234     return IsPCRel ? ELF::R_MIPS_PC16 : ELF::R_MIPS_16;
 235   case Mips::fixup_Mips_32:
 236   case FK_Data_4:
 237     return IsPCRel ? ELF::R_MIPS_PC32 : ELF::R_MIPS_32;
 238   }
 239
 240   if (IsPCRel) {
 241     switch (Kind) {
 242     case FK_Data_8:
 243       Ctx.reportError(Fixup.getLoc(),
 244                       "MIPS does not support 64-bit PC-relative relocations");
 245       return ELF::R_MIPS_NONE;
 246     case Mips::fixup_Mips_Branch_PCRel:
 247     case Mips::fixup_Mips_PC16:
 248       return ELF::R_MIPS_PC16;
 249     case Mips::fixup_MICROMIPS_PC7_S1:
 250       return ELF::R_MICROMIPS_PC7_S1;
 251     case Mips::fixup_MICROMIPS_PC10_S1:
 252       return ELF::R_MICROMIPS_PC10_S1;
 253     case Mips::fixup_MICROMIPS_PC16_S1:
 254       return ELF::R_MICROMIPS_PC16_S1;
 255     case Mips::fixup_MICROMIPS_PC26_S1:
 256       return ELF::R_MICROMIPS_PC26_S1;
 257     case Mips::fixup_MICROMIPS_PC19_S2:
 258       return ELF::R_MICROMIPS_PC19_S2;
 259     case Mips::fixup_MICROMIPS_PC18_S3:
 260       return ELF::R_MICROMIPS_PC18_S3;
 261     case Mips::fixup_MICROMIPS_PC21_S1:
 262       return ELF::R_MICROMIPS_PC21_S1;
 263     case Mips::fixup_MIPS_PC19_S2:
 264       return ELF::R_MIPS_PC19_S2;
 265     case Mips::fixup_MIPS_PC18_S3:
 266       return ELF::R_MIPS_PC18_S3;
 267     case Mips::fixup_MIPS_PC21_S2:
 268       return ELF::R_MIPS_PC21_S2;
 269     case Mips::fixup_MIPS_PC26_S2:
 270       return ELF::R_MIPS_PC26_S2;
 271     case Mips::fixup_MIPS_PCHI16:
 272       return ELF::R_MIPS_PCHI16;
 273     case Mips::fixup_MIPS_PCLO16:
 274       return ELF::R_MIPS_PCLO16;
 275     }
 276
 277     llvm_unreachable("invalid PC-relative fixup kind!");
 278   }
 279
 280   switch (Kind) {
 281   case Mips::fixup_Mips_64:
 282   case FK_Data_8:
 283     return ELF::R_MIPS_64;
 284   case FK_DTPRel_4:
 285     return ELF::R_MIPS_TLS_DTPREL32;
 286   case FK_DTPRel_8:
 287     return ELF::R_MIPS_TLS_DTPREL64;
 288   case FK_TPRel_4:
 289     return ELF::R_MIPS_TLS_TPREL32;
 290   case FK_TPRel_8:
 291     return ELF::R_MIPS_TLS_TPREL64;
 292   case FK_GPRel_4:
 293     if (is64Bit()) {
 294       unsigned Type = (unsigned)ELF::R_MIPS_NONE;
 295       Type = setRType((unsigned)ELF::R_MIPS_GPREL32, Type);
 296       Type = setRType2((unsigned)ELF::R_MIPS_64, Type);
 297       Type = setRType3((unsigned)ELF::R_MIPS_NONE, Type);
 298       return Type;
 299     }
 300     return ELF::R_MIPS_GPREL32;
 301   case Mips::fixup_Mips_GPREL16:
 302     return ELF::R_MIPS_GPREL16;
 303   case Mips::fixup_Mips_26:
 304     return ELF::R_MIPS_26;
 305   case Mips::fixup_Mips_CALL16:
 306     return ELF::R_MIPS_CALL16;
 307   case Mips::fixup_Mips_GOT:
 308     return ELF::R_MIPS_GOT16;
 309   case Mips::fixup_Mips_HI16:
 310     return ELF::R_MIPS_HI16;
 311   case Mips::fixup_Mips_LO16:
 312     return ELF::R_MIPS_LO16;
 313   case Mips::fixup_Mips_TLSGD:
 314     return ELF::R_MIPS_TLS_GD;
 315   case Mips::fixup_Mips_GOTTPREL:
 316     return ELF::R_MIPS_TLS_GOTTPREL;
 317   case Mips::fixup_Mips_TPREL_HI:
 318     return ELF::R_MIPS_TLS_TPREL_HI16;
 319   case Mips::fixup_Mips_TPREL_LO:
 320     return ELF::R_MIPS_TLS_TPREL_LO16;
 321   case Mips::fixup_Mips_TLSLDM:
 322     return ELF::R_MIPS_TLS_LDM;
 323   case Mips::fixup_Mips_DTPREL_HI:
 324     return ELF::R_MIPS_TLS_DTPREL_HI16;
 325   case Mips::fixup_Mips_DTPREL_LO:
 326     return ELF::R_MIPS_TLS_DTPREL_LO16;
 327   case Mips::fixup_Mips_GOT_PAGE:
 328     return ELF::R_MIPS_GOT_PAGE;
 329   case Mips::fixup_Mips_GOT_OFST:
 330     return ELF::R_MIPS_GOT_OFST;
 331   case Mips::fixup_Mips_GOT_DISP:
 332     return ELF::R_MIPS_GOT_DISP;
 333   case Mips::fixup_Mips_GPOFF_HI: {
 334     unsigned Type = (unsigned)ELF::R_MIPS_NONE;
 335     Type = setRType((unsigned)ELF::R_MIPS_GPREL16, Type);
 336     Type = setRType2((unsigned)ELF::R_MIPS_SUB, Type);
 337     Type = setRType3((unsigned)ELF::R_MIPS_HI16, Type);
 338     return Type;
 339   }
 340   case Mips::fixup_MICROMIPS_GPOFF_HI: {
 341     unsigned Type = (unsigned)ELF::R_MIPS_NONE;
 342     Type = setRType((unsigned)ELF::R_MICROMIPS_GPREL16, Type);
 343     Type = setRType2((unsigned)ELF::R_MICROMIPS_SUB, Type);
 344     Type = setRType3((unsigned)ELF::R_MICROMIPS_HI16, Type);
 345     return Type;
 346   }
 347   case Mips::fixup_Mips_GPOFF_LO: {
 348     unsigned Type = (unsigned)ELF::R_MIPS_NONE;
 349     Type = setRType((unsigned)ELF::R_MIPS_GPREL16, Type);
 350     Type = setRType2((unsigned)ELF::R_MIPS_SUB, Type);
 351     Type = setRType3((unsigned)ELF::R_MIPS_LO16, Type);
 352     return Type;
 353   }
 354   case Mips::fixup_MICROMIPS_GPOFF_LO: {
 355     unsigned Type = (unsigned)ELF::R_MIPS_NONE;
 356     Type = setRType((unsigned)ELF::R_MICROMIPS_GPREL16, Type);
 357     Type = setRType2((unsigned)ELF::R_MICROMIPS_SUB, Type);
 358     Type = setRType3((unsigned)ELF::R_MICROMIPS_LO16, Type);
 359     return Type;
 360   }
 361   case Mips::fixup_Mips_HIGHER:
 362     return ELF::R_MIPS_HIGHER;
 363   case Mips::fixup_Mips_HIGHEST:
 364     return ELF::R_MIPS_HIGHEST;
 365   case Mips::fixup_Mips_SUB:
 366     return ELF::R_MIPS_SUB;
 367   case Mips::fixup_Mips_GOT_HI16:
 368     return ELF::R_MIPS_GOT_HI16;
 369   case Mips::fixup_Mips_GOT_LO16:
 370     return ELF::R_MIPS_GOT_LO16;
 371   case Mips::fixup_Mips_CALL_HI16:
 372     return ELF::R_MIPS_CALL_HI16;
 373   case Mips::fixup_Mips_CALL_LO16:
 374     return ELF::R_MIPS_CALL_LO16;
 375   case Mips::fixup_MICROMIPS_26_S1:
 376     return ELF::R_MICROMIPS_26_S1;
 377   case Mips::fixup_MICROMIPS_HI16:
 378     return ELF::R_MICROMIPS_HI16;
 379   case Mips::fixup_MICROMIPS_LO16:
 380     return ELF::R_MICROMIPS_LO16;
 381   case Mips::fixup_MICROMIPS_GOT16:
 382     return ELF::R_MICROMIPS_GOT16;
 383   case Mips::fixup_MICROMIPS_CALL16:
 384     return ELF::R_MICROMIPS_CALL16;
 385   case Mips::fixup_MICROMIPS_GOT_DISP:
 386     return ELF::R_MICROMIPS_GOT_DISP;
 387   case Mips::fixup_MICROMIPS_GOT_PAGE:
 388     return ELF::R_MICROMIPS_GOT_PAGE;
 389   case Mips::fixup_MICROMIPS_GOT_OFST:
 390     return ELF::R_MICROMIPS_GOT_OFST;
 391   case Mips::fixup_MICROMIPS_TLS_GD:
 392     return ELF::R_MICROMIPS_TLS_GD;
 393   case Mips::fixup_MICROMIPS_TLS_LDM:
 394     return ELF::R_MICROMIPS_TLS_LDM;
 395   case Mips::fixup_MICROMIPS_TLS_DTPREL_HI16:
 396     return ELF::R_MICROMIPS_TLS_DTPREL_HI16;
 397   case Mips::fixup_MICROMIPS_TLS_DTPREL_LO16:
 398     return ELF::R_MICROMIPS_TLS_DTPREL_LO16;
 399   case Mips::fixup_MICROMIPS_GOTTPREL:
 400     return ELF::R_MICROMIPS_TLS_GOTTPREL;
 401   case Mips::fixup_MICROMIPS_TLS_TPREL_HI16:
 402     return ELF::R_MICROMIPS_TLS_TPREL_HI16;
 403   case Mips::fixup_MICROMIPS_TLS_TPREL_LO16:
 404     return ELF::R_MICROMIPS_TLS_TPREL_LO16;
 405   case Mips::fixup_MICROMIPS_SUB:
 406     return ELF::R_MICROMIPS_SUB;
 407   case Mips::fixup_MICROMIPS_HIGHER:
 408     return ELF::R_MICROMIPS_HIGHER;
 409   case Mips::fixup_MICROMIPS_HIGHEST:
 410     return ELF::R_MICROMIPS_HIGHEST;
 411   case Mips::fixup_Mips_JALR:
 412     return ELF::R_MIPS_JALR;
 413   case Mips::fixup_MICROMIPS_JALR:
 414     return ELF::R_MICROMIPS_JALR;
 415   }
 416
 417   llvm_unreachable("invalid fixup kind!");
 418 }
 419
 420 /// Sort relocation table entries by offset except where another order is
 421 /// required by the MIPS ABI.
 422 ///
 423 /// MIPS has a few relocations that have an AHL component in the expression used
 424 /// to evaluate them. This AHL component is an addend with the same number of
 425 /// bits as a symbol value but not all of our ABI's are able to supply a
 426 /// sufficiently sized addend in a single relocation.
 427 ///
 428 /// The O32 ABI for example, uses REL relocations which store the addend in the
 429 /// section data. All the relocations with AHL components affect 16-bit fields
 430 /// so the addend for a single relocation is limited to 16-bit. This ABI
 431 /// resolves the limitation by linking relocations (e.g. R_MIPS_HI16 and
 432 /// R_MIPS_LO16) and distributing the addend between the linked relocations. The
 433 /// ABI mandates that such relocations must be next to each other in a
 434 /// particular order (e.g. R_MIPS_HI16 must be immediately followed by a
 435 /// matching R_MIPS_LO16) but the rule is less strict in practice.
 436 ///
 437 /// The de facto standard is lenient in the following ways:
 438 /// - 'Immediately following' does not refer to the next relocation entry but
 439 ///   the next matching relocation.
 440 /// - There may be multiple high parts relocations for one low part relocation.
 441 /// - There may be multiple low part relocations for one high part relocation.
 442 /// - The AHL addend in each part does not have to be exactly equal as long as
 443 ///   the difference does not affect the carry bit from bit 15 into 16. This is
 444 ///   to allow, for example, the use of %lo(foo) and %lo(foo+4) when loading
 445 ///   both halves of a long long.
 446 ///
 447 /// See getMatchingLoType() for a description of which high part relocations
 448 /// match which low part relocations. One particular thing to note is that
 449 /// R_MIPS_GOT16 and similar only have AHL addends if they refer to local
 450 /// symbols.
 451 ///
 452 /// It should also be noted that this function is not affected by whether
 453 /// the symbol was kept or rewritten into a section-relative equivalent. We
 454 /// always match using the expressions from the source.
 455 void MipsELFObjectWriter::sortRelocs(const MCAssembler &Asm,
 456                                      std::vector<ELFRelocationEntry> &Relocs) {
 457   // We do not need to sort the relocation table for RELA relocations which
 458   // N32/N64 uses as the relocation addend contains the value we require,
 459   // rather than it being split across a pair of relocations.
 460   if (hasRelocationAddend())
 461     return;
 462
 463   if (Relocs.size() < 2)
 464     return;
 465
 466   // Sort relocations by the address they are applied to.
 467   llvm::sort(Relocs,
 468              [](const ELFRelocationEntry &A, const ELFRelocationEntry &B) {
 469                return A.Offset < B.Offset;
 470              });
 471
 472   std::list<MipsRelocationEntry> Sorted;
 473   std::list<ELFRelocationEntry> Remainder;
 474
 475   LLVM_DEBUG(dumpRelocs("R: ", Relocs));
 476
 477   // Separate the movable relocations (AHL relocations using the high bits) from
 478   // the immobile relocations (everything else). This does not preserve high/low
 479   // matches that already existed in the input.
 480   copy_if_else(Relocs.begin(), Relocs.end(), std::back_inserter(Remainder),
 481                std::back_inserter(Sorted), [](const ELFRelocationEntry &Reloc) {
 482                  return getMatchingLoType(Reloc) != ELF::R_MIPS_NONE;
 483                });
 484
 485   for (auto &R : Remainder) {
 486     LLVM_DEBUG(dbgs() << "Matching: " << R << "\n");
 487
 488     unsigned MatchingType = getMatchingLoType(R);
 489     assert(MatchingType != ELF::R_MIPS_NONE &&
 490            "Wrong list for reloc that doesn't need a match");
 491
 492     // Find the best matching relocation for the current high part.
 493     // See isMatchingReloc for a description of a matching relocation and
 494     // compareMatchingRelocs for a description of what 'best' means.
 495     auto InsertionPoint =
 496         find_best(Sorted.begin(), Sorted.end(),
 497                   [&R, &MatchingType](const MipsRelocationEntry &X) {
 498                     return isMatchingReloc(X, R, MatchingType);
 499                   },
 500                   compareMatchingRelocs);
 501
 502     // If we matched then insert the high part in front of the match and mark
 503     // both relocations as being involved in a match. We only mark the high
 504     // part for cosmetic reasons in the debug output.
 505     //
 506     // If we failed to find a match then the high part is orphaned. This is not
 507     // permitted since the relocation cannot be evaluated without knowing the
 508     // carry-in. We can sometimes handle this using a matching low part that is
 509     // already used in a match but we already cover that case in
 510     // isMatchingReloc and compareMatchingRelocs. For the remaining cases we
 511     // should insert the high part at the end of the list. This will cause the
 512     // linker to fail but the alternative is to cause the linker to bind the
 513     // high part to a semi-matching low part and silently calculate the wrong
 514     // value. Unfortunately we have no means to warn the user that we did this
 515     // so leave it up to the linker to complain about it.
 516     if (InsertionPoint != Sorted.end())
 517       InsertionPoint->Matched = true;
 518     Sorted.insert(InsertionPoint, R)->Matched = true;
 519   }
 520
 521   LLVM_DEBUG(dumpRelocs("S: ", Sorted));
 522
 523   assert(Relocs.size() == Sorted.size() && "Some relocs were not consumed");
 524
 525   // Overwrite the original vector with the sorted elements. The caller expects
 526   // them in reverse order.
 527   unsigned CopyTo = 0;
 528   for (const auto &R : reverse(Sorted))
 529     Relocs[CopyTo++] = R.R;
 530 }
 531
 532 bool MipsELFObjectWriter::needsRelocateWithSymbol(const MCSymbol &Sym,
 533                                                   unsigned Type) const {
 534   // If it's a compound relocation for N64 then we need the relocation if any
 535   // sub-relocation needs it.
 536   if (!isUInt<8>(Type))
 537     return needsRelocateWithSymbol(Sym, Type & 0xff) ||
 538            needsRelocateWithSymbol(Sym, (Type >> 8) & 0xff) ||
 539            needsRelocateWithSymbol(Sym, (Type >> 16) & 0xff);
 540
 541   switch (Type) {
 542   default:
 543     errs() << Type << "\n";
 544     llvm_unreachable("Unexpected relocation");
 545     return true;
 546
 547   // This relocation doesn't affect the section data.
 548   case ELF::R_MIPS_NONE:
 549     return false;
 550
 551   // On REL ABI's (e.g. O32), these relocations form pairs. The pairing is done
 552   // by the static linker by matching the symbol and offset.
 553   // We only see one relocation at a time but it's still safe to relocate with
 554   // the section so long as both relocations make the same decision.
 555   //
 556   // Some older linkers may require the symbol for particular cases. Such cases
 557   // are not supported yet but can be added as required.
 558   case ELF::R_MIPS_GOT16:
 559   case ELF::R_MIPS16_GOT16:
 560   case ELF::R_MICROMIPS_GOT16:
 561   case ELF::R_MIPS_HIGHER:
 562   case ELF::R_MIPS_HIGHEST:
 563   case ELF::R_MIPS_HI16:
 564   case ELF::R_MIPS16_HI16:
 565   case ELF::R_MICROMIPS_HI16:
 566   case ELF::R_MIPS_LO16:
 567   case ELF::R_MIPS16_LO16:
 568   case ELF::R_MICROMIPS_LO16:
 569     // FIXME: It should be safe to return false for the STO_MIPS_MICROMIPS but
 570     //        we neglect to handle the adjustment to the LSB of the addend that
 571     //        it causes in applyFixup() and similar.
 572     if (cast<MCSymbolELF>(Sym).getOther() & ELF::STO_MIPS_MICROMIPS)
 573       return true;
 574     return false;
 575
 576   case ELF::R_MIPS_GOT_PAGE:
 577   case ELF::R_MICROMIPS_GOT_PAGE:
 578   case ELF::R_MIPS_GOT_OFST:
 579   case ELF::R_MICROMIPS_GOT_OFST:
 580   case ELF::R_MIPS_16:
 581   case ELF::R_MIPS_32:
 582   case ELF::R_MIPS_GPREL32:
 583     if (cast<MCSymbolELF>(Sym).getOther() & ELF::STO_MIPS_MICROMIPS)
 584       return true;
 585     LLVM_FALLTHROUGH;
 586   case ELF::R_MIPS_26:
 587   case ELF::R_MIPS_64:
 588   case ELF::R_MIPS_GPREL16:
 589   case ELF::R_MIPS_PC16:
 590   case ELF::R_MIPS_SUB:
 591     return false;
 592
 593   // FIXME: Many of these relocations should probably return false but this
 594   //        hasn't been confirmed to be safe yet.
 595   case ELF::R_MIPS_REL32:
 596   case ELF::R_MIPS_LITERAL:
 597   case ELF::R_MIPS_CALL16:
 598   case ELF::R_MIPS_SHIFT5:
 599   case ELF::R_MIPS_SHIFT6:
 600   case ELF::R_MIPS_GOT_DISP:
 601   case ELF::R_MIPS_GOT_HI16:
 602   case ELF::R_MIPS_GOT_LO16:
 603   case ELF::R_MIPS_INSERT_A:
 604   case ELF::R_MIPS_INSERT_B:
 605   case ELF::R_MIPS_DELETE:
 606   case ELF::R_MIPS_CALL_HI16:
 607   case ELF::R_MIPS_CALL_LO16:
 608   case ELF::R_MIPS_SCN_DISP:
 609   case ELF::R_MIPS_REL16:
 610   case ELF::R_MIPS_ADD_IMMEDIATE:
 611   case ELF::R_MIPS_PJUMP:
 612   case ELF::R_MIPS_RELGOT:
 613   case ELF::R_MIPS_JALR:
 614   case ELF::R_MIPS_TLS_DTPMOD32:
 615   case ELF::R_MIPS_TLS_DTPREL32:
 616   case ELF::R_MIPS_TLS_DTPMOD64:
 617   case ELF::R_MIPS_TLS_DTPREL64:
 618   case ELF::R_MIPS_TLS_GD:
 619   case ELF::R_MIPS_TLS_LDM:
 620   case ELF::R_MIPS_TLS_DTPREL_HI16:
 621   case ELF::R_MIPS_TLS_DTPREL_LO16:
 622   case ELF::R_MIPS_TLS_GOTTPREL:
 623   case ELF::R_MIPS_TLS_TPREL32:
 624   case ELF::R_MIPS_TLS_TPREL64:
 625   case ELF::R_MIPS_TLS_TPREL_HI16:
 626   case ELF::R_MIPS_TLS_TPREL_LO16:
 627   case ELF::R_MIPS_GLOB_DAT:
 628   case ELF::R_MIPS_PC21_S2:
 629   case ELF::R_MIPS_PC26_S2:
 630   case ELF::R_MIPS_PC18_S3:
 631   case ELF::R_MIPS_PC19_S2:
 632   case ELF::R_MIPS_PCHI16:
 633   case ELF::R_MIPS_PCLO16:
 634   case ELF::R_MIPS_COPY:
 635   case ELF::R_MIPS_JUMP_SLOT:
 636   case ELF::R_MIPS_NUM:
 637   case ELF::R_MIPS_PC32:
 638   case ELF::R_MIPS_EH:
 639   case ELF::R_MICROMIPS_26_S1:
 640   case ELF::R_MICROMIPS_GPREL16:
 641   case ELF::R_MICROMIPS_LITERAL:
 642   case ELF::R_MICROMIPS_PC7_S1:
 643   case ELF::R_MICROMIPS_PC10_S1:
 644   case ELF::R_MICROMIPS_PC16_S1:
 645   case ELF::R_MICROMIPS_CALL16:
 646   case ELF::R_MICROMIPS_GOT_DISP:
 647   case ELF::R_MICROMIPS_GOT_HI16:
 648   case ELF::R_MICROMIPS_GOT_LO16:
 649   case ELF::R_MICROMIPS_SUB:
 650   case ELF::R_MICROMIPS_HIGHER:
 651   case ELF::R_MICROMIPS_HIGHEST:
 652   case ELF::R_MICROMIPS_CALL_HI16:
 653   case ELF::R_MICROMIPS_CALL_LO16:
 654   case ELF::R_MICROMIPS_SCN_DISP:
 655   case ELF::R_MICROMIPS_JALR:
 656   case ELF::R_MICROMIPS_HI0_LO16:
 657   case ELF::R_MICROMIPS_TLS_GD:
 658   case ELF::R_MICROMIPS_TLS_LDM:
 659   case ELF::R_MICROMIPS_TLS_DTPREL_HI16:
 660   case ELF::R_MICROMIPS_TLS_DTPREL_LO16:
 661   case ELF::R_MICROMIPS_TLS_GOTTPREL:
 662   case ELF::R_MICROMIPS_TLS_TPREL_HI16:
 663   case ELF::R_MICROMIPS_TLS_TPREL_LO16:
 664   case ELF::R_MICROMIPS_GPREL7_S2:
 665   case ELF::R_MICROMIPS_PC23_S2:
 666   case ELF::R_MICROMIPS_PC21_S1:
 667   case ELF::R_MICROMIPS_PC26_S1:
 668   case ELF::R_MICROMIPS_PC18_S3:
 669   case ELF::R_MICROMIPS_PC19_S2:
 670     return true;
 671
 672   // FIXME: Many of these should probably return false but MIPS16 isn't
 673   //        supported by the integrated assembler.
 674   case ELF::R_MIPS16_26:
 675   case ELF::R_MIPS16_GPREL:
 676   case ELF::R_MIPS16_CALL16:
 677   case ELF::R_MIPS16_TLS_GD:
 678   case ELF::R_MIPS16_TLS_LDM:
 679   case ELF::R_MIPS16_TLS_DTPREL_HI16:
 680   case ELF::R_MIPS16_TLS_DTPREL_LO16:
 681   case ELF::R_MIPS16_TLS_GOTTPREL:
 682   case ELF::R_MIPS16_TLS_TPREL_HI16:
 683   case ELF::R_MIPS16_TLS_TPREL_LO16:
 684     llvm_unreachable("Unsupported MIPS16 relocation");
 685     return true;
 686   }
 687 }
 688
 689 std::unique_ptr<MCObjectTargetWriter>
 690 llvm::createMipsELFObjectWriter(const Triple &TT, bool IsN32) {
 691   uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TT.getOS());
 692   bool IsN64 = TT.isArch64Bit() && !IsN32;
 693   bool HasRelocationAddend = TT.isArch64Bit();
 694   return llvm::make_unique<MipsELFObjectWriter>(OSABI, HasRelocationAddend,
 695                                                 IsN64);
 696 }