llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp

   1 //===-- ARMMachObjectWriter.cpp - ARM Mach Object Writer ------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "MCTargetDesc/ARMFixupKinds.h"
  10 #include "MCTargetDesc/ARMMCTargetDesc.h"
  11 #include "llvm/ADT/StringExtras.h"
  12 #include "llvm/ADT/Twine.h"
  13 #include "llvm/BinaryFormat/MachO.h"
  14 #include "llvm/MC/MCAssembler.h"
  15 #include "llvm/MC/MCContext.h"
  16 #include "llvm/MC/MCExpr.h"
  17 #include "llvm/MC/MCFixup.h"
  18 #include "llvm/MC/MCMachObjectWriter.h"
  19 #include "llvm/MC/MCSection.h"
  20 #include "llvm/MC/MCValue.h"
  21 #include "llvm/Support/ErrorHandling.h"
  22
  23 using namespace llvm;
  24
  25 namespace {
  26 class ARMMachObjectWriter : public MCMachObjectTargetWriter {
  27   void recordARMScatteredRelocation(MachObjectWriter *Writer,
  28                                     const MCAssembler &Asm,
  29                                     const MCFragment *Fragment,
  30                                     const MCFixup &Fixup, MCValue Target,
  31                                     unsigned Type, unsigned Log2Size,
  32                                     uint64_t &FixedValue);
  33   void recordARMScatteredHalfRelocation(MachObjectWriter *Writer,
  34                                         const MCAssembler &Asm,
  35                                         const MCFragment *Fragment,
  36                                         const MCFixup &Fixup, MCValue Target,
  37                                         uint64_t &FixedValue);
  38
  39   bool requiresExternRelocation(MachObjectWriter *Writer,
  40                                 const MCAssembler &Asm,
  41                                 const MCFragment &Fragment, unsigned RelocType,
  42                                 const MCSymbol &S, uint64_t FixedValue);
  43
  44 public:
  45   ARMMachObjectWriter(bool Is64Bit, uint32_t CPUType, uint32_t CPUSubtype)
  46       : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype) {}
  47
  48   void recordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
  49                         const MCFragment *Fragment, const MCFixup &Fixup,
  50                         MCValue Target, uint64_t &FixedValue) override;
  51 };
  52 }
  53
  54 static bool getARMFixupKindMachOInfo(unsigned Kind, unsigned &RelocType,
  55                               unsigned &Log2Size) {
  56   RelocType = unsigned(MachO::ARM_RELOC_VANILLA);
  57   Log2Size = ~0U;
  58
  59   switch (Kind) {
  60   default:
  61     return false;
  62
  63   case FK_Data_1:
  64     Log2Size = llvm::Log2_32(1);
  65     return true;
  66   case FK_Data_2:
  67     Log2Size = llvm::Log2_32(2);
  68     return true;
  69   case FK_Data_4:
  70     Log2Size = llvm::Log2_32(4);
  71     return true;
  72   case FK_Data_8:
  73     Log2Size = llvm::Log2_32(8);
  74     return false;
  75
  76     // These fixups are expected to always be resolvable at assembly time and
  77     // have no relocations supported.
  78   case ARM::fixup_arm_ldst_pcrel_12:
  79   case ARM::fixup_arm_pcrel_10:
  80   case ARM::fixup_arm_adr_pcrel_12:
  81   case ARM::fixup_arm_thumb_br:
  82     return false;
  83
  84     // Handle 24-bit branch kinds.
  85   case ARM::fixup_arm_condbranch:
  86   case ARM::fixup_arm_uncondbranch:
  87   case ARM::fixup_arm_uncondbl:
  88   case ARM::fixup_arm_condbl:
  89   case ARM::fixup_arm_blx:
  90     RelocType = unsigned(MachO::ARM_RELOC_BR24);
  91     // Report as 'long', even though that is not quite accurate.
  92     Log2Size = llvm::Log2_32(4);
  93     return true;
  94
  95   case ARM::fixup_t2_uncondbranch:
  96   case ARM::fixup_arm_thumb_bl:
  97   case ARM::fixup_arm_thumb_blx:
  98     RelocType = unsigned(MachO::ARM_THUMB_RELOC_BR22);
  99     Log2Size = llvm::Log2_32(4);
 100     return true;
 101
 102   // For movw/movt r_type relocations they always have a pair following them and
 103   // the r_length bits are used differently.  The encoding of the r_length is as
 104   // follows:
 105   //   low bit of r_length:
 106   //      0 - :lower16: for movw instructions
 107   //      1 - :upper16: for movt instructions
 108   //   high bit of r_length:
 109   //      0 - arm instructions
 110   //      1 - thumb instructions
 111   case ARM::fixup_arm_movt_hi16:
 112     RelocType = unsigned(MachO::ARM_RELOC_HALF);
 113     Log2Size = 1;
 114     return true;
 115   case ARM::fixup_t2_movt_hi16:
 116     RelocType = unsigned(MachO::ARM_RELOC_HALF);
 117     Log2Size = 3;
 118     return true;
 119
 120   case ARM::fixup_arm_movw_lo16:
 121     RelocType = unsigned(MachO::ARM_RELOC_HALF);
 122     Log2Size = 0;
 123     return true;
 124   case ARM::fixup_t2_movw_lo16:
 125     RelocType = unsigned(MachO::ARM_RELOC_HALF);
 126     Log2Size = 2;
 127     return true;
 128   }
 129 }
 130
 131 void ARMMachObjectWriter::recordARMScatteredHalfRelocation(
 132     MachObjectWriter *Writer, const MCAssembler &Asm,
 133     const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target,
 134     uint64_t &FixedValue) {
 135   uint32_t FixupOffset = Asm.getFragmentOffset(*Fragment) + Fixup.getOffset();
 136
 137   if (FixupOffset & 0xff000000) {
 138     Asm.getContext().reportError(Fixup.getLoc(),
 139                                  "can not encode offset '0x" +
 140                                      utohexstr(FixupOffset) +
 141                                      "' in resulting scattered relocation.");
 142     return;
 143   }
 144
 145   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
 146   unsigned Type = MachO::ARM_RELOC_HALF;
 147
 148   // See <reloc.h>.
 149   const MCSymbol *A = &Target.getSymA()->getSymbol();
 150
 151   if (!A->getFragment()) {
 152     Asm.getContext().reportError(Fixup.getLoc(),
 153                        "symbol '" + A->getName() +
 154                        "' can not be undefined in a subtraction expression");
 155     return;
 156   }
 157
 158   uint32_t Value = Writer->getSymbolAddress(*A, Asm);
 159   uint32_t Value2 = 0;
 160   uint64_t SecAddr = Writer->getSectionAddress(A->getFragment()->getParent());
 161   FixedValue += SecAddr;
 162
 163   if (const MCSymbolRefExpr *B = Target.getSymB()) {
 164     const MCSymbol *SB = &B->getSymbol();
 165
 166     if (!SB->getFragment()) {
 167       Asm.getContext().reportError(Fixup.getLoc(),
 168                          "symbol '" + B->getSymbol().getName() +
 169                          "' can not be undefined in a subtraction expression");
 170       return;
 171     }
 172
 173     // Select the appropriate difference relocation type.
 174     Type = MachO::ARM_RELOC_HALF_SECTDIFF;
 175     Value2 = Writer->getSymbolAddress(B->getSymbol(), Asm);
 176     FixedValue -= Writer->getSectionAddress(SB->getFragment()->getParent());
 177   }
 178
 179   // Relocations are written out in reverse order, so the PAIR comes first.
 180   // ARM_RELOC_HALF and ARM_RELOC_HALF_SECTDIFF abuse the r_length field:
 181   //
 182   // For these two r_type relocations they always have a pair following them and
 183   // the r_length bits are used differently.  The encoding of the r_length is as
 184   // follows:
 185   //   low bit of r_length:
 186   //      0 - :lower16: for movw instructions
 187   //      1 - :upper16: for movt instructions
 188   //   high bit of r_length:
 189   //      0 - arm instructions
 190   //      1 - thumb instructions
 191   // the other half of the relocated expression is in the following pair
 192   // relocation entry in the low 16 bits of r_address field.
 193   unsigned ThumbBit = 0;
 194   unsigned MovtBit = 0;
 195   switch (Fixup.getTargetKind()) {
 196   default: break;
 197   case ARM::fixup_arm_movt_hi16:
 198     MovtBit = 1;
 199     // The thumb bit shouldn't be set in the 'other-half' bit of the
 200     // relocation, but it will be set in FixedValue if the base symbol
 201     // is a thumb function. Clear it out here.
 202     if (Asm.isThumbFunc(A))
 203       FixedValue &= 0xfffffffe;
 204     break;
 205   case ARM::fixup_t2_movt_hi16:
 206     if (Asm.isThumbFunc(A))
 207       FixedValue &= 0xfffffffe;
 208     MovtBit = 1;
 209     [[fallthrough]];
 210   case ARM::fixup_t2_movw_lo16:
 211     ThumbBit = 1;
 212     break;
 213   }
 214
 215   if (Type == MachO::ARM_RELOC_HALF_SECTDIFF) {
 216     uint32_t OtherHalf = MovtBit
 217       ? (FixedValue & 0xffff) : ((FixedValue & 0xffff0000) >> 16);
 218
 219     MachO::any_relocation_info MRE;
 220     MRE.r_word0 = ((OtherHalf             <<  0) |
 221                    (MachO::ARM_RELOC_PAIR << 24) |
 222                    (MovtBit               << 28) |
 223                    (ThumbBit              << 29) |
 224                    (IsPCRel               << 30) |
 225                    MachO::R_SCATTERED);
 226     MRE.r_word1 = Value2;
 227     Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
 228   }
 229
 230   MachO::any_relocation_info MRE;
 231   MRE.r_word0 = ((FixupOffset <<  0) |
 232                  (Type        << 24) |
 233                  (MovtBit     << 28) |
 234                  (ThumbBit    << 29) |
 235                  (IsPCRel     << 30) |
 236                  MachO::R_SCATTERED);
 237   MRE.r_word1 = Value;
 238   Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
 239 }
 240
 241 void ARMMachObjectWriter::recordARMScatteredRelocation(
 242     MachObjectWriter *Writer, const MCAssembler &Asm,
 243     const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target,
 244     unsigned Type, unsigned Log2Size, uint64_t &FixedValue) {
 245   uint32_t FixupOffset = Asm.getFragmentOffset(*Fragment) + Fixup.getOffset();
 246
 247   if (FixupOffset & 0xff000000) {
 248     Asm.getContext().reportError(Fixup.getLoc(),
 249                                  "can not encode offset '0x" +
 250                                      utohexstr(FixupOffset) +
 251                                      "' in resulting scattered relocation.");
 252     return;
 253   }
 254
 255   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
 256
 257   // See <reloc.h>.
 258   const MCSymbol *A = &Target.getSymA()->getSymbol();
 259
 260   if (!A->getFragment()) {
 261     Asm.getContext().reportError(Fixup.getLoc(),
 262                        "symbol '" + A->getName() +
 263                        "' can not be undefined in a subtraction expression");
 264     return;
 265   }
 266
 267   uint32_t Value = Writer->getSymbolAddress(*A, Asm);
 268   uint64_t SecAddr = Writer->getSectionAddress(A->getFragment()->getParent());
 269   FixedValue += SecAddr;
 270   uint32_t Value2 = 0;
 271
 272   if (const MCSymbolRefExpr *B = Target.getSymB()) {
 273     assert(Type == MachO::ARM_RELOC_VANILLA && "invalid reloc for 2 symbols");
 274     const MCSymbol *SB = &B->getSymbol();
 275
 276     if (!SB->getFragment()) {
 277       Asm.getContext().reportError(Fixup.getLoc(),
 278                          "symbol '" + B->getSymbol().getName() +
 279                          "' can not be undefined in a subtraction expression");
 280       return;
 281     }
 282
 283     // Select the appropriate difference relocation type.
 284     Type = MachO::ARM_RELOC_SECTDIFF;
 285     Value2 = Writer->getSymbolAddress(B->getSymbol(), Asm);
 286     FixedValue -= Writer->getSectionAddress(SB->getFragment()->getParent());
 287   }
 288
 289   // Relocations are written out in reverse order, so the PAIR comes first.
 290   if (Type == MachO::ARM_RELOC_SECTDIFF ||
 291       Type == MachO::ARM_RELOC_LOCAL_SECTDIFF) {
 292     MachO::any_relocation_info MRE;
 293     MRE.r_word0 = ((0                     <<  0) |
 294                    (MachO::ARM_RELOC_PAIR << 24) |
 295                    (Log2Size              << 28) |
 296                    (IsPCRel               << 30) |
 297                    MachO::R_SCATTERED);
 298     MRE.r_word1 = Value2;
 299     Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
 300   }
 301
 302   MachO::any_relocation_info MRE;
 303   MRE.r_word0 = ((FixupOffset <<  0) |
 304                  (Type        << 24) |
 305                  (Log2Size    << 28) |
 306                  (IsPCRel     << 30) |
 307                  MachO::R_SCATTERED);
 308   MRE.r_word1 = Value;
 309   Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
 310 }
 311
 312 bool ARMMachObjectWriter::requiresExternRelocation(MachObjectWriter *Writer,
 313                                                    const MCAssembler &Asm,
 314                                                    const MCFragment &Fragment,
 315                                                    unsigned RelocType,
 316                                                    const MCSymbol &S,
 317                                                    uint64_t FixedValue) {
 318   // Most cases can be identified purely from the symbol.
 319   if (Writer->doesSymbolRequireExternRelocation(S))
 320     return true;
 321   int64_t Value = (int64_t)FixedValue;  // The displacement is signed.
 322   int64_t Range;
 323   switch (RelocType) {
 324   default:
 325     return false;
 326   case MachO::ARM_RELOC_BR24:
 327     // An ARM call might be to a Thumb function, in which case the offset may
 328     // not be encodable in the instruction and we must use an external
 329     // relocation that explicitly mentions the function. Not a problem if it's
 330     // to a temporary "Lwhatever" symbol though, and in fact trying to use an
 331     // external relocation there causes more issues.
 332     if (!S.isTemporary())
 333        return true;
 334
 335     // PC pre-adjustment of 8 for these instructions.
 336     Value -= 8;
 337     // ARM BL/BLX has a 25-bit offset.
 338     Range = 0x1ffffff;
 339     break;
 340   case MachO::ARM_THUMB_RELOC_BR22:
 341     // PC pre-adjustment of 4 for these instructions.
 342     Value -= 4;
 343     // Thumb BL/BLX has a 24-bit offset.
 344     Range = 0xffffff;
 345   }
 346   // BL/BLX also use external relocations when an internal relocation
 347   // would result in the target being out of range. This gives the linker
 348   // enough information to generate a branch island.
 349   Value += Writer->getSectionAddress(&S.getSection());
 350   Value -= Writer->getSectionAddress(Fragment.getParent());
 351   // If the resultant value would be out of range for an internal relocation,
 352   // use an external instead.
 353   if (Value > Range || Value < -(Range + 1))
 354     return true;
 355   return false;
 356 }
 357
 358 void ARMMachObjectWriter::recordRelocation(MachObjectWriter *Writer,
 359                                            MCAssembler &Asm,
 360                                            const MCFragment *Fragment,
 361                                            const MCFixup &Fixup, MCValue Target,
 362                                            uint64_t &FixedValue) {
 363   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
 364   unsigned Log2Size;
 365   unsigned RelocType = MachO::ARM_RELOC_VANILLA;
 366   if (!getARMFixupKindMachOInfo(Fixup.getKind(), RelocType, Log2Size)) {
 367     // If we failed to get fixup kind info, it's because there's no legal
 368     // relocation type for the fixup kind. This happens when it's a fixup that's
 369     // expected to always be resolvable at assembly time and not have any
 370     // relocations needed.
 371     Asm.getContext().reportError(Fixup.getLoc(), "unsupported relocation type");
 372     return;
 373   }
 374
 375   // If this is a difference or a defined symbol plus an offset, then we need a
 376   // scattered relocation entry.  Differences always require scattered
 377   // relocations.
 378   if (Target.getSymB()) {
 379     if (RelocType == MachO::ARM_RELOC_HALF)
 380       return recordARMScatteredHalfRelocation(Writer, Asm, Fragment, Fixup,
 381                                               Target, FixedValue);
 382     return recordARMScatteredRelocation(Writer, Asm, Fragment, Fixup, Target,
 383                                         RelocType, Log2Size, FixedValue);
 384   }
 385
 386   // Get the symbol data, if any.
 387   const MCSymbol *A = nullptr;
 388   if (Target.getSymA())
 389     A = &Target.getSymA()->getSymbol();
 390
 391   // FIXME: For other platforms, we need to use scattered relocations for
 392   // internal relocations with offsets.  If this is an internal relocation with
 393   // an offset, it also needs a scattered relocation entry.
 394   //
 395   // Is this right for ARM?
 396   uint32_t Offset = Target.getConstant();
 397   if (IsPCRel && RelocType == MachO::ARM_RELOC_VANILLA)
 398     Offset += 1 << Log2Size;
 399   if (Offset && A && !Writer->doesSymbolRequireExternRelocation(*A) &&
 400       RelocType != MachO::ARM_RELOC_HALF)
 401     return recordARMScatteredRelocation(Writer, Asm, Fragment, Fixup, Target,
 402                                         RelocType, Log2Size, FixedValue);
 403
 404   // See <reloc.h>.
 405   uint32_t FixupOffset = Asm.getFragmentOffset(*Fragment) + Fixup.getOffset();
 406   unsigned Index = 0;
 407   unsigned Type = 0;
 408   const MCSymbol *RelSymbol = nullptr;
 409
 410   if (!A) { // constant
 411     // FIXME! This is Target.isAbsolute() case as we check SymB above. We check
 412     // !A to ensure that null pointer isn't dereferenced and suppress static
 413     // analyzer warnings.
 414     report_fatal_error("FIXME: relocations to absolute targets "
 415                        "not yet implemented");
 416   } else {
 417     // Resolve constant variables.
 418     if (A->isVariable()) {
 419       int64_t Res;
 420       if (A->getVariableValue()->evaluateAsAbsolute(
 421               Res, Asm, Writer->getSectionAddressMap())) {
 422         FixedValue = Res;
 423         return;
 424       }
 425     }
 426
 427     // Check whether we need an external or internal relocation.
 428     if (requiresExternRelocation(Writer, Asm, *Fragment, RelocType, *A,
 429                                  FixedValue)) {
 430       RelSymbol = A;
 431
 432       // For external relocations, make sure to offset the fixup value to
 433       // compensate for the addend of the symbol address, if it was
 434       // undefined. This occurs with weak definitions, for example.
 435       if (!A->isUndefined())
 436         FixedValue -= Asm.getSymbolOffset(*A);
 437     } else {
 438       // The index is the section ordinal (1-based).
 439       const MCSection &Sec = A->getSection();
 440       Index = Sec.getOrdinal() + 1;
 441       FixedValue += Writer->getSectionAddress(&Sec);
 442     }
 443     if (IsPCRel)
 444       FixedValue -= Writer->getSectionAddress(Fragment->getParent());
 445
 446     // The type is determined by the fixup kind.
 447     Type = RelocType;
 448   }
 449
 450   // struct relocation_info (8 bytes)
 451   MachO::any_relocation_info MRE;
 452   MRE.r_word0 = FixupOffset;
 453   MRE.r_word1 =
 454       (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
 455
 456   // Even when it's not a scattered relocation, movw/movt always uses
 457   // a PAIR relocation.
 458   if (Type == MachO::ARM_RELOC_HALF) {
 459     // The entire addend is needed to correctly apply a relocation. One half is
 460     // extracted from the instruction itself, the other comes from this
 461     // PAIR. I.e. it's correct that we insert the high bits of the addend in the
 462     // MOVW case here.  relocation entries.
 463     uint32_t Value = 0;
 464     switch (Fixup.getTargetKind()) {
 465     default: break;
 466     case ARM::fixup_arm_movw_lo16:
 467     case ARM::fixup_t2_movw_lo16:
 468       Value = (FixedValue >> 16) & 0xffff;
 469       break;
 470     case ARM::fixup_arm_movt_hi16:
 471     case ARM::fixup_t2_movt_hi16:
 472       Value = FixedValue & 0xffff;
 473       break;
 474     }
 475     MachO::any_relocation_info MREPair;
 476     MREPair.r_word0 = Value;
 477     MREPair.r_word1 = ((0xffffff              <<  0) |
 478                        (Log2Size              << 25) |
 479                        (MachO::ARM_RELOC_PAIR << 28));
 480
 481     Writer->addRelocation(nullptr, Fragment->getParent(), MREPair);
 482   }
 483
 484   Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
 485 }
 486
 487 std::unique_ptr<MCObjectTargetWriter>
 488 llvm::createARMMachObjectWriter(bool Is64Bit, uint32_t CPUType,
 489                                 uint32_t CPUSubtype) {
 490   return std::make_unique<ARMMachObjectWriter>(Is64Bit, CPUType, CPUSubtype);
 491 }