lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp

   1 //===-- ARMELFObjectWriter.cpp - ARM 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/ARMMCTargetDesc.h"
  11 #include "MCTargetDesc/ARMFixupKinds.h"
  12 #include "llvm/ADT/Statistic.h"
  13 #include "llvm/ADT/StringSwitch.h"
  14 #include "llvm/MC/MCELFObjectWriter.h"
  15 #include "llvm/MC/MCExpr.h"
  16 #include "llvm/MC/MCSectionELF.h"
  17 #include "llvm/MC/MCValue.h"
  18 #include "llvm/Support/Debug.h"
  19 #include "llvm/Support/ErrorHandling.h"
  20 #include "llvm/Support/raw_ostream.h"
  21
  22 using namespace llvm;
  23
  24 namespace {
  25   class ARMELFObjectWriter : public MCELFObjectTargetWriter {
  26     enum { DefaultEABIVersion = 0x05000000U };
  27     unsigned GetRelocTypeInner(const MCValue &Target,
  28                                const MCFixup &Fixup,
  29                                bool IsPCRel) const;
  30
  31
  32   public:
  33     ARMELFObjectWriter(uint8_t OSABI);
  34
  35     virtual ~ARMELFObjectWriter();
  36
  37     unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
  38                           bool IsPCRel, bool IsRelocWithSymbol,
  39                           int64_t Addend) const override;
  40     const MCSymbol *ExplicitRelSym(const MCAssembler &Asm,
  41                                    const MCValue &Target, const MCFragment &F,
  42                                    const MCFixup &Fixup,
  43                                    bool IsPCRel) const override;
  44   };
  45 }
  46
  47 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
  48   : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
  49                             ELF::EM_ARM,
  50                             /*HasRelocationAddend*/ false) {}
  51
  52 ARMELFObjectWriter::~ARMELFObjectWriter() {}
  53
  54 // In ARM, _MergedGlobals and other most symbols get emitted directly.
  55 // I.e. not as an offset to a section symbol.
  56 // This code is an approximation of what ARM/gcc does.
  57
  58 STATISTIC(PCRelCount, "Total number of PIC Relocations");
  59 STATISTIC(NonPCRelCount, "Total number of non-PIC relocations");
  60
  61 const MCSymbol *ARMELFObjectWriter::ExplicitRelSym(const MCAssembler &Asm,
  62                                                    const MCValue &Target,
  63                                                    const MCFragment &F,
  64                                                    const MCFixup &Fixup,
  65                                                    bool IsPCRel) const {
  66   const MCSymbol &Symbol = Target.getSymA()->getSymbol().AliasedSymbol();
  67   bool EmitThisSym = false;
  68
  69   const MCSectionELF &Section =
  70     static_cast<const MCSectionELF&>(Symbol.getSection());
  71   bool InNormalSection = true;
  72   unsigned RelocType = 0;
  73   RelocType = GetRelocTypeInner(Target, Fixup, IsPCRel);
  74   assert(!Target.getSymB() ||
  75          Target.getSymB()->getKind() == MCSymbolRefExpr::VK_None);
  76
  77   DEBUG(
  78       MCSymbolRefExpr::VariantKind Kind = Fixup.getAccessVariant();
  79       dbgs() << "considering symbol "
  80         << Section.getSectionName() << "/"
  81         << Symbol.getName() << "/"
  82         << " Rel:" << (unsigned)RelocType
  83         << " Kind: " << (int)Kind
  84         << " Tmp:"
  85         << Symbol.isAbsolute() << "/" << Symbol.isDefined() << "/"
  86         << Symbol.isVariable() << "/" << Symbol.isTemporary()
  87         << " Counts:" << PCRelCount << "/" << NonPCRelCount << "\n");
  88
  89   if (IsPCRel) { ++PCRelCount;
  90     switch (RelocType) {
  91     default:
  92       // Most relocation types are emitted as explicit symbols
  93       InNormalSection =
  94         StringSwitch<bool>(Section.getSectionName())
  95         .Case(".data.rel.ro.local", false)
  96         .Case(".data.rel", false)
  97         .Case(".bss", false)
  98         .Default(true);
  99       EmitThisSym = true;
 100       break;
 101     case ELF::R_ARM_ABS32:
 102       // But things get strange with R_ARM_ABS32
 103       // In this case, most things that go in .rodata show up
 104       // as section relative relocations
 105       InNormalSection =
 106         StringSwitch<bool>(Section.getSectionName())
 107         .Case(".data.rel.ro.local", false)
 108         .Case(".data.rel", false)
 109         .Case(".rodata", false)
 110         .Case(".bss", false)
 111         .Default(true);
 112       EmitThisSym = false;
 113       break;
 114     }
 115   } else {
 116     NonPCRelCount++;
 117     InNormalSection =
 118       StringSwitch<bool>(Section.getSectionName())
 119       .Case(".data.rel.ro.local", false)
 120       .Case(".rodata", false)
 121       .Case(".data.rel", false)
 122       .Case(".bss", false)
 123       .Default(true);
 124
 125     switch (RelocType) {
 126     default: EmitThisSym = true; break;
 127     case ELF::R_ARM_ABS32: EmitThisSym = false; break;
 128     case ELF::R_ARM_PREL31: EmitThisSym = false; break;
 129     }
 130   }
 131
 132   if (EmitThisSym)
 133     return &Symbol;
 134   if (! Symbol.isTemporary() && InNormalSection) {
 135     return &Symbol;
 136   }
 137   return NULL;
 138 }
 139
 140 // Need to examine the Fixup when determining whether to
 141 // emit the relocation as an explicit symbol or as a section relative
 142 // offset
 143 unsigned ARMELFObjectWriter::GetRelocType(const MCValue &Target,
 144                                           const MCFixup &Fixup,
 145                                           bool IsPCRel,
 146                                           bool IsRelocWithSymbol,
 147                                           int64_t Addend) const {
 148   return GetRelocTypeInner(Target, Fixup, IsPCRel);
 149 }
 150
 151 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
 152                                                const MCFixup &Fixup,
 153                                                bool IsPCRel) const  {
 154   MCSymbolRefExpr::VariantKind Modifier = Fixup.getAccessVariant();
 155
 156   unsigned Type = 0;
 157   if (IsPCRel) {
 158     switch ((unsigned)Fixup.getKind()) {
 159     default: llvm_unreachable("Unimplemented");
 160     case FK_Data_4:
 161       switch (Modifier) {
 162       default: llvm_unreachable("Unsupported Modifier");
 163       case MCSymbolRefExpr::VK_None:
 164         Type = ELF::R_ARM_REL32;
 165         break;
 166       case MCSymbolRefExpr::VK_TLSGD:
 167         llvm_unreachable("unimplemented");
 168       case MCSymbolRefExpr::VK_GOTTPOFF:
 169         Type = ELF::R_ARM_TLS_IE32;
 170         break;
 171       }
 172       break;
 173     case ARM::fixup_arm_blx:
 174     case ARM::fixup_arm_uncondbl:
 175       switch (Modifier) {
 176       case MCSymbolRefExpr::VK_PLT:
 177         Type = ELF::R_ARM_PLT32;
 178         break;
 179       case MCSymbolRefExpr::VK_ARM_TLSCALL:
 180         Type = ELF::R_ARM_TLS_CALL;
 181         break;
 182       default:
 183         Type = ELF::R_ARM_CALL;
 184         break;
 185       }
 186       break;
 187     case ARM::fixup_arm_condbl:
 188     case ARM::fixup_arm_condbranch:
 189     case ARM::fixup_arm_uncondbranch:
 190       Type = ELF::R_ARM_JUMP24;
 191       break;
 192     case ARM::fixup_t2_condbranch:
 193     case ARM::fixup_t2_uncondbranch:
 194       Type = ELF::R_ARM_THM_JUMP24;
 195       break;
 196     case ARM::fixup_arm_movt_hi16:
 197     case ARM::fixup_arm_movt_hi16_pcrel:
 198       Type = ELF::R_ARM_MOVT_PREL;
 199       break;
 200     case ARM::fixup_arm_movw_lo16:
 201     case ARM::fixup_arm_movw_lo16_pcrel:
 202       Type = ELF::R_ARM_MOVW_PREL_NC;
 203       break;
 204     case ARM::fixup_t2_movt_hi16:
 205     case ARM::fixup_t2_movt_hi16_pcrel:
 206       Type = ELF::R_ARM_THM_MOVT_PREL;
 207       break;
 208     case ARM::fixup_t2_movw_lo16:
 209     case ARM::fixup_t2_movw_lo16_pcrel:
 210       Type = ELF::R_ARM_THM_MOVW_PREL_NC;
 211       break;
 212     case ARM::fixup_arm_thumb_bl:
 213     case ARM::fixup_arm_thumb_blx:
 214       switch (Modifier) {
 215       case MCSymbolRefExpr::VK_ARM_TLSCALL:
 216         Type = ELF::R_ARM_THM_TLS_CALL;
 217         break;
 218       default:
 219         Type = ELF::R_ARM_THM_CALL;
 220         break;
 221       }
 222       break;
 223     }
 224   } else {
 225     switch ((unsigned)Fixup.getKind()) {
 226     default: llvm_unreachable("invalid fixup kind!");
 227     case FK_Data_4:
 228       switch (Modifier) {
 229       default: llvm_unreachable("Unsupported Modifier");
 230       case MCSymbolRefExpr::VK_ARM_NONE:
 231         Type = ELF::R_ARM_NONE;
 232         break;
 233       case MCSymbolRefExpr::VK_GOT:
 234         Type = ELF::R_ARM_GOT_BREL;
 235         break;
 236       case MCSymbolRefExpr::VK_TLSGD:
 237         Type = ELF::R_ARM_TLS_GD32;
 238         break;
 239       case MCSymbolRefExpr::VK_TPOFF:
 240         Type = ELF::R_ARM_TLS_LE32;
 241         break;
 242       case MCSymbolRefExpr::VK_GOTTPOFF:
 243         Type = ELF::R_ARM_TLS_IE32;
 244         break;
 245       case MCSymbolRefExpr::VK_None:
 246         Type = ELF::R_ARM_ABS32;
 247         break;
 248       case MCSymbolRefExpr::VK_GOTOFF:
 249         Type = ELF::R_ARM_GOTOFF32;
 250         break;
 251       case MCSymbolRefExpr::VK_ARM_TARGET1:
 252         Type = ELF::R_ARM_TARGET1;
 253         break;
 254       case MCSymbolRefExpr::VK_ARM_TARGET2:
 255         Type = ELF::R_ARM_TARGET2;
 256         break;
 257       case MCSymbolRefExpr::VK_ARM_PREL31:
 258         Type = ELF::R_ARM_PREL31;
 259         break;
 260       case MCSymbolRefExpr::VK_ARM_TLSLDO:
 261         Type = ELF::R_ARM_TLS_LDO32;
 262         break;
 263       case MCSymbolRefExpr::VK_ARM_TLSCALL:
 264         Type = ELF::R_ARM_TLS_CALL;
 265         break;
 266       case MCSymbolRefExpr::VK_ARM_TLSDESC:
 267         Type = ELF::R_ARM_TLS_GOTDESC;
 268         break;
 269       case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
 270         Type = ELF::R_ARM_TLS_DESCSEQ;
 271         break;
 272       }
 273       break;
 274     case ARM::fixup_arm_ldst_pcrel_12:
 275     case ARM::fixup_arm_pcrel_10:
 276     case ARM::fixup_arm_adr_pcrel_12:
 277     case ARM::fixup_arm_thumb_bl:
 278     case ARM::fixup_arm_thumb_cb:
 279     case ARM::fixup_arm_thumb_cp:
 280     case ARM::fixup_arm_thumb_br:
 281       llvm_unreachable("Unimplemented");
 282     case ARM::fixup_arm_condbranch:
 283     case ARM::fixup_arm_uncondbranch:
 284       Type = ELF::R_ARM_JUMP24;
 285       break;
 286     case ARM::fixup_arm_movt_hi16:
 287       Type = ELF::R_ARM_MOVT_ABS;
 288       break;
 289     case ARM::fixup_arm_movw_lo16:
 290       Type = ELF::R_ARM_MOVW_ABS_NC;
 291       break;
 292     case ARM::fixup_t2_movt_hi16:
 293       Type = ELF::R_ARM_THM_MOVT_ABS;
 294       break;
 295     case ARM::fixup_t2_movw_lo16:
 296       Type = ELF::R_ARM_THM_MOVW_ABS_NC;
 297       break;
 298     }
 299   }
 300
 301   return Type;
 302 }
 303
 304 MCObjectWriter *llvm::createARMELFObjectWriter(raw_ostream &OS,
 305                                                uint8_t OSABI) {
 306   MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
 307   return createELFObjectWriter(MOTW, OS,  /*IsLittleEndian=*/true);
 308 }