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