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     virtual unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
  38                                   bool IsPCRel, bool IsRelocWithSymbol,
  39                                   int64_t Addend) const;
  40     virtual const MCSymbol *ExplicitRelSym(const MCAssembler &Asm,
  41                                    const MCValue &Target,
  42                                    const MCFragment &F,
  43                                    const MCFixup &Fixup,
  44                                    bool IsPCRel) const;
  45   };
  46 }
  47
  48 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
  49   : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
  50                             ELF::EM_ARM,
  51                             /*HasRelocationAddend*/ false) {}
  52
  53 ARMELFObjectWriter::~ARMELFObjectWriter() {}
  54
  55 // In ARM, _MergedGlobals and other most symbols get emitted directly.
  56 // I.e. not as an offset to a section symbol.
  57 // This code is an approximation of what ARM/gcc does.
  58
  59 STATISTIC(PCRelCount, "Total number of PIC Relocations");
  60 STATISTIC(NonPCRelCount, "Total number of non-PIC relocations");
  61
  62 const MCSymbol *ARMELFObjectWriter::ExplicitRelSym(const MCAssembler &Asm,
  63                                                    const MCValue &Target,
  64                                                    const MCFragment &F,
  65                                                    const MCFixup &Fixup,
  66                                                    bool IsPCRel) const {
  67   const MCSymbol &Symbol = Target.getSymA()->getSymbol().AliasedSymbol();
  68   bool EmitThisSym = false;
  69
  70   const MCSectionELF &Section =
  71     static_cast<const MCSectionELF&>(Symbol.getSection());
  72   bool InNormalSection = true;
  73   unsigned RelocType = 0;
  74   RelocType = GetRelocTypeInner(Target, Fixup, IsPCRel);
  75
  76   DEBUG(
  77       const MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
  78       MCSymbolRefExpr::VariantKind Kind2;
  79       Kind2 = Target.getSymB() ?  Target.getSymB()->getKind() :
  80         MCSymbolRefExpr::VK_None;
  81       dbgs() << "considering symbol "
  82         << Section.getSectionName() << "/"
  83         << Symbol.getName() << "/"
  84         << " Rel:" << (unsigned)RelocType
  85         << " Kind: " << (int)Kind << "/" << (int)Kind2
  86         << " Tmp:"
  87         << Symbol.isAbsolute() << "/" << Symbol.isDefined() << "/"
  88         << Symbol.isVariable() << "/" << Symbol.isTemporary()
  89         << " Counts:" << PCRelCount << "/" << NonPCRelCount << "\n");
  90
  91   if (IsPCRel) { ++PCRelCount;
  92     switch (RelocType) {
  93     default:
  94       // Most relocation types are emitted as explicit symbols
  95       InNormalSection =
  96         StringSwitch<bool>(Section.getSectionName())
  97         .Case(".data.rel.ro.local", false)
  98         .Case(".data.rel", false)
  99         .Case(".bss", false)
 100         .Default(true);
 101       EmitThisSym = true;
 102       break;
 103     case ELF::R_ARM_ABS32:
 104       // But things get strange with R_ARM_ABS32
 105       // In this case, most things that go in .rodata show up
 106       // as section relative relocations
 107       InNormalSection =
 108         StringSwitch<bool>(Section.getSectionName())
 109         .Case(".data.rel.ro.local", false)
 110         .Case(".data.rel", false)
 111         .Case(".rodata", false)
 112         .Case(".bss", false)
 113         .Default(true);
 114       EmitThisSym = false;
 115       break;
 116     }
 117   } else {
 118     NonPCRelCount++;
 119     InNormalSection =
 120       StringSwitch<bool>(Section.getSectionName())
 121       .Case(".data.rel.ro.local", false)
 122       .Case(".rodata", false)
 123       .Case(".data.rel", false)
 124       .Case(".bss", false)
 125       .Default(true);
 126
 127     switch (RelocType) {
 128     default: EmitThisSym = true; break;
 129     case ELF::R_ARM_ABS32: EmitThisSym = false; break;
 130     case ELF::R_ARM_PREL31: EmitThisSym = false; break;
 131     }
 132   }
 133
 134   if (EmitThisSym)
 135     return &Symbol;
 136   if (! Symbol.isTemporary() && InNormalSection) {
 137     return &Symbol;
 138   }
 139   return NULL;
 140 }
 141
 142 // Need to examine the Fixup when determining whether to
 143 // emit the relocation as an explicit symbol or as a section relative
 144 // offset
 145 unsigned ARMELFObjectWriter::GetRelocType(const MCValue &Target,
 146                                           const MCFixup &Fixup,
 147                                           bool IsPCRel,
 148                                           bool IsRelocWithSymbol,
 149                                           int64_t Addend) const {
 150   return GetRelocTypeInner(Target, Fixup, IsPCRel);
 151 }
 152
 153 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
 154                                                const MCFixup &Fixup,
 155                                                bool IsPCRel) const  {
 156   MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ?
 157     MCSymbolRefExpr::VK_None : Target.getSymA()->getKind();
 158
 159   unsigned Type = 0;
 160   if (IsPCRel) {
 161     switch ((unsigned)Fixup.getKind()) {
 162     default: llvm_unreachable("Unimplemented");
 163     case FK_Data_4:
 164       switch (Modifier) {
 165       default: llvm_unreachable("Unsupported Modifier");
 166       case MCSymbolRefExpr::VK_None:
 167         Type = ELF::R_ARM_REL32;
 168         break;
 169       case MCSymbolRefExpr::VK_TLSGD:
 170         llvm_unreachable("unimplemented");
 171       case MCSymbolRefExpr::VK_GOTTPOFF:
 172         Type = ELF::R_ARM_TLS_IE32;
 173         break;
 174       }
 175       break;
 176     case ARM::fixup_arm_blx:
 177     case ARM::fixup_arm_uncondbl:
 178       switch (Modifier) {
 179       case MCSymbolRefExpr::VK_PLT:
 180         Type = ELF::R_ARM_PLT32;
 181         break;
 182       case MCSymbolRefExpr::VK_ARM_TLSCALL:
 183         Type = ELF::R_ARM_TLS_CALL;
 184         break;
 185       default:
 186         Type = ELF::R_ARM_CALL;
 187         break;
 188       }
 189       break;
 190     case ARM::fixup_arm_condbl:
 191     case ARM::fixup_arm_condbranch:
 192     case ARM::fixup_arm_uncondbranch:
 193       Type = ELF::R_ARM_JUMP24;
 194       break;
 195     case ARM::fixup_t2_condbranch:
 196     case ARM::fixup_t2_uncondbranch:
 197       Type = ELF::R_ARM_THM_JUMP24;
 198       break;
 199     case ARM::fixup_arm_movt_hi16:
 200     case ARM::fixup_arm_movt_hi16_pcrel:
 201       Type = ELF::R_ARM_MOVT_PREL;
 202       break;
 203     case ARM::fixup_arm_movw_lo16:
 204     case ARM::fixup_arm_movw_lo16_pcrel:
 205       Type = ELF::R_ARM_MOVW_PREL_NC;
 206       break;
 207     case ARM::fixup_t2_movt_hi16:
 208     case ARM::fixup_t2_movt_hi16_pcrel:
 209       Type = ELF::R_ARM_THM_MOVT_PREL;
 210       break;
 211     case ARM::fixup_t2_movw_lo16:
 212     case ARM::fixup_t2_movw_lo16_pcrel:
 213       Type = ELF::R_ARM_THM_MOVW_PREL_NC;
 214       break;
 215     case ARM::fixup_arm_thumb_bl:
 216     case ARM::fixup_arm_thumb_blx:
 217       switch (Modifier) {
 218       case MCSymbolRefExpr::VK_ARM_TLSCALL:
 219         Type = ELF::R_ARM_THM_TLS_CALL;
 220         break;
 221       default:
 222         Type = ELF::R_ARM_THM_CALL;
 223         break;
 224       }
 225       break;
 226     }
 227   } else {
 228     switch ((unsigned)Fixup.getKind()) {
 229     default: llvm_unreachable("invalid fixup kind!");
 230     case FK_Data_4:
 231       switch (Modifier) {
 232       default: llvm_unreachable("Unsupported Modifier");
 233       case MCSymbolRefExpr::VK_ARM_NONE:
 234         Type = ELF::R_ARM_NONE;
 235         break;
 236       case MCSymbolRefExpr::VK_GOT:
 237         Type = ELF::R_ARM_GOT_BREL;
 238         break;
 239       case MCSymbolRefExpr::VK_TLSGD:
 240         Type = ELF::R_ARM_TLS_GD32;
 241         break;
 242       case MCSymbolRefExpr::VK_TPOFF:
 243         Type = ELF::R_ARM_TLS_LE32;
 244         break;
 245       case MCSymbolRefExpr::VK_GOTTPOFF:
 246         Type = ELF::R_ARM_TLS_IE32;
 247         break;
 248       case MCSymbolRefExpr::VK_None:
 249         Type = ELF::R_ARM_ABS32;
 250         break;
 251       case MCSymbolRefExpr::VK_GOTOFF:
 252         Type = ELF::R_ARM_GOTOFF32;
 253         break;
 254       case MCSymbolRefExpr::VK_ARM_TARGET1:
 255         Type = ELF::R_ARM_TARGET1;
 256         break;
 257       case MCSymbolRefExpr::VK_ARM_TARGET2:
 258         Type = ELF::R_ARM_TARGET2;
 259         break;
 260       case MCSymbolRefExpr::VK_ARM_PREL31:
 261         Type = ELF::R_ARM_PREL31;
 262         break;
 263       case MCSymbolRefExpr::VK_ARM_TLSLDO:
 264         Type = ELF::R_ARM_TLS_LDO32;
 265         break;
 266       case MCSymbolRefExpr::VK_ARM_TLSCALL:
 267         Type = ELF::R_ARM_TLS_CALL;
 268         break;
 269       case MCSymbolRefExpr::VK_ARM_TLSDESC:
 270         Type = ELF::R_ARM_TLS_GOTDESC;
 271         break;
 272       case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
 273         Type = ELF::R_ARM_TLS_DESCSEQ;
 274         break;
 275       }
 276       break;
 277     case ARM::fixup_arm_ldst_pcrel_12:
 278     case ARM::fixup_arm_pcrel_10:
 279     case ARM::fixup_arm_adr_pcrel_12:
 280     case ARM::fixup_arm_thumb_bl:
 281     case ARM::fixup_arm_thumb_cb:
 282     case ARM::fixup_arm_thumb_cp:
 283     case ARM::fixup_arm_thumb_br:
 284       llvm_unreachable("Unimplemented");
 285     case ARM::fixup_arm_condbranch:
 286     case ARM::fixup_arm_uncondbranch:
 287       Type = ELF::R_ARM_JUMP24;
 288       break;
 289     case ARM::fixup_arm_movt_hi16:
 290       Type = ELF::R_ARM_MOVT_ABS;
 291       break;
 292     case ARM::fixup_arm_movw_lo16:
 293       Type = ELF::R_ARM_MOVW_ABS_NC;
 294       break;
 295     case ARM::fixup_t2_movt_hi16:
 296       Type = ELF::R_ARM_THM_MOVT_ABS;
 297       break;
 298     case ARM::fixup_t2_movw_lo16:
 299       Type = ELF::R_ARM_THM_MOVW_ABS_NC;
 300       break;
 301     }
 302   }
 303
 304   return Type;
 305 }
 306
 307 MCObjectWriter *llvm::createARMELFObjectWriter(raw_ostream &OS,
 308                                                uint8_t OSABI) {
 309   MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
 310   return createELFObjectWriter(MOTW, OS,  /*IsLittleEndian=*/true);
 311 }