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) 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,
 145                                           bool IsRelocWithSymbol) const {
 146   return GetRelocTypeInner(Target, Fixup, IsPCRel);
 147 }
 148
 149 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
 150                                                const MCFixup &Fixup,
 151                                                bool IsPCRel) const  {
 152   MCSymbolRefExpr::VariantKind Modifier = Fixup.getAccessVariant();
 153
 154   unsigned Type = 0;
 155   if (IsPCRel) {
 156     switch ((unsigned)Fixup.getKind()) {
 157     default: llvm_unreachable("Unimplemented");
 158     case FK_Data_4:
 159       switch (Modifier) {
 160       default: llvm_unreachable("Unsupported Modifier");
 161       case MCSymbolRefExpr::VK_None:
 162         Type = ELF::R_ARM_REL32;
 163         break;
 164       case MCSymbolRefExpr::VK_TLSGD:
 165         llvm_unreachable("unimplemented");
 166       case MCSymbolRefExpr::VK_GOTTPOFF:
 167         Type = ELF::R_ARM_TLS_IE32;
 168         break;
 169       }
 170       break;
 171     case ARM::fixup_arm_blx:
 172     case ARM::fixup_arm_uncondbl:
 173       switch (Modifier) {
 174       case MCSymbolRefExpr::VK_PLT:
 175         Type = ELF::R_ARM_PLT32;
 176         break;
 177       case MCSymbolRefExpr::VK_ARM_TLSCALL:
 178         Type = ELF::R_ARM_TLS_CALL;
 179         break;
 180       default:
 181         Type = ELF::R_ARM_CALL;
 182         break;
 183       }
 184       break;
 185     case ARM::fixup_arm_condbl:
 186     case ARM::fixup_arm_condbranch:
 187     case ARM::fixup_arm_uncondbranch:
 188       Type = ELF::R_ARM_JUMP24;
 189       break;
 190     case ARM::fixup_t2_condbranch:
 191     case ARM::fixup_t2_uncondbranch:
 192       Type = ELF::R_ARM_THM_JUMP24;
 193       break;
 194     case ARM::fixup_arm_movt_hi16:
 195     case ARM::fixup_arm_movt_hi16_pcrel:
 196       Type = ELF::R_ARM_MOVT_PREL;
 197       break;
 198     case ARM::fixup_arm_movw_lo16:
 199     case ARM::fixup_arm_movw_lo16_pcrel:
 200       Type = ELF::R_ARM_MOVW_PREL_NC;
 201       break;
 202     case ARM::fixup_t2_movt_hi16:
 203     case ARM::fixup_t2_movt_hi16_pcrel:
 204       Type = ELF::R_ARM_THM_MOVT_PREL;
 205       break;
 206     case ARM::fixup_t2_movw_lo16:
 207     case ARM::fixup_t2_movw_lo16_pcrel:
 208       Type = ELF::R_ARM_THM_MOVW_PREL_NC;
 209       break;
 210     case ARM::fixup_arm_thumb_bl:
 211     case ARM::fixup_arm_thumb_blx:
 212       switch (Modifier) {
 213       case MCSymbolRefExpr::VK_ARM_TLSCALL:
 214         Type = ELF::R_ARM_THM_TLS_CALL;
 215         break;
 216       default:
 217         Type = ELF::R_ARM_THM_CALL;
 218         break;
 219       }
 220       break;
 221     }
 222   } else {
 223     switch ((unsigned)Fixup.getKind()) {
 224     default: llvm_unreachable("invalid fixup kind!");
 225     case FK_Data_4:
 226       switch (Modifier) {
 227       default: llvm_unreachable("Unsupported Modifier");
 228       case MCSymbolRefExpr::VK_ARM_NONE:
 229         Type = ELF::R_ARM_NONE;
 230         break;
 231       case MCSymbolRefExpr::VK_GOT:
 232         Type = ELF::R_ARM_GOT_BREL;
 233         break;
 234       case MCSymbolRefExpr::VK_TLSGD:
 235         Type = ELF::R_ARM_TLS_GD32;
 236         break;
 237       case MCSymbolRefExpr::VK_TPOFF:
 238         Type = ELF::R_ARM_TLS_LE32;
 239         break;
 240       case MCSymbolRefExpr::VK_GOTTPOFF:
 241         Type = ELF::R_ARM_TLS_IE32;
 242         break;
 243       case MCSymbolRefExpr::VK_None:
 244         Type = ELF::R_ARM_ABS32;
 245         break;
 246       case MCSymbolRefExpr::VK_GOTOFF:
 247         Type = ELF::R_ARM_GOTOFF32;
 248         break;
 249       case MCSymbolRefExpr::VK_ARM_TARGET1:
 250         Type = ELF::R_ARM_TARGET1;
 251         break;
 252       case MCSymbolRefExpr::VK_ARM_TARGET2:
 253         Type = ELF::R_ARM_TARGET2;
 254         break;
 255       case MCSymbolRefExpr::VK_ARM_PREL31:
 256         Type = ELF::R_ARM_PREL31;
 257         break;
 258       case MCSymbolRefExpr::VK_ARM_TLSLDO:
 259         Type = ELF::R_ARM_TLS_LDO32;
 260         break;
 261       case MCSymbolRefExpr::VK_ARM_TLSCALL:
 262         Type = ELF::R_ARM_TLS_CALL;
 263         break;
 264       case MCSymbolRefExpr::VK_ARM_TLSDESC:
 265         Type = ELF::R_ARM_TLS_GOTDESC;
 266         break;
 267       case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
 268         Type = ELF::R_ARM_TLS_DESCSEQ;
 269         break;
 270       }
 271       break;
 272     case ARM::fixup_arm_ldst_pcrel_12:
 273     case ARM::fixup_arm_pcrel_10:
 274     case ARM::fixup_arm_adr_pcrel_12:
 275     case ARM::fixup_arm_thumb_bl:
 276     case ARM::fixup_arm_thumb_cb:
 277     case ARM::fixup_arm_thumb_cp:
 278     case ARM::fixup_arm_thumb_br:
 279       llvm_unreachable("Unimplemented");
 280     case ARM::fixup_arm_condbranch:
 281     case ARM::fixup_arm_uncondbranch:
 282       Type = ELF::R_ARM_JUMP24;
 283       break;
 284     case ARM::fixup_arm_movt_hi16:
 285       Type = ELF::R_ARM_MOVT_ABS;
 286       break;
 287     case ARM::fixup_arm_movw_lo16:
 288       Type = ELF::R_ARM_MOVW_ABS_NC;
 289       break;
 290     case ARM::fixup_t2_movt_hi16:
 291       Type = ELF::R_ARM_THM_MOVT_ABS;
 292       break;
 293     case ARM::fixup_t2_movw_lo16:
 294       Type = ELF::R_ARM_THM_MOVW_ABS_NC;
 295       break;
 296     }
 297   }
 298
 299   return Type;
 300 }
 301
 302 MCObjectWriter *llvm::createARMELFObjectWriter(raw_ostream &OS,
 303                                                uint8_t OSABI) {
 304   MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
 305   return createELFObjectWriter(MOTW, OS,  /*IsLittleEndian=*/true);
 306 }