lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp

   1 //===-- ARMELFObjectWriter.cpp - ARM ELF 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/BinaryFormat/ELF.h"
  12 #include "llvm/MC/MCContext.h"
  13 #include "llvm/MC/MCELFObjectWriter.h"
  14 #include "llvm/MC/MCExpr.h"
  15 #include "llvm/MC/MCFixup.h"
  16 #include "llvm/MC/MCObjectFileInfo.h"
  17 #include "llvm/MC/MCObjectWriter.h"
  18 #include "llvm/MC/MCValue.h"
  19 #include "llvm/Support/ErrorHandling.h"
  20 #include "llvm/Support/raw_ostream.h"
  21 #include <cstdint>
  22
  23 using namespace llvm;
  24
  25 namespace {
  26
  27   class ARMELFObjectWriter : public MCELFObjectTargetWriter {
  28     enum { DefaultEABIVersion = 0x05000000U };
  29
  30     unsigned GetRelocTypeInner(const MCValue &Target, const MCFixup &Fixup,
  31                                bool IsPCRel, MCContext &Ctx) const;
  32
  33   public:
  34     ARMELFObjectWriter(uint8_t OSABI);
  35
  36     ~ARMELFObjectWriter() override = default;
  37
  38     unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
  39                           const MCFixup &Fixup, bool IsPCRel) const override;
  40
  41     bool needsRelocateWithSymbol(const MCSymbol &Sym,
  42                                  unsigned Type) const override;
  43
  44     void addTargetSectionFlags(MCContext &Ctx, MCSectionELF &Sec) override;
  45   };
  46
  47 } // end anonymous namespace
  48
  49 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
  50   : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
  51                             ELF::EM_ARM,
  52                             /*HasRelocationAddend*/ false) {}
  53
  54 bool ARMELFObjectWriter::needsRelocateWithSymbol(const MCSymbol &Sym,
  55                                                  unsigned Type) const {
  56   // FIXME: This is extremely conservative. This really needs to use a
  57   // whitelist with a clear explanation for why each realocation needs to
  58   // point to the symbol, not to the section.
  59   switch (Type) {
  60   default:
  61     return true;
  62
  63   case ELF::R_ARM_PREL31:
  64   case ELF::R_ARM_ABS32:
  65     return false;
  66   }
  67 }
  68
  69 // Need to examine the Fixup when determining whether to
  70 // emit the relocation as an explicit symbol or as a section relative
  71 // offset
  72 unsigned ARMELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
  73                                           const MCFixup &Fixup,
  74                                           bool IsPCRel) const {
  75   return GetRelocTypeInner(Target, Fixup, IsPCRel, Ctx);
  76 }
  77
  78 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
  79                                                const MCFixup &Fixup,
  80                                                bool IsPCRel,
  81                                                MCContext &Ctx) const {
  82   MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
  83
  84   if (IsPCRel) {
  85     switch ((unsigned)Fixup.getKind()) {
  86     default:
  87       Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol");
  88       return ELF::R_ARM_NONE;
  89     case FK_Data_4:
  90       switch (Modifier) {
  91       default:
  92         llvm_unreachable("Unsupported Modifier");
  93       case MCSymbolRefExpr::VK_None:
  94         return ELF::R_ARM_REL32;
  95       case MCSymbolRefExpr::VK_GOTTPOFF:
  96         return ELF::R_ARM_TLS_IE32;
  97       case MCSymbolRefExpr::VK_ARM_GOT_PREL:
  98         return ELF::R_ARM_GOT_PREL;
  99       case MCSymbolRefExpr::VK_ARM_PREL31:
 100         return ELF::R_ARM_PREL31;
 101       }
 102     case ARM::fixup_arm_blx:
 103     case ARM::fixup_arm_uncondbl:
 104       switch (Modifier) {
 105       case MCSymbolRefExpr::VK_PLT:
 106         return ELF::R_ARM_CALL;
 107       case MCSymbolRefExpr::VK_TLSCALL:
 108         return ELF::R_ARM_TLS_CALL;
 109       default:
 110         return ELF::R_ARM_CALL;
 111       }
 112     case ARM::fixup_arm_condbl:
 113     case ARM::fixup_arm_condbranch:
 114     case ARM::fixup_arm_uncondbranch:
 115       return ELF::R_ARM_JUMP24;
 116     case ARM::fixup_t2_condbranch:
 117       return ELF::R_ARM_THM_JUMP19;
 118     case ARM::fixup_t2_uncondbranch:
 119       return ELF::R_ARM_THM_JUMP24;
 120     case ARM::fixup_arm_movt_hi16:
 121       return ELF::R_ARM_MOVT_PREL;
 122     case ARM::fixup_arm_movw_lo16:
 123       return ELF::R_ARM_MOVW_PREL_NC;
 124     case ARM::fixup_t2_movt_hi16:
 125       return ELF::R_ARM_THM_MOVT_PREL;
 126     case ARM::fixup_t2_movw_lo16:
 127       return ELF::R_ARM_THM_MOVW_PREL_NC;
 128     case ARM::fixup_arm_thumb_br:
 129       return ELF::R_ARM_THM_JUMP11;
 130     case ARM::fixup_arm_thumb_bcc:
 131       return ELF::R_ARM_THM_JUMP8;
 132     case ARM::fixup_arm_thumb_bl:
 133     case ARM::fixup_arm_thumb_blx:
 134       switch (Modifier) {
 135       case MCSymbolRefExpr::VK_TLSCALL:
 136         return ELF::R_ARM_THM_TLS_CALL;
 137       default:
 138         return ELF::R_ARM_THM_CALL;
 139       }
 140     }
 141   }
 142   switch ((unsigned)Fixup.getKind()) {
 143   default:
 144     Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol");
 145     return ELF::R_ARM_NONE;
 146   case FK_Data_1:
 147     switch (Modifier) {
 148     default:
 149       llvm_unreachable("unsupported Modifier");
 150     case MCSymbolRefExpr::VK_None:
 151       return ELF::R_ARM_ABS8;
 152     }
 153   case FK_Data_2:
 154     switch (Modifier) {
 155     default:
 156       llvm_unreachable("unsupported modifier");
 157     case MCSymbolRefExpr::VK_None:
 158       return ELF::R_ARM_ABS16;
 159     }
 160   case FK_Data_4:
 161     switch (Modifier) {
 162     default:
 163       llvm_unreachable("Unsupported Modifier");
 164     case MCSymbolRefExpr::VK_ARM_NONE:
 165       return ELF::R_ARM_NONE;
 166     case MCSymbolRefExpr::VK_GOT:
 167       return ELF::R_ARM_GOT_BREL;
 168     case MCSymbolRefExpr::VK_TLSGD:
 169       return ELF::R_ARM_TLS_GD32;
 170     case MCSymbolRefExpr::VK_TPOFF:
 171       return ELF::R_ARM_TLS_LE32;
 172     case MCSymbolRefExpr::VK_GOTTPOFF:
 173       return ELF::R_ARM_TLS_IE32;
 174     case MCSymbolRefExpr::VK_None:
 175       return ELF::R_ARM_ABS32;
 176     case MCSymbolRefExpr::VK_GOTOFF:
 177       return ELF::R_ARM_GOTOFF32;
 178     case MCSymbolRefExpr::VK_ARM_GOT_PREL:
 179       return ELF::R_ARM_GOT_PREL;
 180     case MCSymbolRefExpr::VK_ARM_TARGET1:
 181       return ELF::R_ARM_TARGET1;
 182     case MCSymbolRefExpr::VK_ARM_TARGET2:
 183       return ELF::R_ARM_TARGET2;
 184     case MCSymbolRefExpr::VK_ARM_PREL31:
 185       return ELF::R_ARM_PREL31;
 186     case MCSymbolRefExpr::VK_ARM_SBREL:
 187       return ELF::R_ARM_SBREL32;
 188     case MCSymbolRefExpr::VK_ARM_TLSLDO:
 189       return ELF::R_ARM_TLS_LDO32;
 190     case MCSymbolRefExpr::VK_TLSCALL:
 191       return ELF::R_ARM_TLS_CALL;
 192     case MCSymbolRefExpr::VK_TLSDESC:
 193       return ELF::R_ARM_TLS_GOTDESC;
 194     case MCSymbolRefExpr::VK_TLSLDM:
 195       return ELF::R_ARM_TLS_LDM32;
 196     case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
 197       return ELF::R_ARM_TLS_DESCSEQ;
 198     }
 199   case ARM::fixup_arm_condbranch:
 200   case ARM::fixup_arm_uncondbranch:
 201     return ELF::R_ARM_JUMP24;
 202   case ARM::fixup_arm_movt_hi16:
 203     switch (Modifier) {
 204     default:
 205       llvm_unreachable("Unsupported Modifier");
 206     case MCSymbolRefExpr::VK_None:
 207       return ELF::R_ARM_MOVT_ABS;
 208     case MCSymbolRefExpr::VK_ARM_SBREL:
 209       return ELF::R_ARM_MOVT_BREL;
 210     }
 211   case ARM::fixup_arm_movw_lo16:
 212     switch (Modifier) {
 213     default:
 214       llvm_unreachable("Unsupported Modifier");
 215     case MCSymbolRefExpr::VK_None:
 216       return ELF::R_ARM_MOVW_ABS_NC;
 217     case MCSymbolRefExpr::VK_ARM_SBREL:
 218       return ELF::R_ARM_MOVW_BREL_NC;
 219     }
 220   case ARM::fixup_t2_movt_hi16:
 221     switch (Modifier) {
 222     default:
 223       llvm_unreachable("Unsupported Modifier");
 224     case MCSymbolRefExpr::VK_None:
 225       return ELF::R_ARM_THM_MOVT_ABS;
 226     case MCSymbolRefExpr::VK_ARM_SBREL:
 227       return ELF::R_ARM_THM_MOVT_BREL;
 228     }
 229   case ARM::fixup_t2_movw_lo16:
 230     switch (Modifier) {
 231     default:
 232       llvm_unreachable("Unsupported Modifier");
 233     case MCSymbolRefExpr::VK_None:
 234       return ELF::R_ARM_THM_MOVW_ABS_NC;
 235     case MCSymbolRefExpr::VK_ARM_SBREL:
 236       return ELF::R_ARM_THM_MOVW_BREL_NC;
 237     }
 238   }
 239 }
 240
 241 void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx,
 242                                                MCSectionELF &Sec) {
 243   // The mix of execute-only and non-execute-only at link time is
 244   // non-execute-only. To avoid the empty implicitly created .text
 245   // section from making the whole .text section non-execute-only, we
 246   // mark it execute-only if it is empty and there is at least one
 247   // execute-only section in the object.
 248   MCSectionELF *TextSection =
 249       static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection());
 250   if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions() &&
 251       !TextSection->hasData()) {
 252     TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE);
 253   }
 254 }
 255
 256 std::unique_ptr<MCObjectTargetWriter>
 257 llvm::createARMELFObjectWriter(uint8_t OSABI) {
 258   return llvm::make_unique<ARMELFObjectWriter>(OSABI);
 259 }