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 } 260