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 unsigned Kind = Fixup.getTargetKind(); 83 if (Kind >= FirstLiteralRelocationKind) 84 return Kind - FirstLiteralRelocationKind; 85 MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant(); 86 87 if (IsPCRel) { 88 switch (Fixup.getTargetKind()) { 89 default: 90 Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol"); 91 return ELF::R_ARM_NONE; 92 case FK_Data_4: 93 switch (Modifier) { 94 default: 95 llvm_unreachable("Unsupported Modifier"); 96 case MCSymbolRefExpr::VK_None: { 97 if (const MCSymbolRefExpr *SymRef = Target.getSymA()) { 98 // For GNU AS compatibility expressions such as 99 // _GLOBAL_OFFSET_TABLE_ - label emit a R_ARM_BASE_PREL relocation. 100 if (SymRef->getSymbol().getName() == "_GLOBAL_OFFSET_TABLE_") 101 return ELF::R_ARM_BASE_PREL; 102 } 103 return ELF::R_ARM_REL32; 104 } 105 case MCSymbolRefExpr::VK_GOTTPOFF: 106 return ELF::R_ARM_TLS_IE32; 107 case MCSymbolRefExpr::VK_ARM_GOT_PREL: 108 return ELF::R_ARM_GOT_PREL; 109 case MCSymbolRefExpr::VK_ARM_PREL31: 110 return ELF::R_ARM_PREL31; 111 } 112 case ARM::fixup_arm_blx: 113 case ARM::fixup_arm_uncondbl: 114 switch (Modifier) { 115 case MCSymbolRefExpr::VK_PLT: 116 return ELF::R_ARM_CALL; 117 case MCSymbolRefExpr::VK_TLSCALL: 118 return ELF::R_ARM_TLS_CALL; 119 default: 120 return ELF::R_ARM_CALL; 121 } 122 case ARM::fixup_arm_condbl: 123 case ARM::fixup_arm_condbranch: 124 case ARM::fixup_arm_uncondbranch: 125 return ELF::R_ARM_JUMP24; 126 case ARM::fixup_t2_condbranch: 127 return ELF::R_ARM_THM_JUMP19; 128 case ARM::fixup_t2_uncondbranch: 129 return ELF::R_ARM_THM_JUMP24; 130 case ARM::fixup_arm_movt_hi16: 131 return ELF::R_ARM_MOVT_PREL; 132 case ARM::fixup_arm_movw_lo16: 133 return ELF::R_ARM_MOVW_PREL_NC; 134 case ARM::fixup_t2_movt_hi16: 135 return ELF::R_ARM_THM_MOVT_PREL; 136 case ARM::fixup_t2_movw_lo16: 137 return ELF::R_ARM_THM_MOVW_PREL_NC; 138 case ARM::fixup_arm_thumb_br: 139 return ELF::R_ARM_THM_JUMP11; 140 case ARM::fixup_arm_thumb_bcc: 141 return ELF::R_ARM_THM_JUMP8; 142 case ARM::fixup_arm_thumb_bl: 143 case ARM::fixup_arm_thumb_blx: 144 switch (Modifier) { 145 case MCSymbolRefExpr::VK_TLSCALL: 146 return ELF::R_ARM_THM_TLS_CALL; 147 default: 148 return ELF::R_ARM_THM_CALL; 149 } 150 case ARM::fixup_thumb_adr_pcrel_10: 151 case ARM::fixup_arm_thumb_cp: 152 return ELF::R_ARM_THM_PC8; 153 case ARM::fixup_t2_adr_pcrel_12: 154 return ELF::R_ARM_THM_ALU_PREL_11_0; 155 case ARM::fixup_t2_ldst_pcrel_12: 156 return ELF::R_ARM_THM_PC12; 157 case ARM::fixup_bf_target: 158 return ELF::R_ARM_THM_BF16; 159 case ARM::fixup_bfc_target: 160 return ELF::R_ARM_THM_BF12; 161 case ARM::fixup_bfl_target: 162 return ELF::R_ARM_THM_BF18; 163 } 164 } 165 switch (Kind) { 166 default: 167 Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol"); 168 return ELF::R_ARM_NONE; 169 case FK_Data_1: 170 switch (Modifier) { 171 default: 172 llvm_unreachable("unsupported Modifier"); 173 case MCSymbolRefExpr::VK_None: 174 return ELF::R_ARM_ABS8; 175 } 176 case FK_Data_2: 177 switch (Modifier) { 178 default: 179 llvm_unreachable("unsupported modifier"); 180 case MCSymbolRefExpr::VK_None: 181 return ELF::R_ARM_ABS16; 182 } 183 case FK_Data_4: 184 switch (Modifier) { 185 default: 186 llvm_unreachable("Unsupported Modifier"); 187 case MCSymbolRefExpr::VK_ARM_NONE: 188 return ELF::R_ARM_NONE; 189 case MCSymbolRefExpr::VK_GOT: 190 return ELF::R_ARM_GOT_BREL; 191 case MCSymbolRefExpr::VK_TLSGD: 192 return ELF::R_ARM_TLS_GD32; 193 case MCSymbolRefExpr::VK_TPOFF: 194 return ELF::R_ARM_TLS_LE32; 195 case MCSymbolRefExpr::VK_GOTTPOFF: 196 return ELF::R_ARM_TLS_IE32; 197 case MCSymbolRefExpr::VK_None: 198 return ELF::R_ARM_ABS32; 199 case MCSymbolRefExpr::VK_GOTOFF: 200 return ELF::R_ARM_GOTOFF32; 201 case MCSymbolRefExpr::VK_ARM_GOT_PREL: 202 return ELF::R_ARM_GOT_PREL; 203 case MCSymbolRefExpr::VK_ARM_TARGET1: 204 return ELF::R_ARM_TARGET1; 205 case MCSymbolRefExpr::VK_ARM_TARGET2: 206 return ELF::R_ARM_TARGET2; 207 case MCSymbolRefExpr::VK_ARM_PREL31: 208 return ELF::R_ARM_PREL31; 209 case MCSymbolRefExpr::VK_ARM_SBREL: 210 return ELF::R_ARM_SBREL32; 211 case MCSymbolRefExpr::VK_ARM_TLSLDO: 212 return ELF::R_ARM_TLS_LDO32; 213 case MCSymbolRefExpr::VK_TLSCALL: 214 return ELF::R_ARM_TLS_CALL; 215 case MCSymbolRefExpr::VK_TLSDESC: 216 return ELF::R_ARM_TLS_GOTDESC; 217 case MCSymbolRefExpr::VK_TLSLDM: 218 return ELF::R_ARM_TLS_LDM32; 219 case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ: 220 return ELF::R_ARM_TLS_DESCSEQ; 221 } 222 case ARM::fixup_arm_condbranch: 223 case ARM::fixup_arm_uncondbranch: 224 return ELF::R_ARM_JUMP24; 225 case ARM::fixup_arm_movt_hi16: 226 switch (Modifier) { 227 default: 228 llvm_unreachable("Unsupported Modifier"); 229 case MCSymbolRefExpr::VK_None: 230 return ELF::R_ARM_MOVT_ABS; 231 case MCSymbolRefExpr::VK_ARM_SBREL: 232 return ELF::R_ARM_MOVT_BREL; 233 } 234 case ARM::fixup_arm_movw_lo16: 235 switch (Modifier) { 236 default: 237 llvm_unreachable("Unsupported Modifier"); 238 case MCSymbolRefExpr::VK_None: 239 return ELF::R_ARM_MOVW_ABS_NC; 240 case MCSymbolRefExpr::VK_ARM_SBREL: 241 return ELF::R_ARM_MOVW_BREL_NC; 242 } 243 case ARM::fixup_t2_movt_hi16: 244 switch (Modifier) { 245 default: 246 llvm_unreachable("Unsupported Modifier"); 247 case MCSymbolRefExpr::VK_None: 248 return ELF::R_ARM_THM_MOVT_ABS; 249 case MCSymbolRefExpr::VK_ARM_SBREL: 250 return ELF::R_ARM_THM_MOVT_BREL; 251 } 252 case ARM::fixup_t2_movw_lo16: 253 switch (Modifier) { 254 default: 255 llvm_unreachable("Unsupported Modifier"); 256 case MCSymbolRefExpr::VK_None: 257 return ELF::R_ARM_THM_MOVW_ABS_NC; 258 case MCSymbolRefExpr::VK_ARM_SBREL: 259 return ELF::R_ARM_THM_MOVW_BREL_NC; 260 } 261 } 262 } 263 264 void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx, 265 MCSectionELF &Sec) { 266 // The mix of execute-only and non-execute-only at link time is 267 // non-execute-only. To avoid the empty implicitly created .text 268 // section from making the whole .text section non-execute-only, we 269 // mark it execute-only if it is empty and there is at least one 270 // execute-only section in the object. 271 MCSectionELF *TextSection = 272 static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection()); 273 if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions()) { 274 for (auto &F : TextSection->getFragmentList()) 275 if (auto *DF = dyn_cast<MCDataFragment>(&F)) 276 if (!DF->getContents().empty()) 277 return; 278 TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE); 279 } 280 } 281 282 std::unique_ptr<MCObjectTargetWriter> 283 llvm::createARMELFObjectWriter(uint8_t OSABI) { 284 return std::make_unique<ARMELFObjectWriter>(OSABI); 285 } 286