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 MCValue &Val, 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 MCValue &, 55 const MCSymbol &, 56 unsigned Type) const { 57 // FIXME: This is extremely conservative. This really needs to use an 58 // explicit list with a clear explanation for why each realocation needs to 59 // point to the symbol, not to the section. 60 switch (Type) { 61 default: 62 return true; 63 64 case ELF::R_ARM_PREL31: 65 case ELF::R_ARM_ABS32: 66 return false; 67 } 68 } 69 70 // Need to examine the Fixup when determining whether to 71 // emit the relocation as an explicit symbol or as a section relative 72 // offset 73 unsigned ARMELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target, 74 const MCFixup &Fixup, 75 bool IsPCRel) const { 76 return GetRelocTypeInner(Target, Fixup, IsPCRel, Ctx); 77 } 78 79 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target, 80 const MCFixup &Fixup, 81 bool IsPCRel, 82 MCContext &Ctx) const { 83 unsigned Kind = Fixup.getTargetKind(); 84 if (Kind >= FirstLiteralRelocationKind) 85 return Kind - FirstLiteralRelocationKind; 86 MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant(); 87 88 if (IsPCRel) { 89 switch (Fixup.getTargetKind()) { 90 default: 91 Ctx.reportError(Fixup.getLoc(), "unsupported relocation type"); 92 return ELF::R_ARM_NONE; 93 case FK_Data_4: 94 switch (Modifier) { 95 default: 96 Ctx.reportError(Fixup.getLoc(), 97 "invalid fixup for 4-byte pc-relative data relocation"); 98 return ELF::R_ARM_NONE; 99 case MCSymbolRefExpr::VK_None: { 100 if (const MCSymbolRefExpr *SymRef = Target.getSymA()) { 101 // For GNU AS compatibility expressions such as 102 // _GLOBAL_OFFSET_TABLE_ - label emit a R_ARM_BASE_PREL relocation. 103 if (SymRef->getSymbol().getName() == "_GLOBAL_OFFSET_TABLE_") 104 return ELF::R_ARM_BASE_PREL; 105 } 106 return ELF::R_ARM_REL32; 107 } 108 case MCSymbolRefExpr::VK_GOTTPOFF: 109 return ELF::R_ARM_TLS_IE32; 110 case MCSymbolRefExpr::VK_ARM_GOT_PREL: 111 return ELF::R_ARM_GOT_PREL; 112 case MCSymbolRefExpr::VK_ARM_PREL31: 113 return ELF::R_ARM_PREL31; 114 } 115 case ARM::fixup_arm_blx: 116 case ARM::fixup_arm_uncondbl: 117 switch (Modifier) { 118 case MCSymbolRefExpr::VK_PLT: 119 return ELF::R_ARM_CALL; 120 case MCSymbolRefExpr::VK_TLSCALL: 121 return ELF::R_ARM_TLS_CALL; 122 default: 123 return ELF::R_ARM_CALL; 124 } 125 case ARM::fixup_arm_condbl: 126 case ARM::fixup_arm_condbranch: 127 case ARM::fixup_arm_uncondbranch: 128 return ELF::R_ARM_JUMP24; 129 case ARM::fixup_t2_condbranch: 130 return ELF::R_ARM_THM_JUMP19; 131 case ARM::fixup_t2_uncondbranch: 132 return ELF::R_ARM_THM_JUMP24; 133 case ARM::fixup_arm_movt_hi16: 134 return ELF::R_ARM_MOVT_PREL; 135 case ARM::fixup_arm_movw_lo16: 136 return ELF::R_ARM_MOVW_PREL_NC; 137 case ARM::fixup_t2_movt_hi16: 138 return ELF::R_ARM_THM_MOVT_PREL; 139 case ARM::fixup_t2_movw_lo16: 140 return ELF::R_ARM_THM_MOVW_PREL_NC; 141 case ARM::fixup_arm_thumb_upper_8_15: 142 return ELF::R_ARM_THM_ALU_ABS_G3; 143 case ARM::fixup_arm_thumb_upper_0_7: 144 return ELF::R_ARM_THM_ALU_ABS_G2_NC; 145 case ARM::fixup_arm_thumb_lower_8_15: 146 return ELF::R_ARM_THM_ALU_ABS_G1_NC; 147 case ARM::fixup_arm_thumb_lower_0_7: 148 return ELF::R_ARM_THM_ALU_ABS_G0_NC; 149 case ARM::fixup_arm_thumb_br: 150 return ELF::R_ARM_THM_JUMP11; 151 case ARM::fixup_arm_thumb_bcc: 152 return ELF::R_ARM_THM_JUMP8; 153 case ARM::fixup_arm_thumb_bl: 154 case ARM::fixup_arm_thumb_blx: 155 switch (Modifier) { 156 case MCSymbolRefExpr::VK_TLSCALL: 157 return ELF::R_ARM_THM_TLS_CALL; 158 default: 159 return ELF::R_ARM_THM_CALL; 160 } 161 case ARM::fixup_arm_ldst_pcrel_12: 162 return ELF::R_ARM_LDR_PC_G0; 163 case ARM::fixup_arm_pcrel_10_unscaled: 164 return ELF::R_ARM_LDRS_PC_G0; 165 case ARM::fixup_t2_ldst_pcrel_12: 166 return ELF::R_ARM_THM_PC12; 167 case ARM::fixup_arm_adr_pcrel_12: 168 return ELF::R_ARM_ALU_PC_G0; 169 case ARM::fixup_thumb_adr_pcrel_10: 170 return ELF::R_ARM_THM_PC8; 171 case ARM::fixup_t2_adr_pcrel_12: 172 return ELF::R_ARM_THM_ALU_PREL_11_0; 173 case ARM::fixup_bf_target: 174 return ELF::R_ARM_THM_BF16; 175 case ARM::fixup_bfc_target: 176 return ELF::R_ARM_THM_BF12; 177 case ARM::fixup_bfl_target: 178 return ELF::R_ARM_THM_BF18; 179 } 180 } 181 switch (Kind) { 182 default: 183 Ctx.reportError(Fixup.getLoc(), "unsupported relocation type"); 184 return ELF::R_ARM_NONE; 185 case FK_Data_1: 186 switch (Modifier) { 187 default: 188 Ctx.reportError(Fixup.getLoc(), 189 "invalid fixup for 1-byte data relocation"); 190 return ELF::R_ARM_NONE; 191 case MCSymbolRefExpr::VK_None: 192 return ELF::R_ARM_ABS8; 193 } 194 case FK_Data_2: 195 switch (Modifier) { 196 default: 197 Ctx.reportError(Fixup.getLoc(), 198 "invalid fixup for 2-byte data relocation"); 199 return ELF::R_ARM_NONE; 200 case MCSymbolRefExpr::VK_None: 201 return ELF::R_ARM_ABS16; 202 } 203 case FK_Data_4: 204 switch (Modifier) { 205 default: 206 Ctx.reportError(Fixup.getLoc(), 207 "invalid fixup for 4-byte data relocation"); 208 return ELF::R_ARM_NONE; 209 case MCSymbolRefExpr::VK_ARM_NONE: 210 return ELF::R_ARM_NONE; 211 case MCSymbolRefExpr::VK_GOT: 212 return ELF::R_ARM_GOT_BREL; 213 case MCSymbolRefExpr::VK_TLSGD: 214 return ELF::R_ARM_TLS_GD32; 215 case MCSymbolRefExpr::VK_TPOFF: 216 return ELF::R_ARM_TLS_LE32; 217 case MCSymbolRefExpr::VK_GOTTPOFF: 218 return ELF::R_ARM_TLS_IE32; 219 case MCSymbolRefExpr::VK_None: 220 return ELF::R_ARM_ABS32; 221 case MCSymbolRefExpr::VK_GOTOFF: 222 return ELF::R_ARM_GOTOFF32; 223 case MCSymbolRefExpr::VK_ARM_GOT_PREL: 224 return ELF::R_ARM_GOT_PREL; 225 case MCSymbolRefExpr::VK_ARM_TARGET1: 226 return ELF::R_ARM_TARGET1; 227 case MCSymbolRefExpr::VK_ARM_TARGET2: 228 return ELF::R_ARM_TARGET2; 229 case MCSymbolRefExpr::VK_ARM_PREL31: 230 return ELF::R_ARM_PREL31; 231 case MCSymbolRefExpr::VK_ARM_SBREL: 232 return ELF::R_ARM_SBREL32; 233 case MCSymbolRefExpr::VK_ARM_TLSLDO: 234 return ELF::R_ARM_TLS_LDO32; 235 case MCSymbolRefExpr::VK_TLSCALL: 236 return ELF::R_ARM_TLS_CALL; 237 case MCSymbolRefExpr::VK_TLSDESC: 238 return ELF::R_ARM_TLS_GOTDESC; 239 case MCSymbolRefExpr::VK_TLSLDM: 240 return ELF::R_ARM_TLS_LDM32; 241 case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ: 242 return ELF::R_ARM_TLS_DESCSEQ; 243 } 244 case ARM::fixup_arm_condbranch: 245 case ARM::fixup_arm_uncondbranch: 246 return ELF::R_ARM_JUMP24; 247 case ARM::fixup_arm_movt_hi16: 248 switch (Modifier) { 249 default: 250 Ctx.reportError(Fixup.getLoc(), "invalid fixup for ARM MOVT instruction"); 251 return ELF::R_ARM_NONE; 252 case MCSymbolRefExpr::VK_None: 253 return ELF::R_ARM_MOVT_ABS; 254 case MCSymbolRefExpr::VK_ARM_SBREL: 255 return ELF::R_ARM_MOVT_BREL; 256 } 257 case ARM::fixup_arm_movw_lo16: 258 switch (Modifier) { 259 default: 260 Ctx.reportError(Fixup.getLoc(), "invalid fixup for ARM MOVW instruction"); 261 return ELF::R_ARM_NONE; 262 case MCSymbolRefExpr::VK_None: 263 return ELF::R_ARM_MOVW_ABS_NC; 264 case MCSymbolRefExpr::VK_ARM_SBREL: 265 return ELF::R_ARM_MOVW_BREL_NC; 266 } 267 case ARM::fixup_t2_movt_hi16: 268 switch (Modifier) { 269 default: 270 Ctx.reportError(Fixup.getLoc(), 271 "invalid fixup for Thumb MOVT instruction"); 272 return ELF::R_ARM_NONE; 273 case MCSymbolRefExpr::VK_None: 274 return ELF::R_ARM_THM_MOVT_ABS; 275 case MCSymbolRefExpr::VK_ARM_SBREL: 276 return ELF::R_ARM_THM_MOVT_BREL; 277 } 278 case ARM::fixup_t2_movw_lo16: 279 switch (Modifier) { 280 default: 281 Ctx.reportError(Fixup.getLoc(), 282 "invalid fixup for Thumb MOVW instruction"); 283 return ELF::R_ARM_NONE; 284 case MCSymbolRefExpr::VK_None: 285 return ELF::R_ARM_THM_MOVW_ABS_NC; 286 case MCSymbolRefExpr::VK_ARM_SBREL: 287 return ELF::R_ARM_THM_MOVW_BREL_NC; 288 } 289 290 case ARM::fixup_arm_thumb_upper_8_15: 291 return ELF::R_ARM_THM_ALU_ABS_G3; 292 case ARM::fixup_arm_thumb_upper_0_7: 293 return ELF::R_ARM_THM_ALU_ABS_G2_NC; 294 case ARM::fixup_arm_thumb_lower_8_15: 295 return ELF::R_ARM_THM_ALU_ABS_G1_NC; 296 case ARM::fixup_arm_thumb_lower_0_7: 297 return ELF::R_ARM_THM_ALU_ABS_G0_NC; 298 } 299 } 300 301 void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx, 302 MCSectionELF &Sec) { 303 // The mix of execute-only and non-execute-only at link time is 304 // non-execute-only. To avoid the empty implicitly created .text 305 // section from making the whole .text section non-execute-only, we 306 // mark it execute-only if it is empty and there is at least one 307 // execute-only section in the object. 308 MCSectionELF *TextSection = 309 static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection()); 310 if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions()) { 311 for (auto &F : TextSection->getFragmentList()) 312 if (auto *DF = dyn_cast<MCDataFragment>(&F)) 313 if (!DF->getContents().empty()) 314 return; 315 TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE); 316 } 317 } 318 319 std::unique_ptr<MCObjectTargetWriter> 320 llvm::createARMELFObjectWriter(uint8_t OSABI) { 321 return std::make_unique<ARMELFObjectWriter>(OSABI); 322 } 323