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_bf_target: 168 return ELF::R_ARM_THM_BF16; 169 case ARM::fixup_bfc_target: 170 return ELF::R_ARM_THM_BF12; 171 case ARM::fixup_bfl_target: 172 return ELF::R_ARM_THM_BF18; 173 } 174 } 175 switch (Kind) { 176 default: 177 Ctx.reportError(Fixup.getLoc(), "unsupported relocation type"); 178 return ELF::R_ARM_NONE; 179 case FK_Data_1: 180 switch (Modifier) { 181 default: 182 Ctx.reportError(Fixup.getLoc(), 183 "invalid fixup for 1-byte data relocation"); 184 return ELF::R_ARM_NONE; 185 case MCSymbolRefExpr::VK_None: 186 return ELF::R_ARM_ABS8; 187 } 188 case FK_Data_2: 189 switch (Modifier) { 190 default: 191 Ctx.reportError(Fixup.getLoc(), 192 "invalid fixup for 2-byte data relocation"); 193 return ELF::R_ARM_NONE; 194 case MCSymbolRefExpr::VK_None: 195 return ELF::R_ARM_ABS16; 196 } 197 case FK_Data_4: 198 switch (Modifier) { 199 default: 200 Ctx.reportError(Fixup.getLoc(), 201 "invalid fixup for 4-byte data relocation"); 202 return ELF::R_ARM_NONE; 203 case MCSymbolRefExpr::VK_ARM_NONE: 204 return ELF::R_ARM_NONE; 205 case MCSymbolRefExpr::VK_GOT: 206 return ELF::R_ARM_GOT_BREL; 207 case MCSymbolRefExpr::VK_TLSGD: 208 return ELF::R_ARM_TLS_GD32; 209 case MCSymbolRefExpr::VK_TPOFF: 210 return ELF::R_ARM_TLS_LE32; 211 case MCSymbolRefExpr::VK_GOTTPOFF: 212 return ELF::R_ARM_TLS_IE32; 213 case MCSymbolRefExpr::VK_None: 214 return ELF::R_ARM_ABS32; 215 case MCSymbolRefExpr::VK_GOTOFF: 216 return ELF::R_ARM_GOTOFF32; 217 case MCSymbolRefExpr::VK_ARM_GOT_PREL: 218 return ELF::R_ARM_GOT_PREL; 219 case MCSymbolRefExpr::VK_ARM_TARGET1: 220 return ELF::R_ARM_TARGET1; 221 case MCSymbolRefExpr::VK_ARM_TARGET2: 222 return ELF::R_ARM_TARGET2; 223 case MCSymbolRefExpr::VK_ARM_PREL31: 224 return ELF::R_ARM_PREL31; 225 case MCSymbolRefExpr::VK_ARM_SBREL: 226 return ELF::R_ARM_SBREL32; 227 case MCSymbolRefExpr::VK_ARM_TLSLDO: 228 return ELF::R_ARM_TLS_LDO32; 229 case MCSymbolRefExpr::VK_TLSCALL: 230 return ELF::R_ARM_TLS_CALL; 231 case MCSymbolRefExpr::VK_TLSDESC: 232 return ELF::R_ARM_TLS_GOTDESC; 233 case MCSymbolRefExpr::VK_TLSLDM: 234 return ELF::R_ARM_TLS_LDM32; 235 case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ: 236 return ELF::R_ARM_TLS_DESCSEQ; 237 } 238 case ARM::fixup_arm_condbranch: 239 case ARM::fixup_arm_uncondbranch: 240 return ELF::R_ARM_JUMP24; 241 case ARM::fixup_arm_movt_hi16: 242 switch (Modifier) { 243 default: 244 Ctx.reportError(Fixup.getLoc(), "invalid fixup for ARM MOVT instruction"); 245 return ELF::R_ARM_NONE; 246 case MCSymbolRefExpr::VK_None: 247 return ELF::R_ARM_MOVT_ABS; 248 case MCSymbolRefExpr::VK_ARM_SBREL: 249 return ELF::R_ARM_MOVT_BREL; 250 } 251 case ARM::fixup_arm_movw_lo16: 252 switch (Modifier) { 253 default: 254 Ctx.reportError(Fixup.getLoc(), "invalid fixup for ARM MOVW instruction"); 255 return ELF::R_ARM_NONE; 256 case MCSymbolRefExpr::VK_None: 257 return ELF::R_ARM_MOVW_ABS_NC; 258 case MCSymbolRefExpr::VK_ARM_SBREL: 259 return ELF::R_ARM_MOVW_BREL_NC; 260 } 261 case ARM::fixup_t2_movt_hi16: 262 switch (Modifier) { 263 default: 264 Ctx.reportError(Fixup.getLoc(), 265 "invalid fixup for Thumb MOVT instruction"); 266 return ELF::R_ARM_NONE; 267 case MCSymbolRefExpr::VK_None: 268 return ELF::R_ARM_THM_MOVT_ABS; 269 case MCSymbolRefExpr::VK_ARM_SBREL: 270 return ELF::R_ARM_THM_MOVT_BREL; 271 } 272 case ARM::fixup_t2_movw_lo16: 273 switch (Modifier) { 274 default: 275 Ctx.reportError(Fixup.getLoc(), 276 "invalid fixup for Thumb MOVW instruction"); 277 return ELF::R_ARM_NONE; 278 case MCSymbolRefExpr::VK_None: 279 return ELF::R_ARM_THM_MOVW_ABS_NC; 280 case MCSymbolRefExpr::VK_ARM_SBREL: 281 return ELF::R_ARM_THM_MOVW_BREL_NC; 282 } 283 284 case ARM::fixup_arm_thumb_upper_8_15: 285 return ELF::R_ARM_THM_ALU_ABS_G3; 286 case ARM::fixup_arm_thumb_upper_0_7: 287 return ELF::R_ARM_THM_ALU_ABS_G2_NC; 288 case ARM::fixup_arm_thumb_lower_8_15: 289 return ELF::R_ARM_THM_ALU_ABS_G1_NC; 290 case ARM::fixup_arm_thumb_lower_0_7: 291 return ELF::R_ARM_THM_ALU_ABS_G0_NC; 292 } 293 } 294 295 void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx, 296 MCSectionELF &Sec) { 297 // The mix of execute-only and non-execute-only at link time is 298 // non-execute-only. To avoid the empty implicitly created .text 299 // section from making the whole .text section non-execute-only, we 300 // mark it execute-only if it is empty and there is at least one 301 // execute-only section in the object. 302 MCSectionELF *TextSection = 303 static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection()); 304 if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions()) { 305 for (auto &F : TextSection->getFragmentList()) 306 if (auto *DF = dyn_cast<MCDataFragment>(&F)) 307 if (!DF->getContents().empty()) 308 return; 309 TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE); 310 } 311 } 312 313 std::unique_ptr<MCObjectTargetWriter> 314 llvm::createARMELFObjectWriter(uint8_t OSABI) { 315 return std::make_unique<ARMELFObjectWriter>(OSABI); 316 } 317