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 an 57 // explicit list 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.reportError(Fixup.getLoc(), "unsupported relocation type"); 91 return ELF::R_ARM_NONE; 92 case FK_Data_4: 93 switch (Modifier) { 94 default: 95 Ctx.reportError(Fixup.getLoc(), 96 "invalid fixup for 4-byte pc-relative data relocation"); 97 return ELF::R_ARM_NONE; 98 case MCSymbolRefExpr::VK_None: { 99 if (const MCSymbolRefExpr *SymRef = Target.getSymA()) { 100 // For GNU AS compatibility expressions such as 101 // _GLOBAL_OFFSET_TABLE_ - label emit a R_ARM_BASE_PREL relocation. 102 if (SymRef->getSymbol().getName() == "_GLOBAL_OFFSET_TABLE_") 103 return ELF::R_ARM_BASE_PREL; 104 } 105 return ELF::R_ARM_REL32; 106 } 107 case MCSymbolRefExpr::VK_GOTTPOFF: 108 return ELF::R_ARM_TLS_IE32; 109 case MCSymbolRefExpr::VK_ARM_GOT_PREL: 110 return ELF::R_ARM_GOT_PREL; 111 case MCSymbolRefExpr::VK_ARM_PREL31: 112 return ELF::R_ARM_PREL31; 113 } 114 case ARM::fixup_arm_blx: 115 case ARM::fixup_arm_uncondbl: 116 switch (Modifier) { 117 case MCSymbolRefExpr::VK_PLT: 118 return ELF::R_ARM_CALL; 119 case MCSymbolRefExpr::VK_TLSCALL: 120 return ELF::R_ARM_TLS_CALL; 121 default: 122 return ELF::R_ARM_CALL; 123 } 124 case ARM::fixup_arm_condbl: 125 case ARM::fixup_arm_condbranch: 126 case ARM::fixup_arm_uncondbranch: 127 return ELF::R_ARM_JUMP24; 128 case ARM::fixup_t2_condbranch: 129 return ELF::R_ARM_THM_JUMP19; 130 case ARM::fixup_t2_uncondbranch: 131 return ELF::R_ARM_THM_JUMP24; 132 case ARM::fixup_arm_movt_hi16: 133 return ELF::R_ARM_MOVT_PREL; 134 case ARM::fixup_arm_movw_lo16: 135 return ELF::R_ARM_MOVW_PREL_NC; 136 case ARM::fixup_t2_movt_hi16: 137 return ELF::R_ARM_THM_MOVT_PREL; 138 case ARM::fixup_t2_movw_lo16: 139 return ELF::R_ARM_THM_MOVW_PREL_NC; 140 case ARM::fixup_arm_thumb_upper_8_15: 141 return ELF::R_ARM_THM_ALU_ABS_G3; 142 case ARM::fixup_arm_thumb_upper_0_7: 143 return ELF::R_ARM_THM_ALU_ABS_G2_NC; 144 case ARM::fixup_arm_thumb_lower_8_15: 145 return ELF::R_ARM_THM_ALU_ABS_G1_NC; 146 case ARM::fixup_arm_thumb_lower_0_7: 147 return ELF::R_ARM_THM_ALU_ABS_G0_NC; 148 case ARM::fixup_arm_thumb_br: 149 return ELF::R_ARM_THM_JUMP11; 150 case ARM::fixup_arm_thumb_bcc: 151 return ELF::R_ARM_THM_JUMP8; 152 case ARM::fixup_arm_thumb_bl: 153 case ARM::fixup_arm_thumb_blx: 154 switch (Modifier) { 155 case MCSymbolRefExpr::VK_TLSCALL: 156 return ELF::R_ARM_THM_TLS_CALL; 157 default: 158 return ELF::R_ARM_THM_CALL; 159 } 160 case ARM::fixup_bf_target: 161 return ELF::R_ARM_THM_BF16; 162 case ARM::fixup_bfc_target: 163 return ELF::R_ARM_THM_BF12; 164 case ARM::fixup_bfl_target: 165 return ELF::R_ARM_THM_BF18; 166 } 167 } 168 switch (Kind) { 169 default: 170 Ctx.reportError(Fixup.getLoc(), "unsupported relocation type"); 171 return ELF::R_ARM_NONE; 172 case FK_Data_1: 173 switch (Modifier) { 174 default: 175 Ctx.reportError(Fixup.getLoc(), 176 "invalid fixup for 1-byte data relocation"); 177 return ELF::R_ARM_NONE; 178 case MCSymbolRefExpr::VK_None: 179 return ELF::R_ARM_ABS8; 180 } 181 case FK_Data_2: 182 switch (Modifier) { 183 default: 184 Ctx.reportError(Fixup.getLoc(), 185 "invalid fixup for 2-byte data relocation"); 186 return ELF::R_ARM_NONE; 187 case MCSymbolRefExpr::VK_None: 188 return ELF::R_ARM_ABS16; 189 } 190 case FK_Data_4: 191 switch (Modifier) { 192 default: 193 Ctx.reportError(Fixup.getLoc(), 194 "invalid fixup for 4-byte data relocation"); 195 return ELF::R_ARM_NONE; 196 case MCSymbolRefExpr::VK_ARM_NONE: 197 return ELF::R_ARM_NONE; 198 case MCSymbolRefExpr::VK_GOT: 199 return ELF::R_ARM_GOT_BREL; 200 case MCSymbolRefExpr::VK_TLSGD: 201 return ELF::R_ARM_TLS_GD32; 202 case MCSymbolRefExpr::VK_TPOFF: 203 return ELF::R_ARM_TLS_LE32; 204 case MCSymbolRefExpr::VK_GOTTPOFF: 205 return ELF::R_ARM_TLS_IE32; 206 case MCSymbolRefExpr::VK_None: 207 return ELF::R_ARM_ABS32; 208 case MCSymbolRefExpr::VK_GOTOFF: 209 return ELF::R_ARM_GOTOFF32; 210 case MCSymbolRefExpr::VK_ARM_GOT_PREL: 211 return ELF::R_ARM_GOT_PREL; 212 case MCSymbolRefExpr::VK_ARM_TARGET1: 213 return ELF::R_ARM_TARGET1; 214 case MCSymbolRefExpr::VK_ARM_TARGET2: 215 return ELF::R_ARM_TARGET2; 216 case MCSymbolRefExpr::VK_ARM_PREL31: 217 return ELF::R_ARM_PREL31; 218 case MCSymbolRefExpr::VK_ARM_SBREL: 219 return ELF::R_ARM_SBREL32; 220 case MCSymbolRefExpr::VK_ARM_TLSLDO: 221 return ELF::R_ARM_TLS_LDO32; 222 case MCSymbolRefExpr::VK_TLSCALL: 223 return ELF::R_ARM_TLS_CALL; 224 case MCSymbolRefExpr::VK_TLSDESC: 225 return ELF::R_ARM_TLS_GOTDESC; 226 case MCSymbolRefExpr::VK_TLSLDM: 227 return ELF::R_ARM_TLS_LDM32; 228 case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ: 229 return ELF::R_ARM_TLS_DESCSEQ; 230 } 231 case ARM::fixup_arm_condbranch: 232 case ARM::fixup_arm_uncondbranch: 233 return ELF::R_ARM_JUMP24; 234 case ARM::fixup_arm_movt_hi16: 235 switch (Modifier) { 236 default: 237 Ctx.reportError(Fixup.getLoc(), "invalid fixup for ARM MOVT instruction"); 238 return ELF::R_ARM_NONE; 239 case MCSymbolRefExpr::VK_None: 240 return ELF::R_ARM_MOVT_ABS; 241 case MCSymbolRefExpr::VK_ARM_SBREL: 242 return ELF::R_ARM_MOVT_BREL; 243 } 244 case ARM::fixup_arm_movw_lo16: 245 switch (Modifier) { 246 default: 247 Ctx.reportError(Fixup.getLoc(), "invalid fixup for ARM MOVW instruction"); 248 return ELF::R_ARM_NONE; 249 case MCSymbolRefExpr::VK_None: 250 return ELF::R_ARM_MOVW_ABS_NC; 251 case MCSymbolRefExpr::VK_ARM_SBREL: 252 return ELF::R_ARM_MOVW_BREL_NC; 253 } 254 case ARM::fixup_t2_movt_hi16: 255 switch (Modifier) { 256 default: 257 Ctx.reportError(Fixup.getLoc(), 258 "invalid fixup for Thumb MOVT instruction"); 259 return ELF::R_ARM_NONE; 260 case MCSymbolRefExpr::VK_None: 261 return ELF::R_ARM_THM_MOVT_ABS; 262 case MCSymbolRefExpr::VK_ARM_SBREL: 263 return ELF::R_ARM_THM_MOVT_BREL; 264 } 265 case ARM::fixup_t2_movw_lo16: 266 switch (Modifier) { 267 default: 268 Ctx.reportError(Fixup.getLoc(), 269 "invalid fixup for Thumb MOVW instruction"); 270 return ELF::R_ARM_NONE; 271 case MCSymbolRefExpr::VK_None: 272 return ELF::R_ARM_THM_MOVW_ABS_NC; 273 case MCSymbolRefExpr::VK_ARM_SBREL: 274 return ELF::R_ARM_THM_MOVW_BREL_NC; 275 } 276 277 case ARM::fixup_arm_thumb_upper_8_15: 278 return ELF::R_ARM_THM_ALU_ABS_G3; 279 case ARM::fixup_arm_thumb_upper_0_7: 280 return ELF::R_ARM_THM_ALU_ABS_G2_NC; 281 case ARM::fixup_arm_thumb_lower_8_15: 282 return ELF::R_ARM_THM_ALU_ABS_G1_NC; 283 case ARM::fixup_arm_thumb_lower_0_7: 284 return ELF::R_ARM_THM_ALU_ABS_G0_NC; 285 } 286 } 287 288 void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx, 289 MCSectionELF &Sec) { 290 // The mix of execute-only and non-execute-only at link time is 291 // non-execute-only. To avoid the empty implicitly created .text 292 // section from making the whole .text section non-execute-only, we 293 // mark it execute-only if it is empty and there is at least one 294 // execute-only section in the object. 295 MCSectionELF *TextSection = 296 static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection()); 297 if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions()) { 298 for (auto &F : TextSection->getFragmentList()) 299 if (auto *DF = dyn_cast<MCDataFragment>(&F)) 300 if (!DF->getContents().empty()) 301 return; 302 TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE); 303 } 304 } 305 306 std::unique_ptr<MCObjectTargetWriter> 307 llvm::createARMELFObjectWriter(uint8_t OSABI) { 308 return std::make_unique<ARMELFObjectWriter>(OSABI); 309 } 310