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.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol"); 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_br: 141 return ELF::R_ARM_THM_JUMP11; 142 case ARM::fixup_arm_thumb_bcc: 143 return ELF::R_ARM_THM_JUMP8; 144 case ARM::fixup_arm_thumb_bl: 145 case ARM::fixup_arm_thumb_blx: 146 switch (Modifier) { 147 case MCSymbolRefExpr::VK_TLSCALL: 148 return ELF::R_ARM_THM_TLS_CALL; 149 default: 150 return ELF::R_ARM_THM_CALL; 151 } 152 case ARM::fixup_bf_target: 153 return ELF::R_ARM_THM_BF16; 154 case ARM::fixup_bfc_target: 155 return ELF::R_ARM_THM_BF12; 156 case ARM::fixup_bfl_target: 157 return ELF::R_ARM_THM_BF18; 158 } 159 } 160 switch (Kind) { 161 default: 162 Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol"); 163 return ELF::R_ARM_NONE; 164 case FK_Data_1: 165 switch (Modifier) { 166 default: 167 Ctx.reportError(Fixup.getLoc(), 168 "invalid fixup for 1-byte data relocation"); 169 return ELF::R_ARM_NONE; 170 case MCSymbolRefExpr::VK_None: 171 return ELF::R_ARM_ABS8; 172 } 173 case FK_Data_2: 174 switch (Modifier) { 175 default: 176 Ctx.reportError(Fixup.getLoc(), 177 "invalid fixup for 2-byte data relocation"); 178 return ELF::R_ARM_NONE; 179 case MCSymbolRefExpr::VK_None: 180 return ELF::R_ARM_ABS16; 181 } 182 case FK_Data_4: 183 switch (Modifier) { 184 default: 185 Ctx.reportError(Fixup.getLoc(), 186 "invalid fixup for 4-byte data relocation"); 187 return ELF::R_ARM_NONE; 188 case MCSymbolRefExpr::VK_ARM_NONE: 189 return ELF::R_ARM_NONE; 190 case MCSymbolRefExpr::VK_GOT: 191 return ELF::R_ARM_GOT_BREL; 192 case MCSymbolRefExpr::VK_TLSGD: 193 return ELF::R_ARM_TLS_GD32; 194 case MCSymbolRefExpr::VK_TPOFF: 195 return ELF::R_ARM_TLS_LE32; 196 case MCSymbolRefExpr::VK_GOTTPOFF: 197 return ELF::R_ARM_TLS_IE32; 198 case MCSymbolRefExpr::VK_None: 199 return ELF::R_ARM_ABS32; 200 case MCSymbolRefExpr::VK_GOTOFF: 201 return ELF::R_ARM_GOTOFF32; 202 case MCSymbolRefExpr::VK_ARM_GOT_PREL: 203 return ELF::R_ARM_GOT_PREL; 204 case MCSymbolRefExpr::VK_ARM_TARGET1: 205 return ELF::R_ARM_TARGET1; 206 case MCSymbolRefExpr::VK_ARM_TARGET2: 207 return ELF::R_ARM_TARGET2; 208 case MCSymbolRefExpr::VK_ARM_PREL31: 209 return ELF::R_ARM_PREL31; 210 case MCSymbolRefExpr::VK_ARM_SBREL: 211 return ELF::R_ARM_SBREL32; 212 case MCSymbolRefExpr::VK_ARM_TLSLDO: 213 return ELF::R_ARM_TLS_LDO32; 214 case MCSymbolRefExpr::VK_TLSCALL: 215 return ELF::R_ARM_TLS_CALL; 216 case MCSymbolRefExpr::VK_TLSDESC: 217 return ELF::R_ARM_TLS_GOTDESC; 218 case MCSymbolRefExpr::VK_TLSLDM: 219 return ELF::R_ARM_TLS_LDM32; 220 case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ: 221 return ELF::R_ARM_TLS_DESCSEQ; 222 } 223 case ARM::fixup_arm_condbranch: 224 case ARM::fixup_arm_uncondbranch: 225 return ELF::R_ARM_JUMP24; 226 case ARM::fixup_arm_movt_hi16: 227 switch (Modifier) { 228 default: 229 Ctx.reportError(Fixup.getLoc(), "invalid fixup for ARM MOVT instruction"); 230 return ELF::R_ARM_NONE; 231 case MCSymbolRefExpr::VK_None: 232 return ELF::R_ARM_MOVT_ABS; 233 case MCSymbolRefExpr::VK_ARM_SBREL: 234 return ELF::R_ARM_MOVT_BREL; 235 } 236 case ARM::fixup_arm_movw_lo16: 237 switch (Modifier) { 238 default: 239 Ctx.reportError(Fixup.getLoc(), "invalid fixup for ARM MOVW instruction"); 240 return ELF::R_ARM_NONE; 241 case MCSymbolRefExpr::VK_None: 242 return ELF::R_ARM_MOVW_ABS_NC; 243 case MCSymbolRefExpr::VK_ARM_SBREL: 244 return ELF::R_ARM_MOVW_BREL_NC; 245 } 246 case ARM::fixup_t2_movt_hi16: 247 switch (Modifier) { 248 default: 249 Ctx.reportError(Fixup.getLoc(), 250 "invalid fixup for Thumb MOVT instruction"); 251 return ELF::R_ARM_NONE; 252 case MCSymbolRefExpr::VK_None: 253 return ELF::R_ARM_THM_MOVT_ABS; 254 case MCSymbolRefExpr::VK_ARM_SBREL: 255 return ELF::R_ARM_THM_MOVT_BREL; 256 } 257 case ARM::fixup_t2_movw_lo16: 258 switch (Modifier) { 259 default: 260 Ctx.reportError(Fixup.getLoc(), 261 "invalid fixup for Thumb MOVW instruction"); 262 return ELF::R_ARM_NONE; 263 case MCSymbolRefExpr::VK_None: 264 return ELF::R_ARM_THM_MOVW_ABS_NC; 265 case MCSymbolRefExpr::VK_ARM_SBREL: 266 return ELF::R_ARM_THM_MOVW_BREL_NC; 267 } 268 } 269 } 270 271 void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx, 272 MCSectionELF &Sec) { 273 // The mix of execute-only and non-execute-only at link time is 274 // non-execute-only. To avoid the empty implicitly created .text 275 // section from making the whole .text section non-execute-only, we 276 // mark it execute-only if it is empty and there is at least one 277 // execute-only section in the object. 278 MCSectionELF *TextSection = 279 static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection()); 280 if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions()) { 281 for (auto &F : TextSection->getFragmentList()) 282 if (auto *DF = dyn_cast<MCDataFragment>(&F)) 283 if (!DF->getContents().empty()) 284 return; 285 TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE); 286 } 287 } 288 289 std::unique_ptr<MCObjectTargetWriter> 290 llvm::createARMELFObjectWriter(uint8_t OSABI) { 291 return std::make_unique<ARMELFObjectWriter>(OSABI); 292 } 293