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