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 MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant(); 83 84 if (IsPCRel) { 85 switch (Fixup.getTargetKind()) { 86 default: 87 Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol"); 88 return ELF::R_ARM_NONE; 89 case FK_Data_4: 90 switch (Modifier) { 91 default: 92 llvm_unreachable("Unsupported Modifier"); 93 case MCSymbolRefExpr::VK_None: 94 return ELF::R_ARM_REL32; 95 case MCSymbolRefExpr::VK_GOTTPOFF: 96 return ELF::R_ARM_TLS_IE32; 97 case MCSymbolRefExpr::VK_ARM_GOT_PREL: 98 return ELF::R_ARM_GOT_PREL; 99 case MCSymbolRefExpr::VK_ARM_PREL31: 100 return ELF::R_ARM_PREL31; 101 } 102 case ARM::fixup_arm_blx: 103 case ARM::fixup_arm_uncondbl: 104 switch (Modifier) { 105 case MCSymbolRefExpr::VK_PLT: 106 return ELF::R_ARM_CALL; 107 case MCSymbolRefExpr::VK_TLSCALL: 108 return ELF::R_ARM_TLS_CALL; 109 default: 110 return ELF::R_ARM_CALL; 111 } 112 case ARM::fixup_arm_condbl: 113 case ARM::fixup_arm_condbranch: 114 case ARM::fixup_arm_uncondbranch: 115 return ELF::R_ARM_JUMP24; 116 case ARM::fixup_t2_condbranch: 117 return ELF::R_ARM_THM_JUMP19; 118 case ARM::fixup_t2_uncondbranch: 119 return ELF::R_ARM_THM_JUMP24; 120 case ARM::fixup_arm_movt_hi16: 121 return ELF::R_ARM_MOVT_PREL; 122 case ARM::fixup_arm_movw_lo16: 123 return ELF::R_ARM_MOVW_PREL_NC; 124 case ARM::fixup_t2_movt_hi16: 125 return ELF::R_ARM_THM_MOVT_PREL; 126 case ARM::fixup_t2_movw_lo16: 127 return ELF::R_ARM_THM_MOVW_PREL_NC; 128 case ARM::fixup_arm_thumb_br: 129 return ELF::R_ARM_THM_JUMP11; 130 case ARM::fixup_arm_thumb_bcc: 131 return ELF::R_ARM_THM_JUMP8; 132 case ARM::fixup_arm_thumb_bl: 133 case ARM::fixup_arm_thumb_blx: 134 switch (Modifier) { 135 case MCSymbolRefExpr::VK_TLSCALL: 136 return ELF::R_ARM_THM_TLS_CALL; 137 default: 138 return ELF::R_ARM_THM_CALL; 139 } 140 case ARM::fixup_bf_target: 141 return ELF::R_ARM_THM_BF16; 142 case ARM::fixup_bfc_target: 143 return ELF::R_ARM_THM_BF12; 144 case ARM::fixup_bfl_target: 145 return ELF::R_ARM_THM_BF18; 146 } 147 } 148 switch (Fixup.getTargetKind()) { 149 default: 150 Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol"); 151 return ELF::R_ARM_NONE; 152 case FK_NONE: 153 return ELF::R_ARM_NONE; 154 case FK_Data_1: 155 switch (Modifier) { 156 default: 157 llvm_unreachable("unsupported Modifier"); 158 case MCSymbolRefExpr::VK_None: 159 return ELF::R_ARM_ABS8; 160 } 161 case FK_Data_2: 162 switch (Modifier) { 163 default: 164 llvm_unreachable("unsupported modifier"); 165 case MCSymbolRefExpr::VK_None: 166 return ELF::R_ARM_ABS16; 167 } 168 case FK_Data_4: 169 switch (Modifier) { 170 default: 171 llvm_unreachable("Unsupported Modifier"); 172 case MCSymbolRefExpr::VK_ARM_NONE: 173 return ELF::R_ARM_NONE; 174 case MCSymbolRefExpr::VK_GOT: 175 return ELF::R_ARM_GOT_BREL; 176 case MCSymbolRefExpr::VK_TLSGD: 177 return ELF::R_ARM_TLS_GD32; 178 case MCSymbolRefExpr::VK_TPOFF: 179 return ELF::R_ARM_TLS_LE32; 180 case MCSymbolRefExpr::VK_GOTTPOFF: 181 return ELF::R_ARM_TLS_IE32; 182 case MCSymbolRefExpr::VK_None: 183 return ELF::R_ARM_ABS32; 184 case MCSymbolRefExpr::VK_GOTOFF: 185 return ELF::R_ARM_GOTOFF32; 186 case MCSymbolRefExpr::VK_ARM_GOT_PREL: 187 return ELF::R_ARM_GOT_PREL; 188 case MCSymbolRefExpr::VK_ARM_TARGET1: 189 return ELF::R_ARM_TARGET1; 190 case MCSymbolRefExpr::VK_ARM_TARGET2: 191 return ELF::R_ARM_TARGET2; 192 case MCSymbolRefExpr::VK_ARM_PREL31: 193 return ELF::R_ARM_PREL31; 194 case MCSymbolRefExpr::VK_ARM_SBREL: 195 return ELF::R_ARM_SBREL32; 196 case MCSymbolRefExpr::VK_ARM_TLSLDO: 197 return ELF::R_ARM_TLS_LDO32; 198 case MCSymbolRefExpr::VK_TLSCALL: 199 return ELF::R_ARM_TLS_CALL; 200 case MCSymbolRefExpr::VK_TLSDESC: 201 return ELF::R_ARM_TLS_GOTDESC; 202 case MCSymbolRefExpr::VK_TLSLDM: 203 return ELF::R_ARM_TLS_LDM32; 204 case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ: 205 return ELF::R_ARM_TLS_DESCSEQ; 206 } 207 case ARM::fixup_arm_condbranch: 208 case ARM::fixup_arm_uncondbranch: 209 return ELF::R_ARM_JUMP24; 210 case ARM::fixup_arm_movt_hi16: 211 switch (Modifier) { 212 default: 213 llvm_unreachable("Unsupported Modifier"); 214 case MCSymbolRefExpr::VK_None: 215 return ELF::R_ARM_MOVT_ABS; 216 case MCSymbolRefExpr::VK_ARM_SBREL: 217 return ELF::R_ARM_MOVT_BREL; 218 } 219 case ARM::fixup_arm_movw_lo16: 220 switch (Modifier) { 221 default: 222 llvm_unreachable("Unsupported Modifier"); 223 case MCSymbolRefExpr::VK_None: 224 return ELF::R_ARM_MOVW_ABS_NC; 225 case MCSymbolRefExpr::VK_ARM_SBREL: 226 return ELF::R_ARM_MOVW_BREL_NC; 227 } 228 case ARM::fixup_t2_movt_hi16: 229 switch (Modifier) { 230 default: 231 llvm_unreachable("Unsupported Modifier"); 232 case MCSymbolRefExpr::VK_None: 233 return ELF::R_ARM_THM_MOVT_ABS; 234 case MCSymbolRefExpr::VK_ARM_SBREL: 235 return ELF::R_ARM_THM_MOVT_BREL; 236 } 237 case ARM::fixup_t2_movw_lo16: 238 switch (Modifier) { 239 default: 240 llvm_unreachable("Unsupported Modifier"); 241 case MCSymbolRefExpr::VK_None: 242 return ELF::R_ARM_THM_MOVW_ABS_NC; 243 case MCSymbolRefExpr::VK_ARM_SBREL: 244 return ELF::R_ARM_THM_MOVW_BREL_NC; 245 } 246 } 247 } 248 249 void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx, 250 MCSectionELF &Sec) { 251 // The mix of execute-only and non-execute-only at link time is 252 // non-execute-only. To avoid the empty implicitly created .text 253 // section from making the whole .text section non-execute-only, we 254 // mark it execute-only if it is empty and there is at least one 255 // execute-only section in the object. 256 MCSectionELF *TextSection = 257 static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection()); 258 if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions()) { 259 for (auto &F : TextSection->getFragmentList()) 260 if (auto *DF = dyn_cast<MCDataFragment>(&F)) 261 if (!DF->getContents().empty()) 262 return; 263 TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE); 264 } 265 } 266 267 std::unique_ptr<MCObjectTargetWriter> 268 llvm::createARMELFObjectWriter(uint8_t OSABI) { 269 return std::make_unique<ARMELFObjectWriter>(OSABI); 270 } 271