1 //===-- HexagonTargetObjectFile.cpp ---------------------------------------===// 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 // This file contains the declarations of the HexagonTargetAsmInfo properties. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #define DEBUG_TYPE "hexagon-sdata" 14 15 #include "HexagonTargetObjectFile.h" 16 #include "llvm/ADT/SmallString.h" 17 #include "llvm/ADT/StringRef.h" 18 #include "llvm/ADT/Twine.h" 19 #include "llvm/BinaryFormat/ELF.h" 20 #include "llvm/IR/DataLayout.h" 21 #include "llvm/IR/DerivedTypes.h" 22 #include "llvm/IR/GlobalObject.h" 23 #include "llvm/IR/GlobalValue.h" 24 #include "llvm/IR/GlobalVariable.h" 25 #include "llvm/IR/Type.h" 26 #include "llvm/MC/MCContext.h" 27 #include "llvm/MC/SectionKind.h" 28 #include "llvm/Support/Casting.h" 29 #include "llvm/Support/CommandLine.h" 30 #include "llvm/Support/Debug.h" 31 #include "llvm/Support/raw_ostream.h" 32 #include "llvm/Target/TargetMachine.h" 33 34 using namespace llvm; 35 36 static cl::opt<unsigned> SmallDataThreshold("hexagon-small-data-threshold", 37 cl::init(8), cl::Hidden, 38 cl::desc("The maximum size of an object in the sdata section")); 39 40 static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(false), 41 cl::Hidden, cl::desc("Disable small data sections sorting")); 42 43 static cl::opt<bool> StaticsInSData("hexagon-statics-in-small-data", 44 cl::init(false), cl::Hidden, cl::ZeroOrMore, 45 cl::desc("Allow static variables in .sdata")); 46 47 static cl::opt<bool> TraceGVPlacement("trace-gv-placement", 48 cl::Hidden, cl::init(false), 49 cl::desc("Trace global value placement")); 50 51 static cl::opt<bool> 52 EmitJtInText("hexagon-emit-jt-text", cl::Hidden, cl::init(false), 53 cl::desc("Emit hexagon jump tables in function section")); 54 55 static cl::opt<bool> 56 EmitLutInText("hexagon-emit-lut-text", cl::Hidden, cl::init(false), 57 cl::desc("Emit hexagon lookup tables in function section")); 58 59 // TraceGVPlacement controls messages for all builds. For builds with assertions 60 // (debug or release), messages are also controlled by the usual debug flags 61 // (e.g. -debug and -debug-only=globallayout) 62 #define TRACE_TO(s, X) s << X 63 #ifdef NDEBUG 64 #define TRACE(X) \ 65 do { \ 66 if (TraceGVPlacement) { \ 67 TRACE_TO(errs(), X); \ 68 } \ 69 } while (false) 70 #else 71 #define TRACE(X) \ 72 do { \ 73 if (TraceGVPlacement) { \ 74 TRACE_TO(errs(), X); \ 75 } else { \ 76 LLVM_DEBUG(TRACE_TO(dbgs(), X)); \ 77 } \ 78 } while (false) 79 #endif 80 81 // Returns true if the section name is such that the symbol will be put 82 // in a small data section. 83 // For instance, global variables with section attributes such as ".sdata" 84 // ".sdata.*", ".sbss", and ".sbss.*" will go into small data. 85 static bool isSmallDataSection(StringRef Sec) { 86 // sectionName is either ".sdata" or ".sbss". Looking for an exact match 87 // obviates the need for checks for section names such as ".sdatafoo". 88 if (Sec.equals(".sdata") || Sec.equals(".sbss") || Sec.equals(".scommon")) 89 return true; 90 // If either ".sdata." or ".sbss." is a substring of the section name 91 // then put the symbol in small data. 92 return Sec.find(".sdata.") != StringRef::npos || 93 Sec.find(".sbss.") != StringRef::npos || 94 Sec.find(".scommon.") != StringRef::npos; 95 } 96 97 static const char *getSectionSuffixForSize(unsigned Size) { 98 switch (Size) { 99 default: 100 return ""; 101 case 1: 102 return ".1"; 103 case 2: 104 return ".2"; 105 case 4: 106 return ".4"; 107 case 8: 108 return ".8"; 109 } 110 } 111 112 void HexagonTargetObjectFile::Initialize(MCContext &Ctx, 113 const TargetMachine &TM) { 114 TargetLoweringObjectFileELF::Initialize(Ctx, TM); 115 InitializeELF(TM.Options.UseInitArray); 116 117 SmallDataSection = 118 getContext().getELFSection(".sdata", ELF::SHT_PROGBITS, 119 ELF::SHF_WRITE | ELF::SHF_ALLOC | 120 ELF::SHF_HEX_GPREL); 121 SmallBSSSection = 122 getContext().getELFSection(".sbss", ELF::SHT_NOBITS, 123 ELF::SHF_WRITE | ELF::SHF_ALLOC | 124 ELF::SHF_HEX_GPREL); 125 } 126 127 MCSection *HexagonTargetObjectFile::SelectSectionForGlobal( 128 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const { 129 TRACE("[SelectSectionForGlobal] GO(" << GO->getName() << ") "); 130 TRACE("input section(" << GO->getSection() << ") "); 131 132 TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "") 133 << (GO->hasLocalLinkage() ? "local_linkage " : "") 134 << (GO->hasInternalLinkage() ? "internal " : "") 135 << (GO->hasExternalLinkage() ? "external " : "") 136 << (GO->hasCommonLinkage() ? "common_linkage " : "") 137 << (GO->hasCommonLinkage() ? "common " : "" ) 138 << (Kind.isCommon() ? "kind_common " : "" ) 139 << (Kind.isBSS() ? "kind_bss " : "" ) 140 << (Kind.isBSSLocal() ? "kind_bss_local " : "" )); 141 142 // If the lookup table is used by more than one function, do not place 143 // it in text section. 144 if (EmitLutInText && GO->getName().startswith("switch.table")) { 145 if (const Function *Fn = getLutUsedFunction(GO)) 146 return selectSectionForLookupTable(GO, TM, Fn); 147 } 148 149 if (isGlobalInSmallSection(GO, TM)) 150 return selectSmallSectionForGlobal(GO, Kind, TM); 151 152 if (Kind.isCommon()) { 153 // This is purely for LTO+Linker Script because commons don't really have a 154 // section. However, the BitcodeSectionWriter pass will query for the 155 // sections of commons (and the linker expects us to know their section) so 156 // we'll return one here. 157 return BSSSection; 158 } 159 160 TRACE("default_ELF_section\n"); 161 // Otherwise, we work the same as ELF. 162 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM); 163 } 164 165 MCSection *HexagonTargetObjectFile::getExplicitSectionGlobal( 166 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const { 167 TRACE("[getExplicitSectionGlobal] GO(" << GO->getName() << ") from(" 168 << GO->getSection() << ") "); 169 TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "") 170 << (GO->hasLocalLinkage() ? "local_linkage " : "") 171 << (GO->hasInternalLinkage() ? "internal " : "") 172 << (GO->hasExternalLinkage() ? "external " : "") 173 << (GO->hasCommonLinkage() ? "common_linkage " : "") 174 << (GO->hasCommonLinkage() ? "common " : "" ) 175 << (Kind.isCommon() ? "kind_common " : "" ) 176 << (Kind.isBSS() ? "kind_bss " : "" ) 177 << (Kind.isBSSLocal() ? "kind_bss_local " : "" )); 178 179 if (GO->hasSection()) { 180 StringRef Section = GO->getSection(); 181 if (Section.find(".access.text.group") != StringRef::npos) 182 return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS, 183 ELF::SHF_ALLOC | ELF::SHF_EXECINSTR); 184 if (Section.find(".access.data.group") != StringRef::npos) 185 return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS, 186 ELF::SHF_WRITE | ELF::SHF_ALLOC); 187 } 188 189 if (isGlobalInSmallSection(GO, TM)) 190 return selectSmallSectionForGlobal(GO, Kind, TM); 191 192 // Otherwise, we work the same as ELF. 193 TRACE("default_ELF_section\n"); 194 return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GO, Kind, TM); 195 } 196 197 /// Return true if this global value should be placed into small data/bss 198 /// section. 199 bool HexagonTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO, 200 const TargetMachine &TM) const { 201 bool HaveSData = isSmallDataEnabled(TM); 202 if (!HaveSData) 203 LLVM_DEBUG(dbgs() << "Small-data allocation is disabled, but symbols " 204 "may have explicit section assignments...\n"); 205 // Only global variables, not functions. 206 LLVM_DEBUG(dbgs() << "Checking if value is in small-data, -G" 207 << SmallDataThreshold << ": \"" << GO->getName() << "\": "); 208 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO); 209 if (!GVar) { 210 LLVM_DEBUG(dbgs() << "no, not a global variable\n"); 211 return false; 212 } 213 214 // Globals with external linkage that have an original section set must be 215 // emitted to that section, regardless of whether we would put them into 216 // small data or not. This is how we can support mixing -G0/-G8 in LTO. 217 if (GVar->hasSection()) { 218 bool IsSmall = isSmallDataSection(GVar->getSection()); 219 LLVM_DEBUG(dbgs() << (IsSmall ? "yes" : "no") 220 << ", has section: " << GVar->getSection() << '\n'); 221 return IsSmall; 222 } 223 224 // If sdata is disabled, stop the checks here. 225 if (!HaveSData) { 226 LLVM_DEBUG(dbgs() << "no, small-data allocation is disabled\n"); 227 return false; 228 } 229 230 if (GVar->isConstant()) { 231 LLVM_DEBUG(dbgs() << "no, is a constant\n"); 232 return false; 233 } 234 235 bool IsLocal = GVar->hasLocalLinkage(); 236 if (!StaticsInSData && IsLocal) { 237 LLVM_DEBUG(dbgs() << "no, is static\n"); 238 return false; 239 } 240 241 Type *GType = GVar->getValueType(); 242 if (isa<ArrayType>(GType)) { 243 LLVM_DEBUG(dbgs() << "no, is an array\n"); 244 return false; 245 } 246 247 // If the type is a struct with no body provided, treat is conservatively. 248 // There cannot be actual definitions of object of such a type in this CU 249 // (only references), so assuming that they are not in sdata is safe. If 250 // these objects end up in the sdata, the references will still be valid. 251 if (StructType *ST = dyn_cast<StructType>(GType)) { 252 if (ST->isOpaque()) { 253 LLVM_DEBUG(dbgs() << "no, has opaque type\n"); 254 return false; 255 } 256 } 257 258 unsigned Size = GVar->getParent()->getDataLayout().getTypeAllocSize(GType); 259 if (Size == 0) { 260 LLVM_DEBUG(dbgs() << "no, has size 0\n"); 261 return false; 262 } 263 if (Size > SmallDataThreshold) { 264 LLVM_DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n'); 265 return false; 266 } 267 268 LLVM_DEBUG(dbgs() << "yes\n"); 269 return true; 270 } 271 272 bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM) 273 const { 274 return SmallDataThreshold > 0 && !TM.isPositionIndependent(); 275 } 276 277 unsigned HexagonTargetObjectFile::getSmallDataSize() const { 278 return SmallDataThreshold; 279 } 280 281 bool HexagonTargetObjectFile::shouldPutJumpTableInFunctionSection( 282 bool UsesLabelDifference, const Function &F) const { 283 return EmitJtInText; 284 } 285 286 /// Descends any type down to "elementary" components, 287 /// discovering the smallest addressable one. 288 /// If zero is returned, declaration will not be modified. 289 unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty, 290 const GlobalValue *GV, const TargetMachine &TM) const { 291 // Assign the smallest element access size to the highest 292 // value which assembler can handle. 293 unsigned SmallestElement = 8; 294 295 if (!Ty) 296 return 0; 297 switch (Ty->getTypeID()) { 298 case Type::StructTyID: { 299 const StructType *STy = cast<const StructType>(Ty); 300 for (auto &E : STy->elements()) { 301 unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM); 302 if (AtomicSize < SmallestElement) 303 SmallestElement = AtomicSize; 304 } 305 return (STy->getNumElements() == 0) ? 0 : SmallestElement; 306 } 307 case Type::ArrayTyID: { 308 const ArrayType *ATy = cast<const ArrayType>(Ty); 309 return getSmallestAddressableSize(ATy->getElementType(), GV, TM); 310 } 311 case Type::VectorTyID: { 312 const VectorType *PTy = cast<const VectorType>(Ty); 313 return getSmallestAddressableSize(PTy->getElementType(), GV, TM); 314 } 315 case Type::PointerTyID: 316 case Type::HalfTyID: 317 case Type::FloatTyID: 318 case Type::DoubleTyID: 319 case Type::IntegerTyID: { 320 const DataLayout &DL = GV->getParent()->getDataLayout(); 321 // It is unfortunate that DL's function take non-const Type*. 322 return DL.getTypeAllocSize(const_cast<Type*>(Ty)); 323 } 324 case Type::FunctionTyID: 325 case Type::VoidTyID: 326 case Type::X86_FP80TyID: 327 case Type::FP128TyID: 328 case Type::PPC_FP128TyID: 329 case Type::LabelTyID: 330 case Type::MetadataTyID: 331 case Type::X86_MMXTyID: 332 case Type::TokenTyID: 333 return 0; 334 } 335 336 return 0; 337 } 338 339 MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal( 340 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const { 341 const Type *GTy = GO->getValueType(); 342 unsigned Size = getSmallestAddressableSize(GTy, GO, TM); 343 344 // If we have -ffunction-section or -fdata-section then we should emit the 345 // global value to a unique section specifically for it... even for sdata. 346 bool EmitUniquedSection = TM.getDataSections(); 347 348 TRACE("Small data. Size(" << Size << ")"); 349 // Handle Small Section classification here. 350 if (Kind.isBSS() || Kind.isBSSLocal()) { 351 // If -mno-sort-sda is not set, find out smallest accessible entity in 352 // declaration and add it to the section name string. 353 // Note. It does not track the actual usage of the value, only its de- 354 // claration. Also, compiler adds explicit pad fields to some struct 355 // declarations - they are currently counted towards smallest addres- 356 // sable entity. 357 if (NoSmallDataSorting) { 358 TRACE(" default sbss\n"); 359 return SmallBSSSection; 360 } 361 362 StringRef Prefix(".sbss"); 363 SmallString<128> Name(Prefix); 364 Name.append(getSectionSuffixForSize(Size)); 365 366 if (EmitUniquedSection) { 367 Name.append("."); 368 Name.append(GO->getName()); 369 } 370 TRACE(" unique sbss(" << Name << ")\n"); 371 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS, 372 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL); 373 } 374 375 if (Kind.isCommon()) { 376 // This is purely for LTO+Linker Script because commons don't really have a 377 // section. However, the BitcodeSectionWriter pass will query for the 378 // sections of commons (and the linker expects us to know their section) so 379 // we'll return one here. 380 if (NoSmallDataSorting) 381 return BSSSection; 382 383 Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size); 384 TRACE(" small COMMON (" << Name << ")\n"); 385 386 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS, 387 ELF::SHF_WRITE | ELF::SHF_ALLOC | 388 ELF::SHF_HEX_GPREL); 389 } 390 391 // We could have changed sdata object to a constant... in this 392 // case the Kind could be wrong for it. 393 if (Kind.isMergeableConst()) { 394 TRACE(" const_object_as_data "); 395 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO); 396 if (GVar->hasSection() && isSmallDataSection(GVar->getSection())) 397 Kind = SectionKind::getData(); 398 } 399 400 if (Kind.isData()) { 401 if (NoSmallDataSorting) { 402 TRACE(" default sdata\n"); 403 return SmallDataSection; 404 } 405 406 StringRef Prefix(".sdata"); 407 SmallString<128> Name(Prefix); 408 Name.append(getSectionSuffixForSize(Size)); 409 410 if (EmitUniquedSection) { 411 Name.append("."); 412 Name.append(GO->getName()); 413 } 414 TRACE(" unique sdata(" << Name << ")\n"); 415 return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS, 416 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL); 417 } 418 419 TRACE("default ELF section\n"); 420 // Otherwise, we work the same as ELF. 421 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM); 422 } 423 424 // Return the function that uses the lookup table. If there are more 425 // than one live function that uses this look table, bail out and place 426 // the lookup table in default section. 427 const Function * 428 HexagonTargetObjectFile::getLutUsedFunction(const GlobalObject *GO) const { 429 const Function *ReturnFn = nullptr; 430 for (auto U : GO->users()) { 431 // validate each instance of user to be a live function. 432 auto *I = dyn_cast<Instruction>(U); 433 if (!I) 434 continue; 435 auto *Bb = I->getParent(); 436 if (!Bb) 437 continue; 438 auto *UserFn = Bb->getParent(); 439 if (!ReturnFn) 440 ReturnFn = UserFn; 441 else if (ReturnFn != UserFn) 442 return nullptr; 443 } 444 return ReturnFn; 445 } 446 447 MCSection *HexagonTargetObjectFile::selectSectionForLookupTable( 448 const GlobalObject *GO, const TargetMachine &TM, const Function *Fn) const { 449 450 SectionKind Kind = SectionKind::getText(); 451 // If the function has explicit section, place the lookup table in this 452 // explicit section. 453 if (Fn->hasSection()) 454 return getExplicitSectionGlobal(Fn, Kind, TM); 455 456 const auto *FuncObj = dyn_cast<GlobalObject>(Fn); 457 return SelectSectionForGlobal(FuncObj, Kind, TM); 458 } 459