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/Module.h" 26 #include "llvm/IR/Type.h" 27 #include "llvm/MC/MCContext.h" 28 #include "llvm/MC/SectionKind.h" 29 #include "llvm/Support/Casting.h" 30 #include "llvm/Support/CommandLine.h" 31 #include "llvm/Support/Debug.h" 32 #include "llvm/Support/raw_ostream.h" 33 #include "llvm/Target/TargetMachine.h" 34 35 using namespace llvm; 36 37 static cl::opt<unsigned> SmallDataThreshold("hexagon-small-data-threshold", 38 cl::init(8), cl::Hidden, 39 cl::desc("The maximum size of an object in the sdata section")); 40 41 static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(false), 42 cl::Hidden, cl::desc("Disable small data sections sorting")); 43 44 static cl::opt<bool> StaticsInSData("hexagon-statics-in-small-data", 45 cl::init(false), cl::Hidden, cl::ZeroOrMore, 46 cl::desc("Allow static variables in .sdata")); 47 48 static cl::opt<bool> TraceGVPlacement("trace-gv-placement", 49 cl::Hidden, cl::init(false), 50 cl::desc("Trace global value placement")); 51 52 static cl::opt<bool> 53 EmitJtInText("hexagon-emit-jt-text", cl::Hidden, cl::init(false), 54 cl::desc("Emit hexagon jump tables in function section")); 55 56 static cl::opt<bool> 57 EmitLutInText("hexagon-emit-lut-text", cl::Hidden, cl::init(false), 58 cl::desc("Emit hexagon lookup tables in function section")); 59 60 // TraceGVPlacement controls messages for all builds. For builds with assertions 61 // (debug or release), messages are also controlled by the usual debug flags 62 // (e.g. -debug and -debug-only=globallayout) 63 #define TRACE_TO(s, X) s << X 64 #ifdef NDEBUG 65 #define TRACE(X) \ 66 do { \ 67 if (TraceGVPlacement) { \ 68 TRACE_TO(errs(), X); \ 69 } \ 70 } while (false) 71 #else 72 #define TRACE(X) \ 73 do { \ 74 if (TraceGVPlacement) { \ 75 TRACE_TO(errs(), X); \ 76 } else { \ 77 LLVM_DEBUG(TRACE_TO(dbgs(), X)); \ 78 } \ 79 } while (false) 80 #endif 81 82 // Returns true if the section name is such that the symbol will be put 83 // in a small data section. 84 // For instance, global variables with section attributes such as ".sdata" 85 // ".sdata.*", ".sbss", and ".sbss.*" will go into small data. 86 static bool isSmallDataSection(StringRef Sec) { 87 // sectionName is either ".sdata" or ".sbss". Looking for an exact match 88 // obviates the need for checks for section names such as ".sdatafoo". 89 if (Sec.equals(".sdata") || Sec.equals(".sbss") || Sec.equals(".scommon")) 90 return true; 91 // If either ".sdata." or ".sbss." is a substring of the section name 92 // then put the symbol in small data. 93 return Sec.find(".sdata.") != StringRef::npos || 94 Sec.find(".sbss.") != StringRef::npos || 95 Sec.find(".scommon.") != StringRef::npos; 96 } 97 98 static const char *getSectionSuffixForSize(unsigned Size) { 99 switch (Size) { 100 default: 101 return ""; 102 case 1: 103 return ".1"; 104 case 2: 105 return ".2"; 106 case 4: 107 return ".4"; 108 case 8: 109 return ".8"; 110 } 111 } 112 113 void HexagonTargetObjectFile::Initialize(MCContext &Ctx, 114 const TargetMachine &TM) { 115 TargetLoweringObjectFileELF::Initialize(Ctx, TM); 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::FixedVectorTyID: 312 case Type::ScalableVectorTyID: { 313 const VectorType *PTy = cast<const VectorType>(Ty); 314 return getSmallestAddressableSize(PTy->getElementType(), GV, TM); 315 } 316 case Type::PointerTyID: 317 case Type::HalfTyID: 318 case Type::FloatTyID: 319 case Type::DoubleTyID: 320 case Type::IntegerTyID: { 321 const DataLayout &DL = GV->getParent()->getDataLayout(); 322 // It is unfortunate that DL's function take non-const Type*. 323 return DL.getTypeAllocSize(const_cast<Type*>(Ty)); 324 } 325 case Type::FunctionTyID: 326 case Type::VoidTyID: 327 case Type::BFloatTyID: 328 case Type::X86_FP80TyID: 329 case Type::FP128TyID: 330 case Type::PPC_FP128TyID: 331 case Type::LabelTyID: 332 case Type::MetadataTyID: 333 case Type::X86_MMXTyID: 334 case Type::TokenTyID: 335 return 0; 336 } 337 338 return 0; 339 } 340 341 MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal( 342 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const { 343 const Type *GTy = GO->getValueType(); 344 unsigned Size = getSmallestAddressableSize(GTy, GO, TM); 345 346 // If we have -ffunction-section or -fdata-section then we should emit the 347 // global value to a unique section specifically for it... even for sdata. 348 bool EmitUniquedSection = TM.getDataSections(); 349 350 TRACE("Small data. Size(" << Size << ")"); 351 // Handle Small Section classification here. 352 if (Kind.isBSS() || Kind.isBSSLocal()) { 353 // If -mno-sort-sda is not set, find out smallest accessible entity in 354 // declaration and add it to the section name string. 355 // Note. It does not track the actual usage of the value, only its de- 356 // claration. Also, compiler adds explicit pad fields to some struct 357 // declarations - they are currently counted towards smallest addres- 358 // sable entity. 359 if (NoSmallDataSorting) { 360 TRACE(" default sbss\n"); 361 return SmallBSSSection; 362 } 363 364 StringRef Prefix(".sbss"); 365 SmallString<128> Name(Prefix); 366 Name.append(getSectionSuffixForSize(Size)); 367 368 if (EmitUniquedSection) { 369 Name.append("."); 370 Name.append(GO->getName()); 371 } 372 TRACE(" unique sbss(" << Name << ")\n"); 373 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS, 374 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL); 375 } 376 377 if (Kind.isCommon()) { 378 // This is purely for LTO+Linker Script because commons don't really have a 379 // section. However, the BitcodeSectionWriter pass will query for the 380 // sections of commons (and the linker expects us to know their section) so 381 // we'll return one here. 382 if (NoSmallDataSorting) 383 return BSSSection; 384 385 Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size); 386 TRACE(" small COMMON (" << Name << ")\n"); 387 388 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS, 389 ELF::SHF_WRITE | ELF::SHF_ALLOC | 390 ELF::SHF_HEX_GPREL); 391 } 392 393 // We could have changed sdata object to a constant... in this 394 // case the Kind could be wrong for it. 395 if (Kind.isMergeableConst()) { 396 TRACE(" const_object_as_data "); 397 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO); 398 if (GVar->hasSection() && isSmallDataSection(GVar->getSection())) 399 Kind = SectionKind::getData(); 400 } 401 402 if (Kind.isData()) { 403 if (NoSmallDataSorting) { 404 TRACE(" default sdata\n"); 405 return SmallDataSection; 406 } 407 408 StringRef Prefix(".sdata"); 409 SmallString<128> Name(Prefix); 410 Name.append(getSectionSuffixForSize(Size)); 411 412 if (EmitUniquedSection) { 413 Name.append("."); 414 Name.append(GO->getName()); 415 } 416 TRACE(" unique sdata(" << Name << ")\n"); 417 return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS, 418 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL); 419 } 420 421 TRACE("default ELF section\n"); 422 // Otherwise, we work the same as ELF. 423 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM); 424 } 425 426 // Return the function that uses the lookup table. If there are more 427 // than one live function that uses this look table, bail out and place 428 // the lookup table in default section. 429 const Function * 430 HexagonTargetObjectFile::getLutUsedFunction(const GlobalObject *GO) const { 431 const Function *ReturnFn = nullptr; 432 for (auto U : GO->users()) { 433 // validate each instance of user to be a live function. 434 auto *I = dyn_cast<Instruction>(U); 435 if (!I) 436 continue; 437 auto *Bb = I->getParent(); 438 if (!Bb) 439 continue; 440 auto *UserFn = Bb->getParent(); 441 if (!ReturnFn) 442 ReturnFn = UserFn; 443 else if (ReturnFn != UserFn) 444 return nullptr; 445 } 446 return ReturnFn; 447 } 448 449 MCSection *HexagonTargetObjectFile::selectSectionForLookupTable( 450 const GlobalObject *GO, const TargetMachine &TM, const Function *Fn) const { 451 452 SectionKind Kind = SectionKind::getText(); 453 // If the function has explicit section, place the lookup table in this 454 // explicit section. 455 if (Fn->hasSection()) 456 return getExplicitSectionGlobal(Fn, Kind, TM); 457 458 const auto *FuncObj = dyn_cast<GlobalObject>(Fn); 459 return SelectSectionForGlobal(FuncObj, Kind, TM); 460 } 461