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); 115 116 SmallDataSection = 117 getContext().getELFSection(".sdata", ELF::SHT_PROGBITS, 118 ELF::SHF_WRITE | ELF::SHF_ALLOC | 119 ELF::SHF_HEX_GPREL); 120 SmallBSSSection = 121 getContext().getELFSection(".sbss", ELF::SHT_NOBITS, 122 ELF::SHF_WRITE | ELF::SHF_ALLOC | 123 ELF::SHF_HEX_GPREL); 124 } 125 126 MCSection *HexagonTargetObjectFile::SelectSectionForGlobal( 127 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const { 128 TRACE("[SelectSectionForGlobal] GO(" << GO->getName() << ") "); 129 TRACE("input section(" << GO->getSection() << ") "); 130 131 TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "") 132 << (GO->hasLocalLinkage() ? "local_linkage " : "") 133 << (GO->hasInternalLinkage() ? "internal " : "") 134 << (GO->hasExternalLinkage() ? "external " : "") 135 << (GO->hasCommonLinkage() ? "common_linkage " : "") 136 << (GO->hasCommonLinkage() ? "common " : "" ) 137 << (Kind.isCommon() ? "kind_common " : "" ) 138 << (Kind.isBSS() ? "kind_bss " : "" ) 139 << (Kind.isBSSLocal() ? "kind_bss_local " : "" )); 140 141 // If the lookup table is used by more than one function, do not place 142 // it in text section. 143 if (EmitLutInText && GO->getName().startswith("switch.table")) { 144 if (const Function *Fn = getLutUsedFunction(GO)) 145 return selectSectionForLookupTable(GO, TM, Fn); 146 } 147 148 if (isGlobalInSmallSection(GO, TM)) 149 return selectSmallSectionForGlobal(GO, Kind, TM); 150 151 if (Kind.isCommon()) { 152 // This is purely for LTO+Linker Script because commons don't really have a 153 // section. However, the BitcodeSectionWriter pass will query for the 154 // sections of commons (and the linker expects us to know their section) so 155 // we'll return one here. 156 return BSSSection; 157 } 158 159 TRACE("default_ELF_section\n"); 160 // Otherwise, we work the same as ELF. 161 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM); 162 } 163 164 MCSection *HexagonTargetObjectFile::getExplicitSectionGlobal( 165 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const { 166 TRACE("[getExplicitSectionGlobal] GO(" << GO->getName() << ") from(" 167 << GO->getSection() << ") "); 168 TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "") 169 << (GO->hasLocalLinkage() ? "local_linkage " : "") 170 << (GO->hasInternalLinkage() ? "internal " : "") 171 << (GO->hasExternalLinkage() ? "external " : "") 172 << (GO->hasCommonLinkage() ? "common_linkage " : "") 173 << (GO->hasCommonLinkage() ? "common " : "" ) 174 << (Kind.isCommon() ? "kind_common " : "" ) 175 << (Kind.isBSS() ? "kind_bss " : "" ) 176 << (Kind.isBSSLocal() ? "kind_bss_local " : "" )); 177 178 if (GO->hasSection()) { 179 StringRef Section = GO->getSection(); 180 if (Section.find(".access.text.group") != StringRef::npos) 181 return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS, 182 ELF::SHF_ALLOC | ELF::SHF_EXECINSTR); 183 if (Section.find(".access.data.group") != StringRef::npos) 184 return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS, 185 ELF::SHF_WRITE | ELF::SHF_ALLOC); 186 } 187 188 if (isGlobalInSmallSection(GO, TM)) 189 return selectSmallSectionForGlobal(GO, Kind, TM); 190 191 // Otherwise, we work the same as ELF. 192 TRACE("default_ELF_section\n"); 193 return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GO, Kind, TM); 194 } 195 196 /// Return true if this global value should be placed into small data/bss 197 /// section. 198 bool HexagonTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO, 199 const TargetMachine &TM) const { 200 bool HaveSData = isSmallDataEnabled(TM); 201 if (!HaveSData) 202 LLVM_DEBUG(dbgs() << "Small-data allocation is disabled, but symbols " 203 "may have explicit section assignments...\n"); 204 // Only global variables, not functions. 205 LLVM_DEBUG(dbgs() << "Checking if value is in small-data, -G" 206 << SmallDataThreshold << ": \"" << GO->getName() << "\": "); 207 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO); 208 if (!GVar) { 209 LLVM_DEBUG(dbgs() << "no, not a global variable\n"); 210 return false; 211 } 212 213 // Globals with external linkage that have an original section set must be 214 // emitted to that section, regardless of whether we would put them into 215 // small data or not. This is how we can support mixing -G0/-G8 in LTO. 216 if (GVar->hasSection()) { 217 bool IsSmall = isSmallDataSection(GVar->getSection()); 218 LLVM_DEBUG(dbgs() << (IsSmall ? "yes" : "no") 219 << ", has section: " << GVar->getSection() << '\n'); 220 return IsSmall; 221 } 222 223 // If sdata is disabled, stop the checks here. 224 if (!HaveSData) { 225 LLVM_DEBUG(dbgs() << "no, small-data allocation is disabled\n"); 226 return false; 227 } 228 229 if (GVar->isConstant()) { 230 LLVM_DEBUG(dbgs() << "no, is a constant\n"); 231 return false; 232 } 233 234 bool IsLocal = GVar->hasLocalLinkage(); 235 if (!StaticsInSData && IsLocal) { 236 LLVM_DEBUG(dbgs() << "no, is static\n"); 237 return false; 238 } 239 240 Type *GType = GVar->getValueType(); 241 if (isa<ArrayType>(GType)) { 242 LLVM_DEBUG(dbgs() << "no, is an array\n"); 243 return false; 244 } 245 246 // If the type is a struct with no body provided, treat is conservatively. 247 // There cannot be actual definitions of object of such a type in this CU 248 // (only references), so assuming that they are not in sdata is safe. If 249 // these objects end up in the sdata, the references will still be valid. 250 if (StructType *ST = dyn_cast<StructType>(GType)) { 251 if (ST->isOpaque()) { 252 LLVM_DEBUG(dbgs() << "no, has opaque type\n"); 253 return false; 254 } 255 } 256 257 unsigned Size = GVar->getParent()->getDataLayout().getTypeAllocSize(GType); 258 if (Size == 0) { 259 LLVM_DEBUG(dbgs() << "no, has size 0\n"); 260 return false; 261 } 262 if (Size > SmallDataThreshold) { 263 LLVM_DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n'); 264 return false; 265 } 266 267 LLVM_DEBUG(dbgs() << "yes\n"); 268 return true; 269 } 270 271 bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM) 272 const { 273 return SmallDataThreshold > 0 && !TM.isPositionIndependent(); 274 } 275 276 unsigned HexagonTargetObjectFile::getSmallDataSize() const { 277 return SmallDataThreshold; 278 } 279 280 bool HexagonTargetObjectFile::shouldPutJumpTableInFunctionSection( 281 bool UsesLabelDifference, const Function &F) const { 282 return EmitJtInText; 283 } 284 285 /// Descends any type down to "elementary" components, 286 /// discovering the smallest addressable one. 287 /// If zero is returned, declaration will not be modified. 288 unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty, 289 const GlobalValue *GV, const TargetMachine &TM) const { 290 // Assign the smallest element access size to the highest 291 // value which assembler can handle. 292 unsigned SmallestElement = 8; 293 294 if (!Ty) 295 return 0; 296 switch (Ty->getTypeID()) { 297 case Type::StructTyID: { 298 const StructType *STy = cast<const StructType>(Ty); 299 for (auto &E : STy->elements()) { 300 unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM); 301 if (AtomicSize < SmallestElement) 302 SmallestElement = AtomicSize; 303 } 304 return (STy->getNumElements() == 0) ? 0 : SmallestElement; 305 } 306 case Type::ArrayTyID: { 307 const ArrayType *ATy = cast<const ArrayType>(Ty); 308 return getSmallestAddressableSize(ATy->getElementType(), GV, TM); 309 } 310 case Type::FixedVectorTyID: 311 case Type::ScalableVectorTyID: { 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::BFloatTyID: 327 case Type::X86_FP80TyID: 328 case Type::FP128TyID: 329 case Type::PPC_FP128TyID: 330 case Type::LabelTyID: 331 case Type::MetadataTyID: 332 case Type::X86_MMXTyID: 333 case Type::TokenTyID: 334 return 0; 335 } 336 337 return 0; 338 } 339 340 MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal( 341 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const { 342 const Type *GTy = GO->getValueType(); 343 unsigned Size = getSmallestAddressableSize(GTy, GO, TM); 344 345 // If we have -ffunction-section or -fdata-section then we should emit the 346 // global value to a unique section specifically for it... even for sdata. 347 bool EmitUniquedSection = TM.getDataSections(); 348 349 TRACE("Small data. Size(" << Size << ")"); 350 // Handle Small Section classification here. 351 if (Kind.isBSS() || Kind.isBSSLocal()) { 352 // If -mno-sort-sda is not set, find out smallest accessible entity in 353 // declaration and add it to the section name string. 354 // Note. It does not track the actual usage of the value, only its de- 355 // claration. Also, compiler adds explicit pad fields to some struct 356 // declarations - they are currently counted towards smallest addres- 357 // sable entity. 358 if (NoSmallDataSorting) { 359 TRACE(" default sbss\n"); 360 return SmallBSSSection; 361 } 362 363 StringRef Prefix(".sbss"); 364 SmallString<128> Name(Prefix); 365 Name.append(getSectionSuffixForSize(Size)); 366 367 if (EmitUniquedSection) { 368 Name.append("."); 369 Name.append(GO->getName()); 370 } 371 TRACE(" unique sbss(" << Name << ")\n"); 372 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS, 373 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL); 374 } 375 376 if (Kind.isCommon()) { 377 // This is purely for LTO+Linker Script because commons don't really have a 378 // section. However, the BitcodeSectionWriter pass will query for the 379 // sections of commons (and the linker expects us to know their section) so 380 // we'll return one here. 381 if (NoSmallDataSorting) 382 return BSSSection; 383 384 Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size); 385 TRACE(" small COMMON (" << Name << ")\n"); 386 387 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS, 388 ELF::SHF_WRITE | ELF::SHF_ALLOC | 389 ELF::SHF_HEX_GPREL); 390 } 391 392 // We could have changed sdata object to a constant... in this 393 // case the Kind could be wrong for it. 394 if (Kind.isMergeableConst()) { 395 TRACE(" const_object_as_data "); 396 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO); 397 if (GVar->hasSection() && isSmallDataSection(GVar->getSection())) 398 Kind = SectionKind::getData(); 399 } 400 401 if (Kind.isData()) { 402 if (NoSmallDataSorting) { 403 TRACE(" default sdata\n"); 404 return SmallDataSection; 405 } 406 407 StringRef Prefix(".sdata"); 408 SmallString<128> Name(Prefix); 409 Name.append(getSectionSuffixForSize(Size)); 410 411 if (EmitUniquedSection) { 412 Name.append("."); 413 Name.append(GO->getName()); 414 } 415 TRACE(" unique sdata(" << Name << ")\n"); 416 return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS, 417 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL); 418 } 419 420 TRACE("default ELF section\n"); 421 // Otherwise, we work the same as ELF. 422 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM); 423 } 424 425 // Return the function that uses the lookup table. If there are more 426 // than one live function that uses this look table, bail out and place 427 // the lookup table in default section. 428 const Function * 429 HexagonTargetObjectFile::getLutUsedFunction(const GlobalObject *GO) const { 430 const Function *ReturnFn = nullptr; 431 for (auto U : GO->users()) { 432 // validate each instance of user to be a live function. 433 auto *I = dyn_cast<Instruction>(U); 434 if (!I) 435 continue; 436 auto *Bb = I->getParent(); 437 if (!Bb) 438 continue; 439 auto *UserFn = Bb->getParent(); 440 if (!ReturnFn) 441 ReturnFn = UserFn; 442 else if (ReturnFn != UserFn) 443 return nullptr; 444 } 445 return ReturnFn; 446 } 447 448 MCSection *HexagonTargetObjectFile::selectSectionForLookupTable( 449 const GlobalObject *GO, const TargetMachine &TM, const Function *Fn) const { 450 451 SectionKind Kind = SectionKind::getText(); 452 // If the function has explicit section, place the lookup table in this 453 // explicit section. 454 if (Fn->hasSection()) 455 return getExplicitSectionGlobal(Fn, Kind, TM); 456 457 const auto *FuncObj = dyn_cast<GlobalObject>(Fn); 458 return SelectSectionForGlobal(FuncObj, Kind, TM); 459 } 460