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
34using namespace llvm;
35
36static 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
40static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(false),
41  cl::Hidden, cl::desc("Disable small data sections sorting"));
42
43static 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
47static cl::opt<bool> TraceGVPlacement("trace-gv-placement",
48  cl::Hidden, cl::init(false),
49  cl::desc("Trace global value placement"));
50
51static 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
55static 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.
85static 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
97static 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
112void 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
127MCSection *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
165MCSection *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.
199bool 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
272bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM)
273    const {
274  return SmallDataThreshold > 0 && !TM.isPositionIndependent();
275}
276
277unsigned HexagonTargetObjectFile::getSmallDataSize() const {
278  return SmallDataThreshold;
279}
280
281bool 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.
289unsigned 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
339MCSection *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.
427const Function *
428HexagonTargetObjectFile::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
447MCSection *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