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.
isSmallDataSection(StringRef Sec)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 
getSectionSuffixForSize(unsigned Size)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 
Initialize(MCContext & Ctx,const TargetMachine & TM)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 
SelectSectionForGlobal(const GlobalObject * GO,SectionKind Kind,const TargetMachine & TM) const127 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 
getExplicitSectionGlobal(const GlobalObject * GO,SectionKind Kind,const TargetMachine & TM) const165 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.
isGlobalInSmallSection(const GlobalObject * GO,const TargetMachine & TM) const199 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 
isSmallDataEnabled(const TargetMachine & TM) const272 bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM)
273     const {
274   return SmallDataThreshold > 0 && !TM.isPositionIndependent();
275 }
276 
getSmallDataSize() const277 unsigned HexagonTargetObjectFile::getSmallDataSize() const {
278   return SmallDataThreshold;
279 }
280 
shouldPutJumpTableInFunctionSection(bool UsesLabelDifference,const Function & F) const281 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.
getSmallestAddressableSize(const Type * Ty,const GlobalValue * GV,const TargetMachine & TM) const289 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 
selectSmallSectionForGlobal(const GlobalObject * GO,SectionKind Kind,const TargetMachine & TM) const341 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 *
getLutUsedFunction(const GlobalObject * GO) const430 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 
selectSectionForLookupTable(const GlobalObject * GO,const TargetMachine & TM,const Function * Fn) const449 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