1 //===-- HexagonTargetObjectFile.cpp ---------------------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file contains the declarations of the HexagonTargetAsmInfo properties.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #define DEBUG_TYPE "hexagon-sdata"
15 
16 #include "HexagonTargetObjectFile.h"
17 #include "llvm/ADT/SmallString.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/ADT/Twine.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/ELF.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 // TraceGVPlacement controls messages for all builds. For builds with assertions
53 // (debug or release), messages are also controlled by the usual debug flags
54 // (e.g. -debug and -debug-only=globallayout)
55 #define TRACE_TO(s, X) s << X
56 #ifdef NDEBUG
57 #define TRACE(X)                                                               \
58   do {                                                                         \
59     if (TraceGVPlacement) {                                                    \
60       TRACE_TO(errs(), X);                                                     \
61     }                                                                          \
62   } while (false)
63 #else
64 #define TRACE(X)                                                               \
65   do {                                                                         \
66     if (TraceGVPlacement) {                                                    \
67       TRACE_TO(errs(), X);                                                     \
68     } else {                                                                   \
69       DEBUG(TRACE_TO(dbgs(), X));                                              \
70     }                                                                          \
71   } while (false)
72 #endif
73 
74 // Returns true if the section name is such that the symbol will be put
75 // in a small data section.
76 // For instance, global variables with section attributes such as ".sdata"
77 // ".sdata.*", ".sbss", and ".sbss.*" will go into small data.
78 static bool isSmallDataSection(StringRef Sec) {
79   // sectionName is either ".sdata" or ".sbss". Looking for an exact match
80   // obviates the need for checks for section names such as ".sdatafoo".
81   if (Sec.equals(".sdata") || Sec.equals(".sbss") || Sec.equals(".scommon"))
82     return true;
83   // If either ".sdata." or ".sbss." is a substring of the section name
84   // then put the symbol in small data.
85   return Sec.find(".sdata.") != StringRef::npos ||
86          Sec.find(".sbss.") != StringRef::npos ||
87          Sec.find(".scommon.") != StringRef::npos;
88 }
89 
90 static const char *getSectionSuffixForSize(unsigned Size) {
91   switch (Size) {
92   default:
93     return "";
94   case 1:
95     return ".1";
96   case 2:
97     return ".2";
98   case 4:
99     return ".4";
100   case 8:
101     return ".8";
102   }
103 }
104 
105 void HexagonTargetObjectFile::Initialize(MCContext &Ctx,
106       const TargetMachine &TM) {
107   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
108   InitializeELF(TM.Options.UseInitArray);
109 
110   SmallDataSection =
111     getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
112                                ELF::SHF_WRITE | ELF::SHF_ALLOC |
113                                ELF::SHF_HEX_GPREL);
114   SmallBSSSection =
115     getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
116                                ELF::SHF_WRITE | ELF::SHF_ALLOC |
117                                ELF::SHF_HEX_GPREL);
118 }
119 
120 MCSection *HexagonTargetObjectFile::SelectSectionForGlobal(
121     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
122   TRACE("[SelectSectionForGlobal] GO(" << GO->getName() << ") ");
123   TRACE("input section(" << GO->getSection() << ") ");
124 
125   TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
126          << (GO->hasLocalLinkage() ? "local_linkage " : "")
127          << (GO->hasInternalLinkage() ? "internal " : "")
128          << (GO->hasExternalLinkage() ? "external " : "")
129          << (GO->hasCommonLinkage() ? "common_linkage " : "")
130          << (GO->hasCommonLinkage() ? "common " : "" )
131          << (Kind.isCommon() ? "kind_common " : "" )
132          << (Kind.isBSS() ? "kind_bss " : "" )
133          << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
134 
135   if (isGlobalInSmallSection(GO, TM))
136     return selectSmallSectionForGlobal(GO, Kind, TM);
137 
138   if (Kind.isCommon()) {
139     // This is purely for LTO+Linker Script because commons don't really have a
140     // section. However, the BitcodeSectionWriter pass will query for the
141     // sections of commons (and the linker expects us to know their section) so
142     // we'll return one here.
143     return BSSSection;
144   }
145 
146   TRACE("default_ELF_section\n");
147   // Otherwise, we work the same as ELF.
148   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
149 }
150 
151 MCSection *HexagonTargetObjectFile::getExplicitSectionGlobal(
152     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
153   TRACE("[getExplicitSectionGlobal] GO(" << GO->getName() << ") from("
154         << GO->getSection() << ") ");
155   TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
156          << (GO->hasLocalLinkage() ? "local_linkage " : "")
157          << (GO->hasInternalLinkage() ? "internal " : "")
158          << (GO->hasExternalLinkage() ? "external " : "")
159          << (GO->hasCommonLinkage() ? "common_linkage " : "")
160          << (GO->hasCommonLinkage() ? "common " : "" )
161          << (Kind.isCommon() ? "kind_common " : "" )
162          << (Kind.isBSS() ? "kind_bss " : "" )
163          << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
164 
165   if (GO->hasSection()) {
166     StringRef Section = GO->getSection();
167     if (Section.find(".access.text.group") != StringRef::npos)
168       return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
169                                         ELF::SHF_ALLOC | ELF::SHF_EXECINSTR);
170     if (Section.find(".access.data.group") != StringRef::npos)
171       return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
172                                         ELF::SHF_WRITE | ELF::SHF_ALLOC);
173   }
174 
175   if (isGlobalInSmallSection(GO, TM))
176     return selectSmallSectionForGlobal(GO, Kind, TM);
177 
178   // Otherwise, we work the same as ELF.
179   TRACE("default_ELF_section\n");
180   return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GO, Kind, TM);
181 }
182 
183 /// Return true if this global value should be placed into small data/bss
184 /// section.
185 bool HexagonTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO,
186       const TargetMachine &TM) const {
187   // Only global variables, not functions.
188   DEBUG(dbgs() << "Checking if value is in small-data, -G"
189                << SmallDataThreshold << ": \"" << GO->getName() << "\": ");
190   const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
191   if (!GVar) {
192     DEBUG(dbgs() << "no, not a global variable\n");
193     return false;
194   }
195 
196   // Globals with external linkage that have an original section set must be
197   // emitted to that section, regardless of whether we would put them into
198   // small data or not. This is how we can support mixing -G0/-G8 in LTO.
199   if (GVar->hasSection()) {
200     bool IsSmall = isSmallDataSection(GVar->getSection());
201     DEBUG(dbgs() << (IsSmall ? "yes" : "no") << ", has section: "
202                  << GVar->getSection() << '\n');
203     return IsSmall;
204   }
205 
206   if (GVar->isConstant()) {
207     DEBUG(dbgs() << "no, is a constant\n");
208     return false;
209   }
210 
211   bool IsLocal = GVar->hasLocalLinkage();
212   if (!StaticsInSData && IsLocal) {
213     DEBUG(dbgs() << "no, is static\n");
214     return false;
215   }
216 
217   Type *GType = GVar->getType();
218   if (PointerType *PT = dyn_cast<PointerType>(GType))
219     GType = PT->getElementType();
220 
221   if (isa<ArrayType>(GType)) {
222     DEBUG(dbgs() << "no, is an array\n");
223     return false;
224   }
225 
226   // If the type is a struct with no body provided, treat is conservatively.
227   // There cannot be actual definitions of object of such a type in this CU
228   // (only references), so assuming that they are not in sdata is safe. If
229   // these objects end up in the sdata, the references will still be valid.
230   if (StructType *ST = dyn_cast<StructType>(GType)) {
231     if (ST->isOpaque()) {
232       DEBUG(dbgs() << "no, has opaque type\n");
233       return false;
234     }
235   }
236 
237   unsigned Size = GVar->getParent()->getDataLayout().getTypeAllocSize(GType);
238   if (Size == 0) {
239     DEBUG(dbgs() << "no, has size 0\n");
240     return false;
241   }
242   if (Size > SmallDataThreshold) {
243     DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n');
244     return false;
245   }
246 
247   DEBUG(dbgs() << "yes\n");
248   return true;
249 }
250 
251 bool HexagonTargetObjectFile::isSmallDataEnabled() const {
252   return SmallDataThreshold > 0;
253 }
254 
255 unsigned HexagonTargetObjectFile::getSmallDataSize() const {
256   return SmallDataThreshold;
257 }
258 
259 /// Descends any type down to "elementary" components,
260 /// discovering the smallest addressable one.
261 /// If zero is returned, declaration will not be modified.
262 unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty,
263       const GlobalValue *GV, const TargetMachine &TM) const {
264   // Assign the smallest element access size to the highest
265   // value which assembler can handle.
266   unsigned SmallestElement = 8;
267 
268   if (!Ty)
269     return 0;
270   switch (Ty->getTypeID()) {
271   case Type::StructTyID: {
272     const StructType *STy = cast<const StructType>(Ty);
273     for (auto &E : STy->elements()) {
274       unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM);
275       if (AtomicSize < SmallestElement)
276         SmallestElement = AtomicSize;
277     }
278     return (STy->getNumElements() == 0) ? 0 : SmallestElement;
279   }
280   case Type::ArrayTyID: {
281     const ArrayType *ATy = cast<const ArrayType>(Ty);
282     return getSmallestAddressableSize(ATy->getElementType(), GV, TM);
283   }
284   case Type::VectorTyID: {
285     const VectorType *PTy = cast<const VectorType>(Ty);
286     return getSmallestAddressableSize(PTy->getElementType(), GV, TM);
287   }
288   case Type::PointerTyID:
289   case Type::HalfTyID:
290   case Type::FloatTyID:
291   case Type::DoubleTyID:
292   case Type::IntegerTyID: {
293     const DataLayout &DL = GV->getParent()->getDataLayout();
294     // It is unfortunate that DL's function take non-const Type*.
295     return DL.getTypeAllocSize(const_cast<Type*>(Ty));
296   }
297   case Type::FunctionTyID:
298   case Type::VoidTyID:
299   case Type::X86_FP80TyID:
300   case Type::FP128TyID:
301   case Type::PPC_FP128TyID:
302   case Type::LabelTyID:
303   case Type::MetadataTyID:
304   case Type::X86_MMXTyID:
305   case Type::TokenTyID:
306     return 0;
307   }
308 
309   return 0;
310 }
311 
312 MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal(
313     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
314   const Type *GTy = GO->getType()->getElementType();
315   unsigned Size = getSmallestAddressableSize(GTy, GO, TM);
316 
317   // If we have -ffunction-section or -fdata-section then we should emit the
318   // global value to a unique section specifically for it... even for sdata.
319   bool EmitUniquedSection = TM.getDataSections();
320 
321   TRACE("Small data. Size(" << Size << ")");
322   // Handle Small Section classification here.
323   if (Kind.isBSS() || Kind.isBSSLocal()) {
324     // If -mno-sort-sda is not set, find out smallest accessible entity in
325     // declaration and add it to the section name string.
326     // Note. It does not track the actual usage of the value, only its de-
327     // claration. Also, compiler adds explicit pad fields to some struct
328     // declarations - they are currently counted towards smallest addres-
329     // sable entity.
330     if (NoSmallDataSorting) {
331       TRACE(" default sbss\n");
332       return SmallBSSSection;
333     }
334 
335     StringRef Prefix(".sbss");
336     SmallString<128> Name(Prefix);
337     Name.append(getSectionSuffixForSize(Size));
338 
339     if (EmitUniquedSection) {
340       Name.append(".");
341       Name.append(GO->getName());
342     }
343     TRACE(" unique sbss(" << Name << ")\n");
344     return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
345                 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
346   }
347 
348   if (Kind.isCommon()) {
349     // This is purely for LTO+Linker Script because commons don't really have a
350     // section. However, the BitcodeSectionWriter pass will query for the
351     // sections of commons (and the linker expects us to know their section) so
352     // we'll return one here.
353     if (NoSmallDataSorting)
354       return BSSSection;
355 
356     Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size);
357     TRACE(" small COMMON (" << Name << ")\n");
358 
359     return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
360                                       ELF::SHF_WRITE | ELF::SHF_ALLOC |
361                                       ELF::SHF_HEX_GPREL);
362   }
363 
364   // We could have changed sdata object to a constant... in this
365   // case the Kind could be wrong for it.
366   if (Kind.isMergeableConst()) {
367     TRACE(" const_object_as_data ");
368     const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
369     if (GVar->hasSection() && isSmallDataSection(GVar->getSection()))
370       Kind = SectionKind::getData();
371   }
372 
373   if (Kind.isData()) {
374     if (NoSmallDataSorting) {
375       TRACE(" default sdata\n");
376       return SmallDataSection;
377     }
378 
379     StringRef Prefix(".sdata");
380     SmallString<128> Name(Prefix);
381     Name.append(getSectionSuffixForSize(Size));
382 
383     if (EmitUniquedSection) {
384       Name.append(".");
385       Name.append(GO->getName());
386     }
387     TRACE(" unique sdata(" << Name << ")\n");
388     return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS,
389                 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
390   }
391 
392   TRACE("default ELF section\n");
393   // Otherwise, we work the same as ELF.
394   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
395 }
396