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#include "HexagonTargetObjectFile.h"
14#include "llvm/ADT/SmallString.h"
15#include "llvm/ADT/StringRef.h"
16#include "llvm/ADT/Twine.h"
17#include "llvm/BinaryFormat/ELF.h"
18#include "llvm/IR/DataLayout.h"
19#include "llvm/IR/DerivedTypes.h"
20#include "llvm/IR/GlobalObject.h"
21#include "llvm/IR/GlobalValue.h"
22#include "llvm/IR/GlobalVariable.h"
23#include "llvm/IR/Module.h"
24#include "llvm/IR/Type.h"
25#include "llvm/MC/MCContext.h"
26#include "llvm/MC/SectionKind.h"
27#include "llvm/Support/Casting.h"
28#include "llvm/Support/CommandLine.h"
29#include "llvm/Support/Debug.h"
30#include "llvm/Support/raw_ostream.h"
31#include "llvm/Target/TargetMachine.h"
32
33#define DEBUG_TYPE "hexagon-sdata"
34
35using namespace llvm;
36
37static cl::opt<unsigned> SmallDataThreshold("hexagon-small-data-threshold",
38 cl::init(Val: 8), cl::Hidden,
39 cl::desc("The maximum size of an object in the sdata section"));
40
41static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(Val: false),
42 cl::Hidden, cl::desc("Disable small data sections sorting"));
43
44static cl::opt<bool>
45 StaticsInSData("hexagon-statics-in-small-data", cl::Hidden,
46 cl::desc("Allow static variables in .sdata"));
47
48static cl::opt<bool> TraceGVPlacement("trace-gv-placement",
49 cl::Hidden, cl::init(Val: false),
50 cl::desc("Trace global value placement"));
51
52static cl::opt<bool>
53 EmitJtInText("hexagon-emit-jt-text", cl::Hidden, cl::init(Val: false),
54 cl::desc("Emit hexagon jump tables in function section"));
55
56static cl::opt<bool>
57 EmitLutInText("hexagon-emit-lut-text", cl::Hidden, cl::init(Val: 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.
86static 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 == ".sdata" || Sec == ".sbss" || Sec == ".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.contains(Other: ".sdata.") || Sec.contains(Other: ".sbss.") ||
94 Sec.contains(Other: ".scommon.");
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
116 SmallDataSection =
117 getContext().getELFSection(Section: ".sdata", Type: ELF::SHT_PROGBITS,
118 Flags: ELF::SHF_WRITE | ELF::SHF_ALLOC |
119 ELF::SHF_HEX_GPREL);
120 SmallBSSSection =
121 getContext().getELFSection(Section: ".sbss", Type: ELF::SHT_NOBITS,
122 Flags: ELF::SHF_WRITE | ELF::SHF_ALLOC |
123 ELF::SHF_HEX_GPREL);
124}
125
126MCSection *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().starts_with(Prefix: "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
164MCSection *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.contains(Other: ".access.text.group"))
181 return getContext().getELFSection(Section: GO->getSection(), Type: ELF::SHT_PROGBITS,
182 Flags: ELF::SHF_ALLOC | ELF::SHF_EXECINSTR);
183 if (Section.contains(Other: ".access.data.group"))
184 return getContext().getELFSection(Section: GO->getSection(), Type: ELF::SHT_PROGBITS,
185 Flags: 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.
198bool 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>(Val: 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(Sec: 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>(Val: 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>(Val: GType)) {
251 if (ST->isOpaque()) {
252 LLVM_DEBUG(dbgs() << "no, has opaque type\n");
253 return false;
254 }
255 }
256
257 unsigned Size = GVar->getDataLayout().getTypeAllocSize(Ty: 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
271bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM)
272 const {
273 return SmallDataThreshold > 0 && !TM.isPositionIndependent();
274}
275
276unsigned HexagonTargetObjectFile::getSmallDataSize() const {
277 return SmallDataThreshold;
278}
279
280bool 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.
288unsigned 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>(Val: Ty);
299 for (auto &E : STy->elements()) {
300 unsigned AtomicSize = getSmallestAddressableSize(Ty: 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>(Val: Ty);
308 return getSmallestAddressableSize(Ty: ATy->getElementType(), GV, TM);
309 }
310 case Type::FixedVectorTyID:
311 case Type::ScalableVectorTyID: {
312 const VectorType *PTy = cast<const VectorType>(Val: Ty);
313 return getSmallestAddressableSize(Ty: 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->getDataLayout();
321 // It is unfortunate that DL's function take non-const Type*.
322 return DL.getTypeAllocSize(Ty: 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_AMXTyID:
333 case Type::TokenTyID:
334 case Type::TypedPointerTyID:
335 case Type::TargetExtTyID:
336 return 0;
337 }
338
339 return 0;
340}
341
342MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal(
343 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
344 const Type *GTy = GO->getValueType();
345 unsigned Size = getSmallestAddressableSize(Ty: GTy, GV: GO, TM);
346
347 // If we have -ffunction-section or -fdata-section then we should emit the
348 // global value to a unique section specifically for it... even for sdata.
349 bool EmitUniquedSection = TM.getDataSections();
350
351 TRACE("Small data. Size(" << Size << ")");
352 // Handle Small Section classification here.
353 if (Kind.isBSS() || Kind.isBSSLocal()) {
354 // If -mno-sort-sda is not set, find out smallest accessible entity in
355 // declaration and add it to the section name string.
356 // Note. It does not track the actual usage of the value, only its de-
357 // claration. Also, compiler adds explicit pad fields to some struct
358 // declarations - they are currently counted towards smallest addres-
359 // sable entity.
360 if (NoSmallDataSorting) {
361 TRACE(" default sbss\n");
362 return SmallBSSSection;
363 }
364
365 StringRef Prefix(".sbss");
366 SmallString<128> Name(Prefix);
367 Name.append(RHS: getSectionSuffixForSize(Size));
368
369 if (EmitUniquedSection) {
370 Name.append(RHS: ".");
371 Name.append(RHS: GO->getName());
372 }
373 TRACE(" unique sbss(" << Name << ")\n");
374 return getContext().getELFSection(Section: Name.str(), Type: ELF::SHT_NOBITS,
375 Flags: ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
376 }
377
378 if (Kind.isCommon()) {
379 // This is purely for LTO+Linker Script because commons don't really have a
380 // section. However, the BitcodeSectionWriter pass will query for the
381 // sections of commons (and the linker expects us to know their section) so
382 // we'll return one here.
383 if (NoSmallDataSorting)
384 return BSSSection;
385
386 Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size);
387 TRACE(" small COMMON (" << Name << ")\n");
388
389 return getContext().getELFSection(Section: Name.str(), Type: ELF::SHT_NOBITS,
390 Flags: ELF::SHF_WRITE | ELF::SHF_ALLOC |
391 ELF::SHF_HEX_GPREL);
392 }
393
394 // We could have changed sdata object to a constant... in this
395 // case the Kind could be wrong for it.
396 if (Kind.isMergeableConst()) {
397 TRACE(" const_object_as_data ");
398 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(Val: GO);
399 if (GVar->hasSection() && isSmallDataSection(Sec: GVar->getSection()))
400 Kind = SectionKind::getData();
401 }
402
403 if (Kind.isData()) {
404 if (NoSmallDataSorting) {
405 TRACE(" default sdata\n");
406 return SmallDataSection;
407 }
408
409 StringRef Prefix(".sdata");
410 SmallString<128> Name(Prefix);
411 Name.append(RHS: getSectionSuffixForSize(Size));
412
413 if (EmitUniquedSection) {
414 Name.append(RHS: ".");
415 Name.append(RHS: GO->getName());
416 }
417 TRACE(" unique sdata(" << Name << ")\n");
418 return getContext().getELFSection(Section: Name.str(), Type: ELF::SHT_PROGBITS,
419 Flags: ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
420 }
421
422 TRACE("default ELF section\n");
423 // Otherwise, we work the same as ELF.
424 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
425}
426
427// Return the function that uses the lookup table. If there are more
428// than one live function that uses this look table, bail out and place
429// the lookup table in default section.
430const Function *
431HexagonTargetObjectFile::getLutUsedFunction(const GlobalObject *GO) const {
432 const Function *ReturnFn = nullptr;
433 for (const auto *U : GO->users()) {
434 // validate each instance of user to be a live function.
435 auto *I = dyn_cast<Instruction>(Val: U);
436 if (!I)
437 continue;
438 auto *Bb = I->getParent();
439 if (!Bb)
440 continue;
441 auto *UserFn = Bb->getParent();
442 if (!ReturnFn)
443 ReturnFn = UserFn;
444 else if (ReturnFn != UserFn)
445 return nullptr;
446 }
447 return ReturnFn;
448}
449
450MCSection *HexagonTargetObjectFile::selectSectionForLookupTable(
451 const GlobalObject *GO, const TargetMachine &TM, const Function *Fn) const {
452
453 SectionKind Kind = SectionKind::getText();
454 // If the function has explicit section, place the lookup table in this
455 // explicit section.
456 if (Fn->hasSection())
457 return getExplicitSectionGlobal(GO: Fn, Kind, TM);
458
459 const auto *FuncObj = dyn_cast<GlobalObject>(Val: Fn);
460 return SelectSectionForGlobal(GO: FuncObj, Kind, TM);
461}
462