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1 : //===-- llvm/Target/TargetLoweringObjectFile.cpp - Object File Info -------===//
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 implements classes used to handle lowerings specific to common
11 : // object file formats.
12 : //
13 : //===----------------------------------------------------------------------===//
14 :
15 : #include "llvm/Target/TargetLoweringObjectFile.h"
16 : #include "llvm/BinaryFormat/Dwarf.h"
17 : #include "llvm/IR/Constants.h"
18 : #include "llvm/IR/DataLayout.h"
19 : #include "llvm/IR/DerivedTypes.h"
20 : #include "llvm/IR/Function.h"
21 : #include "llvm/IR/GlobalVariable.h"
22 : #include "llvm/IR/Mangler.h"
23 : #include "llvm/MC/MCContext.h"
24 : #include "llvm/MC/MCExpr.h"
25 : #include "llvm/MC/MCStreamer.h"
26 : #include "llvm/MC/MCSymbol.h"
27 : #include "llvm/Support/ErrorHandling.h"
28 : #include "llvm/Support/raw_ostream.h"
29 : #include "llvm/Target/TargetMachine.h"
30 : #include "llvm/Target/TargetOptions.h"
31 : using namespace llvm;
32 :
33 : //===----------------------------------------------------------------------===//
34 : // Generic Code
35 : //===----------------------------------------------------------------------===//
36 :
37 : /// Initialize - this method must be called before any actual lowering is
38 : /// done. This specifies the current context for codegen, and gives the
39 : /// lowering implementations a chance to set up their default sections.
40 27325 : void TargetLoweringObjectFile::Initialize(MCContext &ctx,
41 : const TargetMachine &TM) {
42 27325 : Ctx = &ctx;
43 : // `Initialize` can be called more than once.
44 27382 : delete Mang;
45 27325 : Mang = new Mangler();
46 27325 : InitMCObjectFileInfo(TM.getTargetTriple(), TM.isPositionIndependent(), *Ctx,
47 27325 : TM.getCodeModel() == CodeModel::Large);
48 :
49 : // Reset various EH DWARF encodings.
50 27325 : PersonalityEncoding = LSDAEncoding = TTypeEncoding = dwarf::DW_EH_PE_absptr;
51 27325 : }
52 :
53 34295 : TargetLoweringObjectFile::~TargetLoweringObjectFile() {
54 55230 : delete Mang;
55 34294 : }
56 0 :
57 : static bool isNullOrUndef(const Constant *C) {
58 0 : // Check that the constant isn't all zeros or undefs.
59 34295 : if (C->isNullValue() || isa<UndefValue>(C))
60 55230 : return true;
61 34294 : if (!isa<ConstantAggregate>(C))
62 : return false;
63 307327 : for (auto Operand : C->operand_values()) {
64 : if (!isNullOrUndef(cast<Constant>(Operand)))
65 307327 : return false;
66 : }
67 : return true;
68 : }
69 57936 :
70 32294 : static bool isSuitableForBSS(const GlobalVariable *GV) {
71 : const Constant *C = GV->getInitializer();
72 :
73 : // Must have zero initializer.
74 : if (!isNullOrUndef(C))
75 : return false;
76 275033 :
77 : // Leave constant zeros in readonly constant sections, so they can be shared.
78 : if (GV->isConstant())
79 : return false;
80 275033 :
81 : // If the global has an explicit section specified, don't put it in BSS.
82 : if (GV->hasSection())
83 : return false;
84 45968 :
85 : // Otherwise, put it in BSS!
86 : return true;
87 : }
88 42947 :
89 63 : /// IsNullTerminatedString - Return true if the specified constant (which is
90 : /// known to have a type that is an array of 1/2/4 byte elements) ends with a
91 : /// nul value and contains no other nuls in it. Note that this is more general
92 : /// than ConstantDataSequential::isString because we allow 2 & 4 byte strings.
93 : static bool IsNullTerminatedString(const Constant *C) {
94 : // First check: is we have constant array terminated with zero
95 : if (const ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(C)) {
96 : unsigned NumElts = CDS->getNumElements();
97 : assert(NumElts != 0 && "Can't have an empty CDS");
98 :
99 197173 : if (CDS->getElementAsInteger(NumElts-1) != 0)
100 : return false; // Not null terminated.
101 :
102 196625 : // Verify that the null doesn't occur anywhere else in the string.
103 : for (unsigned i = 0; i != NumElts-1; ++i)
104 : if (CDS->getElementAsInteger(i) == 0)
105 196625 : return false;
106 : return true;
107 : }
108 :
109 12236876 : // Another possibility: [1 x i8] zeroinitializer
110 12049807 : if (isa<ConstantAggregateZero>(C))
111 : return cast<ArrayType>(C->getType())->getNumElements() == 1;
112 :
113 : return false;
114 : }
115 :
116 548 : MCSymbol *TargetLoweringObjectFile::getSymbolWithGlobalValueBase(
117 544 : const GlobalValue *GV, StringRef Suffix, const TargetMachine &TM) const {
118 : assert(!Suffix.empty());
119 :
120 : SmallString<60> NameStr;
121 : NameStr += GV->getParent()->getDataLayout().getPrivateGlobalPrefix();
122 1004 : TM.getNameWithPrefix(NameStr, GV, *Mang);
123 : NameStr.append(Suffix.begin(), Suffix.end());
124 : return Ctx->getOrCreateSymbol(NameStr);
125 : }
126 :
127 1004 : MCSymbol *TargetLoweringObjectFile::getCFIPersonalitySymbol(
128 1004 : const GlobalValue *GV, const TargetMachine &TM,
129 1004 : MachineModuleInfo *MMI) const {
130 2008 : return TM.getSymbol(GV);
131 : }
132 :
133 165 : void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer,
134 : const DataLayout &,
135 : const MCSymbol *Sym) const {
136 165 : }
137 :
138 :
139 27 : /// getKindForGlobal - This is a top-level target-independent classifier for
140 : /// a global object. Given a global variable and information from the TM, this
141 : /// function classifies the global in a target independent manner. This function
142 27 : /// may be overridden by the target implementation.
143 : SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalObject *GO,
144 : const TargetMachine &TM){
145 : assert(!GO->isDeclaration() && !GO->hasAvailableExternallyLinkage() &&
146 : "Can only be used for global definitions");
147 :
148 : // Functions are classified as text sections.
149 684443 : if (isa<Function>(GO))
150 : return SectionKind::getText();
151 :
152 : // Global variables require more detailed analysis.
153 : const auto *GVar = cast<GlobalVariable>(GO);
154 :
155 684443 : // Handle thread-local data first.
156 : if (GVar->isThreadLocal()) {
157 : if (isSuitableForBSS(GVar) && !TM.Options.NoZerosInBSS)
158 : return SectionKind::getThreadBSS();
159 : return SectionKind::getThreadData();
160 : }
161 :
162 278440 : // Variables with common linkage always get classified as common.
163 376 : if (GVar->hasCommonLinkage())
164 : return SectionKind::getCommon();
165 :
166 : // Most non-mergeable zero data can be put in the BSS section unless otherwise
167 : // specified.
168 : if (isSuitableForBSS(GVar) && !TM.Options.NoZerosInBSS) {
169 278064 : if (GVar->hasLocalLinkage())
170 : return SectionKind::getBSSLocal();
171 : else if (GVar->hasExternalLinkage())
172 : return SectionKind::getBSSExtern();
173 : return SectionKind::getBSS();
174 274657 : }
175 :
176 : // If the global is marked constant, we can put it into a mergable section,
177 14162 : // a mergable string section, or general .data if it contains relocations.
178 : if (GVar->isConstant()) {
179 : // If the initializer for the global contains something that requires a
180 : // relocation, then we may have to drop this into a writable data section
181 : // even though it is marked const.
182 : const Constant *C = GVar->getInitializer();
183 : if (!C->needsRelocation()) {
184 232011 : // If the global is required to have a unique address, it can't be put
185 : // into a mergable section: just drop it into the general read-only
186 : // section instead.
187 : if (!GVar->hasGlobalUnnamedAddr())
188 : return SectionKind::getReadOnly();
189 224369 :
190 : // If initializer is a null-terminated string, put it in a "cstring"
191 : // section of the right width.
192 : if (ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
193 209840 : if (IntegerType *ITy =
194 : dyn_cast<IntegerType>(ATy->getElementType())) {
195 : if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
196 : ITy->getBitWidth() == 32) &&
197 : IsNullTerminatedString(C)) {
198 199251 : if (ITy->getBitWidth() == 8)
199 : return SectionKind::getMergeable1ByteCString();
200 197486 : if (ITy->getBitWidth() == 16)
201 10303 : return SectionKind::getMergeable2ByteCString();
202 394434 :
203 197173 : assert(ITy->getBitWidth() == 32 && "Unknown width");
204 187601 : return SectionKind::getMergeable4ByteCString();
205 : }
206 1299 : }
207 : }
208 :
209 : // Otherwise, just drop it into a mergable constant section. If we have
210 : // a section for this size, use it, otherwise use the arbitrary sized
211 : // mergable section.
212 : switch (
213 : GVar->getParent()->getDataLayout().getTypeAllocSize(C->getType())) {
214 : case 4: return SectionKind::getMergeableConst4();
215 : case 8: return SectionKind::getMergeableConst8();
216 : case 16: return SectionKind::getMergeableConst16();
217 : case 32: return SectionKind::getMergeableConst32();
218 11650 : default:
219 11650 : return SectionKind::getReadOnly();
220 : }
221 :
222 : } else {
223 : // In static, ROPI and RWPI relocation models, the linker will resolve
224 : // all addresses, so the relocation entries will actually be constants by
225 : // the time the app starts up. However, we can't put this into a
226 : // mergable section, because the linker doesn't take relocations into
227 : // consideration when it tries to merge entries in the section.
228 : Reloc::Model ReloModel = TM.getRelocationModel();
229 : if (ReloModel == Reloc::Static || ReloModel == Reloc::ROPI ||
230 : ReloModel == Reloc::RWPI || ReloModel == Reloc::ROPI_RWPI)
231 : return SectionKind::getReadOnly();
232 :
233 : // Otherwise, the dynamic linker needs to fix it up, put it in the
234 14529 : // writable data.rel section.
235 14529 : return SectionKind::getReadOnlyWithRel();
236 1662 : }
237 : }
238 :
239 : // Okay, this isn't a constant.
240 : return SectionKind::getData();
241 : }
242 :
243 : /// This method computes the appropriate section to emit the specified global
244 : /// variable or function definition. This should not be passed external (or
245 : /// available externally) globals.
246 : MCSection *TargetLoweringObjectFile::SectionForGlobal(
247 : const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
248 : // Select section name.
249 : if (GO->hasSection())
250 : return getExplicitSectionGlobal(GO, Kind, TM);
251 :
252 677747 : if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
253 : auto Attrs = GVar->getAttributes();
254 : if ((Attrs.hasAttribute("bss-section") && Kind.isBSS()) ||
255 677747 : (Attrs.hasAttribute("data-section") && Kind.isData()) ||
256 4537 : (Attrs.hasAttribute("rodata-section") && Kind.isReadOnly())) {
257 : return getExplicitSectionGlobal(GO, Kind, TM);
258 : }
259 270747 : }
260 541500 :
261 541496 : if (auto *F = dyn_cast<Function>(GO)) {
262 541471 : if (F->hasFnAttribute("implicit-section-name"))
263 13 : return getExplicitSectionGlobal(GO, Kind, TM);
264 : }
265 :
266 : // Use default section depending on the 'type' of global
267 : return SelectSectionForGlobal(GO, Kind, TM);
268 402463 : }
269 2 :
270 : MCSection *TargetLoweringObjectFile::getSectionForJumpTable(
271 : const Function &F, const TargetMachine &TM) const {
272 : unsigned Align = 0;
273 673195 : return getSectionForConstant(F.getParent()->getDataLayout(),
274 : SectionKind::getReadOnly(), /*C=*/nullptr,
275 : Align);
276 6 : }
277 :
278 6 : bool TargetLoweringObjectFile::shouldPutJumpTableInFunctionSection(
279 6 : bool UsesLabelDifference, const Function &F) const {
280 : // In PIC mode, we need to emit the jump table to the same section as the
281 6 : // function body itself, otherwise the label differences won't make sense.
282 : // FIXME: Need a better predicate for this: what about custom entries?
283 : if (UsesLabelDifference)
284 31 : return true;
285 :
286 : // We should also do if the section name is NULL or function is declared
287 : // in discardable section
288 : // FIXME: this isn't the right predicate, should be based on the MCSection
289 31 : // for the function.
290 : return F.isWeakForLinker();
291 : }
292 :
293 : /// Given a mergable constant with the specified size and relocation
294 : /// information, return a section that it should be placed in.
295 : MCSection *TargetLoweringObjectFile::getSectionForConstant(
296 : const DataLayout &DL, SectionKind Kind, const Constant *C,
297 : unsigned &Align) const {
298 : if (Kind.isReadOnly() && ReadOnlySection != nullptr)
299 : return ReadOnlySection;
300 :
301 21 : return DataSection;
302 : }
303 :
304 21 : /// getTTypeGlobalReference - Return an MCExpr to use for a
305 : /// reference to the specified global variable from exception
306 : /// handling information.
307 0 : const MCExpr *TargetLoweringObjectFile::getTTypeGlobalReference(
308 : const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM,
309 : MachineModuleInfo *MMI, MCStreamer &Streamer) const {
310 : const MCSymbolRefExpr *Ref =
311 : MCSymbolRefExpr::create(TM.getSymbol(GV), getContext());
312 :
313 11505 : return getTTypeReference(Ref, Encoding, Streamer);
314 : }
315 :
316 : const MCExpr *TargetLoweringObjectFile::
317 11505 : getTTypeReference(const MCSymbolRefExpr *Sym, unsigned Encoding,
318 : MCStreamer &Streamer) const {
319 11505 : switch (Encoding & 0x70) {
320 : default:
321 : report_fatal_error("We do not support this DWARF encoding yet!");
322 11562 : case dwarf::DW_EH_PE_absptr:
323 : // Do nothing special
324 : return Sym;
325 11562 : case dwarf::DW_EH_PE_pcrel: {
326 0 : // Emit a label to the streamer for the current position. This gives us
327 0 : // .-foo addressing.
328 : MCSymbol *PCSym = getContext().createTempSymbol();
329 : Streamer.EmitLabel(PCSym);
330 : const MCExpr *PC = MCSymbolRefExpr::create(PCSym, getContext());
331 57 : return MCBinaryExpr::createSub(Sym, PC, getContext());
332 : }
333 : }
334 57 : }
335 57 :
336 57 : const MCExpr *TargetLoweringObjectFile::getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
337 57 : // FIXME: It's not clear what, if any, default this should have - perhaps a
338 : // null return could mean 'no location' & we should just do that here.
339 : return MCSymbolRefExpr::create(Sym, *Ctx);
340 : }
341 :
342 6 : void TargetLoweringObjectFile::getNameWithPrefix(
343 : SmallVectorImpl<char> &OutName, const GlobalValue *GV,
344 : const TargetMachine &TM) const {
345 6 : Mang->getNameWithPrefix(OutName, GV, /*CannotUsePrivateLabel=*/false);
346 : }
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