1//===- IRSymtab.cpp - implementation of IR symbol tables ------------------===//
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#include "llvm/Object/IRSymtab.h"
10#include "llvm/ADT/ArrayRef.h"
11#include "llvm/ADT/SmallPtrSet.h"
12#include "llvm/ADT/SmallString.h"
13#include "llvm/ADT/SmallVector.h"
14#include "llvm/ADT/StringRef.h"
15#include "llvm/ADT/StringSet.h"
16#include "llvm/Bitcode/BitcodeReader.h"
17#include "llvm/Config/llvm-config.h"
18#include "llvm/IR/Comdat.h"
19#include "llvm/IR/DataLayout.h"
20#include "llvm/IR/GlobalAlias.h"
21#include "llvm/IR/GlobalObject.h"
22#include "llvm/IR/Mangler.h"
23#include "llvm/IR/Metadata.h"
24#include "llvm/IR/Module.h"
25#include "llvm/MC/StringTableBuilder.h"
26#include "llvm/Object/ModuleSymbolTable.h"
27#include "llvm/Object/SymbolicFile.h"
28#include "llvm/Support/Allocator.h"
29#include "llvm/Support/Casting.h"
30#include "llvm/Support/CommandLine.h"
31#include "llvm/Support/Error.h"
32#include "llvm/Support/StringSaver.h"
33#include "llvm/Support/VCSRevision.h"
34#include "llvm/Support/raw_ostream.h"
35#include "llvm/TargetParser/Triple.h"
36#include <cassert>
37#include <string>
38#include <utility>
39#include <vector>
40
41using namespace llvm;
42using namespace irsymtab;
43
44static cl::opt<bool> DisableBitcodeVersionUpgrade(
45 "disable-bitcode-version-upgrade", cl::Hidden,
46 cl::desc("Disable automatic bitcode upgrade for version mismatch"));
47
48namespace {
49
50const char *getExpectedProducerName() {
51 static char DefaultName[] = LLVM_VERSION_STRING
52#ifdef LLVM_REVISION
53 " " LLVM_REVISION
54#endif
55 ;
56 // Allows for testing of the irsymtab writer and upgrade mechanism. This
57 // environment variable should not be set by users.
58 if (char *OverrideName = getenv(name: "LLVM_OVERRIDE_PRODUCER"))
59 return OverrideName;
60 return DefaultName;
61}
62
63const char *kExpectedProducerName = getExpectedProducerName();
64
65/// Stores the temporary state that is required to build an IR symbol table.
66struct Builder {
67 SmallVector<char, 0> &Symtab;
68 StringTableBuilder &StrtabBuilder;
69 StringSaver Saver;
70
71 // This ctor initializes a StringSaver using the passed in BumpPtrAllocator.
72 // The StringTableBuilder does not create a copy of any strings added to it,
73 // so this provides somewhere to store any strings that we create.
74 Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder,
75 BumpPtrAllocator &Alloc, const Triple &TT)
76 : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc), TT(TT) {}
77
78 DenseMap<const Comdat *, int> ComdatMap;
79 Mangler Mang;
80 const Triple &TT;
81
82 std::vector<storage::Comdat> Comdats;
83 std::vector<storage::Module> Mods;
84 std::vector<storage::Symbol> Syms;
85 std::vector<storage::Uncommon> Uncommons;
86
87 std::string COFFLinkerOpts;
88 raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};
89
90 std::vector<storage::Str> DependentLibraries;
91
92 void setStr(storage::Str &S, StringRef Value) {
93 S.Offset = StrtabBuilder.add(S: Value);
94 S.Size = Value.size();
95 }
96
97 template <typename T>
98 void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
99 R.Offset = Symtab.size();
100 R.Size = Objs.size();
101 Symtab.insert(I: Symtab.end(), From: reinterpret_cast<const char *>(Objs.data()),
102 To: reinterpret_cast<const char *>(Objs.data() + Objs.size()));
103 }
104
105 Expected<int> getComdatIndex(const Comdat *C, const Module *M);
106
107 Error addModule(Module *M);
108 Error addSymbol(const ModuleSymbolTable &Msymtab,
109 const SmallPtrSet<GlobalValue *, 4> &Used,
110 ModuleSymbolTable::Symbol Sym);
111
112 Error build(ArrayRef<Module *> Mods);
113};
114
115Error Builder::addModule(Module *M) {
116 if (M->getDataLayoutStr().empty())
117 return make_error<StringError>(Args: "input module has no datalayout",
118 Args: inconvertibleErrorCode());
119
120 // Symbols in the llvm.used list will get the FB_Used bit and will not be
121 // internalized. We do this for llvm.compiler.used as well:
122 //
123 // IR symbol table tracks module-level asm symbol references but not inline
124 // asm. A symbol only referenced by inline asm is not in the IR symbol table,
125 // so we may not know that the definition (in another translation unit) is
126 // referenced. That definition may have __attribute__((used)) (which lowers to
127 // llvm.compiler.used on ELF targets) to communicate to the compiler that it
128 // may be used by inline asm. The usage is perfectly fine, so we treat
129 // llvm.compiler.used conservatively as llvm.used to work around our own
130 // limitation.
131 SmallVector<GlobalValue *, 4> UsedV;
132 collectUsedGlobalVariables(M: *M, Vec&: UsedV, /*CompilerUsed=*/false);
133 collectUsedGlobalVariables(M: *M, Vec&: UsedV, /*CompilerUsed=*/true);
134 SmallPtrSet<GlobalValue *, 4> Used(llvm::from_range, UsedV);
135
136 ModuleSymbolTable Msymtab;
137 Msymtab.addModule(M);
138
139 storage::Module Mod;
140 Mod.Begin = Syms.size();
141 Mod.End = Syms.size() + Msymtab.symbols().size();
142 Mod.UncBegin = Uncommons.size();
143 Mods.push_back(x: Mod);
144
145 if (TT.isOSBinFormatCOFF()) {
146 if (auto E = M->materializeMetadata())
147 return E;
148 if (NamedMDNode *LinkerOptions =
149 M->getNamedMetadata(Name: "llvm.linker.options")) {
150 for (MDNode *MDOptions : LinkerOptions->operands())
151 for (const MDOperand &MDOption : cast<MDNode>(Val: MDOptions)->operands())
152 COFFLinkerOptsOS << " " << cast<MDString>(Val: MDOption)->getString();
153 }
154 }
155
156 if (TT.isOSBinFormatELF()) {
157 if (auto E = M->materializeMetadata())
158 return E;
159 if (NamedMDNode *N = M->getNamedMetadata(Name: "llvm.dependent-libraries")) {
160 for (MDNode *MDOptions : N->operands()) {
161 const auto OperandStr =
162 cast<MDString>(Val: cast<MDNode>(Val: MDOptions)->getOperand(I: 0))->getString();
163 storage::Str Specifier;
164 setStr(S&: Specifier, Value: OperandStr);
165 DependentLibraries.emplace_back(args&: Specifier);
166 }
167 }
168 }
169
170 for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
171 if (Error Err = addSymbol(Msymtab, Used, Sym: Msym))
172 return Err;
173
174 return Error::success();
175}
176
177Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {
178 auto P = ComdatMap.insert(KV: std::make_pair(x&: C, y: Comdats.size()));
179 if (P.second) {
180 std::string Name;
181 if (TT.isOSBinFormatCOFF()) {
182 const GlobalValue *GV = M->getNamedValue(Name: C->getName());
183 if (!GV)
184 return make_error<StringError>(Args: "Could not find leader",
185 Args: inconvertibleErrorCode());
186 // Internal leaders do not affect symbol resolution, therefore they do not
187 // appear in the symbol table.
188 if (GV->hasLocalLinkage()) {
189 P.first->second = -1;
190 return -1;
191 }
192 llvm::raw_string_ostream OS(Name);
193 Mang.getNameWithPrefix(OS, GV, CannotUsePrivateLabel: false);
194 } else {
195 Name = std::string(C->getName());
196 }
197
198 storage::Comdat Comdat;
199 setStr(S&: Comdat.Name, Value: Saver.save(S: Name));
200 Comdat.SelectionKind = C->getSelectionKind();
201 Comdats.push_back(x: Comdat);
202 }
203
204 return P.first->second;
205}
206
207Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
208 const SmallPtrSet<GlobalValue *, 4> &Used,
209 ModuleSymbolTable::Symbol Msym) {
210 Syms.emplace_back();
211 storage::Symbol &Sym = Syms.back();
212 Sym = {};
213
214 storage::Uncommon *Unc = nullptr;
215 auto Uncommon = [&]() -> storage::Uncommon & {
216 if (Unc)
217 return *Unc;
218 Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
219 Uncommons.emplace_back();
220 Unc = &Uncommons.back();
221 *Unc = {};
222 setStr(S&: Unc->COFFWeakExternFallbackName, Value: "");
223 setStr(S&: Unc->SectionName, Value: "");
224 return *Unc;
225 };
226
227 SmallString<64> Name;
228 {
229 raw_svector_ostream OS(Name);
230 Msymtab.printSymbolName(OS, S: Msym);
231 }
232 setStr(S&: Sym.Name, Value: Saver.save(S: Name.str()));
233
234 auto Flags = Msymtab.getSymbolFlags(S: Msym);
235 if (Flags & object::BasicSymbolRef::SF_Undefined)
236 Sym.Flags |= 1 << storage::Symbol::FB_undefined;
237 if (Flags & object::BasicSymbolRef::SF_Weak)
238 Sym.Flags |= 1 << storage::Symbol::FB_weak;
239 if (Flags & object::BasicSymbolRef::SF_Common)
240 Sym.Flags |= 1 << storage::Symbol::FB_common;
241 if (Flags & object::BasicSymbolRef::SF_Indirect)
242 Sym.Flags |= 1 << storage::Symbol::FB_indirect;
243 if (Flags & object::BasicSymbolRef::SF_Global)
244 Sym.Flags |= 1 << storage::Symbol::FB_global;
245 if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
246 Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
247 if (Flags & object::BasicSymbolRef::SF_Executable)
248 Sym.Flags |= 1 << storage::Symbol::FB_executable;
249
250 Sym.ComdatIndex = -1;
251 auto *GV = dyn_cast_if_present<GlobalValue *>(Val&: Msym);
252 if (!GV) {
253 // Undefined module asm symbols act as GC roots and are implicitly used.
254 if (Flags & object::BasicSymbolRef::SF_Undefined)
255 Sym.Flags |= 1 << storage::Symbol::FB_used;
256 setStr(S&: Sym.IRName, Value: "");
257 return Error::success();
258 }
259
260 StringRef GVName = GV->getName();
261 setStr(S&: Sym.IRName, Value: GVName);
262
263 if (Used.count(Ptr: GV))
264 Sym.Flags |= 1 << storage::Symbol::FB_used;
265 if (GV->isThreadLocal())
266 Sym.Flags |= 1 << storage::Symbol::FB_tls;
267 if (GV->hasGlobalUnnamedAddr())
268 Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
269 if (GV->canBeOmittedFromSymbolTable())
270 Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
271 Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
272
273 if (Flags & object::BasicSymbolRef::SF_Common) {
274 auto *GVar = dyn_cast<GlobalVariable>(Val: GV);
275 if (!GVar)
276 return make_error<StringError>(Args: "Only variables can have common linkage!",
277 Args: inconvertibleErrorCode());
278 Uncommon().CommonSize = GVar->getGlobalSize(DL: GV->getDataLayout());
279 Uncommon().CommonAlign = GVar->getAlign() ? GVar->getAlign()->value() : 0;
280 }
281
282 const GlobalObject *GO = GV->getAliaseeObject();
283 if (!GO) {
284 if (isa<GlobalIFunc>(Val: GV))
285 GO = cast<GlobalIFunc>(Val: GV)->getResolverFunction();
286 if (!GO)
287 return make_error<StringError>(Args: "Unable to determine comdat of alias!",
288 Args: inconvertibleErrorCode());
289 }
290 if (const Comdat *C = GO->getComdat()) {
291 Expected<int> ComdatIndexOrErr = getComdatIndex(C, M: GV->getParent());
292 if (!ComdatIndexOrErr)
293 return ComdatIndexOrErr.takeError();
294 Sym.ComdatIndex = *ComdatIndexOrErr;
295 }
296
297 if (TT.isOSBinFormatCOFF()) {
298 emitLinkerFlagsForGlobalCOFF(OS&: COFFLinkerOptsOS, GV, TT, Mangler&: Mang);
299
300 if ((Flags & object::BasicSymbolRef::SF_Weak) &&
301 (Flags & object::BasicSymbolRef::SF_Indirect)) {
302 auto *Fallback = dyn_cast<GlobalValue>(
303 Val: cast<GlobalAlias>(Val: GV)->getAliasee()->stripPointerCasts());
304 if (!Fallback)
305 return make_error<StringError>(Args: "Invalid weak external",
306 Args: inconvertibleErrorCode());
307 std::string FallbackName;
308 raw_string_ostream OS(FallbackName);
309 Msymtab.printSymbolName(OS, S: Fallback);
310 setStr(S&: Uncommon().COFFWeakExternFallbackName, Value: Saver.save(S: FallbackName));
311 }
312 }
313
314 if (!GO->getSection().empty())
315 setStr(S&: Uncommon().SectionName, Value: Saver.save(S: GO->getSection()));
316
317 return Error::success();
318}
319
320Error Builder::build(ArrayRef<Module *> IRMods) {
321 storage::Header Hdr;
322
323 assert(!IRMods.empty());
324 Hdr.Version = storage::Header::kCurrentVersion;
325 setStr(S&: Hdr.Producer, Value: kExpectedProducerName);
326 setStr(S&: Hdr.TargetTriple, Value: IRMods[0]->getTargetTriple().str());
327 setStr(S&: Hdr.SourceFileName, Value: IRMods[0]->getSourceFileName());
328
329 for (auto *M : IRMods)
330 if (Error Err = addModule(M))
331 return Err;
332
333 setStr(S&: Hdr.COFFLinkerOpts, Value: Saver.save(S: COFFLinkerOpts));
334
335 // We are about to fill in the header's range fields, so reserve space for it
336 // and copy it in afterwards.
337 Symtab.resize(N: sizeof(storage::Header));
338 writeRange(R&: Hdr.Modules, Objs: Mods);
339 writeRange(R&: Hdr.Comdats, Objs: Comdats);
340 writeRange(R&: Hdr.Symbols, Objs: Syms);
341 writeRange(R&: Hdr.Uncommons, Objs: Uncommons);
342 writeRange(R&: Hdr.DependentLibraries, Objs: DependentLibraries);
343 *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
344 return Error::success();
345}
346
347} // end anonymous namespace
348
349Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
350 StringTableBuilder &StrtabBuilder,
351 BumpPtrAllocator &Alloc) {
352 const Triple &TT = Mods[0]->getTargetTriple();
353 return Builder(Symtab, StrtabBuilder, Alloc, TT).build(IRMods: Mods);
354}
355
356// Upgrade a vector of bitcode modules created by an old version of LLVM by
357// creating an irsymtab for them in the current format.
358static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
359 FileContents FC;
360
361 LLVMContext Ctx;
362 std::vector<Module *> Mods;
363 std::vector<std::unique_ptr<Module>> OwnedMods;
364 for (auto BM : BMs) {
365 Expected<std::unique_ptr<Module>> MOrErr =
366 BM.getLazyModule(Context&: Ctx, /*ShouldLazyLoadMetadata*/ true,
367 /*IsImporting*/ false);
368 if (!MOrErr)
369 return MOrErr.takeError();
370
371 Mods.push_back(x: MOrErr->get());
372 OwnedMods.push_back(x: std::move(*MOrErr));
373 }
374
375 StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
376 BumpPtrAllocator Alloc;
377 if (Error E = build(Mods, Symtab&: FC.Symtab, StrtabBuilder, Alloc))
378 return std::move(E);
379
380 StrtabBuilder.finalizeInOrder();
381 FC.Strtab.resize(N: StrtabBuilder.getSize());
382 StrtabBuilder.write(Buf: (uint8_t *)FC.Strtab.data());
383
384 FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
385 {FC.Strtab.data(), FC.Strtab.size()}};
386 return std::move(FC);
387}
388
389Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
390 if (BFC.Mods.empty())
391 return make_error<StringError>(Args: "Bitcode file does not contain any modules",
392 Args: inconvertibleErrorCode());
393
394 if (!DisableBitcodeVersionUpgrade) {
395 if (BFC.StrtabForSymtab.empty() ||
396 BFC.Symtab.size() < sizeof(storage::Header))
397 return upgrade(BMs: BFC.Mods);
398
399 // We cannot use the regular reader to read the version and producer,
400 // because it will expect the header to be in the current format. The only
401 // thing we can rely on is that the version and producer will be present as
402 // the first struct elements.
403 auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
404 unsigned Version = Hdr->Version;
405 StringRef Producer = Hdr->Producer.get(Strtab: BFC.StrtabForSymtab);
406 if (Version != storage::Header::kCurrentVersion ||
407 Producer != kExpectedProducerName)
408 return upgrade(BMs: BFC.Mods);
409 }
410
411 FileContents FC;
412 FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
413 {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};
414
415 // Finally, make sure that the number of modules in the symbol table matches
416 // the number of modules in the bitcode file. If they differ, it may mean that
417 // the bitcode file was created by binary concatenation, so we need to create
418 // a new symbol table from scratch.
419 if (FC.TheReader.getNumModules() != BFC.Mods.size())
420 return upgrade(BMs: std::move(BFC.Mods));
421
422 return std::move(FC);
423}
424