1 //===---- ELF_x86_64.cpp -JIT linker implementation for ELF/x86-64 ----===//
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 // ELF/x86-64 jit-link implementation.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/ExecutionEngine/JITLink/ELF_x86_64.h"
14 #include "llvm/ExecutionEngine/JITLink/DWARFRecordSectionSplitter.h"
15 #include "llvm/ExecutionEngine/JITLink/JITLink.h"
16 #include "llvm/ExecutionEngine/JITLink/TableManager.h"
17 #include "llvm/ExecutionEngine/JITLink/x86_64.h"
18 #include "llvm/Object/ELFObjectFile.h"
19 #include "llvm/Support/Endian.h"
20 
21 #include "DefineExternalSectionStartAndEndSymbols.h"
22 #include "EHFrameSupportImpl.h"
23 #include "ELFLinkGraphBuilder.h"
24 #include "JITLinkGeneric.h"
25 
26 #define DEBUG_TYPE "jitlink"
27 
28 using namespace llvm;
29 using namespace llvm::jitlink;
30 using namespace llvm::jitlink::ELF_x86_64_Edges;
31 
32 namespace {
33 
34 constexpr StringRef ELFGOTSymbolName = "_GLOBAL_OFFSET_TABLE_";
35 constexpr StringRef ELFTLSInfoSectionName = "$__TLSINFO";
36 
37 class TLSInfoTableManager_ELF_x86_64
38     : public TableManager<TLSInfoTableManager_ELF_x86_64> {
39 public:
40   static const uint8_t TLSInfoEntryContent[16];
41 
42   static StringRef getSectionName() { return ELFTLSInfoSectionName; }
43 
44   bool visitEdge(LinkGraph &G, Block *B, Edge &E) {
45     if (E.getKind() == x86_64::RequestTLSDescInGOTAndTransformToDelta32) {
46       LLVM_DEBUG({
47         dbgs() << "  Fixing " << G.getEdgeKindName(E.getKind()) << " edge at "
48                << formatv("{0:x}", B->getFixupAddress(E)) << " ("
49                << formatv("{0:x}", B->getAddress()) << " + "
50                << formatv("{0:x}", E.getOffset()) << ")\n";
51       });
52       E.setKind(x86_64::Delta32);
53       E.setTarget(getEntryForTarget(G, E.getTarget()));
54       return true;
55     }
56     return false;
57   }
58 
59   Symbol &createEntry(LinkGraph &G, Symbol &Target) {
60     // the TLS Info entry's key value will be written by the fixTLVSectionByName
61     // pass, so create mutable content.
62     auto &TLSInfoEntry = G.createMutableContentBlock(
63         getTLSInfoSection(G), G.allocateContent(getTLSInfoEntryContent()),
64         orc::ExecutorAddr(), 8, 0);
65     TLSInfoEntry.addEdge(x86_64::Pointer64, 8, Target, 0);
66     return G.addAnonymousSymbol(TLSInfoEntry, 0, 16, false, false);
67   }
68 
69 private:
70   Section &getTLSInfoSection(LinkGraph &G) {
71     if (!TLSInfoTable)
72       TLSInfoTable = &G.createSection(ELFTLSInfoSectionName, MemProt::Read);
73     return *TLSInfoTable;
74   }
75 
76   ArrayRef<char> getTLSInfoEntryContent() const {
77     return {reinterpret_cast<const char *>(TLSInfoEntryContent),
78             sizeof(TLSInfoEntryContent)};
79   }
80 
81   Section *TLSInfoTable = nullptr;
82 };
83 
84 const uint8_t TLSInfoTableManager_ELF_x86_64::TLSInfoEntryContent[16] = {
85     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /*pthread key */
86     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  /*data address*/
87 };
88 
89 Error buildTables_ELF_x86_64(LinkGraph &G) {
90   LLVM_DEBUG(dbgs() << "Visiting edges in graph:\n");
91 
92   x86_64::GOTTableManager GOT;
93   x86_64::PLTTableManager PLT(GOT);
94   TLSInfoTableManager_ELF_x86_64 TLSInfo;
95   visitExistingEdges(G, GOT, PLT, TLSInfo);
96   return Error::success();
97 }
98 } // namespace
99 
100 static const char *getELFX86_64RelocName(uint32_t Type) {
101   switch (Type) {
102 #define ELF_RELOC(Name, Number)                                                \
103   case Number:                                                                 \
104     return #Name;
105 #include "llvm/BinaryFormat/ELFRelocs/x86_64.def"
106 #undef ELF_RELOC
107   }
108   return "Unrecognized ELF/x86-64 relocation type";
109 }
110 
111 namespace llvm {
112 namespace jitlink {
113 
114 // This should become a template as the ELFFile is so a lot of this could become
115 // generic
116 class ELFLinkGraphBuilder_x86_64 : public ELFLinkGraphBuilder<object::ELF64LE> {
117 private:
118   using ELFT = object::ELF64LE;
119 
120   static Expected<ELF_x86_64_Edges::ELFX86RelocationKind>
121   getRelocationKind(const uint32_t Type) {
122     switch (Type) {
123     case ELF::R_X86_64_32S:
124       return ELF_x86_64_Edges::ELFX86RelocationKind::Pointer32Signed;
125     case ELF::R_X86_64_PC32:
126       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel32;
127     case ELF::R_X86_64_PC64:
128     case ELF::R_X86_64_GOTPC64:
129       return ELF_x86_64_Edges::ELFX86RelocationKind::Delta64;
130     case ELF::R_X86_64_64:
131       return ELF_x86_64_Edges::ELFX86RelocationKind::Pointer64;
132     case ELF::R_X86_64_GOTPCREL:
133       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel32GOTLoad;
134     case ELF::R_X86_64_GOTPCRELX:
135       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel32GOTLoadRelaxable;
136     case ELF::R_X86_64_REX_GOTPCRELX:
137       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel32REXGOTLoadRelaxable;
138     case ELF::R_X86_64_GOTPCREL64:
139       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel64GOT;
140     case ELF::R_X86_64_GOT64:
141       return ELF_x86_64_Edges::ELFX86RelocationKind::GOT64;
142     case ELF::R_X86_64_GOTOFF64:
143       return ELF_x86_64_Edges::ELFX86RelocationKind::GOTOFF64;
144     case ELF::R_X86_64_PLT32:
145       return ELF_x86_64_Edges::ELFX86RelocationKind::Branch32;
146     case ELF::R_X86_64_TLSGD:
147       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel32TLV;
148     }
149     return make_error<JITLinkError>("Unsupported x86-64 relocation type " +
150                                     formatv("{0:d}: ", Type) +
151                                     getELFX86_64RelocName(Type));
152   }
153 
154   Error addRelocations() override {
155     LLVM_DEBUG(dbgs() << "Processing relocations:\n");
156 
157     using Base = ELFLinkGraphBuilder<ELFT>;
158     using Self = ELFLinkGraphBuilder_x86_64;
159     for (const auto &RelSect : Base::Sections) {
160       // Validate the section to read relocation entries from.
161       if (RelSect.sh_type == ELF::SHT_REL)
162         return make_error<StringError>(
163             "No SHT_REL in valid x64 ELF object files",
164             inconvertibleErrorCode());
165 
166       if (Error Err = Base::forEachRelocation(RelSect, this,
167                                               &Self::addSingleRelocation))
168         return Err;
169     }
170 
171     return Error::success();
172   }
173 
174   Error addSingleRelocation(const typename ELFT::Rela &Rel,
175                             const typename ELFT::Shdr &FixupSection,
176                             Block &BlockToFix) {
177     using Base = ELFLinkGraphBuilder<ELFT>;
178 
179     uint32_t SymbolIndex = Rel.getSymbol(false);
180     auto ObjSymbol = Base::Obj.getRelocationSymbol(Rel, Base::SymTabSec);
181     if (!ObjSymbol)
182       return ObjSymbol.takeError();
183 
184     Symbol *GraphSymbol = Base::getGraphSymbol(SymbolIndex);
185     if (!GraphSymbol)
186       return make_error<StringError>(
187           formatv("Could not find symbol at given index, did you add it to "
188                   "JITSymbolTable? index: {0}, shndx: {1} Size of table: {2}",
189                   SymbolIndex, (*ObjSymbol)->st_shndx,
190                   Base::GraphSymbols.size()),
191           inconvertibleErrorCode());
192 
193     // Validate the relocation kind.
194     auto ELFRelocKind = getRelocationKind(Rel.getType(false));
195     if (!ELFRelocKind)
196       return ELFRelocKind.takeError();
197 
198     int64_t Addend = Rel.r_addend;
199     Edge::Kind Kind = Edge::Invalid;
200     switch (*ELFRelocKind) {
201     case PCRel32:
202       Kind = x86_64::Delta32;
203       break;
204     case Delta64:
205       Kind = x86_64::Delta64;
206       break;
207     case Pointer32Signed:
208       Kind = x86_64::Pointer32Signed;
209       break;
210     case Pointer64:
211       Kind = x86_64::Pointer64;
212       break;
213     case PCRel32GOTLoad: {
214       Kind = x86_64::RequestGOTAndTransformToDelta32;
215       break;
216     }
217     case PCRel32REXGOTLoadRelaxable: {
218       Kind = x86_64::RequestGOTAndTransformToPCRel32GOTLoadREXRelaxable;
219       Addend = 0;
220       break;
221     }
222     case PCRel32TLV: {
223       Kind = x86_64::RequestTLSDescInGOTAndTransformToDelta32;
224       break;
225     }
226     case PCRel32GOTLoadRelaxable: {
227       Kind = x86_64::RequestGOTAndTransformToPCRel32GOTLoadRelaxable;
228       Addend = 0;
229       break;
230     }
231     case PCRel64GOT: {
232       Kind = x86_64::RequestGOTAndTransformToDelta64;
233       break;
234     }
235     case GOT64: {
236       Kind = x86_64::RequestGOTAndTransformToDelta64FromGOT;
237       break;
238     }
239     case GOTOFF64: {
240       Kind = x86_64::Delta64FromGOT;
241       break;
242     }
243     case Branch32: {
244       Kind = x86_64::BranchPCRel32;
245       // BranchPCRel32 implicitly handles the '-4' PC adjustment, so we have to
246       // adjust the addend by '+4' to compensate.
247       Addend += 4;
248       break;
249     }
250     }
251 
252     auto FixupAddress = orc::ExecutorAddr(FixupSection.sh_addr) + Rel.r_offset;
253     Edge::OffsetT Offset = FixupAddress - BlockToFix.getAddress();
254     Edge GE(Kind, Offset, *GraphSymbol, Addend);
255     LLVM_DEBUG({
256       dbgs() << "    ";
257       printEdge(dbgs(), BlockToFix, GE, x86_64::getEdgeKindName(Kind));
258       dbgs() << "\n";
259     });
260 
261     BlockToFix.addEdge(std::move(GE));
262     return Error::success();
263   }
264 
265 public:
266   ELFLinkGraphBuilder_x86_64(StringRef FileName,
267                              const object::ELFFile<object::ELF64LE> &Obj)
268       : ELFLinkGraphBuilder(Obj, Triple("x86_64-unknown-linux"), FileName,
269                             x86_64::getEdgeKindName) {}
270 };
271 
272 class ELFJITLinker_x86_64 : public JITLinker<ELFJITLinker_x86_64> {
273   friend class JITLinker<ELFJITLinker_x86_64>;
274 
275 public:
276   ELFJITLinker_x86_64(std::unique_ptr<JITLinkContext> Ctx,
277                       std::unique_ptr<LinkGraph> G,
278                       PassConfiguration PassConfig)
279       : JITLinker(std::move(Ctx), std::move(G), std::move(PassConfig)) {
280     getPassConfig().PostAllocationPasses.push_back(
281         [this](LinkGraph &G) { return getOrCreateGOTSymbol(G); });
282   }
283 
284 private:
285   Symbol *GOTSymbol = nullptr;
286 
287   Error getOrCreateGOTSymbol(LinkGraph &G) {
288     auto DefineExternalGOTSymbolIfPresent =
289         createDefineExternalSectionStartAndEndSymbolsPass(
290             [&](LinkGraph &LG, Symbol &Sym) -> SectionRangeSymbolDesc {
291               if (Sym.getName() == ELFGOTSymbolName)
292                 if (auto *GOTSection = G.findSectionByName(
293                         x86_64::GOTTableManager::getSectionName())) {
294                   GOTSymbol = &Sym;
295                   return {*GOTSection, true};
296                 }
297               return {};
298             });
299 
300     // Try to attach _GLOBAL_OFFSET_TABLE_ to the GOT if it's defined as an
301     // external.
302     if (auto Err = DefineExternalGOTSymbolIfPresent(G))
303       return Err;
304 
305     // If we succeeded then we're done.
306     if (GOTSymbol)
307       return Error::success();
308 
309     // Otherwise look for a GOT section: If it already has a start symbol we'll
310     // record it, otherwise we'll create our own.
311     // If there's a GOT section but we didn't find an external GOT symbol...
312     if (auto *GOTSection =
313             G.findSectionByName(x86_64::GOTTableManager::getSectionName())) {
314 
315       // Check for an existing defined symbol.
316       for (auto *Sym : GOTSection->symbols())
317         if (Sym->getName() == ELFGOTSymbolName) {
318           GOTSymbol = Sym;
319           return Error::success();
320         }
321 
322       // If there's no defined symbol then create one.
323       SectionRange SR(*GOTSection);
324       if (SR.empty())
325         GOTSymbol =
326             &G.addAbsoluteSymbol(ELFGOTSymbolName, orc::ExecutorAddr(), 0,
327                                  Linkage::Strong, Scope::Local, true);
328       else
329         GOTSymbol =
330             &G.addDefinedSymbol(*SR.getFirstBlock(), 0, ELFGOTSymbolName, 0,
331                                 Linkage::Strong, Scope::Local, false, true);
332     }
333 
334     return Error::success();
335   }
336 
337   Error applyFixup(LinkGraph &G, Block &B, const Edge &E) const {
338     return x86_64::applyFixup(G, B, E, GOTSymbol);
339   }
340 };
341 
342 Expected<std::unique_ptr<LinkGraph>>
343 createLinkGraphFromELFObject_x86_64(MemoryBufferRef ObjectBuffer) {
344   LLVM_DEBUG({
345     dbgs() << "Building jitlink graph for new input "
346            << ObjectBuffer.getBufferIdentifier() << "...\n";
347   });
348 
349   auto ELFObj = object::ObjectFile::createELFObjectFile(ObjectBuffer);
350   if (!ELFObj)
351     return ELFObj.takeError();
352 
353   auto &ELFObjFile = cast<object::ELFObjectFile<object::ELF64LE>>(**ELFObj);
354   return ELFLinkGraphBuilder_x86_64((*ELFObj)->getFileName(),
355                                     ELFObjFile.getELFFile())
356       .buildGraph();
357 }
358 
359 static SectionRangeSymbolDesc
360 identifyELFSectionStartAndEndSymbols(LinkGraph &G, Symbol &Sym) {
361   constexpr StringRef StartSymbolPrefix = "__start";
362   constexpr StringRef EndSymbolPrefix = "__end";
363 
364   auto SymName = Sym.getName();
365   if (SymName.startswith(StartSymbolPrefix)) {
366     if (auto *Sec =
367             G.findSectionByName(SymName.drop_front(StartSymbolPrefix.size())))
368       return {*Sec, true};
369   } else if (SymName.startswith(EndSymbolPrefix)) {
370     if (auto *Sec =
371             G.findSectionByName(SymName.drop_front(EndSymbolPrefix.size())))
372       return {*Sec, false};
373   }
374   return {};
375 }
376 
377 void link_ELF_x86_64(std::unique_ptr<LinkGraph> G,
378                      std::unique_ptr<JITLinkContext> Ctx) {
379   PassConfiguration Config;
380 
381   if (Ctx->shouldAddDefaultTargetPasses(G->getTargetTriple())) {
382 
383     Config.PrePrunePasses.push_back(DWARFRecordSectionSplitter(".eh_frame"));
384     Config.PrePrunePasses.push_back(EHFrameEdgeFixer(
385         ".eh_frame", x86_64::PointerSize, x86_64::Pointer32, x86_64::Pointer64,
386         x86_64::Delta32, x86_64::Delta64, x86_64::NegDelta32));
387     Config.PrePrunePasses.push_back(EHFrameNullTerminator(".eh_frame"));
388 
389     // Construct a JITLinker and run the link function.
390     // Add a mark-live pass.
391     if (auto MarkLive = Ctx->getMarkLivePass(G->getTargetTriple()))
392       Config.PrePrunePasses.push_back(std::move(MarkLive));
393     else
394       Config.PrePrunePasses.push_back(markAllSymbolsLive);
395 
396     // Add an in-place GOT/Stubs/TLSInfoEntry build pass.
397     Config.PostPrunePasses.push_back(buildTables_ELF_x86_64);
398 
399     // Resolve any external section start / end symbols.
400     Config.PostAllocationPasses.push_back(
401         createDefineExternalSectionStartAndEndSymbolsPass(
402             identifyELFSectionStartAndEndSymbols));
403 
404     // Add GOT/Stubs optimizer pass.
405     Config.PreFixupPasses.push_back(x86_64::optimizeGOTAndStubAccesses);
406   }
407 
408   if (auto Err = Ctx->modifyPassConfig(*G, Config))
409     return Ctx->notifyFailed(std::move(Err));
410 
411   ELFJITLinker_x86_64::link(std::move(Ctx), std::move(G), std::move(Config));
412 }
413 const char *getELFX86RelocationKindName(Edge::Kind R) {
414   switch (R) {
415   case Branch32:
416     return "Branch32";
417   case Pointer32Signed:
418     return "Pointer32Signed";
419   case Pointer64:
420     return "Pointer64";
421   case PCRel32:
422     return "PCRel32";
423   case PCRel32GOTLoad:
424     return "PCRel32GOTLoad";
425   case PCRel32GOTLoadRelaxable:
426     return "PCRel32GOTLoadRelaxable";
427   case PCRel32REXGOTLoadRelaxable:
428     return "PCRel32REXGOTLoad";
429   case PCRel64GOT:
430     return "PCRel64GOT";
431   case Delta64:
432     return "Delta64";
433   case GOT64:
434     return "GOT64";
435   case GOTOFF64:
436     return "GOTOFF64";
437   }
438   return getGenericEdgeKindName(static_cast<Edge::Kind>(R));
439 }
440 } // end namespace jitlink
441 } // end namespace llvm
442