xref: /freebsd/contrib/llvm-project/llvm/lib/ExecutionEngine/JITLink/ELF_x86_64.cpp (revision 5e801ac66d24704442eba426ed13c3effb8a34e7) 
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/JITLink.h"
15 #include "llvm/ExecutionEngine/JITLink/TableManager.h"
16 #include "llvm/ExecutionEngine/JITLink/x86_64.h"
17 #include "llvm/Object/ELFObjectFile.h"
18 #include "llvm/Support/Endian.h"
19 
20 #include "DefineExternalSectionStartAndEndSymbols.h"
21 #include "EHFrameSupportImpl.h"
22 #include "ELFLinkGraphBuilder.h"
23 #include "JITLinkGeneric.h"
24 
25 #define DEBUG_TYPE "jitlink"
26 
27 using namespace llvm;
28 using namespace llvm::jitlink;
29 using namespace llvm::jitlink::ELF_x86_64_Edges;
30 
31 namespace {
32 
33 constexpr StringRef ELFGOTSymbolName = "_GLOBAL_OFFSET_TABLE_";
34 constexpr StringRef ELFTLSInfoSectionName = "$__TLSINFO";
35 
36 class TLSInfoTableManager_ELF_x86_64
37     : public TableManager<TLSInfoTableManager_ELF_x86_64> {
38 public:
39   static const uint8_t TLSInfoEntryContent[16];
40 
41   static StringRef getSectionName() { return ELFTLSInfoSectionName; }
42 
43   bool visitEdge(LinkGraph &G, Block *B, Edge &E) {
44     if (E.getKind() == x86_64::RequestTLSDescInGOTAndTransformToDelta32) {
45       LLVM_DEBUG({
46         dbgs() << "  Fixing " << G.getEdgeKindName(E.getKind()) << " edge at "
47                << formatv("{0:x}", B->getFixupAddress(E)) << " ("
48                << formatv("{0:x}", B->getAddress()) << " + "
49                << formatv("{0:x}", E.getOffset()) << ")\n";
50       });
51       E.setKind(x86_64::Delta32);
52       E.setTarget(getEntryForTarget(G, E.getTarget()));
53       return true;
54     }
55     return false;
56   }
57 
58   Symbol &createEntry(LinkGraph &G, Symbol &Target) {
59     // the TLS Info entry's key value will be written by the fixTLVSectionByName
60     // pass, so create mutable content.
61     auto &TLSInfoEntry = G.createMutableContentBlock(
62         getTLSInfoSection(G), G.allocateContent(getTLSInfoEntryContent()), 0, 8,
63         0);
64     TLSInfoEntry.addEdge(x86_64::Pointer64, 8, Target, 0);
65     return G.addAnonymousSymbol(TLSInfoEntry, 0, 16, false, false);
66   }
67 
68 private:
69   Section &getTLSInfoSection(LinkGraph &G) {
70     if (!TLSInfoTable)
71       TLSInfoTable = &G.createSection(ELFTLSInfoSectionName, MemProt::Read);
72     return *TLSInfoTable;
73   }
74 
75   ArrayRef<char> getTLSInfoEntryContent() const {
76     return {reinterpret_cast<const char *>(TLSInfoEntryContent),
77             sizeof(TLSInfoEntryContent)};
78   }
79 
80   Section *TLSInfoTable = nullptr;
81 };
82 
83 const uint8_t TLSInfoTableManager_ELF_x86_64::TLSInfoEntryContent[16] = {
84     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /*pthread key */
85     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  /*data address*/
86 };
87 
88 Error buildTables_ELF_x86_64(LinkGraph &G) {
89   LLVM_DEBUG(dbgs() << "Visiting edges in graph:\n");
90 
91   x86_64::GOTTableManager GOT;
92   x86_64::PLTTableManager PLT(GOT);
93   TLSInfoTableManager_ELF_x86_64 TLSInfo;
94   visitExistingEdges(G, GOT, PLT, TLSInfo);
95   return Error::success();
96 }
97 } // namespace
98 
99 static const char *getELFX86_64RelocName(uint32_t Type) {
100   switch (Type) {
101 #define ELF_RELOC(Name, Number)                                                \
102   case Number:                                                                 \
103     return #Name;
104 #include "llvm/BinaryFormat/ELFRelocs/x86_64.def"
105 #undef ELF_RELOC
106   }
107   return "Unrecognized ELF/x86-64 relocation type";
108 }
109 
110 namespace llvm {
111 namespace jitlink {
112 
113 // This should become a template as the ELFFile is so a lot of this could become
114 // generic
115 class ELFLinkGraphBuilder_x86_64 : public ELFLinkGraphBuilder<object::ELF64LE> {
116 private:
117   using ELFT = object::ELF64LE;
118 
119   static Expected<ELF_x86_64_Edges::ELFX86RelocationKind>
120   getRelocationKind(const uint32_t Type) {
121     switch (Type) {
122     case ELF::R_X86_64_32S:
123       return ELF_x86_64_Edges::ELFX86RelocationKind::Pointer32Signed;
124     case ELF::R_X86_64_PC32:
125       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel32;
126     case ELF::R_X86_64_PC64:
127     case ELF::R_X86_64_GOTPC64:
128       return ELF_x86_64_Edges::ELFX86RelocationKind::Delta64;
129     case ELF::R_X86_64_64:
130       return ELF_x86_64_Edges::ELFX86RelocationKind::Pointer64;
131     case ELF::R_X86_64_GOTPCREL:
132       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel32GOTLoad;
133     case ELF::R_X86_64_GOTPCRELX:
134       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel32GOTLoadRelaxable;
135     case ELF::R_X86_64_REX_GOTPCRELX:
136       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel32REXGOTLoadRelaxable;
137     case ELF::R_X86_64_GOTPCREL64:
138       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel64GOT;
139     case ELF::R_X86_64_GOT64:
140       return ELF_x86_64_Edges::ELFX86RelocationKind::GOT64;
141     case ELF::R_X86_64_GOTOFF64:
142       return ELF_x86_64_Edges::ELFX86RelocationKind::GOTOFF64;
143     case ELF::R_X86_64_PLT32:
144       return ELF_x86_64_Edges::ELFX86RelocationKind::Branch32;
145     case ELF::R_X86_64_TLSGD:
146       return ELF_x86_64_Edges::ELFX86RelocationKind::PCRel32TLV;
147     }
148     return make_error<JITLinkError>("Unsupported x86-64 relocation type " +
149                                     formatv("{0:d}: ", Type) +
150                                     getELFX86_64RelocName(Type));
151   }
152 
153   Error addRelocations() override {
154     LLVM_DEBUG(dbgs() << "Processing relocations:\n");
155 
156     using Base = ELFLinkGraphBuilder<ELFT>;
157     using Self = ELFLinkGraphBuilder_x86_64;
158     for (const auto &RelSect : Base::Sections) {
159       // Validate the section to read relocation entries from.
160       if (RelSect.sh_type == ELF::SHT_REL)
161         return make_error<StringError>(
162             "No SHT_REL in valid x64 ELF object files",
163             inconvertibleErrorCode());
164 
165       if (Error Err = Base::forEachRelocation(RelSect, this,
166                                               &Self::addSingleRelocation))
167         return Err;
168     }
169 
170     return Error::success();
171   }
172 
173   Error addSingleRelocation(const typename ELFT::Rela &Rel,
174                             const typename ELFT::Shdr &FixupSection,
175                             Section &GraphSection) {
176     using Base = ELFLinkGraphBuilder<ELFT>;
177 
178     uint32_t SymbolIndex = Rel.getSymbol(false);
179     auto ObjSymbol = Base::Obj.getRelocationSymbol(Rel, Base::SymTabSec);
180     if (!ObjSymbol)
181       return ObjSymbol.takeError();
182 
183     Symbol *GraphSymbol = Base::getGraphSymbol(SymbolIndex);
184     if (!GraphSymbol)
185       return make_error<StringError>(
186           formatv("Could not find symbol at given index, did you add it to "
187                   "JITSymbolTable? index: {0}, shndx: {1} Size of table: {2}",
188                   SymbolIndex, (*ObjSymbol)->st_shndx,
189                   Base::GraphSymbols.size()),
190           inconvertibleErrorCode());
191 
192     // Validate the relocation kind.
193     auto ELFRelocKind = getRelocationKind(Rel.getType(false));
194     if (!ELFRelocKind)
195       return ELFRelocKind.takeError();
196 
197     int64_t Addend = Rel.r_addend;
198     Edge::Kind Kind = Edge::Invalid;
199     switch (*ELFRelocKind) {
200     case PCRel32:
201       Kind = x86_64::Delta32;
202       break;
203     case Delta64:
204       Kind = x86_64::Delta64;
205       break;
206     case Pointer32Signed:
207       Kind = x86_64::Pointer32Signed;
208       break;
209     case Pointer64:
210       Kind = x86_64::Pointer64;
211       break;
212     case PCRel32GOTLoad: {
213       Kind = x86_64::RequestGOTAndTransformToDelta32;
214       break;
215     }
216     case PCRel32REXGOTLoadRelaxable: {
217       Kind = x86_64::RequestGOTAndTransformToPCRel32GOTLoadREXRelaxable;
218       Addend = 0;
219       break;
220     }
221     case PCRel32TLV: {
222       Kind = x86_64::RequestTLSDescInGOTAndTransformToDelta32;
223       break;
224     }
225     case PCRel32GOTLoadRelaxable: {
226       Kind = x86_64::RequestGOTAndTransformToPCRel32GOTLoadRelaxable;
227       Addend = 0;
228       break;
229     }
230     case PCRel64GOT: {
231       Kind = x86_64::RequestGOTAndTransformToDelta64;
232       break;
233     }
234     case GOT64: {
235       Kind = x86_64::RequestGOTAndTransformToDelta64FromGOT;
236       break;
237     }
238     case GOTOFF64: {
239       Kind = x86_64::Delta64FromGOT;
240       break;
241     }
242     case Branch32: {
243       Kind = x86_64::BranchPCRel32;
244       Addend = 0;
245       break;
246     }
247     }
248 
249     Block *BlockToFix = *(GraphSection.blocks().begin());
250     JITTargetAddress FixupAddress = FixupSection.sh_addr + Rel.r_offset;
251     Edge::OffsetT Offset = FixupAddress - BlockToFix->getAddress();
252     Edge GE(Kind, Offset, *GraphSymbol, Addend);
253     LLVM_DEBUG({
254       dbgs() << "    ";
255       printEdge(dbgs(), *BlockToFix, GE, getELFX86RelocationKindName(Kind));
256       dbgs() << "\n";
257     });
258 
259     BlockToFix->addEdge(std::move(GE));
260     return Error::success();
261   }
262 
263 public:
264   ELFLinkGraphBuilder_x86_64(StringRef FileName,
265                              const object::ELFFile<object::ELF64LE> &Obj)
266       : ELFLinkGraphBuilder(Obj, Triple("x86_64-unknown-linux"), FileName,
267                             x86_64::getEdgeKindName) {}
268 };
269 
270 class ELFJITLinker_x86_64 : public JITLinker<ELFJITLinker_x86_64> {
271   friend class JITLinker<ELFJITLinker_x86_64>;
272 
273 public:
274   ELFJITLinker_x86_64(std::unique_ptr<JITLinkContext> Ctx,
275                       std::unique_ptr<LinkGraph> G,
276                       PassConfiguration PassConfig)
277       : JITLinker(std::move(Ctx), std::move(G), std::move(PassConfig)) {
278     getPassConfig().PostAllocationPasses.push_back(
279         [this](LinkGraph &G) { return getOrCreateGOTSymbol(G); });
280   }
281 
282 private:
283   Symbol *GOTSymbol = nullptr;
284 
285   Error getOrCreateGOTSymbol(LinkGraph &G) {
286     auto DefineExternalGOTSymbolIfPresent =
287         createDefineExternalSectionStartAndEndSymbolsPass(
288             [&](LinkGraph &LG, Symbol &Sym) -> SectionRangeSymbolDesc {
289               if (Sym.getName() == ELFGOTSymbolName)
290                 if (auto *GOTSection = G.findSectionByName(
291                         x86_64::GOTTableManager::getSectionName())) {
292                   GOTSymbol = &Sym;
293                   return {*GOTSection, true};
294                 }
295               return {};
296             });
297 
298     // Try to attach _GLOBAL_OFFSET_TABLE_ to the GOT if it's defined as an
299     // external.
300     if (auto Err = DefineExternalGOTSymbolIfPresent(G))
301       return Err;
302 
303     // If we succeeded then we're done.
304     if (GOTSymbol)
305       return Error::success();
306 
307     // Otherwise look for a GOT section: If it already has a start symbol we'll
308     // record it, otherwise we'll create our own.
309     // If there's a GOT section but we didn't find an external GOT symbol...
310     if (auto *GOTSection =
311             G.findSectionByName(x86_64::GOTTableManager::getSectionName())) {
312 
313       // Check for an existing defined symbol.
314       for (auto *Sym : GOTSection->symbols())
315         if (Sym->getName() == ELFGOTSymbolName) {
316           GOTSymbol = Sym;
317           return Error::success();
318         }
319 
320       // If there's no defined symbol then create one.
321       SectionRange SR(*GOTSection);
322       if (SR.empty())
323         GOTSymbol = &G.addAbsoluteSymbol(ELFGOTSymbolName, 0, 0,
324                                          Linkage::Strong, Scope::Local, true);
325       else
326         GOTSymbol =
327             &G.addDefinedSymbol(*SR.getFirstBlock(), 0, ELFGOTSymbolName, 0,
328                                 Linkage::Strong, Scope::Local, false, true);
329     }
330 
331     return Error::success();
332   }
333 
334   Error applyFixup(LinkGraph &G, Block &B, const Edge &E) const {
335     return x86_64::applyFixup(G, B, E, GOTSymbol);
336   }
337 };
338 
339 Expected<std::unique_ptr<LinkGraph>>
340 createLinkGraphFromELFObject_x86_64(MemoryBufferRef ObjectBuffer) {
341   LLVM_DEBUG({
342     dbgs() << "Building jitlink graph for new input "
343            << ObjectBuffer.getBufferIdentifier() << "...\n";
344   });
345 
346   auto ELFObj = object::ObjectFile::createELFObjectFile(ObjectBuffer);
347   if (!ELFObj)
348     return ELFObj.takeError();
349 
350   auto &ELFObjFile = cast<object::ELFObjectFile<object::ELF64LE>>(**ELFObj);
351   return ELFLinkGraphBuilder_x86_64((*ELFObj)->getFileName(),
352                                     ELFObjFile.getELFFile())
353       .buildGraph();
354 }
355 
356 static SectionRangeSymbolDesc
357 identifyELFSectionStartAndEndSymbols(LinkGraph &G, Symbol &Sym) {
358   constexpr StringRef StartSymbolPrefix = "__start";
359   constexpr StringRef EndSymbolPrefix = "__end";
360 
361   auto SymName = Sym.getName();
362   if (SymName.startswith(StartSymbolPrefix)) {
363     if (auto *Sec =
364             G.findSectionByName(SymName.drop_front(StartSymbolPrefix.size())))
365       return {*Sec, true};
366   } else if (SymName.startswith(EndSymbolPrefix)) {
367     if (auto *Sec =
368             G.findSectionByName(SymName.drop_front(EndSymbolPrefix.size())))
369       return {*Sec, false};
370   }
371   return {};
372 }
373 
374 void link_ELF_x86_64(std::unique_ptr<LinkGraph> G,
375                      std::unique_ptr<JITLinkContext> Ctx) {
376   PassConfiguration Config;
377 
378   if (Ctx->shouldAddDefaultTargetPasses(G->getTargetTriple())) {
379 
380     Config.PrePrunePasses.push_back(EHFrameSplitter(".eh_frame"));
381     Config.PrePrunePasses.push_back(
382         EHFrameEdgeFixer(".eh_frame", x86_64::PointerSize, x86_64::Delta64,
383                          x86_64::Delta32, x86_64::NegDelta32));
384     Config.PrePrunePasses.push_back(EHFrameNullTerminator(".eh_frame"));
385 
386     // Construct a JITLinker and run the link function.
387     // Add a mark-live pass.
388     if (auto MarkLive = Ctx->getMarkLivePass(G->getTargetTriple()))
389       Config.PrePrunePasses.push_back(std::move(MarkLive));
390     else
391       Config.PrePrunePasses.push_back(markAllSymbolsLive);
392 
393     // Add an in-place GOT/Stubs/TLSInfoEntry build pass.
394     Config.PostPrunePasses.push_back(buildTables_ELF_x86_64);
395 
396     // Resolve any external section start / end symbols.
397     Config.PostAllocationPasses.push_back(
398         createDefineExternalSectionStartAndEndSymbolsPass(
399             identifyELFSectionStartAndEndSymbols));
400 
401     // Add GOT/Stubs optimizer pass.
402     Config.PreFixupPasses.push_back(x86_64::optimizeGOTAndStubAccesses);
403   }
404 
405   if (auto Err = Ctx->modifyPassConfig(*G, Config))
406     return Ctx->notifyFailed(std::move(Err));
407 
408   ELFJITLinker_x86_64::link(std::move(Ctx), std::move(G), std::move(Config));
409 }
410 const char *getELFX86RelocationKindName(Edge::Kind R) {
411   switch (R) {
412   case Branch32:
413     return "Branch32";
414   case Pointer32Signed:
415     return "Pointer32Signed";
416   case Pointer64:
417     return "Pointer64";
418   case PCRel32:
419     return "PCRel32";
420   case PCRel32GOTLoad:
421     return "PCRel32GOTLoad";
422   case PCRel32GOTLoadRelaxable:
423     return "PCRel32GOTLoadRelaxable";
424   case PCRel32REXGOTLoadRelaxable:
425     return "PCRel32REXGOTLoad";
426   case PCRel64GOT:
427     return "PCRel64GOT";
428   case Delta64:
429     return "Delta64";
430   case GOT64:
431     return "GOT64";
432   case GOTOFF64:
433     return "GOTOFF64";
434   }
435   return getGenericEdgeKindName(static_cast<Edge::Kind>(R));
436 }
437 } // end namespace jitlink
438 } // end namespace llvm
439