llvm/lib/ExecutionEngine/JITLink/PerGraphGOTAndPLTStubsBuilder.h

   1 //===--------------- PerGraphGOTAndPLTStubBuilder.h -------------*- C++ -*-===//
   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 // Construct GOT and PLT entries for each graph.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #ifndef LLVM_EXECUTIONENGINE_JITLINK_PERGRAPHGOTANDPLTSTUBSBUILDER_H
  14 #define LLVM_EXECUTIONENGINE_JITLINK_PERGRAPHGOTANDPLTSTUBSBUILDER_H
  15
  16 #include "llvm/ExecutionEngine/JITLink/JITLink.h"
  17 #include "llvm/Support/Debug.h"
  18
  19 #define DEBUG_TYPE "jitlink"
  20
  21 namespace llvm {
  22 namespace jitlink {
  23
  24 /// Per-object GOT and PLT Stub builder.
  25 ///
  26 /// Constructs GOT entries and PLT stubs in every graph for referenced symbols.
  27 /// Building these blocks in every graph is likely to lead to duplicate entries
  28 /// in the JITLinkDylib, but allows graphs to be trivially removed independently
  29 /// without affecting other graphs (since those other graphs will have their own
  30 /// copies of any required entries).
  31 template <typename BuilderImplT>
  32 class PerGraphGOTAndPLTStubsBuilder {
  33 public:
  34   PerGraphGOTAndPLTStubsBuilder(LinkGraph &G) : G(G) {}
  35
  36   static Error asPass(LinkGraph &G) { return BuilderImplT(G).run(); }
  37
  38   Error run() {
  39     LLVM_DEBUG(dbgs() << "Running Per-Graph GOT and Stubs builder:\n");
  40
  41     // We're going to be adding new blocks, but we don't want to iterate over
  42     // the new ones, so build a worklist.
  43     std::vector<Block *> Worklist(G.blocks().begin(), G.blocks().end());
  44
  45     for (auto *B : Worklist)
  46       for (auto &E : B->edges()) {
  47         if (impl().isGOTEdgeToFix(E)) {
  48           LLVM_DEBUG({
  49             dbgs() << "  Fixing " << G.getEdgeKindName(E.getKind())
  50                    << " edge at " << B->getFixupAddress(E) << " ("
  51                    << B->getAddress() << " + "
  52                    << formatv("{0:x}", E.getOffset()) << ")\n";
  53           });
  54           impl().fixGOTEdge(E, getGOTEntry(E.getTarget()));
  55         } else if (impl().isExternalBranchEdge(E)) {
  56           LLVM_DEBUG({
  57             dbgs() << "  Fixing " << G.getEdgeKindName(E.getKind())
  58                    << " edge at " << B->getFixupAddress(E) << " ("
  59                    << B->getAddress() << " + "
  60                    << formatv("{0:x}", E.getOffset()) << ")\n";
  61           });
  62           impl().fixPLTEdge(E, getPLTStub(E.getTarget()));
  63         }
  64       }
  65
  66     return Error::success();
  67   }
  68
  69 protected:
  70   Symbol &getGOTEntry(Symbol &Target) {
  71     assert(Target.hasName() && "GOT edge cannot point to anonymous target");
  72
  73     auto GOTEntryI = GOTEntries.find(Target.getName());
  74
  75     // Build the entry if it doesn't exist.
  76     if (GOTEntryI == GOTEntries.end()) {
  77       auto &GOTEntry = impl().createGOTEntry(Target);
  78       LLVM_DEBUG({
  79         dbgs() << "    Created GOT entry for " << Target.getName() << ": "
  80                << GOTEntry << "\n";
  81       });
  82       GOTEntryI =
  83           GOTEntries.insert(std::make_pair(Target.getName(), &GOTEntry)).first;
  84     }
  85
  86     assert(GOTEntryI != GOTEntries.end() && "Could not get GOT entry symbol");
  87     LLVM_DEBUG(
  88         { dbgs() << "    Using GOT entry " << *GOTEntryI->second << "\n"; });
  89     return *GOTEntryI->second;
  90   }
  91
  92   Symbol &getPLTStub(Symbol &Target) {
  93     assert(Target.hasName() &&
  94            "External branch edge can not point to an anonymous target");
  95     auto StubI = PLTStubs.find(Target.getName());
  96
  97     if (StubI == PLTStubs.end()) {
  98       auto &StubSymbol = impl().createPLTStub(Target);
  99       LLVM_DEBUG({
 100         dbgs() << "    Created PLT stub for " << Target.getName() << ": "
 101                << StubSymbol << "\n";
 102       });
 103       StubI =
 104           PLTStubs.insert(std::make_pair(Target.getName(), &StubSymbol)).first;
 105     }
 106
 107     assert(StubI != PLTStubs.end() && "Count not get stub symbol");
 108     LLVM_DEBUG({ dbgs() << "    Using PLT stub " << *StubI->second << "\n"; });
 109     return *StubI->second;
 110   }
 111
 112   LinkGraph &G;
 113
 114 private:
 115   BuilderImplT &impl() { return static_cast<BuilderImplT &>(*this); }
 116
 117   DenseMap<StringRef, Symbol *> GOTEntries;
 118   DenseMap<StringRef, Symbol *> PLTStubs;
 119 };
 120
 121 } // end namespace jitlink
 122 } // end namespace llvm
 123
 124 #undef DEBUG_TYPE
 125
 126 #endif // LLVM_EXECUTIONENGINE_JITLINK_PERGRAPHGOTANDPLTSTUBSBUILDER_H