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      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 " << formatv("{0:x}", B->getFixupAddress(E))
     51                    << " (" << formatv("{0:x}", 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 " << formatv("{0:x}", B->getFixupAddress(E))
     59                    << " (" << formatv("{0:x}", 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
    127