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