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
21namespace llvm {
22namespace 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).
31template <typename BuilderImplT>
32class PerGraphGOTAndPLTStubsBuilder {
33public:
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(Target&: 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(Target&: E.getTarget()));
63 }
64 }
65
66 return Error::success();
67 }
68
69protected:
70 Symbol &getGOTEntry(Symbol &Target) {
71 assert(Target.hasName() && "GOT edge cannot point to anonymous target");
72
73 auto GOTEntryI = GOTEntries.find(Val: 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(Val: 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
114private:
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