1 //===--- BasicGOTAndStubsBuilder.h - Generic GOT/Stub creation --*- 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 // A base for simple GOT and stub creation.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_LIB_EXECUTIONENGINE_JITLINK_BASICGOTANDSTUBSBUILDER_H
14 #define LLVM_LIB_EXECUTIONENGINE_JITLINK_BASICGOTANDSTUBSBUILDER_H
15 
16 #include "llvm/ExecutionEngine/JITLink/JITLink.h"
17 
18 #define DEBUG_TYPE "jitlink"
19 
20 namespace llvm {
21 namespace jitlink {
22 
23 template <typename BuilderImpl> class BasicGOTAndStubsBuilder {
24 public:
BasicGOTAndStubsBuilder(LinkGraph & G)25   BasicGOTAndStubsBuilder(LinkGraph &G) : G(G) {}
26 
run()27   void run() {
28     // We're going to be adding new blocks, but we don't want to iterate over
29     // the newly added ones, so just copy the existing blocks out.
30     std::vector<Block *> Blocks(G.blocks().begin(), G.blocks().end());
31 
32     LLVM_DEBUG(dbgs() << "Creating GOT entries and stubs:\n");
33 
34     for (auto *B : Blocks)
35       for (auto &E : B->edges())
36         if (impl().isGOTEdge(E)) {
37           LLVM_DEBUG({
38             dbgs() << "  Updating GOT edge ";
39             printEdge(dbgs(), *B, E, "<target GOT>");
40             dbgs() << "\n";
41           });
42           impl().fixGOTEdge(E, getGOTEntrySymbol(E.getTarget()));
43         } else if (impl().isExternalBranchEdge(E)) {
44           LLVM_DEBUG({
45             dbgs() << "  Updating external branch edge ";
46             printEdge(dbgs(), *B, E, "<target PC-rel>");
47             dbgs() << "\n";
48           });
49           impl().fixExternalBranchEdge(E, getStubSymbol(E.getTarget()));
50         }
51   }
52 
53 protected:
getGOTEntrySymbol(Symbol & Target)54   Symbol &getGOTEntrySymbol(Symbol &Target) {
55     assert(Target.hasName() && "GOT edge cannot point to anonymous target");
56 
57     auto GOTEntryI = GOTEntries.find(Target.getName());
58 
59     // Build the entry if it doesn't exist.
60     if (GOTEntryI == GOTEntries.end()) {
61       auto &GOTEntry = impl().createGOTEntry(Target);
62       LLVM_DEBUG({
63         dbgs() << "    Created GOT entry for " << Target.getName() << ": "
64                << GOTEntry << "\n";
65       });
66       GOTEntryI =
67           GOTEntries.insert(std::make_pair(Target.getName(), &GOTEntry)).first;
68     }
69 
70     assert(GOTEntryI != GOTEntries.end() && "Could not get GOT entry symbol");
71     LLVM_DEBUG(
72         { dbgs() << "    Using GOT entry " << *GOTEntryI->second << "\n"; });
73     return *GOTEntryI->second;
74   }
75 
getStubSymbol(Symbol & Target)76   Symbol &getStubSymbol(Symbol &Target) {
77     assert(Target.hasName() &&
78            "External branch edge can not point to an anonymous target");
79     auto StubI = Stubs.find(Target.getName());
80 
81     if (StubI == Stubs.end()) {
82       auto &StubSymbol = impl().createStub(Target);
83       LLVM_DEBUG({
84         dbgs() << "    Created stub for " << Target.getName() << ": "
85                << StubSymbol << "\n";
86       });
87       StubI = Stubs.insert(std::make_pair(Target.getName(), &StubSymbol)).first;
88     }
89 
90     assert(StubI != Stubs.end() && "Count not get stub symbol");
91     LLVM_DEBUG({ dbgs() << "    Using stub " << *StubI->second << "\n"; });
92     return *StubI->second;
93   }
94 
95   LinkGraph &G;
96 
97 private:
impl()98   BuilderImpl &impl() { return static_cast<BuilderImpl &>(*this); }
99 
100   DenseMap<StringRef, Symbol *> GOTEntries;
101   DenseMap<StringRef, Symbol *> Stubs;
102 };
103 
104 } // end namespace jitlink
105 } // end namespace llvm
106 
107 #endif // LLVM_LIB_EXECUTIONENGINE_JITLINK_BASICGOTANDSTUBSBUILDER_H
108