1 //===- bolt/Passes/PLTCall.h - PLT call optimization ----------------------===//
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 // This file implements the PLTCall class, which replaces calls to PLT entries
10 // with indirect calls against GOT.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "bolt/Passes/PLTCall.h"
15 #include "llvm/Support/CommandLine.h"
16
17 #define DEBUG_TYPE "bolt-plt"
18
19 using namespace llvm;
20
21 namespace opts {
22
23 extern cl::OptionCategory BoltOptCategory;
24
25 cl::opt<bolt::PLTCall::OptType>
26 PLT("plt",
27 cl::desc("optimize PLT calls (requires linking with -znow)"),
28 cl::init(bolt::PLTCall::OT_NONE),
29 cl::values(clEnumValN(bolt::PLTCall::OT_NONE,
30 "none",
31 "do not optimize PLT calls"),
32 clEnumValN(bolt::PLTCall::OT_HOT,
33 "hot",
34 "optimize executed (hot) PLT calls"),
35 clEnumValN(bolt::PLTCall::OT_ALL,
36 "all",
37 "optimize all PLT calls")),
38 cl::ZeroOrMore,
39 cl::cat(BoltOptCategory));
40
41 }
42
43 namespace llvm {
44 namespace bolt {
45
runOnFunctions(BinaryContext & BC)46 void PLTCall::runOnFunctions(BinaryContext &BC) {
47 if (opts::PLT == OT_NONE)
48 return;
49
50 uint64_t NumCallsOptimized = 0;
51 for (auto &It : BC.getBinaryFunctions()) {
52 BinaryFunction &Function = It.second;
53 if (!shouldOptimize(Function))
54 continue;
55
56 if (opts::PLT == OT_HOT &&
57 Function.getExecutionCount() == BinaryFunction::COUNT_NO_PROFILE)
58 continue;
59
60 for (BinaryBasicBlock &BB : Function) {
61 if (opts::PLT == OT_HOT && !BB.getKnownExecutionCount())
62 continue;
63
64 for (MCInst &Instr : BB) {
65 if (!BC.MIB->isCall(Instr))
66 continue;
67 const MCSymbol *CallSymbol = BC.MIB->getTargetSymbol(Instr);
68 if (!CallSymbol)
69 continue;
70 const BinaryFunction *CalleeBF = BC.getFunctionForSymbol(CallSymbol);
71 if (!CalleeBF || !CalleeBF->isPLTFunction())
72 continue;
73 BC.MIB->convertCallToIndirectCall(Instr, CalleeBF->getPLTSymbol(),
74 BC.Ctx.get());
75 BC.MIB->addAnnotation(Instr, "PLTCall", true);
76 ++NumCallsOptimized;
77 }
78 }
79 }
80
81 if (NumCallsOptimized) {
82 BC.RequiresZNow = true;
83 outs() << "BOLT-INFO: " << NumCallsOptimized
84 << " PLT calls in the binary were optimized.\n";
85 }
86 }
87
88 } // namespace bolt
89 } // namespace llvm
90