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 
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.layout()) {
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