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
19using namespace llvm;
20
21namespace opts {
22
23extern cl::OptionCategory BoltOptCategory;
24
25static cl::opt<bolt::PLTCall::OptType>
26 PLT("plt", cl::desc("optimize PLT calls (requires linking with -znow)"),
27 cl::init(Val: bolt::PLTCall::OT_NONE),
28 cl::values(clEnumValN(bolt::PLTCall::OT_NONE, "none",
29 "do not optimize PLT calls"),
30 clEnumValN(bolt::PLTCall::OT_HOT, "hot",
31 "optimize executed (hot) PLT calls"),
32 clEnumValN(bolt::PLTCall::OT_ALL, "all",
33 "optimize all PLT calls")),
34 cl::ZeroOrMore, cl::cat(BoltOptCategory));
35}
36
37namespace llvm {
38namespace bolt {
39
40Error PLTCall::runOnFunctions(BinaryContext &BC) {
41 if (opts::PLT == OT_NONE)
42 return Error::success();
43
44 uint64_t NumCallsOptimized = 0;
45 for (auto &BFI : BC.getBinaryFunctions()) {
46 BinaryFunction &Function = BFI.second;
47 if (!shouldOptimize(BF: Function))
48 continue;
49
50 if (opts::PLT == OT_HOT &&
51 Function.getExecutionCount() == BinaryFunction::COUNT_NO_PROFILE)
52 continue;
53
54 for (BinaryBasicBlock &BB : Function) {
55 if (opts::PLT == OT_HOT && !BB.getKnownExecutionCount())
56 continue;
57
58 for (auto II = BB.begin(); II != BB.end(); II++) {
59 if (!BC.MIB->isCall(Inst: *II))
60 continue;
61 const MCSymbol *CallSymbol = BC.MIB->getTargetSymbol(Inst: *II);
62 if (!CallSymbol)
63 continue;
64 const BinaryFunction *CalleeBF = BC.getFunctionForSymbol(Symbol: CallSymbol);
65 if (!CalleeBF || !CalleeBF->isPLTFunction())
66 continue;
67 const InstructionListType NewCode = BC.MIB->createIndirectPLTCall(
68 DirectCall: std::move(*II), TargetLocation: CalleeBF->getPLTSymbol(), Ctx: BC.Ctx.get());
69 II = BB.replaceInstruction(II, Replacement: NewCode);
70 assert(!NewCode.empty() && "PLT Call replacement must be non-empty");
71 std::advance(i&: II, n: NewCode.size() - 1);
72 BC.MIB->addAnnotation(Inst&: *II, Name: "PLTCall", Val: true);
73 ++NumCallsOptimized;
74 }
75 }
76 }
77
78 if (NumCallsOptimized) {
79 BC.RequiresZNow = true;
80 BC.outs() << "BOLT-INFO: " << NumCallsOptimized
81 << " PLT calls in the binary were optimized.\n";
82 }
83 return Error::success();
84}
85
86} // namespace bolt
87} // namespace llvm
88

source code of bolt/lib/Passes/PLTCall.cpp