bolt/lib/Passes/PLTCall.cpp

   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 Error PLTCall::runOnFunctions(BinaryContext &BC) {
  47   if (opts::PLT == OT_NONE)
  48     return Error::success();
  49
  50   uint64_t NumCallsOptimized = 0;
  51   for (auto &BFI : BC.getBinaryFunctions()) {
  52     BinaryFunction &Function = BFI.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 (auto II = BB.begin(); II != BB.end(); II++) {
  65         if (!BC.MIB->isCall(*II))
  66           continue;
  67         const MCSymbol *CallSymbol = BC.MIB->getTargetSymbol(*II);
  68         if (!CallSymbol)
  69           continue;
  70         const BinaryFunction *CalleeBF = BC.getFunctionForSymbol(CallSymbol);
  71         if (!CalleeBF || !CalleeBF->isPLTFunction())
  72           continue;
  73         const InstructionListType NewCode = BC.MIB->createIndirectPltCall(
  74             *II, CalleeBF->getPLTSymbol(), BC.Ctx.get());
  75         II = BB.replaceInstruction(II, NewCode);
  76         assert(!NewCode.empty() && "PLT Call replacement must be non-empty");
  77         std::advance(II, NewCode.size() - 1);
  78         BC.MIB->addAnnotation(*II, "PLTCall", true);
  79         ++NumCallsOptimized;
  80       }
  81     }
  82   }
  83
  84   if (NumCallsOptimized) {
  85     BC.RequiresZNow = true;
  86     BC.outs() << "BOLT-INFO: " << NumCallsOptimized
  87               << " PLT calls in the binary were optimized.\n";
  88   }
  89   return Error::success();
  90 }
  91
  92 } // namespace bolt
  93 } // namespace llvm