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//===- bolt/Passes/PLTCall.h - PLT call optimization ----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements the PLTCall class, which replaces calls to PLT entries
// with indirect calls against GOT.
//
//===----------------------------------------------------------------------===//
#include "bolt/Passes/PLTCall.h"
#include "llvm/Support/CommandLine.h"
#define DEBUG_TYPE "bolt-plt"
using namespace llvm;
namespace opts {
extern cl::OptionCategory BoltOptCategory;
cl::opt<bolt::PLTCall::OptType>
PLT("plt",
cl::desc("optimize PLT calls (requires linking with -znow)"),
cl::init(bolt::PLTCall::OT_NONE),
cl::values(clEnumValN(bolt::PLTCall::OT_NONE,
"none",
"do not optimize PLT calls"),
clEnumValN(bolt::PLTCall::OT_HOT,
"hot",
"optimize executed (hot) PLT calls"),
clEnumValN(bolt::PLTCall::OT_ALL,
"all",
"optimize all PLT calls")),
cl::ZeroOrMore,
cl::cat(BoltOptCategory));
}
namespace llvm {
namespace bolt {
void PLTCall::runOnFunctions(BinaryContext &BC) {
if (opts::PLT == OT_NONE)
return;
uint64_t NumCallsOptimized = 0;
for (auto &It : BC.getBinaryFunctions()) {
BinaryFunction &Function = It.second;
if (!shouldOptimize(Function))
continue;
if (opts::PLT == OT_HOT &&
Function.getExecutionCount() == BinaryFunction::COUNT_NO_PROFILE)
continue;
for (BinaryBasicBlock &BB : Function) {
if (opts::PLT == OT_HOT && !BB.getKnownExecutionCount())
continue;
for (MCInst &Instr : BB) {
if (!BC.MIB->isCall(Instr))
continue;
const MCSymbol *CallSymbol = BC.MIB->getTargetSymbol(Instr);
if (!CallSymbol)
continue;
const BinaryFunction *CalleeBF = BC.getFunctionForSymbol(CallSymbol);
if (!CalleeBF || !CalleeBF->isPLTFunction())
continue;
BC.MIB->convertCallToIndirectCall(Instr, CalleeBF->getPLTSymbol(),
BC.Ctx.get());
BC.MIB->addAnnotation(Instr, "PLTCall", true);
++NumCallsOptimized;
}
}
}
if (NumCallsOptimized) {
BC.RequiresZNow = true;
outs() << "BOLT-INFO: " << NumCallsOptimized
<< " PLT calls in the binary were optimized.\n";
}
}
} // namespace bolt
} // namespace llvm
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