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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;
static 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 {
Error PLTCall::runOnFunctions(BinaryContext &BC) {
if (opts::PLT == OT_NONE)
return Error::success();
uint64_t NumCallsOptimized = 0;
for (auto &BFI : BC.getBinaryFunctions()) {
BinaryFunction &Function = BFI.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 (auto II = BB.begin(); II != BB.end(); II++) {
if (!BC.MIB->isCall(*II))
continue;
const MCSymbol *CallSymbol = BC.MIB->getTargetSymbol(*II);
if (!CallSymbol)
continue;
const BinaryFunction *CalleeBF = BC.getFunctionForSymbol(CallSymbol);
if (!CalleeBF || !CalleeBF->isPLTFunction())
continue;
const InstructionListType NewCode = BC.MIB->createIndirectPLTCall(
std::move(*II), CalleeBF->getPLTSymbol(), BC.Ctx.get());
II = BB.replaceInstruction(II, NewCode);
assert(!NewCode.empty() && "PLT Call replacement must be non-empty");
std::advance(II, NewCode.size() - 1);
BC.MIB->addAnnotation(*II, "PLTCall", true);
++NumCallsOptimized;
}
}
}
if (NumCallsOptimized) {
BC.RequiresZNow = true;
BC.outs() << "BOLT-INFO: " << NumCallsOptimized
<< " PLT calls in the binary were optimized.\n";
}
return Error::success();
}
} // namespace bolt
} // namespace llvm
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