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//===- bolt/Passes/VeneerElimination.cpp ----------------------------------===//
//
// 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 class implements a pass that removes linker-inserted veneers from the
// code and redirects veneer callers to call to veneers destinations
//
//===----------------------------------------------------------------------===//
#include "bolt/Passes/VeneerElimination.h"
#define DEBUG_TYPE "veneer-elim"
using namespace llvm;
namespace opts {
extern cl::OptionCategory BoltOptCategory;
static llvm::cl::opt<bool>
EliminateVeneers("elim-link-veneers",
cl::desc("run veneer elimination pass"), cl::init(true),
cl::Hidden, cl::cat(BoltOptCategory));
} // namespace opts
namespace llvm {
namespace bolt {
static bool isPossibleVeneer(const BinaryFunction &BF) {
return BF.isAArch64Veneer() || BF.getOneName().starts_with("__AArch64");
}
Error VeneerElimination::runOnFunctions(BinaryContext &BC) {
if (!opts::EliminateVeneers || !BC.isAArch64())
return Error::success();
std::unordered_map<const MCSymbol *, const MCSymbol *> VeneerDestinations;
uint64_t NumEliminatedVeneers = 0;
for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
if (!isPossibleVeneer(BF))
continue;
if (BF.isIgnored())
continue;
MCInst &FirstInstruction = *(BF.begin()->begin());
const MCSymbol *VeneerTargetSymbol = 0;
uint64_t TargetAddress;
if (BC.MIB->isTailCall(FirstInstruction)) {
VeneerTargetSymbol = BC.MIB->getTargetSymbol(FirstInstruction);
} else if (BC.MIB->matchAbsLongVeneer(BF, TargetAddress)) {
if (BinaryFunction *TargetBF =
BC.getBinaryFunctionAtAddress(TargetAddress))
VeneerTargetSymbol = TargetBF->getSymbol();
} else if (BC.MIB->hasAnnotation(FirstInstruction, "AArch64Veneer")) {
VeneerTargetSymbol = BC.MIB->getTargetSymbol(FirstInstruction, 1);
}
if (!VeneerTargetSymbol)
continue;
for (const MCSymbol *Symbol : BF.getSymbols())
VeneerDestinations[Symbol] = VeneerTargetSymbol;
NumEliminatedVeneers++;
BF.setPseudo(true);
}
BC.outs() << "BOLT-INFO: number of removed linker-inserted veneers: "
<< NumEliminatedVeneers << '\n';
// Handle veneers to veneers in case they occur
for (auto &Entry : VeneerDestinations) {
const MCSymbol *Src = Entry.first;
const MCSymbol *Dest = Entry.second;
while (VeneerDestinations.find(Dest) != VeneerDestinations.end())
Dest = VeneerDestinations[Dest];
VeneerDestinations[Src] = Dest;
}
uint64_t VeneerCallers = 0;
for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
for (BinaryBasicBlock &BB : BF) {
for (MCInst &Instr : BB) {
if (!BC.MIB->isCall(Instr) || BC.MIB->isIndirectCall(Instr))
continue;
const MCSymbol *TargetSymbol = BC.MIB->getTargetSymbol(Instr, 0);
auto It = VeneerDestinations.find(TargetSymbol);
if (It == VeneerDestinations.end())
continue;
VeneerCallers++;
BC.MIB->replaceBranchTarget(Instr, It->second, BC.Ctx.get());
}
}
}
LLVM_DEBUG(
dbgs() << "BOLT-INFO: number of linker-inserted veneers call sites: "
<< VeneerCallers << "\n");
(void)VeneerCallers;
return Error::success();
}
} // namespace bolt
} // namespace llvm
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