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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::ZeroOrMore,
cl::Hidden,
cl::cat(BoltOptCategory));
} // namespace opts
namespace llvm {
namespace bolt {
void VeneerElimination::runOnFunctions(BinaryContext &BC) {
if (!opts::EliminateVeneers || !BC.isAArch64())
return;
auto &BFs = BC.getBinaryFunctions();
std::unordered_map<const MCSymbol *, const MCSymbol *> VeneerDestinations;
uint64_t VeneersCount = 0;
for (auto It = BFs.begin(); It != BFs.end();) {
auto CurrentIt = It;
++It;
if (CurrentIt->second.isAArch64Veneer()) {
VeneersCount++;
BinaryFunction &VeneerFunction = CurrentIt->second;
MCInst &FirstInstruction = *(VeneerFunction.begin()->begin());
const MCSymbol *VeneerTargetSymbol =
BC.MIB->getTargetSymbol(FirstInstruction, 1);
// Functions can have multiple symbols
for (StringRef Name : VeneerFunction.getNames()) {
MCSymbol *Symbol = BC.Ctx->lookupSymbol(Name);
VeneerDestinations[Symbol] = VeneerTargetSymbol;
BC.SymbolToFunctionMap.erase(Symbol);
}
BC.BinaryDataMap.erase(VeneerFunction.getAddress());
BFs.erase(CurrentIt);
}
}
LLVM_DEBUG(dbgs() << "BOLT-INFO: number of removed linker-inserted veneers :"
<< VeneersCount << "\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 (auto &It : BFs) {
BinaryFunction &Function = It.second;
for (BinaryBasicBlock &BB : Function) {
for (MCInst &Instr : BB) {
if (!BC.MIB->isCall(Instr) || BC.MIB->isIndirectCall(Instr))
continue;
const MCSymbol *TargetSymbol = BC.MIB->getTargetSymbol(Instr, 0);
if (VeneerDestinations.find(TargetSymbol) == VeneerDestinations.end())
continue;
VeneerCallers++;
if (!BC.MIB->replaceBranchTarget(
Instr, VeneerDestinations[TargetSymbol], BC.Ctx.get()))
assert(false && "updating veneer call destination failed");
}
}
}
LLVM_DEBUG(
dbgs() << "BOLT-INFO: number of linker-inserted veneers call sites :"
<< VeneerCallers << "\n");
}
} // namespace bolt
} // namespace llvm
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