be89e794f7
Absolute thunks generated by LLD reference function addresses recorded as data in code. Since they are generated by the linker, they don't have relocations associated with them and thus the addresses are left undetected. Use pattern matching to detect such thunks and handle them in VeneerElimination pass.
111 lines
3.5 KiB
C++
111 lines
3.5 KiB
C++
//===- bolt/Passes/VeneerElimination.cpp ----------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This class implements a pass that removes linker-inserted veneers from the
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// code and redirects veneer callers to call to veneers destinations
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//
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//===----------------------------------------------------------------------===//
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#include "bolt/Passes/VeneerElimination.h"
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#define DEBUG_TYPE "veneer-elim"
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using namespace llvm;
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namespace opts {
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extern cl::OptionCategory BoltOptCategory;
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static llvm::cl::opt<bool>
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EliminateVeneers("elim-link-veneers",
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cl::desc("run veneer elimination pass"), cl::init(true),
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cl::Hidden, cl::cat(BoltOptCategory));
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} // namespace opts
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namespace llvm {
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namespace bolt {
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static bool isPossibleVeneer(const BinaryFunction &BF) {
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return BF.isAArch64Veneer() || BF.getOneName().starts_with("__AArch64");
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}
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Error VeneerElimination::runOnFunctions(BinaryContext &BC) {
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if (!opts::EliminateVeneers || !BC.isAArch64())
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return Error::success();
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std::unordered_map<const MCSymbol *, const MCSymbol *> VeneerDestinations;
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uint64_t NumEliminatedVeneers = 0;
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for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
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if (!isPossibleVeneer(BF))
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continue;
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if (BF.isIgnored())
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continue;
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const MCSymbol *VeneerTargetSymbol = 0;
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uint64_t TargetAddress;
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if (BC.MIB->matchAbsLongVeneer(BF, TargetAddress)) {
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if (BinaryFunction *TargetBF =
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BC.getBinaryFunctionAtAddress(TargetAddress))
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VeneerTargetSymbol = TargetBF->getSymbol();
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} else {
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MCInst &FirstInstruction = *(BF.begin()->begin());
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if (BC.MIB->hasAnnotation(FirstInstruction, "AArch64Veneer"))
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VeneerTargetSymbol = BC.MIB->getTargetSymbol(FirstInstruction, 1);
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}
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if (!VeneerTargetSymbol)
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continue;
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for (const MCSymbol *Symbol : BF.getSymbols())
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VeneerDestinations[Symbol] = VeneerTargetSymbol;
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NumEliminatedVeneers++;
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BF.setPseudo(true);
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}
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BC.outs() << "BOLT-INFO: number of removed linker-inserted veneers: "
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<< NumEliminatedVeneers << '\n';
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// Handle veneers to veneers in case they occur
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for (auto &Entry : VeneerDestinations) {
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const MCSymbol *Src = Entry.first;
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const MCSymbol *Dest = Entry.second;
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while (VeneerDestinations.find(Dest) != VeneerDestinations.end())
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Dest = VeneerDestinations[Dest];
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VeneerDestinations[Src] = Dest;
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}
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uint64_t VeneerCallers = 0;
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for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
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for (BinaryBasicBlock &BB : BF) {
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for (MCInst &Instr : BB) {
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if (!BC.MIB->isCall(Instr) || BC.MIB->isIndirectCall(Instr))
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continue;
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const MCSymbol *TargetSymbol = BC.MIB->getTargetSymbol(Instr, 0);
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auto It = VeneerDestinations.find(TargetSymbol);
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if (It == VeneerDestinations.end())
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continue;
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VeneerCallers++;
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BC.MIB->replaceBranchTarget(Instr, It->second, BC.Ctx.get());
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}
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}
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}
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LLVM_DEBUG(
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dbgs() << "BOLT-INFO: number of linker-inserted veneers call sites: "
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<< VeneerCallers << "\n");
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(void)VeneerCallers;
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return Error::success();
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}
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} // namespace bolt
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} // namespace llvm
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