bolt/lib/Passes/VeneerElimination.cpp

   1 //===- bolt/Passes/VeneerElimination.cpp ----------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This class implements a pass that removes linker-inserted veneers from the
  10 // code and redirects veneer callers to call to veneers destinations
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "bolt/Passes/VeneerElimination.h"
  15 #define DEBUG_TYPE "veneer-elim"
  16
  17 using namespace llvm;
  18
  19 namespace opts {
  20
  21 extern cl::OptionCategory BoltOptCategory;
  22
  23 static llvm::cl::opt<bool>
  24     EliminateVeneers("elim-link-veneers",
  25                      cl::desc("run veneer elimination pass"), cl::init(true),
  26                      cl::Hidden, cl::cat(BoltOptCategory));
  27 } // namespace opts
  28
  29 namespace llvm {
  30 namespace bolt {
  31
  32 void VeneerElimination::runOnFunctions(BinaryContext &BC) {
  33   if (!opts::EliminateVeneers || !BC.isAArch64())
  34     return;
  35
  36   std::map<uint64_t, BinaryFunction> &BFs = BC.getBinaryFunctions();
  37   std::unordered_map<const MCSymbol *, const MCSymbol *> VeneerDestinations;
  38   uint64_t VeneersCount = 0;
  39   for (auto &It : BFs) {
  40     BinaryFunction &VeneerFunction = It.second;
  41     if (!VeneerFunction.isAArch64Veneer())
  42       continue;
  43
  44     VeneersCount++;
  45     VeneerFunction.setPseudo(true);
  46     MCInst &FirstInstruction = *(VeneerFunction.begin()->begin());
  47     const MCSymbol *VeneerTargetSymbol =
  48         BC.MIB->getTargetSymbol(FirstInstruction, 1);
  49     assert(VeneerTargetSymbol && "Expecting target symbol for instruction");
  50     for (const MCSymbol *Symbol : VeneerFunction.getSymbols())
  51       VeneerDestinations[Symbol] = VeneerTargetSymbol;
  52   }
  53
  54   outs() << "BOLT-INFO: number of removed linker-inserted veneers: "
  55          << VeneersCount << "\n";
  56
  57   // Handle veneers to veneers in case they occur
  58   for (auto &Entry : VeneerDestinations) {
  59     const MCSymbol *Src = Entry.first;
  60     const MCSymbol *Dest = Entry.second;
  61     while (VeneerDestinations.find(Dest) != VeneerDestinations.end())
  62       Dest = VeneerDestinations[Dest];
  63
  64     VeneerDestinations[Src] = Dest;
  65   }
  66
  67   uint64_t VeneerCallers = 0;
  68   for (auto &It : BFs) {
  69     BinaryFunction &Function = It.second;
  70     for (BinaryBasicBlock &BB : Function) {
  71       for (MCInst &Instr : BB) {
  72         if (!BC.MIB->isCall(Instr) || BC.MIB->isIndirectCall(Instr))
  73           continue;
  74
  75         const MCSymbol *TargetSymbol = BC.MIB->getTargetSymbol(Instr, 0);
  76         if (VeneerDestinations.find(TargetSymbol) == VeneerDestinations.end())
  77           continue;
  78
  79         VeneerCallers++;
  80         if (!BC.MIB->replaceBranchTarget(
  81                 Instr, VeneerDestinations[TargetSymbol], BC.Ctx.get())) {
  82           errs() << "BOLT-ERROR: updating veneer call destination failed\n";
  83           exit(1);
  84         }
  85       }
  86     }
  87   }
  88
  89   LLVM_DEBUG(
  90       dbgs() << "BOLT-INFO: number of linker-inserted veneers call sites: "
  91              << VeneerCallers << "\n");
  92 }
  93
  94 } // namespace bolt
  95 } // namespace llvm