bolt/lib/Passes/FixRelaxationPass.cpp

   1 #include "bolt/Passes/FixRelaxationPass.h"
   2 #include "bolt/Core/ParallelUtilities.h"
   3
   4 using namespace llvm;
   5
   6 namespace llvm {
   7 namespace bolt {
   8
   9 // This function finds ADRP+ADD instruction sequences that originally before
  10 // linker relaxations were ADRP+LDR. We've modified LDR/ADD relocation properly
  11 // during relocation reading, so its targeting right symbol. As for ADRP its
  12 // target is wrong before this pass since we won't be able to recognize and
  13 // properly change R_AARCH64_ADR_GOT_PAGE relocation to
  14 // R_AARCH64_ADR_PREL_PG_HI21 during relocation reading. Now we're searching for
  15 // ADRP+ADD sequences, checking that ADRP points to the GOT-table symbol and the
  16 // target of ADD is another symbol. When found change ADRP symbol reference to
  17 // the ADDs one.
  18 void FixRelaxations::runOnFunction(BinaryFunction &BF) {
  19   BinaryContext &BC = BF.getBinaryContext();
  20   for (BinaryBasicBlock &BB : BF) {
  21     for (auto II = BB.begin(); II != BB.end(); ++II) {
  22       MCInst &Adrp = *II;
  23       if (BC.MIB->isPseudo(Adrp) || !BC.MIB->isADRP(Adrp))
  24         continue;
  25
  26       const MCSymbol *AdrpSymbol = BC.MIB->getTargetSymbol(Adrp);
  27       if (!AdrpSymbol || AdrpSymbol->getName() != "__BOLT_got_zero")
  28         continue;
  29
  30       auto NextII = std::next(II);
  31       if (NextII == BB.end())
  32         continue;
  33
  34       const MCInst &Add = *NextII;
  35       if (!BC.MIB->matchAdrpAddPair(Adrp, Add))
  36         continue;
  37
  38       const MCSymbol *Symbol = BC.MIB->getTargetSymbol(Add);
  39       if (!Symbol || AdrpSymbol == Symbol)
  40         continue;
  41
  42       auto L = BC.scopeLock();
  43       const int64_t Addend = BC.MIB->getTargetAddend(Add);
  44       BC.MIB->setOperandToSymbolRef(Adrp, /*OpNum*/ 1, Symbol, Addend,
  45                                     BC.Ctx.get(), ELF::R_AARCH64_NONE);
  46     }
  47   }
  48 }
  49
  50 void FixRelaxations::runOnFunctions(BinaryContext &BC) {
  51   if (!BC.isAArch64() || !BC.HasRelocations)
  52     return;
  53
  54   ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
  55     runOnFunction(BF);
  56   };
  57
  58   ParallelUtilities::runOnEachFunction(
  59       BC, ParallelUtilities::SchedulingPolicy::SP_INST_LINEAR, WorkFun, nullptr,
  60       "FixRelaxations");
  61 }
  62
  63 } // namespace bolt
  64 } // namespace llvm