revng-revng/lib/BasicAnalyses/GeneratedCodeBasicInfo.cpp

/// \file generatedcodebasicinfo.cpp
/// \brief Implements the GeneratedCodeBasicInfo pass which provides basic
///        information about the translated code (e.g., which CSV is the PC).

//
// This file is distributed under the MIT License. See LICENSE.md for details.
//

// Standard includes
#include <queue>
#include <set>

// LLVM includes
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"

// Local libraries includes
#include "revng/BasicAnalyses/GeneratedCodeBasicInfo.h"
#include "revng/Support/Debug.h"

using namespace llvm;

char GeneratedCodeBasicInfo::ID = 0;
using RegisterGCBI = RegisterPass<GeneratedCodeBasicInfo>;
static RegisterGCBI X("gcbi", "Generated Code Basic Info", true, true);

bool GeneratedCodeBasicInfo::runOnModule(llvm::Module &M) {
  Function &F = *M.getFunction("root");

  revng_log(PassesLog, "Starting GeneratedCodeBasicInfo");

  RootFunction = &F;

  const char *MDName = "revng.input.architecture";
  NamedMDNode *InputArchMD = M.getOrInsertNamedMetadata(MDName);
  auto *Tuple = dyn_cast<MDTuple>(InputArchMD->getOperand(0));

  QuickMetadata QMD(M.getContext());
  InstructionAlignment = QMD.extract<uint32_t>(Tuple, 0);
  DelaySlotSize = QMD.extract<uint32_t>(Tuple, 1);
  PC = M.getGlobalVariable(QMD.extract<StringRef>(Tuple, 2), true);
  SP = M.getGlobalVariable(QMD.extract<StringRef>(Tuple, 3), true);

  Type *PCType = PC->getType()->getPointerElementType();
  PCRegSize = M.getDataLayout().getTypeAllocSize(PCType);

  for (BasicBlock &BB : F) {
    if (!BB.empty()) {
      switch (getType(&BB)) {
      case BlockType::DispatcherBlock:
        revng_assert(Dispatcher == nullptr);
        Dispatcher = &BB;
        break;

      case BlockType::DispatcherFailureBlock:
        revng_assert(DispatcherFail == nullptr);
        DispatcherFail = &BB;
        break;

      case BlockType::AnyPCBlock:
        revng_assert(AnyPC == nullptr);
        AnyPC = &BB;
        break;

      case BlockType::UnexpectedPCBlock:
        revng_assert(UnexpectedPC == nullptr);
        UnexpectedPC = &BB;
        break;

      case BlockType::JumpTargetBlock: {
        auto *Call = cast<CallInst>(&*BB.begin());
        revng_assert(Call->getCalledFunction()->getName() == "newpc");
        JumpTargets[getLimitedValue(Call->getArgOperand(0))] = &BB;
        break;
      }
      case BlockType::EntryPoint:
      case BlockType::ExternalJumpsHandlerBlock:
      case BlockType::UntypedBlock:
        // Nothing to do here
        break;
      }
    }
  }

  revng_assert(Dispatcher != nullptr && AnyPC != nullptr
               && UnexpectedPC != nullptr);

  revng_log(PassesLog, "Ending GeneratedCodeBasicInfo");

  return false;
}

std::pair<uint64_t, uint64_t>
GeneratedCodeBasicInfo::getPC(Instruction *TheInstruction) const {
  CallInst *NewPCCall = nullptr;
  std::set<BasicBlock *> Visited;
  std::queue<BasicBlock::reverse_iterator> WorkList;
  if (TheInstruction->getIterator() == TheInstruction->getParent()->begin())
    WorkList.push(--TheInstruction->getParent()->rend());
  else
    WorkList.push(++TheInstruction->getReverseIterator());

  while (!WorkList.empty()) {
    auto I = WorkList.front();
    WorkList.pop();
    auto *BB = I->getParent();
    auto End = BB->rend();

    // Go through the instructions looking for calls to newpc
    for (; I != End; I++) {
      if (auto Marker = dyn_cast<CallInst>(&*I)) {
        // TODO: comparing strings is not very elegant
        auto *Callee = Marker->getCalledFunction();
        if (Callee != nullptr && Callee->getName() == "newpc") {

          // We found two distinct newpc leading to the requested instruction
          if (NewPCCall != nullptr)
            return { 0, 0 };

          NewPCCall = Marker;
          break;
        }
      }
    }

    // If we haven't find a newpc call yet, continue exploration backward
    if (NewPCCall == nullptr) {
      // If one of the predecessors is the dispatcher, don't explore any further
      for (BasicBlock *Predecessor : predecessors(BB)) {
        // Assert we didn't reach the almighty dispatcher
        revng_assert(!(NewPCCall == nullptr && Predecessor == Dispatcher));
        if (Predecessor == Dispatcher)
          continue;
      }

      for (BasicBlock *Predecessor : predecessors(BB)) {
        // Ignore already visited or empty BBs
        if (!Predecessor->empty()
            && Visited.find(Predecessor) == Visited.end()) {
          WorkList.push(Predecessor->rbegin());
          Visited.insert(Predecessor);
        }
      }
    }
  }

  // Couldn't find the current PC
  if (NewPCCall == nullptr)
    return { 0, 0 };

  uint64_t PC = getLimitedValue(NewPCCall->getArgOperand(0));
  uint64_t Size = getLimitedValue(NewPCCall->getArgOperand(1));
  revng_assert(Size != 0);
  return { PC, Size };
}