tools/llvm-objdump/MCFunction.cpp

//===-- MCFunction.cpp ----------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the algorithm to break down a region of machine code
// into basic blocks and try to reconstruct a CFG from it.
//
//===----------------------------------------------------------------------===//

#include "MCFunction.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/MC/MCDisassembler.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCInstPrinter.h"
#include "llvm/MC/MCInstrAnalysis.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/MC/MCInstrInfo.h"
#include "llvm/Support/MemoryObject.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/system_error.h"
#include <set>
using namespace llvm;

MCFunction
MCFunction::createFunctionFromMC(StringRef Name, const MCDisassembler *DisAsm,
                                 const MemoryObject &Region, uint64_t Start,
                                 uint64_t End, const MCInstrAnalysis *Ana,
                                 raw_ostream &DebugOut) {
  std::set<uint64_t> Splits;
  Splits.insert(Start);
  std::vector<MCDecodedInst> Instructions;
  uint64_t Size;

  // Disassemble code and gather basic block split points.
  for (uint64_t Index = Start; Index < End; Index += Size) {
    MCInst Inst;

    if (DisAsm->getInstruction(Inst, Size, Region, Index, DebugOut)) {
      if (Ana->isBranch(Inst)) {
        uint64_t targ = Ana->evaluateBranch(Inst, Index, Size);
        // FIXME: Distinguish relocations from nop jumps.
        if (targ != -1ULL && (targ == Index+Size || targ >= End)) {
          Instructions.push_back(MCDecodedInst(Index, Size, Inst));
          continue; // Skip branches that leave the function.
        }
        if (targ != -1ULL)
          Splits.insert(targ);
        Splits.insert(Index+Size);
      } else if (Ana->isReturn(Inst)) {
        Splits.insert(Index+Size);
      }

      Instructions.push_back(MCDecodedInst(Index, Size, Inst));
    } else {
      errs() << "warning: invalid instruction encoding\n";
      if (Size == 0)
        Size = 1; // skip illegible bytes
    }

  }

  MCFunction f(Name);

  // Create basic blocks.
  unsigned ii = 0, ie = Instructions.size();
  for (std::set<uint64_t>::iterator spi = Splits.begin(),
       spe = Splits.end(); spi != spe; ++spi) {
    MCBasicBlock BB;
    uint64_t BlockEnd = llvm::next(spi) == spe ? End : *llvm::next(spi);
    // Add instructions to the BB.
    for (; ii != ie; ++ii) {
      if (Instructions[ii].Address < *spi ||
          Instructions[ii].Address >= BlockEnd)
        break;
      BB.addInst(Instructions[ii]);
    }
    f.addBlock(*spi, BB);
  }

  // Calculate successors of each block.
  for (MCFunction::iterator i = f.begin(), e = f.end(); i != e; ++i) {
    MCBasicBlock &BB = i->second;
    if (BB.getInsts().empty()) continue;
    const MCDecodedInst &Inst = BB.getInsts().back();

    if (Ana->isBranch(Inst.Inst)) {
      uint64_t targ = Ana->evaluateBranch(Inst.Inst, Inst.Address, Inst.Size);
      if (targ == -1ULL) {
        // Indirect branch. Bail and add all blocks of the function as a
        // successor.
        for (MCFunction::iterator i = f.begin(), e = f.end(); i != e; ++i)
          BB.addSucc(&i->second);
      } else if (targ != Inst.Address+Inst.Size)
        BB.addSucc(&f.getBlockAtAddress(targ));
      // Conditional branches can also fall through to the next block.
      if (Ana->isConditionalBranch(Inst.Inst) && llvm::next(i) != e)
        BB.addSucc(&llvm::next(i)->second);
    } else {
      // No branch. Fall through to the next block.
      if (!Ana->isReturn(Inst.Inst) && llvm::next(i) != e)
        BB.addSucc(&llvm::next(i)->second);
    }
  }

  return f;
}