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//===-- 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/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 MCInstrInfo *InstrInfo,
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)) {
const MCInstrDesc &Desc = InstrInfo->get(Inst.getOpcode());
if (Desc.isBranch()) {
if (Desc.OpInfo[0].OperandType == MCOI::OPERAND_PCREL) {
int64_t Imm = Inst.getOperand(0).getImm();
// FIXME: Distinguish relocations from nop jumps.
if (Imm != 0) {
assert(Index+Imm+Size < End && "Branch out of function.");
Splits.insert(Index+Imm+Size);
}
}
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();
const MCInstrDesc &Desc = InstrInfo->get(Inst.Inst.getOpcode());
if (Desc.isBranch()) {
// PCRel branch, we know the destination.
if (Desc.OpInfo[0].OperandType == MCOI::OPERAND_PCREL) {
int64_t Imm = Inst.Inst.getOperand(0).getImm();
if (Imm != 0)
BB.addSucc(&f.getBlockAtAddress(Inst.Address+Inst.Size+Imm));
// Conditional branches can also fall through to the next block.
if (Desc.isConditionalBranch() && llvm::next(i) != e)
BB.addSucc(&next(i)->second);
} else {
// 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 {
// No branch. Fall through to the next block.
if (!Desc.isReturn() && next(i) != e)
BB.addSucc(&next(i)->second);
}
}
return f;
}
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