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In "normal" code these only happen when disassembling data, so we won't lose anything if we just drop them. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@135786 91177308-0d34-0410-b5e6-96231b3b80d8
117 lines
4.0 KiB
C++
117 lines
4.0 KiB
C++
//===-- MCFunction.cpp ----------------------------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the algorithm to break down a region of machine code
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// into basic blocks and try to reconstruct a CFG from it.
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//
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//===----------------------------------------------------------------------===//
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#include "MCFunction.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/MC/MCDisassembler.h"
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#include "llvm/MC/MCInst.h"
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#include "llvm/MC/MCInstPrinter.h"
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#include "llvm/MC/MCInstrDesc.h"
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#include "llvm/MC/MCInstrInfo.h"
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#include "llvm/Support/MemoryObject.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Support/system_error.h"
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#include <set>
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using namespace llvm;
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MCFunction
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MCFunction::createFunctionFromMC(StringRef Name, const MCDisassembler *DisAsm,
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const MemoryObject &Region, uint64_t Start,
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uint64_t End, const MCInstrInfo *InstrInfo,
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raw_ostream &DebugOut) {
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std::set<uint64_t> Splits;
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Splits.insert(Start);
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std::vector<MCDecodedInst> Instructions;
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uint64_t Size;
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// Disassemble code and gather basic block split points.
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for (uint64_t Index = Start; Index < End; Index += Size) {
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MCInst Inst;
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if (DisAsm->getInstruction(Inst, Size, Region, Index, DebugOut)) {
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const MCInstrDesc &Desc = InstrInfo->get(Inst.getOpcode());
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if (Desc.isBranch()) {
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if (Desc.OpInfo[0].OperandType == MCOI::OPERAND_PCREL) {
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int64_t Imm = Inst.getOperand(0).getImm();
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// FIXME: Distinguish relocations from nop jumps.
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if (Imm != 0) {
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if (Index+Imm+Size >= End) {
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Instructions.push_back(MCDecodedInst(Index, Size, Inst));
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continue; // Skip branches that leave the function.
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}
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Splits.insert(Index+Imm+Size);
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}
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}
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Splits.insert(Index+Size);
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}
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Instructions.push_back(MCDecodedInst(Index, Size, Inst));
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} else {
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errs() << "warning: invalid instruction encoding\n";
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if (Size == 0)
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Size = 1; // skip illegible bytes
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}
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}
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MCFunction f(Name);
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// Create basic blocks.
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unsigned ii = 0, ie = Instructions.size();
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for (std::set<uint64_t>::iterator spi = Splits.begin(),
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spe = Splits.end(); spi != spe; ++spi) {
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MCBasicBlock BB;
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uint64_t BlockEnd = llvm::next(spi) == spe ? End : *llvm::next(spi);
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// Add instructions to the BB.
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for (; ii != ie; ++ii) {
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if (Instructions[ii].Address < *spi ||
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Instructions[ii].Address >= BlockEnd)
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break;
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BB.addInst(Instructions[ii]);
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}
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f.addBlock(*spi, BB);
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}
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// Calculate successors of each block.
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for (MCFunction::iterator i = f.begin(), e = f.end(); i != e; ++i) {
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MCBasicBlock &BB = i->second;
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if (BB.getInsts().empty()) continue;
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const MCDecodedInst &Inst = BB.getInsts().back();
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const MCInstrDesc &Desc = InstrInfo->get(Inst.Inst.getOpcode());
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if (Desc.isBranch()) {
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// PCRel branch, we know the destination.
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if (Desc.OpInfo[0].OperandType == MCOI::OPERAND_PCREL) {
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int64_t Imm = Inst.Inst.getOperand(0).getImm();
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if (Imm != 0)
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BB.addSucc(&f.getBlockAtAddress(Inst.Address+Inst.Size+Imm));
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// Conditional branches can also fall through to the next block.
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if (Desc.isConditionalBranch() && llvm::next(i) != e)
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BB.addSucc(&llvm::next(i)->second);
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} else {
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// Indirect branch. Bail and add all blocks of the function as a
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// successor.
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for (MCFunction::iterator i = f.begin(), e = f.end(); i != e; ++i)
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BB.addSucc(&i->second);
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}
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} else {
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// No branch. Fall through to the next block.
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if (!Desc.isReturn() && llvm::next(i) != e)
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BB.addSucc(&llvm::next(i)->second);
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}
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}
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return f;
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}
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