Sketch out an CFG reconstruction mode for llvm-objdump.

- Not great yet, but it's a start.
- Requires an object file with a symbol table. (I really want to fix this, but it'll need a whole new algorithm)
- ELF and COFF won't work at the moment due to libObject shortcomings.

To try it out run
$ llvm-objdump -d --cfg foo.o

This will create a graphviz file for every symbol in the object file's text section containing a CFG.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@135608 91177308-0d34-0410-b5e6-96231b3b80d8

tools/llvm-objdump/MCFunction.cpp

@@ -0,0 +1,113 @@
+//===-- 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;
+}