[llvm] r182628 - MC: Disassembled CFG reconstruction.

[Bloom, Louis S.]

Hi Ahmed,

I've been playing with this CFG reconstruction patch and discovered issues with branch evaluation when the operands are encoded as MCExpr types instead of immediates. This is a problem when a disassembler has been set up for symbolic disassembly as many operands are encoded as MCExpr types. See attached patches, I modified the evaluateBranch function inside of MCInstrAnalysis.cpp in order to handle branch evaluation of MCExpr types. I have also modified the tryAddingSymbolicOperand function inside of MCExternalSymbolizer.cpp to encode the immediate values necessary within MCExpr types as they correspond to the immediate operands which the symbols they replace. Ultimately, this allows for CFG reconstruction to occur as expected even during symbolic disassembly.

The patches do the following:

* ext-sym-patch1.txt - Adds the original immediate value to symbolic operands.	
* instr-anal-patch2.txt - Using ext-sym-patch1.txt, adds support for branch evaluation by evaluating MCExprs as immediates.

Very Respectfully,
LOUIS S. BLOOM, 2d Lt, USAF
AFIT Student - Northeastern University
Draper Laboratory Fellow

DISCLAIMER: The views expressed are those of the author and do not reflect the official policy or position of the Department of Defense or the U.S. Government.

-----Original Message-----
From: llvm-commits-bounces at cs.uiuc.edu [mailto:llvm-commits-bounces at cs.uiuc.edu] On Behalf Of Ahmed Bougacha
Sent: Thursday, May 23, 2013 9:07 PM
To: llvm-commits at cs.uiuc.edu
Subject: [llvm] r182628 - MC: Disassembled CFG reconstruction.

Author: ab
Date: Thu May 23 20:07:04 2013
New Revision: 182628

URL: http://llvm.org/viewvc/llvm-project?rev=182628&view=rev
Log:
MC: Disassembled CFG reconstruction.

This patch builds on some existing code to do CFG reconstruction from
a disassembled binary:
- MCModule represents the binary, and has a list of MCAtoms.
- MCAtom represents either disassembled instructions (MCTextAtom), or
  contiguous data (MCDataAtom), and covers a specific range of addresses.
- MCBasicBlock and MCFunction form the reconstructed CFG. An MCBB is
  backed by an MCTextAtom, and has the usual successors/predecessors.
- MCObjectDisassembler creates a module from an ObjectFile using a
  disassembler. It first builds an atom for each section. It can also
  construct the CFG, and this splits the text atoms into basic blocks.

MCModule and MCAtom were only sketched out; MCFunction and MCBB were
implemented under the experimental "-cfg" llvm-objdump -macho option.
This cleans them up for further use; llvm-objdump -d -cfg now generates
graphviz files for each function found in the binary.

In the future, MCObjectDisassembler may be the right place to do
"intelligent" disassembly: for example, handling constant islands is just
a matter of splitting the atom, using information that may be available
in the ObjectFile. Also, better initial atom formation than just using
sections is possible using symbols (and things like Mach-O's
function_starts load command).

This brings two minor regressions in llvm-objdump -macho -cfg:
- The printing of a relocation's referenced symbol.
- An annotation on loop BBs, i.e., which are their own successor.

Relocation printing is replaced by the MCSymbolizer; the basic CFG
annotation will be superseded by more related functionality.


Added:
    llvm/trunk/include/llvm/MC/MCFunction.h
    llvm/trunk/include/llvm/MC/MCObjectDisassembler.h
    llvm/trunk/include/llvm/Support/StringRefMemoryObject.h
    llvm/trunk/lib/MC/MCFunction.cpp
    llvm/trunk/lib/MC/MCObjectDisassembler.cpp
    llvm/trunk/lib/Support/StringRefMemoryObject.cpp
Removed:
    llvm/trunk/tools/llvm-objdump/MCFunction.cpp
    llvm/trunk/tools/llvm-objdump/MCFunction.h
Modified:
    llvm/trunk/include/llvm/MC/MCAtom.h
    llvm/trunk/include/llvm/MC/MCInstrAnalysis.h
    llvm/trunk/include/llvm/MC/MCModule.h
    llvm/trunk/lib/MC/CMakeLists.txt
    llvm/trunk/lib/MC/MCAtom.cpp
    llvm/trunk/lib/MC/MCInstrAnalysis.cpp
    llvm/trunk/lib/MC/MCModule.cpp
    llvm/trunk/lib/Support/CMakeLists.txt
    llvm/trunk/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp
    llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
    llvm/trunk/tools/llvm-objdump/CMakeLists.txt
    llvm/trunk/tools/llvm-objdump/MachODump.cpp
    llvm/trunk/tools/llvm-objdump/llvm-objdump.cpp
    llvm/trunk/tools/llvm-objdump/llvm-objdump.h

_______________________________________________
llvm-commits mailing list
llvm-commits at cs.uiuc.edu
http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: ext-sym-patch1.txt
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130614/f10134e5/attachment.txt>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: instr-anal-patch2.txt
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130614/f10134e5/attachment-0001.txt>