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Juxta: Cross-checking Semantic Correctness for File Systems

Juxta, a tool that automatically infers high-level semantics directly from source code. The key idea in Juxta is to compare and contrast multiple existing implementations that obey latent yet implicit high-level semantics. We applied Juxta to 54 file systems in the stock Linux kernel (680K LoC), found 118 previously unknown semantic bugs (one bug per 5.8K LoC), and provided corresponding patches to 39 different file systems, including mature, popular ones like ext4, btrfs, XFS, and NFS.

This repository is under the terms of MIT license. For execution, llvm was slightly modified in llvm directory.


  • Tested: Ubuntu 14.04
  • Requisite
Linux kernel 4.0-rc2
$ cd ..
$ git clone
$ cd linux
$ git checkout v4.0-rc2
$ cp ../juxta/config/config-x86_64-full-fs .
$ make; make clean
$ cd ../juxta

How to build

Build clang
$  make clang-full  (first time only)
$  make clang       (from the next)

How to create path databases

Merge file system code
$ cd analyzer
$ ./ merge_all  (for all file systems)
$ ./ merge ext4 (for ext4)

Static analysis of merged file system code
$ ./ clang_all  (for all file systems)
$ ./ clang ext4 (for ext4)

Create path database
$ ./ pickle_all (for all file systems)
$ cd ..

Juxta checkers

  • Return code checker: analyzer/
  • Side-effect checker: analyzer/
  • Function call checker: analyzer/
  • Path condition checker: analyzer/
  • Argument checker: analyzer/
  • Error handling checker: analyzer/
  • Lock checker: analyzer/
  • Spec. generator: analyzer/



  title        = {{Cross-checking Semantic Correctness: The Case of Finding File System Bugs}},
  author       = {Changwoo Min and Sanidhya Kashyap and Byoungyoung Lee and Chengyu Song and Taesoo Kim},
  booktitle    = {Proceedings of the 25th ACM Symposium on Operating Systems Principles (SOSP)},
  month        = oct,
  year         = 2015,
  address      = {Monterey, CA},