CHANGES.md

Version 0.5

New Features

• Added experimental support for basic, non-compositional verification of x86 machine code for use in conjunction with LLVM verification.

    crucible_llvm_verify_x86 :
      LLVMModule -> String -> String ->
      [(String, Int)] -> Bool -> CrucibleSetup () ->
      TopLevel CrucibleMethodSpec
  

  The first argument specifies the LLVM module containing the caller. The second and third specify the ELF file name and symbol name of the function to be verifier. The fourth specifies the names and sizes (in bytes) of global variables to initialize, and the fifth whether to perform path satisfiability checking. The last argument is the LLVM specification of the calling context against which to verify the function.

• Added support for using the SMT theory of arrays in the LLVM memory model. In some cases, this can significantly improve performance.

    enable_smt_array_memory_model : TopLevel ()
    disable_smt_array_memory_model : TopLevel ()
  

• Added support for specifying alignment in LLVM allocations. The crucible_alloc_aligned and crucible_alloc_readonly_aligned functions allocate read-write and read-only memory regions, respectively, with the specified alignment (in bytes).

• Added a conditional points-to function, crucible_conditional_points_to, that allows an LLVM function to conditionally modify memory, leaving it in its previous state (potentially uninitialized) when the condition is false.

• Added several new options:

  • New functions enable_what4_hash_consing and disable_what4_hash_consing to enable or disable hash consing to increase sub-formula sharing during symbolic execution.

  • New functions enable_crucible_assert_then_assume and disable_crucible_assert_then_assume to control whether predicates are assumed after asserting them during symbolic execution. The default is now to not assume them, whereas previously they were assumed.

  • New command-line option --no-color to print an ASCII logo without ANSI color or Unicode.

Performance Improvements

• Improved performance of the LLVM memory model.

• Improved performance of bitvector operations during symbolic execution.

• Improved performance of rewriting SAWCore terms.

Bug Fixes

• Fixed SBV interface to fail more gracefully when it cannot find the solver executable.

• Fixed SMT-Lib export negation issues.

Fixes issues #286, #489, #491, #564, #580, #583, #585, #586, #587, #590, #592, #594, #597, #598, #602, #603, #612, #613, #622, #626, #633, #638, #639, and #647.

Version 0.4

• Fixed a long-standing soundness issue (#30) in compositional verification of LLVM programs. Previously, a specification for a function that neglected to mention an effect that the function in fact caused could be successfully verified. When verifying a caller of that function, only the effects mentioned in the specification would be used. The fix for this issue may break some proof scripts: any pointer mentioned using crucible_points_to in the initial state of a specification but not in the final state will be assigned a final value of "invalid", and any subsequent reads from the pointer will fail. To fix this issue, make sure that every specification you use provides a final value for every pointer it touches (which in many cases will be the same as its initial value).

• Added an experimental command, llvm_boilerplate, that emits skeleton function specifications for every function defined in an LLVM module. The additional crucible_llvm_array_size_profile command can be used to refine the results of llvm_boilerplate based on the array sizes used by calls that arise from a call to the named top-level function.

• Added support for using the symbolic execution profiler available in Crucible. The enable_crucible_profiling command causes profiling information to be written to the given directory. This can then be visualized using the rendering code available here.

• Added proof tactics to use Yices (w4_unint_yices) and CVC4 (w4_unint_cvc4) through the What4 backend instead of SBV.

• Modified the messages emitted for failed points-to assertions to be in terms of LLVM values.

• Added support for using the SMT array memory model to reason about the LLVM heap. The enable_smt_array_memory_model command enables it for all future proofs.

• LLVM bitcode format support is improved. Versions 3.5 to 9.0 are known to be mostly well-supported. We consider parsing failures with any version newer than 3.5 to be a bug, so please report them on GitHub.

• New experimental model counting commands sharpSAT and approxmc bind to the external tools of the same name. These were mistakenly listed as included in 0.3.

• Built against Cryptol 2.8.0.

• Improved error messages in general.

• Fixed various additional bugs, including #211, #455, #479, #484, #493, #496, #511, #521, #522, #534, #563

Version 0.3

• Java and LLVM verification has been overhauled to use the new Crucible symbolic execution engine. Highlights include:

  • New crucible_llvm_verify and crucible_llvm_extract commands replace llvm_verify and llvm_extract, with a different structure for specification blocks.

  • LLVM verification tracks undefined behavior more carefully and has a more sophisicated memory model. See the manual for more.

  • New, experimental crucible_jvm_verify and crucible_java_extract commands will eventually replace java_verify and java_extract. For the moment, the former two are enabled with the enable_experimental command and the latter two are enabled with enable_deprecated.

  • More flexible specification language allows convenient description of functions that allocate memory, return arbitrary values, expect explicit aliasing, work with NULL pointers, cast between pointers and integers, or work with opaque pointers.

  • Ghost state is supported in LLVM verification, allowing reasoning about certain complex or unavailable code.

  • Verification of LLVM works for a larger subset of the language, which particularly improves support for C++.

• LLVM bitcode format support is greatly improved. Versions 3.5 to 7.0 are known to be mostly well-supported. We consider parsing failures with any version newer than 3.5 to be a bug, so please report them on GitHub.

• Greatly improved error messages throughout.

• Built against Cryptol 2.7.0.

• New model counting commands sharpSAT and approxmc bind to the external tools of the same name.

• New proof script commands allow multiple goals and related proof tactics. See the manual.

• Can be built with Docker, and will be available on DockerHub.

• Includes an Emacs mode.

Version 0.2-dev

• Released under the 3-clause BSD license

• Major improvements to the Java and LLVM verification infrastructure, as described in more detail here:

  • Major refactoring and polish to java_verify and java_symexec
  • Major refactoring and polish to llvm_verify and llvm_symexec
  • Fixed soundness bug in llvm_verify treatment of heap modifications
  • Fixed soundness bug related to java_assert and llvm_assert
  • Support for branch satisfiability checking to be configured
  • Support for some types of allocation in java_verify, enabled with java_allow_alloc
  • Improved support for LLVM structs (including the llvm_struct type for llvm_verify)
  • Support for non-scalar return values in java_verify and java_symexec
  • Support for using java_ensure_eq on fields of return value
  • Access to safety conditions in java_symexec and llvm_symexec
  • New primitives llvm_assert_eq and java_assert_eq

• Some changes to the SAWScript language:

  • Conditional expressions including the keywords if, then, and else, and the new constants true and false
  • New eval_int and eval_bool functions to expose Cryptol bit vectors and Bit values as Int and Bool values in SAWScript
  • Pattern matching for tuples
  • Improvements to pretty printing, including: set_base and set_ascii commands to control the formatting of values; a show function to convert a value to a string without printing it; and the ability to use print or show instead of llvm_browse_module and java_browse_class
  • New built-in functions for processing lists

• New proof backends:

  • A new rme proof tactic, based on the Reed-Muller Expansion normal form for propositional formulas. This tactic is particularly efficient for dealing with polynomials over Galois fields, as used in AES, for instance.

• Linked against the latest Cryptol code, which includes the following changes since release 2.3.0:

  • An extended prelude with more Haskell-like functions
  • Better, more portable seeding for random
  • Performance improvements for symbolically executing tables of constant values
  • Performance improvements for type checking large constants

• Internal improvements:

  • Simplified Cryptol to SAWCore translation
  • Improved performance of Cryptol to SAWCore translation for recursive functions
  • Updated bitcode parser to support some of the changes in LLVM 3.7
  • Many bug fixes
  • Many code cleanups