r8d8 / evm-semantics

K Semantics of the Ethereum Virtual Machine (EVM)

KEVM: Semantics of EVM in K

In this repository we provide a model of the EVM in K.

Documentation/Support

These may be useful for learning KEVM and K (newest to oldest):

• Jello Paper, generated using Sphinx Documentation Generation.
• 20 minute tour of the semantics at Devcon3.
• KEVM 1.0 technical report, especially sections 3 and 5.

To get support for KEVM, please join our Riot Room.

This Repository

The following files constitute the KEVM semantics:

• krypto.md sets up some basic cryptographic primitives.
• data.md provides the (functional) data of EVM (256 bit words, wordstacks, etc...).
• evm.md is the main KEVM semantics, containing the configuration and transition rules of EVM.

These additional files extend the semantics to make the repository more useful:

• driver.md is an execution harness for KEVM, providing a simple language for describing tests/programs.
• analysis.md contains any automated analysis tools we develop.

Finally, these files pertain to the K Reachability Logic Prover:

• verification.md adds helpers for verification efforts.
• proofs/README.md documents proofs we have performed.

Using the Definition

Dependencies

• ./Build requires xmllint to pretty-print configurations when running programs/tests.
• When developing, the *.k files are generated from the *.md files using Pandoc.
• For generating the Jello Paper, the Sphinx Documentation Generation tool is used. Additionally, you'll need to install the Python pygments for K available in the K Editor Support repository.

K Version

There are two versions of K available, RV-K and UIUC-K. This repository contains the build-products for both versions of K (there are slight differences) in .build/$K_VERSION/. Use RV-K for fast concrete execution, and UIUC-K for any symbolic reasoning. Make sure that you have set the K_VERSION environment variable in your shell (add export K_VERSION=uiuck or export K_VERSION=rvk to your .bashrc or equivalent).

Helper Script with-k

Not everyone wants to go through the process of installing K, so the script ./tests/ci/with-k can be used to avoid that. The following calls to ./Build are prefixed with a call to with-k to download, build, and set up a fresh copy of RV-K or UIUC-K (as specified).

$ ./tests/ci/with-k rvk   ./Build run tests/VMTests/vmArithmeticTest/add0.json
$ ./tests/ci/with-k uiuck ./Build prove tests/proofs/hkg/transfer-else-spec.k
$ ./tests/ci/with-k rvk   ./Build test tests/VMTests/vmArithmeticTest/add0.json
$ ./tests/ci/with-k uiuck ./Build prove tests/proofs/hkg/transfer-else-spec.k
$ ./tests/ci/with-k uiuck ./Build debug tests/VMTests/vmArithmeticTest/add0.json

See ./Build help to see more detailed usage information; ./Build can build and test the definition as well as run EVM programs and proofs. Running any proofs or symbolic reasoning requires UIUC-K.

The semantics are parametric over the MODE and the SCHEDULE. To run in a different mode (eg. in GASANALYZE mode), do export cMODE=<OTHER_MODE> before calling ./Build. To run with a different fee schedule (eg. HOMESTEAD instead of DEFAULT), do export cSCHEDULE=<OTHER_SCHEDULE> before calling ./Build.

Note that running ./tests/ci/with-k takes quite some time, which can be a pain when actively developing. To only download and setup K once for each session, you can do the following:

# Downloads and installs RV-K
$ ./tests/ci/with-k rvk `which bash`

# Now can just run `./Build` directly
$ ./Build run tests/VMTests/vmArithmeticTest/add0.json
$ ./Build test tests/VMTests/vmArithmeticTest/add0.json

The script with-k sets up the development environment with the fresh copy of K built and prefixed to PATH for the remaining commands.

Example Runs

Run the file tests/VMTests/vmArithmeticTest/add0.json:

$ ./Build run tests/VMTests/vmArithmeticTest/add0.json

# Which actually calls:
$ krun --directory .build/uiuck/ -cSCHEDULE=DEFAULT -cMODE=VMTESTS tests/VMTests/vmArithmeticTest/add0.json

Run the same file as a test:

$ ./Build test tests/VMTests/vmArithmeticTest/add0.json

To run proofs, you can similarly use ./Build. For example, to prove the specification tests/proofs/hkg/transfer-else-spec.k:

$ ./Build prove tests/proofs/hkg/transfer-else-spec.k

# Which actually calls:
$ krun --directory .build/uiuck/ -cSCHEDULE=DEFAULT -cMODE=NORMAL \
         --z3-executable tests/templates/dummy-proof-input.json --prove tests/proofs/hkg/transferFrom-else-spec.k \
         </dev/null

Finally, if you want to debug a given program (by stepping through its execution), you can use the debug option:

$ ./Build debug tests/VMTests/vmArithmeticTest/add0.json
...
KDebug> s
1 Step(s) Taken.
KDebug> p
... Big Configuration Here ...
KDebug>

Contributing

Any pull requests into this repository will not be reviewed until at least some conditions are met. Here we'll accumulate the standards that this repository is held to.

Code style guidelines, while somewhat subjective, will still be inspected before going to review. In general, read the rest of the definition for examples about how to style new K code; we collect a few common flubs here.

Writing tests and more contract proofs is always appreciated. Tests can come in the form of proofs done over contracts too :).

Hard - Every Commit

These are hard requirements (must be met before review), and they must be true for every commit in the PR.

• If a new feature is introduced in the PR, and later a bug is fixed in the new feature, the bug fix must be squashed back into the feature introduction. The only exceptions to this are if you want to document the bug because it was quite tricky or is something you believe should be fixed about K. In these exceptional cases, place the bug-fix commit directly after the feature introduction commit and leave useful commit messages. In addition, mark the feature introduction commit with [skip-ci] if tests will fail on that commit so that we know not to waste time testing it.

• No tab characters, 4 spaces instead. Linux-style line endings; if you're on a Windows machine make sure to run dos2unix on the files. No whitespace at the end of any lines.

Hard - PR Tip

These are hard requirements (must be met before review), but they only have to be true for the tip of the PR before review.

• Every test in the repository must pass. We will test this with ./tests/ci/with-k bothk ./Build test-all (or ./tests/ci/with-k bothk ./Build partest-all on parallel machines).

Soft - Every Commit

These are soft requirements (review may start without these being met), and they will be considered for every commit in the PR.

• Comments do not live in the K code blocks, but rather in the surrounding Markdown (unless there is a really good reason to localize the comment).

• You should consider prefixing "internal" symbols (symbols that a user would not write in a program) with a hash (#).

• Place a line of - after each block of syntax declarations.

      syntax Foo ::= "newSymbol"
   // --------------------------
      rule <k> newSymbol => . ... </k>
  

  Notice that if there are rules immediately following the syntax declaration, a commented-out line of - is inserted afterward. Notice that the width of the line of - matches that of the preceding line.

• Place spaces around parentheses and commas in K's pretty functional-style syntax declarations.

      syntax Foo ::= newFunctionalSyntax ( Int , String )
   // ---------------------------------------------------
  

• When multiple structurally-similar rules are present, line up as much as possible (and makes sense).

      rule <k> #do1       => . ... </k> <cell1> not-done => done        </cell1>
      rule <k> #do1Longer => . ... </k> <cell1> not-done => done-longer </cell1>
  
      rule <k> #do2     => . ... </k> <cell2> not-done => done2 </cell2>
      rule <k> #doShort => . ... </k> <cell2> nd       => done2 </cell2>
  

  This makes it simpler to make changes to entire groups of rules at a time using sufficiently modern editors. Notice that if we break alignment (eg. from the #do1 group above to the #do2 group), we put an extra line between the groups of rules.

• Line up the r in requires with the l in rule (if it's not all on one line). Similarly, line up the end of andBool for extra side-conditions with the end of requires.

      rule <k> A => B ... </k>
           SOME_LARGE_CONFIGURATION
  
        requires A > 3
         andBool isPrime(A)
  

Resources

• EVM Yellowpaper: Original specification of EVM.
• LEM Semantics of EVM
• Ethereum Test Set

For more information about The K Framework, refer to these sources:

• The K Tutorial
• Semantics-Based Program Verifiers for All Languages
• Reachability Logic Resources
• Matching Logic Resources
• Logical Frameworks: Discussion of logical frameworks.

We are using GNU Parallel to assist in testing these semantics in parallel.