Emit explicit contract:: symbols for functions with contracts#4612
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tautschnig wants to merge 1 commit into
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Emit explicit contract:: symbols for functions with contracts#4612tautschnig wants to merge 1 commit into
contract:: symbols for functions with contracts#4612tautschnig wants to merge 1 commit into
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CBMC's DFCC contract instrumentation (`--enforce-contract` / `--replace-call-with-contract`) expects a dedicated `contract::<fn>` symbol to exist for any function carrying a contract. For C inputs this symbol is created by the ANSI-C typechecker, which also moves the contract clauses (e.g. `c_spec_assigns`) onto it. Kani builds goto-programs directly and never runs that typechecker, so the symbol was absent. CBMC used to paper over this by deriving an empty contract symbol from the function on the fly, but that fallback was removed for soundness in diffblue/cbmc#8739, turning the missing symbol into a hard error and breaking every `#[kani::proof_for_contract]` harness. Synthesize the companion `contract::<name>` symbol during symbol-table serialization. It shares the function's contract-bearing type, has no body, and is marked as a property, reconstructing exactly the symbol CBMC's typechecker (and its old fallback) produced. Co-authored-by: Kiro <kiro-agent@users.noreply.github.com>
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Pull request overview
This PR updates Kani’s CBMC symbol-table serialization to synthesize the dedicated contract::<fn> symbols required by CBMC’s DFCC contract instrumentation, restoring compatibility with newer CBMC versions where the previous fallback behavior was removed.
Changes:
- Add a helper to derive a
contract::<name>symbol for any function symbol carrying a contract. - Emit the companion
contract::<name>symbol duringgoto_program::SymbolTable -> irep::SymbolTableserialization.
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| fn to_contract_irep(&self, mm: &MachineModel) -> super::Symbol { | ||
| let mut contract_symbol = self.to_irep(mm); | ||
| contract_symbol.name = format!("contract::{}", self.name).into(); | ||
| contract_symbol.is_property = true; | ||
| // The contract symbol is a pure specification and carries no body. | ||
| contract_symbol.value = Irep::nil(); | ||
| contract_symbol | ||
| } |
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CBMC's DFCC contract instrumentation (
--enforce-contract/--replace-call-with-contract) expects a dedicatedcontract::<fn>symbol to exist for any function carrying a contract. For C inputs this symbol is created by the ANSI-C typechecker, which also moves the contract clauses (e.g.c_spec_assigns) onto it.Kani builds goto-programs directly and never runs that typechecker, so the symbol was absent. CBMC used to paper over this by deriving an empty contract symbol from the function on the fly, but that fallback was removed for soundness in diffblue/cbmc#8739, turning the missing symbol into a hard error and breaking every
#[kani::proof_for_contract]harness.Synthesize the companion
contract::<name>symbol during symbol-table serialization. It shares the function's contract-bearing type, has no body, and is marked as a property, reconstructing exactly the symbol CBMC's typechecker (and its old fallback) produced.This is a necessary (though not necessarily sufficient) change to enable upgrading to newer CBMC versions.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.