Line coverage reports (#2609)

Co-authored-by: jaisnan <jaisnan@amazon.com>
Co-authored-by: Jaisurya Nanduri <91620234+jaisnan@users.noreply.github.com>

kani-compiler/src/codegen_cprover_gotoc/codegen/assert.rs

@@ -29,7 +29,7 @@ use tracing::debug;
 /// Classifies the type of CBMC `assert`, as different assertions can have different semantics (e.g. cover)
 ///
 /// Each property class should justify its existence with a note about the special handling it recieves.
-#[derive(Debug, Clone, EnumString, AsRefStr)]
+#[derive(Debug, Clone, EnumString, AsRefStr, PartialEq)]
 #[strum(serialize_all = "snake_case")]
 pub enum PropertyClass {
  /// Overflow panics that can be generated by Intrisics.
@@ -45,6 +45,19 @@ pub enum PropertyClass {
  ///
  /// SPECIAL BEHAVIOR: "Errors" for this type of assertion just mean "reachable" not failure.
  Cover,
+ /// The class of checks used for code coverage instrumentation. Only needed
+ /// when working on coverage-related features.
+ ///
+ /// Do not mistake with `Cover`, they are different:
+ /// - `CodeCoverage` checks have a fixed condition (`false`) and description.
+ /// - `CodeCoverage` checks are filtered out from verification results and
+ /// postprocessed to build coverage reports.
+ /// - `Cover` checks can be added by users (using the `kani::cover` macro),
+ /// while `CodeCoverage` checks are not exposed to users (i.e., they are
+ /// automatically added if running with the coverage option).
+ ///
+ /// SPECIAL BEHAVIOR: "Errors" for this type of assertion just mean "reachable" not failure.
+ CodeCoverage,
  /// Ordinary (Rust) assertions and panics.
  ///
  /// SPECIAL BEHAVIOR: These assertion failures should be observable during normal execution of Rust code.
@@ -134,6 +147,21 @@ impl<'tcx> GotocCtx<'tcx> {
  self.codegen_assert(cond.not(), PropertyClass::Cover, msg, loc)
  }
 
+ /// Generate a cover statement for code coverage reports.
+ pub fn codegen_coverage(&self, span: Span) -> Stmt {
+ let loc = self.codegen_caller_span(&Some(span));
+ // Should use Stmt::cover, but currently this doesn't work with CBMC
+ // unless it is run with '--cover cover' (see
+ // https://github.com/diffblue/cbmc/issues/6613). So for now use
+ // `assert(false)`.
+ self.codegen_assert(
+ Expr::bool_false(),
+ PropertyClass::CodeCoverage,
+ "code coverage for location",
+ loc,
+ )
+ }
+
  // The above represent the basic operations we can perform w.r.t. assert/assume/cover
  // Below are various helper functions for constructing the above more easily.
 

kani-compiler/src/codegen_cprover_gotoc/codegen/block.rs

@@ -16,25 +16,55 @@ impl<'tcx> GotocCtx<'tcx> {
  debug!(?bb, "Codegen basicblock");
  self.current_fn_mut().set_current_bb(bb);
  let label: String = self.current_fn().find_label(&bb);
+ let check_coverage = self.queries.check_coverage;
  // the first statement should be labelled. if there is no statements, then the
  // terminator should be labelled.
  match bbd.statements.len() {
  0 => {
  let term = bbd.terminator();
  let tcode = self.codegen_terminator(term);
- self.current_fn_mut().push_onto_block(tcode.with_label(label));
+ // When checking coverage, the `coverage` check should be
+ // labelled instead.
+ if check_coverage {
+ let span = term.source_info.span;
+ let cover = self.codegen_coverage(span);
+ self.current_fn_mut().push_onto_block(cover.with_label(label));
+ self.current_fn_mut().push_onto_block(tcode);
+ } else {
+ self.current_fn_mut().push_onto_block(tcode.with_label(label));
+ }
  }
  _ => {
  let stmt = &bbd.statements[0];
  let scode = self.codegen_statement(stmt);
- self.current_fn_mut().push_onto_block(scode.with_label(label));
+ // When checking coverage, the `coverage` check should be
+ // labelled instead.
+ if check_coverage {
+ let span = stmt.source_info.span;
+ let cover = self.codegen_coverage(span);
+ self.current_fn_mut().push_onto_block(cover.with_label(label));
+ self.current_fn_mut().push_onto_block(scode);
+ } else {
+ self.current_fn_mut().push_onto_block(scode.with_label(label));
+ }
 
  for s in &bbd.statements[1..] {
+ if check_coverage {
+ let span = s.source_info.span;
+ let cover = self.codegen_coverage(span);
+ self.current_fn_mut().push_onto_block(cover);
+ }
  let stmt = self.codegen_statement(s);
  self.current_fn_mut().push_onto_block(stmt);
  }
- let term = self.codegen_terminator(bbd.terminator());
- self.current_fn_mut().push_onto_block(term);
+ let term = bbd.terminator();
+ if check_coverage {
+ let span = term.source_info.span;
+ let cover = self.codegen_coverage(span);
+ self.current_fn_mut().push_onto_block(cover);
+ }
+ let tcode = self.codegen_terminator(term);
+ self.current_fn_mut().push_onto_block(tcode);
  }
  }
  self.current_fn_mut().reset_current_bb();

kani-compiler/src/codegen_cprover_gotoc/codegen/intrinsic.rs

@@ -188,7 +188,7 @@ impl<'tcx> GotocCtx<'tcx> {
  let a = fargs.remove(0);
  let b = fargs.remove(0);
  let div_does_not_overflow = self.div_does_not_overflow(a.clone(), b.clone());
- let div_overflow_check = self.codegen_assert(
+ let div_overflow_check = self.codegen_assert_assume(
  div_does_not_overflow,
  PropertyClass::ArithmeticOverflow,
  format!("attempt to compute {} which would overflow", intrinsic).as_str(),

kani-compiler/src/kani_compiler.rs

@@ -349,6 +349,7 @@ impl Callbacks for KaniCompiler {
  let queries = &mut (*self.queries.lock().unwrap());
  queries.emit_vtable_restrictions = matches.get_flag(parser::RESTRICT_FN_PTRS);
  queries.check_assertion_reachability = matches.get_flag(parser::ASSERTION_REACH_CHECKS);
+ queries.check_coverage = matches.get_flag(parser::COVERAGE_CHECKS);
  queries.output_pretty_json = matches.get_flag(parser::PRETTY_OUTPUT_FILES);
  queries.ignore_global_asm = matches.get_flag(parser::IGNORE_GLOBAL_ASM);
  queries.write_json_symtab =
@@ -364,6 +365,7 @@ impl Callbacks for KaniCompiler {
  {
  queries.stubbing_enabled = true;
  }
+
  debug!(?queries, "config end");
  }
  }

kani-compiler/src/kani_queries/mod.rs

@@ -28,6 +28,7 @@ pub enum ReachabilityType {
 #[derive(Debug, Default, Clone)]
 pub struct QueryDb {
  pub check_assertion_reachability: bool,
+ pub check_coverage: bool,
  pub emit_vtable_restrictions: bool,
  pub output_pretty_json: bool,
  pub ignore_global_asm: bool,

kani-compiler/src/parser.rs

@@ -28,6 +28,9 @@ pub const RESTRICT_FN_PTRS: &str = "restrict-vtable-fn-ptrs";
 /// Option name used to enable assertion reachability checks.
 pub const ASSERTION_REACH_CHECKS: &str = "assertion-reach-checks";
 
+/// Option name used to enable coverage checks.
+pub const COVERAGE_CHECKS: &str = "coverage-checks";
+
 /// Option name used to use json pretty-print for output files.
 pub const PRETTY_OUTPUT_FILES: &str = "pretty-json-files";
 
@@ -98,6 +101,12 @@ pub fn parser() -> Command {
  .help("Check the reachability of every assertion.")
  .action(ArgAction::SetTrue),
  )
+ .arg(
+ Arg::new(COVERAGE_CHECKS)
+ .long(COVERAGE_CHECKS)
+ .help("Check the reachability of every statement.")
+ .action(ArgAction::SetTrue),
+ )
  .arg(
  Arg::new(REACHABILITY)
  .long(REACHABILITY)

kani-driver/src/args/common.rs

@@ -44,6 +44,8 @@ pub enum UnstableFeatures {
  ConcretePlayback,
  /// Enable Kani's unstable async library.
  AsyncLib,
+ /// Enable line coverage instrumentation/reports
+ LineCoverage,
 }
 
 impl ValidateArgs for CommonArgs {

kani-driver/src/args/mod.rs

@@ -300,6 +300,10 @@ pub struct VerificationArgs {
  )]
  pub enable_stubbing: bool,
 
+ /// Enable Kani coverage output alongside verification result
+ #[arg(long, hide_short_help = true)]
+ pub coverage: bool,
+
  /// Arguments to pass down to Cargo
  #[command(flatten)]
  pub cargo: CargoCommonArgs,
@@ -640,6 +644,16 @@ impl ValidateArgs for VerificationArgs {
  }
  }
 
+ if self.coverage
+ && !self.common_args.unstable_features.contains(&UnstableFeatures::LineCoverage)
+ {
+ return Err(Error::raw(
+ ErrorKind::MissingRequiredArgument,
+ "The `--coverage` argument is unstable and requires `-Z \
+ line-coverage` to be used.",
+ ));
+ }
+
  Ok(())
  }
 }

kani-driver/src/call_cbmc.rs

@@ -13,7 +13,7 @@ use crate::args::{OutputFormat, VerificationArgs};
 use crate::cbmc_output_parser::{
  extract_results, process_cbmc_output, CheckStatus, ParserItem, Property, VerificationOutput,
 };
-use crate::cbmc_property_renderer::{format_result, kani_cbmc_output_filter};
+use crate::cbmc_property_renderer::{format_coverage, format_result, kani_cbmc_output_filter};
 use crate::session::KaniSession;
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
@@ -303,14 +303,23 @@ impl VerificationResult {
  }
  }
 
- pub fn render(&self, output_format: &OutputFormat, should_panic: bool) -> String {
+ pub fn render(
+ &self,
+ output_format: &OutputFormat,
+ should_panic: bool,
+ coverage_mode: bool,
+ ) -> String {
  match &self.results {
  Ok(results) => {
  let status = self.status;
  let failed_properties = self.failed_properties;
  let show_checks = matches!(output_format, OutputFormat::Regular);
- let mut result =
- format_result(results, status, should_panic, failed_properties, show_checks);
+
+ let mut result = if coverage_mode {
+ format_coverage(results, status, should_panic, failed_properties, show_checks)
+ } else {
+ format_result(results, status, should_panic, failed_properties, show_checks)
+ };
  writeln!(result, "Verification Time: {}s", self.runtime.as_secs_f32()).unwrap();
  result
  }

kani-driver/src/call_single_file.rs

@@ -96,6 +96,10 @@ impl KaniSession {
  flags.push("--enable-stubbing".into());
  }
 
+ if self.args.coverage {
+ flags.push("--coverage-checks".into());
+ }
+
  flags.extend(
  self.args
  .common_args

kani-driver/src/cbmc_output_parser.rs

@@ -96,11 +96,17 @@ pub struct PropertyId {
 
 impl Property {
  const COVER_PROPERTY_CLASS: &str = "cover";
+ const COVERAGE_PROPERTY_CLASS: &str = "code_coverage";
 
  pub fn property_class(&self) -> String {
  self.property_id.class.clone()
  }
 
+ // Returns true if this is a code_coverage check
+ pub fn is_code_coverage_property(&self) -> bool {
+ self.property_id.class == Self::COVERAGE_PROPERTY_CLASS
+ }
+
  /// Returns true if this is a cover property
  pub fn is_cover_property(&self) -> bool {
  self.property_id.class == Self::COVER_PROPERTY_CLASS
@@ -322,18 +328,22 @@ impl std::fmt::Display for TraceData {
 #[serde(rename_all = "UPPERCASE")]
 pub enum CheckStatus {
  Failure,
- Satisfied, // for cover properties only
+ Covered, // for `code_coverage` properties only
+ Satisfied, // for `cover` properties only
  Success,
  Undetermined,
  Unreachable,
- Unsatisfiable, // for cover properties only
+ Uncovered, // for `code_coverage` properties only
+ Unsatisfiable, // for `cover` properties only
 }
 
 impl std::fmt::Display for CheckStatus {
  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
  let check_str = match self {
  CheckStatus::Satisfied => style("SATISFIED").green(),
  CheckStatus::Success => style("SUCCESS").green(),
+ CheckStatus::Covered => style("COVERED").green(),
+ CheckStatus::Uncovered => style("UNCOVERED").red(),
  CheckStatus::Failure => style("FAILURE").red(),
  CheckStatus::Unreachable => style("UNREACHABLE").yellow(),
  CheckStatus::Undetermined => style("UNDETERMINED").yellow(),