Line coverage reports

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,
+            "cover_experiment",
+            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 +300,9 @@ pub struct VerificationArgs {
     )]
     pub enable_stubbing: bool,
 
+    #[arg(long, hide_short_help = true)]
+    pub coverage: bool,
+
     /// Arguments to pass down to Cargo
     #[command(flatten)]
     pub cargo: CargoCommonArgs,
@@ -640,6 +643,16 @@ 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

@@ -96,14 +96,16 @@ pub struct PropertyId {
 
 impl Property {
     const COVER_PROPERTY_CLASS: &str = "cover";
+    const COVERAGE_PROPERTY_CLASS: &str = "coverage";
 
     pub fn property_class(&self) -> String {
         self.property_id.class.clone()
     }
 
     /// Returns true if this is a cover property
     pub fn is_cover_property(&self) -> bool {
-        self.property_id.class == Self::COVER_PROPERTY_CLASS
+        self.property_id.class == Self::COVERAGE_PROPERTY_CLASS
+            || self.property_id.class == Self::COVER_PROPERTY_CLASS
     }
 
     pub fn property_name(&self) -> String {

kani-driver/src/cbmc_property_renderer.rs

@@ -8,7 +8,7 @@ use console::style;
 use once_cell::sync::Lazy;
 use regex::Regex;
 use rustc_demangle::demangle;
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 
 type CbmcAltDescriptions = HashMap<&'static str, Vec<(&'static str, Option<&'static str>)>>;
 
@@ -421,6 +421,102 @@ pub fn format_result(
     result_str
 }
 
+/// Seperate checks into coverage and non-coverage based on property class and format them seperately for --coverage. We report both verification and processed coverage
+/// results
+pub fn format_coverage(
+    properties: &[Property],
+    status: VerificationStatus,
+    should_panic: bool,
+    failed_properties: FailedProperties,
+    show_checks: bool,
+) -> String {
+    let non_coverage_checks: Vec<Property> =
+        properties.iter().filter(|&x| x.property_class() != "code_coverage").cloned().collect();
+    let coverage_checks: Vec<Property> =
+        properties.iter().filter(|&x| x.property_class() == "code_coverage").cloned().collect();
+
+    let verification_output =
+        format_result(&non_coverage_checks, status, should_panic, failed_properties, show_checks);
+    let coverage_output = format_result_coverage(&coverage_checks);
+    print!("printing coverage output = {}", coverage_output);
+    let result = format!("{}\n{}", verification_output, coverage_output);
+
+    result
+}
+
+/// Generate coverage result from all coverage properties (i.e., the checks with "coverage" property class).
+/// To be used when the user requests coverage information with --coverage. The output is tested through the coverage-based testing suite, not the regular expected suite.
+/// Loops through each of the check with a coverage property class and gives a status of FULL if all checks pertaining
+/// to a line number are SATISFIED. Similarly, it gives a status of NONE if all checks related to a line are UNSAT. If a line has both, it reports PARTIAL coverage.
+fn format_result_coverage(properties: &[Property]) -> String {
+    let mut formatted_output = String::new();
+    formatted_output.push_str("\nCoverage Results:\n");
+
+    let mut coverage_checks: Vec<&Property> = properties.iter().collect();
+
+    coverage_checks.sort_by_key(|check| (&check.source_location.file, &check.source_location.line));
+
+    let mut files: HashMap<String, Vec<(usize, CheckStatus)>> = HashMap::new();
+    for check in coverage_checks {
+        // Get line number and filename
+        let line_number: usize = check.source_location.line.as_ref().unwrap().parse().unwrap();
+        let file_name: String = check.source_location.file.as_ref().unwrap().to_string();
+
+        // Add to the files lookup map
+        files.entry(file_name.clone()).or_insert_with(Vec::new).push((line_number, check.status));
+    }
+
+    let mut coverage_results: HashMap<String, Vec<(usize, String)>> = HashMap::new();
+
+    for (file, val) in files {
+        let mut lines: HashSet<usize> = HashSet::new();
+        let mut line_results: Vec<(usize, String)> = Vec::new();
+        for check in val.clone() {
+            lines.insert(check.0);
+        }
+
+        // For each of these lines, create a map from line -> status
+        // example - {3 -> ["SAT", "UNSAT"], 4 -> ["UNSAT"] ...}
+        for line in lines.iter() {
+            let is_line_satisfied: Vec<_> = val
+                .iter()
+                .filter(|(line_number_accumulated, _)| *line == *line_number_accumulated)
+                .collect();
+
+            // Report lines as FULL if all of the coverage checks (property class = code_coverage) say FAILURE, NONE if all of the coverage checks say SUCCESS,
+            // and PARTIAL if there is a mix of the two
+            let covered_status: String = if is_line_satisfied
+                .iter()
+                .all(|&is_satisfiable| is_satisfiable.1.to_string().contains("FAILURE"))
+            {
+                "FULL".to_string()
+            } else if is_line_satisfied
+                .iter()
+                .all(|&is_satisfiable| is_satisfiable.1.to_string().contains("SUCCESS"))
+            {
+                "NONE".to_string()
+            } else {
+                "PARTIAL".to_string()
+            };
+
+            line_results.push((*line, covered_status));
+        }
+
+        line_results.sort_by_key(|&(line, _)| line);
+        coverage_results.insert(file.clone(), line_results);
+    }
+
+    // Create formatted string that is returned to the user as output
+    for (file, checks) in coverage_results.iter() {
+        for (line_number, coverage_status) in checks {
+            formatted_output.push_str(&format!("{}, {}, {}\n", file, line_number, coverage_status));
+        }
+        formatted_output.push('\n');
+    }
+
+    formatted_output
+}
+
 /// Attempts to build a message for a failed property with as much detailed
 /// information on the source location as possible.
 fn build_failure_message(description: String, trace: &Option<Vec<TraceItem>>) -> String {

kani-driver/src/harness_runner.rs

@@ -96,7 +96,11 @@ impl KaniSession {
             if !self.args.common_args.quiet && self.args.output_format != OutputFormat::Old {
                 println!(
                     "{}",
-                    result.render(&self.args.output_format, harness.attributes.should_panic)
+                    result.render(
+                        &self.args.output_format,
+                        harness.attributes.should_panic,
+                        self.args.coverage
+                    )
                 );
             }
             self.gen_and_add_concrete_playback(harness, &mut result)?;