Fuzz introspector
For issues and ideas: https://github.com/ossf/fuzz-introspector/issues
Project coverage
Per-fuzzer coverage

Table of contents

Project overview: chrono
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: fuzz_reader
Call tree
Fuzz blockers
Runtime coverage analysis
Files reached
Fuzzer: fuzz_format
Call tree
Fuzz blockers
Runtime coverage analysis
Files reached
Analyses and suggestions
Optimal target analysis
Remaining optimal interesting functions
All functions overview
Fuzz engine guidance
fuzz/fuzz_targets/fuzz_reader.rs
Dictionary
Fuzzer function priority
fuzz/fuzz_targets/fuzz_format.rs
Dictionary
Fuzzer function priority
Runtime coverage analysis
Complex functions with low coverage
Fuzz driver synthesis
New fuzzers
Files and Directories in report
Files in report
Directories in report
Function call coverage
Function in each files in report
Metadata section
Sink analyser for CWEs
Report generation date: 2025-07-11

Project overview: chrono

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
3.0%
33 / 1172
Cyclomatic complexity statically reachable by fuzzers
9.0%
116 / 1229
Runtime code coverage of functions
25.0%
297 / 1172

Warning: The number of runtime covered functions are larger than the number of reachable functions. This means that Fuzz Introspector found there are more functions covered at runtime than what is considered reachable based on the static analysis. This is a limitation in the analysis as anything covered at runtime is by definition reachable by the fuzzers.
This is likely due to a limitation in the static analysis. In this case, the count of functions covered at runtime is the true value, which means this is what should be considered "achieved" by the fuzzer.

Use the project functions table below to query all functions that were not covered at runtime.

Fuzzers overview

Fuzzer Fuzzer filename Functions Reached Functions unreached Fuzzer depth Files reached Basic blocks reached Cyclomatic complexity Details
fuzz_reader fuzz/fuzz_targets/fuzz_reader.rs 108 1141 16 21 0 115 fuzz_reader.rs
fuzz_format fuzz/fuzz_targets/fuzz_format.rs 104 1141 13 22 0 112 fuzz_format.rs

Project functions overview

The following table shows data about each function in the project. The functions included in this table correspond to all functions that exist in the executables of the fuzzers. As such, there may be functions that are from third-party libraries.

For further technical details on the meaning of columns in the below table, please see the Glossary .

Func name Functions filename Args Function call depth Reached by Fuzzers Runtime reached by Fuzzers Combined reached by Fuzzers Fuzzers runtime hit Func lines hit % I Count BB Count Cyclomatic complexity Functions reached Reached by functions Accumulated cyclomatic complexity Undiscovered complexity

Fuzzer details

Fuzzer: fuzz_reader

Call tree

The calltree shows the control flow of the fuzzer. This is overlaid with coverage information to display how much of the potential code a fuzzer can reach is in fact covered at runtime. In the following there is a link to a detailed calltree visualisation as well as a bitmap showing a high-level view of the calltree. For further information about these topics please see the glossary for full calltree and calltree overview

Full calltree

Call tree overview bitmap:

The distribution of callsites in terms of coloring is
Color Runtime hitcount Callsite count Percentage
red 0 651 77.1%
gold [1:9] 10 1.18%
yellow [10:29] 8 0.94%
greenyellow [30:49] 5 0.59%
lawngreen 50+ 170 20.1%
All colors 844 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
60 482 NaiveDate::from_ordinal_and_flags call site: 00482 resolve_week_date
55 103 DateTime::parse_from_rfc2822 call site: 00103 TimeZone::with_ymd_and_hms
41 269 Parsed::to_naive_date call site: 00269 Month::num_days
38 64 FixedOffset::east_opt call site: 00064 NaiveDate::from_ymd_opt
37 159 TimeZone::from_local_datetime call site: 00159 TimeDelta::try_hours
30 29 NaiveDate::and_time call site: 00029 DstTester::offset_from_utc_datetime
27 574 Parsed::to_naive_date call site: 00574 Date::iso_week
27 763 Parsed::to_naive_date call site: 00763 Date::iso_week
22 246 P::a::r::s::e::d::::::::t::o::_::n::a::i::v::e::_::d::a::t::e::resolve_year call site: 00246 TimeDelta::checked_add
18 204 NaiveDateTime::checked_sub_offset call site: 00204 NaiveDateTime::overflowing_sub_offset
18 605 Parsed::to_naive_date call site: 00605 resolve_week_date
18 794 Parsed::to_naive_date call site: 00794 resolve_week_date

Runtime coverage analysis

Covered functions
101
Functions that are reachable but not covered
52
Reachable functions
108
Percentage of reachable functions covered
51.85%
NB: The sum of covered functions and functions that are reachable but not covered need not be equal to Reachable functions . This is because the reachability analysis is an approximation and thus at runtime some functions may be covered that are not included in the reachability analysis. This is a limitation of our static analysis capabilities.
Function name source code lines source lines hit percentage hit

Files reached

filename functions hit
fuzz/fuzz_targets/fuzz_reader.rs 4
src/datetime/mod.rs 20
src/month.rs 14
src/offset/fixed.rs 1
src/datetime/tests.rs 14
src/naive/date/mod.rs 13
src/naive/internals.rs 4
src/naive/isoweek.rs 6
src/date.rs 29
tests/wasm.rs 14
src/naive/time/mod.rs 2
src/weekday_set.rs 8
src/offset/mod.rs 7
src/time_delta.rs 7
src/naive/datetime/mod.rs 8
src/offset/utc.rs 2
src/format/parse.rs 20
src/format/parsed.rs 60
src/traits.rs 10
src/format/strftime.rs 2
src/format/scan.rs 17

Fuzzer: fuzz_format

Call tree

The calltree shows the control flow of the fuzzer. This is overlaid with coverage information to display how much of the potential code a fuzzer can reach is in fact covered at runtime. In the following there is a link to a detailed calltree visualisation as well as a bitmap showing a high-level view of the calltree. For further information about these topics please see the glossary for full calltree and calltree overview

Full calltree

Call tree overview bitmap:

The distribution of callsites in terms of coloring is
Color Runtime hitcount Callsite count Percentage
red 0 487 63.1%
gold [1:9] 18 2.33%
yellow [10:29] 17 2.20%
greenyellow [30:49] 19 2.46%
lawngreen 50+ 230 29.8%
All colors 771 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
55 102 DateTime::parse_from_str call site: 00102 TimeZone::with_ymd_and_hms
41 268 Parsed::to_naive_date call site: 00268 Month::num_days
38 63 FixedOffset::east_opt call site: 00063 NaiveDate::from_ymd_opt
30 28 NaiveDate::and_time call site: 00028 DstTester::offset_from_utc_datetime
27 463 Parsed::to_naive_date call site: 00463 Date::iso_week
27 691 Parsed::to_naive_date call site: 00691 Date::iso_week
24 386 resolve_week_date call site: 00386 MappedLocalTime::and_then
21 174 TimeDelta::new call site: 00174 TimeDelta::try_hours
18 203 NaiveDateTime::checked_sub_offset call site: 00203 NaiveDateTime::overflowing_sub_offset
17 338 NaiveDate::year_flags call site: 00338 StrftimeItems::error
14 158 TimeZone::from_local_datetime call site: 00158 TimeDelta::try_hours
14 224 NaiveDateTime::checked_sub_offset call site: 00224 TimeZone::with_ymd_and_hms

Runtime coverage analysis

Covered functions
220
Functions that are reachable but not covered
34
Reachable functions
104
Percentage of reachable functions covered
67.31%
NB: The sum of covered functions and functions that are reachable but not covered need not be equal to Reachable functions . This is because the reachability analysis is an approximation and thus at runtime some functions may be covered that are not included in the reachability analysis. This is a limitation of our static analysis capabilities.
Warning: The number of covered functions are larger than the number of reachable functions. This means that there are more functions covered at runtime than are extracted using static analysis. This is likely a result of the static analysis component failing to extract the right call graph or the coverage runtime being compiled with sanitizers in code that the static analysis has not analysed. This can happen if lto/gold is not used in all places that coverage instrumentation is used.
Function name source code lines source lines hit percentage hit

Files reached

filename functions hit
fuzz/fuzz_targets/fuzz_format.rs 2
src/datetime/mod.rs 17
src/month.rs 14
src/offset/fixed.rs 1
src/datetime/tests.rs 14
src/naive/date/mod.rs 13
src/naive/internals.rs 4
src/naive/isoweek.rs 6
src/date.rs 29
tests/wasm.rs 14
src/naive/time/mod.rs 2
src/weekday_set.rs 4
src/offset/mod.rs 7
src/time_delta.rs 7
src/naive/datetime/mod.rs 8
src/offset/utc.rs 2
src/format/parse.rs 6
src/format/parsed.rs 60
src/traits.rs 10
src/format/strftime.rs 2
fuzz/fuzz_targets/fuzz_reader.rs 1
src/format/scan.rs 16

Analyses and suggestions

Optimal target analysis

Remaining optimal interesting functions

The following table shows a list of functions that are optimal targets. Optimal targets are identified by finding the functions that in combination, yield a high code coverage.

Func name Functions filename Arg count Args Function depth hitcount instr count bb count cyclomatic complexity Reachable functions Incoming references total cyclomatic complexity Unreached complexity

Implementing fuzzers that target the above functions will improve reachability such that it becomes:

Functions statically reachable by fuzzers
3.0%
33 / 1172
Cyclomatic complexity statically reachable by fuzzers
9.0%
116 / 1229

All functions overview

If you implement fuzzers for these functions, the status of all functions in the project will be:

Func name Functions filename Args Function call depth Reached by Fuzzers Runtime reached by Fuzzers Combined reached by Fuzzers Fuzzers runtime hit Func lines hit % I Count BB Count Cyclomatic complexity Functions reached Reached by functions Accumulated cyclomatic complexity Undiscovered complexity

Fuzz engine guidance

This sections provides heuristics that can be used as input to a fuzz engine when running a given fuzz target. The current focus is on providing input that is usable by libFuzzer.

fuzz/fuzz_targets/fuzz_reader.rs

Dictionary

Use this with the libFuzzer -dict=DICT.file flag


Fuzzer function priority

Use one of these functions as input to libfuzzer with flag: -focus_function name 

-focus_function=['NaiveDate::from_ordinal_and_flags', 'DateTime::parse_from_rfc2822', 'Parsed::to_naive_date', 'FixedOffset::east_opt', 'TimeZone::from_local_datetime', 'NaiveDate::and_time', 'P::a::r::s::e::d::::::::t::o::_::n::a::i::v::e::_::d::a::t::e::resolve_year', 'NaiveDateTime::checked_sub_offset']

fuzz/fuzz_targets/fuzz_format.rs

Dictionary

Use this with the libFuzzer -dict=DICT.file flag


Fuzzer function priority

Use one of these functions as input to libfuzzer with flag: -focus_function name 

-focus_function=['DateTime::parse_from_str', 'Parsed::to_naive_date', 'FixedOffset::east_opt', 'NaiveDate::and_time', 'resolve_week_date', 'TimeDelta::new', 'NaiveDateTime::checked_sub_offset', 'NaiveDate::year_flags']

Runtime coverage analysis

This section shows analysis of runtime coverage data.

For futher technical details on how this section is generated, please see the Glossary .

Complex functions with low coverage

Func name Function total lines Lines covered at runtime percentage covered Reached by fuzzers
chrono::format::parse::parse_internal::core::slice::iter::Iterchrono::format::Item, &chrono::format::Item 148 50 33.78%

Fuzz driver synthesis

New fuzzers

The below fuzzers are templates and suggestions for how to target the set of optimal functions above

Files and Directories in report

This section shows which files and directories are considered in this report. The main reason for showing this is fuzz introspector may include more code in the reasoning than is desired. This section helps identify if too many files/directories are included, e.g. third party code, which may be irrelevant for the threat model. In the event too much is included, fuzz introspector supports a configuration file that can exclude data from the report. See the following link for more information on how to create a config file: link

Files in report

Source file Reached by Covered by
/src/chrono/src/round.rs [] []
/src/chrono/src/lib.rs [] []
/src/chrono/src/offset/mod.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/fuzz/fuzz_targets/fuzz_format.rs ['fuzz_format'] []
/src/chrono/src/date.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/src/weekday.rs [] []
/src/chrono/src/naive/time/mod.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/src/format/scan.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/fuzz/fuzz_targets/fuzz_reader.rs ['fuzz_reader', 'fuzz_format'] []
/src/chrono/src/offset/local/tz_info/timezone.rs [] []
/src/chrono/src/month.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/src/naive/time/tests.rs [] []
/src/chrono/src/format/mod.rs [] []
/src/chrono/src/offset/local/tz_data.rs [] []
/src/chrono/src/offset/local/windows.rs [] []
/src/chrono/src/offset/local/tz_info/parser.rs [] []
/src/chrono/src/naive/datetime/serde.rs [] []
/src/chrono/src/offset/local/tz_info/rule.rs [] []
/src/chrono/src/offset/local/tz_info/mod.rs [] []
/src/chrono/src/format/locales.rs [] []
/src/chrono/src/datetime/serde.rs [] []
/src/chrono/src/format/strftime.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/src/naive/date/mod.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/bench/benches/serde.rs [] []
/src/chrono/src/time_delta.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/tests/wasm.rs ['fuzz_reader', 'fuzz_format'] []
/src/chrono/src/naive/mod.rs [] []
/src/chrono/src/offset/local/unix.rs [] []
/src/chrono/src/naive/datetime/tests.rs [] []
/src/chrono/bench/benches/chrono.rs [] []
/src/chrono/src/weekday_set.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_format']
/src/chrono/src/offset/local/mod.rs [] []
/src/chrono/src/naive/isoweek.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/src/format/formatting.rs [] []
/src/chrono/src/format/parsed.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/tests/win_bindings.rs [] []
/src/chrono/src/offset/fixed.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/src/naive/date/tests.rs [] []
/src/chrono/ci/core-test/src/lib.rs [] []
/src/chrono/src/datetime/tests.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/src/offset/local/win_bindings.rs [] []
/src/chrono/src/naive/internals.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/src/naive/time/serde.rs [] []
/src/chrono/src/format/parse.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/src/traits.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/tests/dateutils.rs [] []
/src/chrono/src/offset/utc.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/src/naive/datetime/mod.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']
/src/chrono/src/datetime/mod.rs ['fuzz_reader', 'fuzz_format'] ['fuzz_reader', 'fuzz_format']

Directories in report

Directory
/src/chrono/src/
/src/chrono/src/naive/datetime/
/src/chrono/src/offset/local/
/src/chrono/src/format/
/src/chrono/fuzz/fuzz_targets/
/src/chrono/tests/
/src/chrono/src/naive/
/src/chrono/src/offset/local/tz_info/
/src/chrono/src/datetime/
/src/chrono/src/naive/time/
/src/chrono/ci/core-test/src/
/src/chrono/bench/benches/
/src/chrono/src/naive/date/
/src/chrono/src/offset/

Function call coverage

This section shows a list of 3rd party function calls and their relative coverage information. By static analysis of the target project code, all of the 3rd party function call and their caller information, including the source file and line number that initiate the call are captured. The caller source code file and line number are shown in column 2 while column 1 is the function name of the 3rd party function call. Each occurrent of the 3rd party function call will occuply a separate row. Column 3 of each row indicate if the 3rd party call in the source file line is unreachable. Column 4 lists all fuzzers that have covered that particular system call in that specific location (source file and line)during their dynamic fuzzing.

Function in each files in report

Target sink Callsite location Reached by fuzzer Covered by Fuzzers

Metadata section

This sections shows the raw data that is used to produce this report. This is mainly used for further processing and developer debugging.

Fuzzer Calltree file Program data file Coverage file
fuzz_reader fuzzerLogFile-fuzz_reader.data fuzzerLogFile-fuzz_reader.data.yaml fuzz_reader.covreport
fuzz_format fuzzerLogFile-fuzz_format.data fuzzerLogFile-fuzz_format.data.yaml fuzz_format.covreport

Sink analyser for CWEs

No sink functions/methods found in the target project.