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

Table of contents

Project overview: mpg123
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: decode_fuzzer
Call tree
Fuzz blockers
Runtime coverage analysis
Files reached
Fuzzer: read_fuzzer
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
/src/decode_fuzzer.cc
Dictionary
Fuzzer function priority
/src/read_fuzzer.c
Dictionary
Fuzzer function priority
Runtime coverage analysis
Complex functions with low coverage
Files and Directories in report
Files in report
Directories in report
Metadata section
Report generation date: 2025-10-10

Project overview: mpg123

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
38.0%
197 / 513
Cyclomatic complexity statically reachable by fuzzers
43.0%
1495 / 3463
Runtime code coverage of functions
42.0%
218 / 513

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
decode_fuzzer /src/decode_fuzzer.cc 193 375 11 24 3566 1486 decode_fuzzer.cc
read_fuzzer /src/read_fuzzer.c 221 341 12 25 3728 1546 read_fuzzer.c

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: decode_fuzzer

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 0 213 39.5%
gold [1:9] 3 0.55%
yellow [10:29] 1 0.18%
greenyellow [30:49] 3 0.55%
lawngreen 50+ 319 59.1%
All colors 539 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
31 392 process_text call site: 00392 process_picture
23 127 cap_fit call site: 00127 enc_chan_fit
22 228 decode_the_frame call site: 00228 swap_endian
18 152 INT123_frame_output_format call site: 00152 enc_chan_fit
10 174 INT123_decode_update call site: 00174 INT123_synth_ntom_set_step
10 197 INT123_frame_buffers call site: 00197 INT123_make_conv16to8_table
5 61 INT123_frame_cpu_opt call site: 00061 INT123_frame_dither_init
3 292 INT123_parse_new_id3 call site: 00292 fprintf
3 327 process_comment call site: 00327 free_mpg123_text
3 334 mpg123_move_string call site: 00334 store_id3_text
3 436 decode_header call site: 00436 fprintf
3 478 check_lame_tag call site: 00478 fprintf

Runtime coverage analysis

Covered functions
195
Functions that are reachable but not covered
43
Reachable functions
193
Percentage of reachable functions covered
77.72%
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
/src/decode_fuzzer.cc 1
/src/mpg123/src/libmpg123/libmpg123.c 20
/src/mpg123/src/libmpg123/../common/sample.h 1
/src/mpg123/src/libmpg123/frame.c 28
/src/mpg123/src/libmpg123/getcpuflags.h 1
/src/mpg123/src/libmpg123/optimize.c 7
/src/mpg123/src/libmpg123/icy.c 3
/src/mpg123/src/libmpg123/id3.c 23
/src/mpg123/src/libmpg123/format.c 20
/src/mpg123/src/libmpg123/readers.c 13
/src/mpg123/src/libmpg123/stringbuf.c 6
/src/mpg123/src/libmpg123/index.c 7
/src/mpg123/src/compat/compat_str.c 1
/src/mpg123/src/libmpg123/layer3.c 4
/src/mpg123/src/libmpg123/dither_impl.h 3
/src/mpg123/src/libmpg123/lfs_wrap.c 4
/src/mpg123/src/libmpg123/parse.c 21
/src/mpg123/src/libmpg123/ntom.c 7
/src/mpg123/src/libmpg123/tabinit.c 1
/src/mpg123/src/libmpg123/layer2.c 3
/src/mpg123/src/libmpg123/../common/swap_bytes_impl.h 1
/usr/include/x86_64-linux-gnu/bits/byteswap.h 3
/src/mpg123/src/libmpg123/gapless.h 1
/src/mpg123/src/libmpg123/getbits.h 1

Fuzzer: read_fuzzer

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 0 266 44.6%
gold [1:9] 4 0.67%
yellow [10:29] 1 0.16%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 325 54.5%
All colors 596 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
39 263 INT123_do_rva call site: 00263 decode_the_frame
31 439 process_text call site: 00439 process_picture
23 175 cap_fit call site: 00175 enc_chan_fit
18 200 INT123_frame_output_format call site: 00200 enc_chan_fit
12 131 INT123_compat_open call site: 00131 mpg123_reader64
10 244 INT123_frame_buffers call site: 00244 INT123_make_conv16to8_table
9 222 INT123_decode_update call site: 00222 INT123_synth_ntom_set_step
8 160 mpg123_decode call site: 00160 INT123_decode_update
6 120 mpg123_reader64 call site: 00120 wrap_lseek
5 80 INT123_frame_cpu_opt call site: 00080 INT123_frame_dither_init
5 583 LLVMFuzzerTestOneInput call site: 00583 mpg123_tell_stream
3 9 fuzzer_get_tmpfile call site: 00009 perror

Runtime coverage analysis

Covered functions
181
Functions that are reachable but not covered
80
Reachable functions
221
Percentage of reachable functions covered
63.8%
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
/src/read_fuzzer.c 3
/src/mpg123/src/libmpg123/libmpg123.c 22
/src/mpg123/src/libmpg123/../common/sample.h 1
/src/mpg123/src/libmpg123/frame.c 28
/src/mpg123/src/libmpg123/getcpuflags.h 1
/src/mpg123/src/libmpg123/optimize.c 7
/src/mpg123/src/libmpg123/icy.c 3
/src/mpg123/src/libmpg123/id3.c 23
/src/mpg123/src/libmpg123/format.c 20
/src/mpg123/src/libmpg123/readers.c 13
/src/mpg123/src/libmpg123/stringbuf.c 6
/src/mpg123/src/libmpg123/index.c 7
/src/mpg123/src/compat/compat_str.c 2
/src/mpg123/src/libmpg123/layer3.c 4
/src/mpg123/src/libmpg123/dither_impl.h 3
/src/mpg123/src/libmpg123/lfs_wrap.c 12
/src/mpg123/src/compat/compat.c 1
/src/mpg123/src/libmpg123/parse.c 21
/src/mpg123/src/libmpg123/ntom.c 7
/src/mpg123/src/libmpg123/tabinit.c 1
/src/mpg123/src/libmpg123/layer2.c 3
/src/mpg123/src/libmpg123/../common/swap_bytes_impl.h 1
/usr/include/x86_64-linux-gnu/bits/byteswap.h 3
/src/mpg123/src/libmpg123/gapless.h 1
/src/mpg123/src/libmpg123/getbits.h 1

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
INT123_do_layer3 /src/mpg123/src/libmpg123/layer3.c 1 ['N/A'] 3 0 1062 137 45 12 0 277 267
mpg123_open_fixed_64 /src/mpg123/src/libmpg123/lfs_wrap.c 4 ['N/A', 'N/A', 'int', 'int'] 18 0 24 3 2 168 0 1320 135
buffered_icy_fullread /src/mpg123/src/libmpg123/readers.c 3 ['N/A', 'N/A', 'size_t'] 5 0 21 3 2 11 0 107 80
INT123_do_layer1 /src/mpg123/src/libmpg123/layer1.c 1 ['N/A'] 3 0 203 30 11 5 0 75 69
mpg123_feedseek /src/mpg123/src/libmpg123/lfs_wrap.c 4 ['N/A', 'size_t', 'int', 'N/A'] 13 0 93 19 7 125 0 1142 54
INT123_do_layer2 /src/mpg123/src/libmpg123/layer2.c 1 ['N/A'] 3 0 275 40 14 5 0 56 50
mpg123_store_utf8_2 /src/mpg123/src/libmpg123/libmpg123.c 4 ['N/A', 'int', 'N/A', 'size_t'] 8 0 24 3 2 16 0 85 49
INT123_synth_ntom_s32_m2s /src/mpg123/src/libmpg123/synth_ntom.h 2 ['N/A', 'N/A'] 2 0 69 7 3 3 0 45 45

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

Functions statically reachable by fuzzers
52.0%
265 / 513
Cyclomatic complexity statically reachable by fuzzers
65.0%
2244 / 3463

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.

/src/decode_fuzzer.cc

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=['process_text', 'cap_fit', 'decode_the_frame', 'INT123_frame_output_format', 'INT123_decode_update', 'INT123_frame_buffers', 'INT123_frame_cpu_opt', 'INT123_parse_new_id3', 'process_comment', 'mpg123_move_string']

/src/read_fuzzer.c

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=['INT123_do_rva', 'process_text', 'cap_fit', 'INT123_frame_output_format', 'INT123_compat_open', 'INT123_frame_buffers', 'INT123_decode_update', 'mpg123_decode', 'mpg123_reader64', 'INT123_frame_cpu_opt']

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
INT123_frame_output_format 138 40 28.98% ['read_fuzzer', 'decode_fuzzer']
INT123_postprocess_buffer 62 13 20.96% ['read_fuzzer', 'decode_fuzzer']
mpg123_par 80 12 15.0% ['read_fuzzer', 'decode_fuzzer']
INT123_set_synth_functions 108 57 52.77% ['read_fuzzer', 'decode_fuzzer']
find_dectype 64 23 35.93% ['read_fuzzer', 'decode_fuzzer']
INT123_wrap_open 52 24 46.15% ['read_fuzzer']
stream_init 47 19 40.42% ['read_fuzzer']
get_fileinfo 32 17 53.12% ['read_fuzzer']
stream_skip_bytes 41 7 17.07% ['read_fuzzer']

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/mpg123/src/libmpg123/synth_real.c [] []
/src/mpg123/src/libmpg123/format.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/mpg123lib_intern.h [] []
/src/mpg123/src/compat/compat.c ['read_fuzzer'] ['read_fuzzer']
/src/mpg123/src/libmpg123/layer3.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/optimize.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/synth_mono.h [] []
/src/mpg123/src/compat/compat_str.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/synth_8bit.h [] []
/usr/include/x86_64-linux-gnu/bits/byteswap.h ['decode_fuzzer', 'read_fuzzer'] []
/src/mpg123/src/libmpg123/../common/swap_bytes_impl.h ['decode_fuzzer', 'read_fuzzer'] []
/src/mpg123/src/libmpg123/lfs_wrap.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/libmpg123.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/synth.h [] []
/usr/local/bin/../include/c++/v1/stdexcept [] []
/src/mpg123/src/libmpg123/getbits.h ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/../common/sample.h ['decode_fuzzer', 'read_fuzzer'] []
/src/mpg123/src/libmpg123/gapless.h ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer']
/src/mpg123/src/libmpg123/readers.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/layer1.c [] []
/src/mpg123/src/libmpg123/dither_impl.h ['decode_fuzzer', 'read_fuzzer'] []
/src/mpg123/src/libmpg123/dct64.c [] []
/src/mpg123/src/libmpg123/icy2utf8.c [] []
/src/mpg123/src/libmpg123/getcpuflags.h ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/synth_ntom.h [] []
/src/read_fuzzer.c ['read_fuzzer'] ['read_fuzzer']
/src/mpg123/src/libmpg123/stringbuf.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/index.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/id3.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/layer2.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/parse.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/decode_fuzzer.cc ['decode_fuzzer'] ['decode_fuzzer']
/src/mpg123/src/libmpg123/synth.c [] []
/src/mpg123/src/libmpg123/frame.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/tabinit.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/icy.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer', 'read_fuzzer']
/src/mpg123/src/libmpg123/synth_s32.c [] []
/src/mpg123/src/libmpg123/equalizer.c [] []
/src/mpg123/src/libmpg123/ntom.c ['decode_fuzzer', 'read_fuzzer'] ['decode_fuzzer']

Directories in report

Directory
/src/mpg123/src/libmpg123/../common/
/usr/include/x86_64-linux-gnu/bits/
/src/mpg123/src/libmpg123/
/src/
/usr/local/bin/../include/c++/v1/
/src/mpg123/src/compat/

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
decode_fuzzer fuzzerLogFile-0-UoICITzBNS.data fuzzerLogFile-0-UoICITzBNS.data.yaml decode_fuzzer.covreport
read_fuzzer fuzzerLogFile-0-YS8HELAHNc.data fuzzerLogFile-0-YS8HELAHNc.data.yaml read_fuzzer.covreport