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

Table of contents

Project overview: htslib
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: hts_open_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/htslib/test/fuzz/hts_open_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: 2026-05-16

Project overview: htslib

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
55.0%
982 / 1778
Cyclomatic complexity statically reachable by fuzzers
64.0%
11300 / 17719
Runtime code coverage of functions
42.0%
752 / 1778

Fuzzers overview

Fuzzer Fuzzer filename Functions Reached Functions unreached Fuzzer depth Files reached Basic blocks reached Cyclomatic complexity Details
hts_open_fuzzer /src/htslib/test/fuzz/hts_open_fuzzer.c 1106 835 19 70 30019 11549 hts_open_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: hts_open_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 2922 52.3%
gold [1:9] 236 4.23%
yellow [10:29] 112 2.00%
greenyellow [30:49] 50 0.89%
lawngreen 50+ 2259 40.4%
All colors 5579 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
234 4075 hts_str2dbl call site: 04075 bam_sym_lookup
142 1563 hts_hopen call site: 01563 hts_process_opts
110 4786 idx_find_and_load call site: 04786 hts_idx_load3
103 1323 bgzf_read_block call site: 01323 bgzf_index_dump
102 3038 ks_free call site: 03038 cram_get_ref
79 2557 zlib_mem_deflate call site: 02557 fqz_compress
76 3942 sam_parse1 call site: 03942 sam_dispatcher_read
69 1492 refs2id call site: 01492 hts_tpool_init
67 2710 rans_compress_to_4x16 call site: 02710 arith_compress_to
64 4928 idx_find_and_load call site: 04928 hts_idx_load3
63 1805 sam_format1_append call site: 01805 hts_set_opt
52 4488 sam_write1 call site: 04488 fastq_format1

Runtime coverage analysis

Covered functions
753
Functions that are reachable but not covered
460
Reachable functions
1106
Percentage of reachable functions covered
58.41%
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/htslib/test/fuzz/hts_open_fuzzer.c 4
/src/htslib/hfile.c 44
/src/htslib/./textutils_internal.h 12
/src/htslib/hts.c 69
/src/htslib/./htslib/khash.h 1
/src/htslib/hfile_libcurl.c 7
/src/htslib/kstring.c 11
/src/htslib/./htslib/kstring.h 17
/src/htslib/hfile_gcs.c 1
/src/htslib/hfile_s3.c 3
/src/htslib/./htslib/hts.h 9
/src/htslib/./hts_internal.h 3
/src/htslib/multipart.c 5
/src/htslib/textutils.c 9
/src/htslib/./htslib/hfile.h 8
/src/htslib/bgzf.c 66
/src/htslib/cram/cram_io.c 75
/src/htslib/cram/../htslib/hfile.h 5
/src/htslib/cram/cram_structs.h 24
/src/htslib/cram/../header.h 4
/src/htslib/cram/string_alloc.c 6
/src/htslib/cram/cram_stats.c 5
/src/htslib/sam.c 86
/src/htslib/./htslib/sam.h 5
/src/htslib/htscodecs/htscodecs/rANS_static.c 6
/src/htslib/htscodecs/htscodecs/utils.c 5
/src/htslib/htscodecs/htscodecs/rANS_byte.h 11
/src/htslib/htscodecs/htscodecs/fqzcomp_qual.c 19
/src/htslib/htscodecs/htscodecs/varint.h 3
/src/htslib/htscodecs/htscodecs/c_simple_model.h 12
/src/htslib/htscodecs/htscodecs/c_range_coder.h 12
/src/htslib/htscodecs/htscodecs/rANS_static4x16pr.c 9
/src/htslib/htscodecs/htscodecs/utils.h 4
/src/htslib/htscodecs/htscodecs/pack.c 3
/usr/local/lib/clang/22/include/cpuid.h 1
/src/htslib/htscodecs/htscodecs/rle.c 3
/src/htslib/htscodecs/htscodecs/arith_dynamic.c 11
/src/htslib/htscodecs/htscodecs/tokenise_name3.c 33
/src/htslib/htscodecs/htscodecs/pooled_alloc.h 4
/src/htslib/header.c 48
/src/htslib/./header.h 13
/src/htslib/cram/pooled_alloc.c 6
/src/htslib/./cram/../htslib/khash.h 1
/src/htslib/cram/mFILE.c 12
/src/htslib/thread_pool.c 29
/src/htslib/./htslib/hts_endian.h 16
/src/htslib/./bgzf_internal.h 3
/src/htslib/cram/../htslib/khash.h 1
/src/htslib/cram/cram_index.c 6
/src/htslib/cram/cram_decode.c 22
/src/htslib/faidx.c 14
/src/htslib/cram/../textutils_internal.h 3
/src/htslib/./sam_internal.h 3
/src/htslib/./cram/cram_io.h 1
/src/htslib/hts_expr.c 21
/src/htslib/cram/cram_encode.c 40
/src/htslib/cram/open_trace_file.c 6
/src/htslib/md5.c 7
/src/htslib/cram/../htslib/hts_endian.h 4
/src/htslib/cram/cram_io.h 10
/src/htslib/cram/../sam_internal.h 1
/src/htslib/cram/../htslib/kstring.h 7
/src/htslib/cram/cram_codecs.c 4
/src/htslib/cram/../hts_internal.h 1
/src/htslib/./htslib/bgzf.h 2
/src/htslib/./htslib/hts_expr.h 4
/src/htslib/vcf.c 100
/src/htslib/tbx.c 5
/src/htslib/./cram/../htslib/hts_endian.h 2
/src/htslib/./htslib/vcf.h 10

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
vhopen_s3 /src/htslib/hfile_s3.c 3 ['N/A', 'N/A', 'N/A'] 13 0 23 3 2 121 0 640 465
sam_itr_regarray /src/htslib/sam.c 4 ['N/A', 'N/A', 'N/A', 'int'] 31 0 119 19 8 685 0 6127 417
vhopen_libcurl /src/htslib/hfile_libcurl.c 3 ['N/A', 'N/A', 'N/A'] 14 0 54 9 4 160 0 867 382
bcf_index_build /src/htslib/vcf.c 2 ['N/A', 'int'] 27 0 18 3 2 952 0 9621 318
bam_mplp_auto /src/htslib/sam.c 5 ['N/A', 'N/A', 'N/A', 'N/A', 'N/A'] 8 0 65 10 4 35 0 333 282
rans_uncompress_O1_32x16_avx2 /src/htslib/htscodecs/htscodecs/rANS_static32x16pr_avx2.c 4 ['N/A', 'int', 'N/A', 'int'] 4 0 4552 103 35 24 0 185 126
bcf_hdr_subset /src/htslib/vcf.c 4 ['N/A', 'int', 'N/A', 'N/A'] 11 0 376 49 18 97 0 795 118
rans_compress_O1_32x16_avx512 /src/htslib/htscodecs/htscodecs/rANS_static32x16pr_avx512.c 4 ['N/A', 'int', 'N/A', 'N/A'] 8 0 1822 92 29 35 0 223 117
sam_hdr_remove_lines /src/htslib/header.c 4 ['N/A', 'N/A', 'N/A', 'N/A'] 11 0 352 59 24 93 0 801 114
tbx_itr_querys1 /src/htslib/tbx.c 2 ['N/A', 'N/A'] 8 0 21 3 2 121 0 872 98

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

Functions statically reachable by fuzzers
68.0%
1210 / 1778
Cyclomatic complexity statically reachable by fuzzers
77.0%
13681 / 17719

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/htslib/test/fuzz/hts_open_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=['hts_str2dbl', 'hts_hopen', 'idx_find_and_load', 'bgzf_read_block', 'ks_free', 'zlib_mem_deflate', 'sam_parse1', 'refs2id', 'rans_compress_to_4x16']

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
bgzf_compress 49 25 51.02% ['hts_open_fuzzer']
bgzf_flush 37 16 43.24% ['hts_open_fuzzer']
bgzf_check_EOF 34 9 26.47% ['hts_open_fuzzer']
bgzf_write_init 49 21 42.85% ['hts_open_fuzzer']
cache_block 38 7 18.42% ['hts_open_fuzzer']
cram_beta_encode_init 70 36 51.42% ['hts_open_fuzzer']
cram_dependent_data_series 227 20 8.810% ['hts_open_fuzzer']
cram_decode_slice 549 66 12.02% ['hts_open_fuzzer']
cram_next_slice 186 73 39.24% ['hts_open_fuzzer']
cram_get_seq 45 11 24.44% ['hts_open_fuzzer']
cram_drain_rqueue 50 4 8.0% ['hts_open_fuzzer']
cram_first_slice 42 20 47.61% ['hts_open_fuzzer']
lossy_read_names 57 6 10.52% ['hts_open_fuzzer']
cram_allocate_block 64 34 53.12% ['hts_open_fuzzer']
cram_block_method2str 36 15 41.66% ['hts_open_fuzzer']
cram_get_ref 108 27 25.0% ['hts_open_fuzzer']
cram_write_SAM_hdr 181 91 50.27% ['hts_open_fuzzer']
cram_set_voption 211 10 4.739% ['hts_open_fuzzer']
ltf8_put 67 22 32.83% ['hts_open_fuzzer']
cram_compress_by_method 106 35 33.01% ['hts_open_fuzzer']
cram_populate_ref 137 33 24.08% ['hts_open_fuzzer']
refs_load_fai 113 27 23.89% ['hts_open_fuzzer']
tokenise_search_path 59 17 28.81% ['hts_open_fuzzer']
open_path_mfile 48 23 47.91% ['hts_open_fuzzer']
expand_path 51 16 31.37% ['hts_open_fuzzer']
fai_build3_core 76 20 26.31% ['hts_open_fuzzer']
sam_hdr_count_lines 35 13 37.14% ['hts_open_fuzzer']
sam_hrecs_find_type_id 53 13 24.52% ['hts_open_fuzzer']
hseek 36 19 52.77% ['hts_open_fuzzer']
hts_open_format 72 36 50.0% ['hts_open_fuzzer']
hts_idx_check_local 110 41 37.27% ['hts_open_fuzzer']
hts_idx_load3 32 7 21.87% ['hts_open_fuzzer']
format_category 34 14 41.17% ['hts_open_fuzzer']
idx_find_and_load 48 10 20.83% ['hts_open_fuzzer']
kh_resize_vdict 62 34 54.83% ['hts_open_fuzzer']
sam_state_destroy 80 5 6.25% ['hts_open_fuzzer']
sam_write1 127 20 15.74% ['hts_open_fuzzer']
sam_read1_sam 83 21 25.30% ['hts_open_fuzzer']
index_load 37 13 35.13% ['hts_open_fuzzer']
bcf_hdr_get_hrec 49 13 26.53% ['hts_open_fuzzer']
vcf_hdr_read 80 34 42.5% ['hts_open_fuzzer']
bcf1_sync 114 12 10.52% ['hts_open_fuzzer']
bcf_fmt_array1 45 11 24.44% ['hts_open_fuzzer']
get_rlen 196 79 40.30% ['hts_open_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/htslib/htscodecs/htscodecs/rANS_static4x16pr.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/rANS_word.h [] []
/src/htslib/htscodecs/htscodecs/arith_dynamic.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/./htslib/hts_defs.h [] []
/src/htslib/./hts_internal.h ['hts_open_fuzzer'] []
/src/htslib/hfile.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/./htslib/vcf.h ['hts_open_fuzzer'] []
/src/htslib/cram/../htslib/hts_endian.h ['hts_open_fuzzer'] []
/src/htslib/cram/../htslib/kstring.h ['hts_open_fuzzer'] []
/src/htslib/./header.h ['hts_open_fuzzer'] []
/src/htslib/./htslib/sam.h ['hts_open_fuzzer'] []
/src/htslib/simd.c [] []
/src/htslib/htscodecs/htscodecs/rANS_static.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/region.c [] []
/src/htslib/hfile_libcurl.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/rANS_static32x16pr_avx2.c [] []
/usr/local/lib/clang/22/include/cpuid.h ['hts_open_fuzzer'] []
/src/htslib/cram/../htslib/hfile.h ['hts_open_fuzzer'] []
/src/htslib/bgzf.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/multipart.c ['hts_open_fuzzer'] []
/src/htslib/hts.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/cram/open_trace_file.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/./htslib/hts.h ['hts_open_fuzzer'] []
/src/htslib/vcf.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/./htslib/bgzf.h ['hts_open_fuzzer'] []
/src/htslib/cram/cram_codecs.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/rANS_static32x16pr_sse4.c [] []
/src/htslib/./textutils_internal.h ['hts_open_fuzzer'] []
/src/htslib/./cram/../htslib/khash.h ['hts_open_fuzzer'] []
/src/htslib/faidx.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/rle.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/cram/pooled_alloc.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/sam.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/utils.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/sam_mods.c [] []
/src/htslib/hts_expr.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/utils.h ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/./htslib/khash.h ['hts_open_fuzzer'] []
/src/htslib/cram/mFILE.c ['hts_open_fuzzer'] []
/src/htslib/test/fuzz/hts_open_fuzzer.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/c_range_coder.h ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/cram/cram_structs.h ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/varint.h ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/./bgzf_internal.h ['hts_open_fuzzer'] []
/src/htslib/htscodecs/htscodecs/fqzcomp_qual.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/htscodecs.c [] []
/src/htslib/cram/../sam_internal.h ['hts_open_fuzzer'] []
/src/htslib/htscodecs/htscodecs/rANS_static16_int.h [] []
/src/htslib/cram/cram_codecs.h [] []
/src/htslib/cram/cram_encode.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/rANS_byte.h ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/textutils.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/./htslib/kstring.h ['hts_open_fuzzer'] []
/src/htslib/./sam_internal.h ['hts_open_fuzzer'] []
/src/htslib/./htslib/hts_expr.h ['hts_open_fuzzer'] []
/src/htslib/cram/cram_io.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/pooled_alloc.h ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/rANS_static32x16pr_avx512.c [] []
/src/htslib/htscodecs/htscodecs/pack.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/md5.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/./htslib/khash_str2int.h [] []
/src/htslib/cram/../htscodecs/htscodecs/varint.h [] ['hts_open_fuzzer']
/src/htslib/thread_pool.c ['hts_open_fuzzer'] []
/src/htslib/htscodecs/htscodecs/c_simple_model.h ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/hfile_gcs.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/cram/cram_io.h ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/cram/string_alloc.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/kstring.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/cram/cram_decode.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/./htslib/hts_endian.h ['hts_open_fuzzer'] []
/src/htslib/hfile_s3.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/header.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/cram/../header.h ['hts_open_fuzzer'] []
/src/htslib/./cram/cram_io.h ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/./hts_time_funcs.h [] []
/src/htslib/cram/cram_index.c ['hts_open_fuzzer'] []
/src/htslib/cram/cram_stats.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/tokenise_name3.c ['hts_open_fuzzer'] ['hts_open_fuzzer']
/src/htslib/htscodecs/htscodecs/rANS_static32x16pr.c [] []
/src/htslib/./htslib/hfile.h ['hts_open_fuzzer'] []
/src/htslib/cram/../textutils_internal.h ['hts_open_fuzzer'] []
/src/htslib/tbx.c ['hts_open_fuzzer'] ['hts_open_fuzzer']

Directories in report

Directory
/src/htslib/cram/../htslib/
/usr/local/lib/clang/22/include/
/src/htslib/./
/src/htslib/cram/../
/src/htslib/
/src/htslib/cram/
/src/htslib/cram/../htscodecs/htscodecs/
/src/htslib/./cram/
/src/htslib/htscodecs/htscodecs/
/src/htslib/test/fuzz/
/src/htslib/./cram/../htslib/
/src/htslib/./htslib/

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
hts_open_fuzzer fuzzerLogFile-0-cKfmoQrmVb.data fuzzerLogFile-0-cKfmoQrmVb.data.yaml hts_open_fuzzer.covreport