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

Table of contents

Project overview: openh264
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: decoder_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/decoder_fuzzer.cpp
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: 2025-07-11

Project overview: openh264

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
2.0%
15 / 613
Cyclomatic complexity statically reachable by fuzzers
1.0%
64 / 6977
Runtime code coverage of functions
69.0%
420 / 613

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
decoder_fuzzer /src/decoder_fuzzer.cpp 28 730 6 9 156 133 decoder_fuzzer.cpp

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: decoder_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 2 8.0%
gold [1:9] 0 0.0%
yellow [10:29] 0 0.0%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 23 92.0%
All colors 25 100

Fuzz blockers

The followings are the branches where fuzzer fails to bypass.

Unique non-covered Complexity Unique Reachable Complexities Unique Reachable Functions All non-covered Complexity All Reachable Complexity Function Name Function Callsite Blocked Branch
2800 2842 6 :

['WelsDec::CWelsDecoder::ReleaseBufferedReadyPictureReorder(WelsDec::TagWelsDecoderContext*, unsigned char**, TagBufferInfo*, bool)', 'WelsDec::CWelsDecoder::ReleaseBufferedReadyPictureNoReorder(WelsDec::TagWelsDecoderContext*, unsigned char**, TagBufferInfo*)', 'EventWait', 'EventReset', 'EventPost', 'WelsDec::CWelsDecoder::ThreadDecodeFrameInternal(unsigned char const*, int, unsigned char**, TagBufferInfo*)']

2800 2842 WelsDec::CWelsDecoder::DecodeFrameNoDelay(unsignedcharconst*,int,unsignedchar**,TagBufferInfo*) call site: 00000 /src/openh264/codec/decoder/plus/src/welsDecoderExt.cpp:700
178 251 10 :

['WelsCommon::CMemoryAlign::WelsMallocz(unsigned int, char const*)', 'WelsCommon::BsRbspTrailingBits(WelsCommon::TagBitStringAux*)', 'WelsCommon::BsWriteUE(WelsCommon::TagBitStringAux*, unsigned int)', 'WelsDec::RBSP2EBSP(unsigned char*, unsigned char*, int)', 'WelsCommon::BsWriteBits(WelsCommon::TagBitStringAux*, int, unsigned int)', 'WelsCommon::CMemoryAlign::WelsFree(void*, char const*)', 'WelsLog(TagLogContext*, int, char const*, ...)', 'WelsCommon::BsWriteSE(WelsCommon::TagBitStringAux*, int)', 'WelsCommon::BsWriteOneBit(WelsCommon::TagBitStringAux*, unsigned int)', 'WelsCommon::InitBits(WelsCommon::TagBitStringAux*, unsigned char const*, int)']

182 351 WelsDec::ParseSps(WelsDec::TagWelsDecoderContext*,WelsCommon::TagBitStringAux*,int*,int*,unsignedchar*,int) call site: 00000 /src/openh264/codec/decoder/core/src/au_parser.cpp:1154
22 22 1 :

['EventWait']

42 3493 WelsDec::CWelsDecoder::DecodeFrame2WithCtx(WelsDec::TagWelsDecoderContext*,unsignedcharconst*,int,unsignedchar**,TagBufferInfo*) call site: 00000 /src/openh264/codec/decoder/plus/src/welsDecoderExt.cpp:800
22 22 1 :

['EventWait']

22 461 WelsDec::GetColocatedMb(WelsDec::TagWelsDecoderContext*,unsignedint&,unsignedint&) call site: 00000 /src/openh264/codec/decoder/core/src/mv_pred.cpp:318
8 21 2 :

['EventPost', 'WelsDec::CWelsDecoder::BufferingReadyPicture(WelsDec::TagWelsDecoderContext*, unsigned char**, TagBufferInfo*)']

8 21 WelsDec::CWelsDecoder::DecodeFrame2WithCtx(WelsDec::TagWelsDecoderContext*,unsignedcharconst*,int,unsignedchar**,TagBufferInfo*) call site: 00000 /src/openh264/codec/decoder/plus/src/welsDecoderExt.cpp:885
8 21 2 :

['EventPost', 'WelsDec::CWelsDecoder::BufferingReadyPicture(WelsDec::TagWelsDecoderContext*, unsigned char**, TagBufferInfo*)']

8 21 WelsDec::CWelsDecoder::DecodeFrame2WithCtx(WelsDec::TagWelsDecoderContext*,unsignedcharconst*,int,unsignedchar**,TagBufferInfo*) call site: 00000 /src/openh264/codec/decoder/plus/src/welsDecoderExt.cpp:909
8 17 2 :

['WelsCommon::CMemoryAlign::WelsMallocz(unsigned int, char const*)', 'EventCreate']

8 17 WelsDec::AllocPicture(WelsDec::TagWelsDecoderContext*,int,int) call site: 00000 /src/openh264/codec/decoder/core/src/pic_queue.cpp:127
8 8 1 :

['EventPost']

8 49 WelsDec::DecodeFrameConstruction(WelsDec::TagWelsDecoderContext*,unsignedchar**,TagBufferInfo*) call site: 00000 /src/openh264/codec/decoder/core/src/decoder_core.cpp:230
8 8 1 :

['EventPost']

8 8 WelsDec::DecodeCurrentAccessUnit(WelsDec::TagWelsDecoderContext*,unsignedchar**,TagBufferInfo*) call site: 00000 /src/openh264/codec/decoder/core/src/decoder_core.cpp:2827
6 6 1 :

['EventDestroy']

6 18 WelsDec::FreePicture(WelsDec::SPicture*,WelsCommon::CMemoryAlign*) call site: 00000 /src/openh264/codec/decoder/core/src/pic_queue.cpp:172
4 4 1 :

['WelsDec::PrefetchLastPicForThread(WelsDec::TagPicBuff*, int const&)']

71 2036 WelsDec::DecodeCurrentAccessUnit(WelsDec::TagWelsDecoderContext*,unsignedchar**,TagBufferInfo*) call site: 00000 /src/openh264/codec/decoder/core/src/decoder_core.cpp:2504
2 2 1 :

['ResetDecStatNums']

10 125 WelsDec::CWelsDecoder::DecodeFrame2WithCtx(WelsDec::TagWelsDecoderContext*,unsignedcharconst*,int,unsignedchar**,TagBufferInfo*) call site: 00000 /src/openh264/codec/decoder/plus/src/welsDecoderExt.cpp:862

Runtime coverage analysis

Covered functions
403
Functions that are reachable but not covered
6
Reachable functions
28
Percentage of reachable functions covered
78.57%
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/decoder_fuzzer.cpp 1
decoder/plus/src/welsDecoderExt.cpp 3
/src/openh264/./codec/api/wels/codec_api.h 2
common/src/welsCodecTrace.cpp 3
common/src/utils.cpp 1
common/src/crt_util_safe_x.cpp 3
decoder/core/src/decoder.cpp 1
decoder/core/src/wels_decoder_thread.cpp 1
common/src/WelsThreadLib.cpp 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
WelsDec::CWelsDecoder::DecodeFrameNoDelay(unsignedcharconst*,int,unsignedchar**,TagBufferInfo*) /src/openh264/codec/decoder/plus/src/welsDecoderExt.cpp 5 ['N/A', 'N/A', 'int', 'N/A', 'N/A'] 14 0 123 15 6 524 0 2764 2736
WelsDec::WelsDeblockingMb(WelsDec::TagDqLayer*,WelsDec::tagDeblockingFilter*,int) /src/openh264/codec/decoder/core/src/deblocking.cpp 3 ['N/A', 'N/A', 'int'] 3 0 418 55 16 38 0 1467 1467
WelsDec::WelsDecodeMbCabacBSlice(WelsDec::TagWelsDecoderContext*,WelsDec::TagNalUnit*,unsignedint&) /src/openh264/codec/decoder/core/src/decode_slice.cpp 3 ['N/A', 'N/A', 'N/A'] 8 0 551 55 20 174 0 1027 950
WelsDec::WelsDecodeMbCavlcBSlice(WelsDec::TagWelsDecoderContext*,WelsDec::TagNalUnit*,unsignedint&) /src/openh264/codec/decoder/core/src/decode_slice.cpp 3 ['N/A', 'N/A', 'N/A'] 8 0 696 80 30 136 0 870 367
WelsDec::WelsDecodeMbCavlcPSlice(WelsDec::TagWelsDecoderContext*,WelsDec::TagNalUnit*,unsignedint&) /src/openh264/codec/decoder/core/src/decode_slice.cpp 3 ['N/A', 'N/A', 'N/A'] 6 0 606 68 24 100 0 623 245
WelsDec::WelsDecodeMbCabacPSlice(WelsDec::TagWelsDecoderContext*,WelsDec::TagNalUnit*,unsignedint&) /src/openh264/codec/decoder/core/src/decode_slice.cpp 3 ['N/A', 'N/A', 'N/A'] 7 0 470 43 14 136 0 755 184
WelsDec::WelsDecodeMbCabacISlice(WelsDec::TagWelsDecoderContext*,WelsDec::TagNalUnit*,unsignedint&) /src/openh264/codec/decoder/core/src/decode_slice.cpp 3 ['N/A', 'N/A', 'N/A'] 7 0 45 8 3 90 0 473 85
WelsDec::WelsDecodeMbCavlcISlice(WelsDec::TagWelsDecoderContext*,WelsDec::TagNalUnit*,unsignedint&) /src/openh264/codec/decoder/core/src/decode_slice.cpp 3 ['N/A', 'N/A', 'N/A'] 5 0 192 23 9 74 0 394 79
WelsDec::CWelsDecoder::SetOption(DECODER_OPTION,void*) /src/openh264/codec/decoder/plus/src/welsDecoderExt.cpp 3 ['N/A', 'int', 'N/A'] 4 0 530 103 39 20 0 86 43
(anonymousnamespace)::McHorVer32_sse2(unsignedcharconst*,int,unsignedchar*,int,int,int) /src/openh264/codec/common/src/mc.cpp 6 ['N/A', 'int', 'N/A', 'int', 'int', 'int'] 3 0 129 9 4 22 0 37 37

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

Functions statically reachable by fuzzers
67.0%
411 / 613
Cyclomatic complexity statically reachable by fuzzers
89.0%
6185 / 6977

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/decoder_fuzzer.cpp

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=['WelsCreateDecoder', 'WelsLog(TagLogContext*, int, char const*, ...)']

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
WelsDec::CheckSpsActive(WelsDec::TagWelsDecoderContext*,WelsDec::TagSps*,bool) 44 22 50.0% ['decoder_fuzzer']
WelsDec::InitBsBuffer(WelsDec::TagWelsDecoderContext*) 38 11 28.94% ['decoder_fuzzer']
WelsDec::WelsFreeStaticMemory(WelsDec::TagWelsDecoderContext*) 39 17 43.58% ['decoder_fuzzer']
WelsDec::CheckAvailNalUnitsListContinuity(WelsDec::TagWelsDecoderContext*,int,int) 34 13 38.23% ['decoder_fuzzer']
WelsDec::RefineIdxNoInterLayerPred(WelsDec::TagAccessUnits*,int*) 43 18 41.86% ['decoder_fuzzer']
WelsDec::DecodeFrameConstruction(WelsDec::TagWelsDecoderContext*,unsignedchar**,TagBufferInfo*) 214 84 39.25% ['decoder_fuzzer']
WelsDec::SetRectBlock(void*,int,int,int,unsignedint,int) 82 22 26.82% ['decoder_fuzzer']
WelsDec::CWelsDecoder::SetOption(DECODER_OPTION,void*) 93 24 25.80% ['decoder_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/openh264/codec/decoder/core/src/parse_mb_syn_cavlc.cpp [] []
/src/openh264/codec/decoder/core/src/cabac_decoder.cpp [] []
/src/openh264/codec/common/src/memory_align.cpp [] []
/src/openh264/./codec/decoder/core/inc/wels_common_basis.h [] []
/src/openh264/codec/common/src/utils.cpp ['decoder_fuzzer'] ['decoder_fuzzer']
/src/openh264/codec/decoder/core/src/pic_queue.cpp [] []
/src/openh264/./codec/common/inc/macros.h [] []
/src/openh264/./codec/decoder/core/inc/dec_golomb.h [] []
/src/openh264/codec/decoder/core/src/decoder.cpp ['decoder_fuzzer'] ['decoder_fuzzer']
/src/decoder_fuzzer.cpp ['decoder_fuzzer'] ['decoder_fuzzer']
/src/openh264/codec/common/src/mc.cpp [] []
/src/openh264/codec/decoder/core/src/au_parser.cpp [] []
/src/openh264/codec/decoder/core/src/mv_pred.cpp [] []
/src/openh264/codec/decoder/core/src/rec_mb.cpp [] []
/src/openh264/./codec/api/wels/codec_api.h ['decoder_fuzzer'] []
/src/openh264/./codec/common/inc/golomb_common.h [] []
/src/openh264/codec/common/src/copy_mb.cpp [] []
/src/openh264/codec/decoder/core/src/error_concealment.cpp [] []
/src/openh264/codec/decoder/core/src/bit_stream.cpp [] []
/src/openh264/codec/common/src/welsCodecTrace.cpp ['decoder_fuzzer'] ['decoder_fuzzer']
/src/openh264/./codec/decoder/core/inc/mv_pred.h [] []
/src/openh264/codec/decoder/core/src/decode_mb_aux.cpp [] []
/src/openh264/codec/decoder/core/src/parse_mb_syn_cabac.cpp [] []
/src/openh264/codec/common/src/deblocking_common.cpp [] []
/src/openh264/codec/decoder/core/src/decoder_core.cpp [] []
/src/openh264/codec/common/src/crt_util_safe_x.cpp ['decoder_fuzzer'] ['decoder_fuzzer']
/src/openh264/codec/common/src/WelsThreadLib.cpp ['decoder_fuzzer'] ['decoder_fuzzer']
/src/openh264/./codec/common/inc/measure_time.h [] []
/src/openh264/codec/decoder/core/src/wels_decoder_thread.cpp ['decoder_fuzzer'] ['decoder_fuzzer']
/src/openh264/codec/decoder/core/src/deblocking.cpp [] []
/src/openh264/codec/decoder/core/src/manage_dec_ref.cpp [] []
/src/openh264/./codec/decoder/core/inc/deblocking.h [] []
/src/openh264/codec/decoder/core/src/fmo.cpp [] []
/src/openh264/./codec/decoder/core/inc/decoder_context.h [] []
/src/openh264/codec/decoder/core/src/get_intra_predictor.cpp [] []
/src/openh264/./codec/decoder/core/inc/vlc_decoder.h [] []
/src/openh264/codec/decoder/core/src/memmgr_nal_unit.cpp [] []
/src/openh264/codec/decoder/core/src/decode_slice.cpp [] []
/src/openh264/codec/decoder/plus/src/welsDecoderExt.cpp ['decoder_fuzzer'] ['decoder_fuzzer']
/src/openh264/codec/common/src/expand_pic.cpp [] []
/src/openh264/codec/common/src/cpu.cpp [] []

Directories in report

Directory
/src/openh264/./codec/decoder/core/inc/
/src/openh264/./codec/api/wels/
/src/openh264/codec/decoder/plus/src/
/src/openh264/codec/decoder/core/src/
/src/openh264/./codec/common/inc/
/src/
/src/openh264/codec/common/src/

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
decoder_fuzzer fuzzerLogFile-0-sDIhoZJXkD.data fuzzerLogFile-0-sDIhoZJXkD.data.yaml decoder_fuzzer.covreport