LCOV(1)

📦
version 2.6 · 14 versions
, in arch rolling

okay bestie, welcome to the lcov(1) page — manual name LCOV — and we're about to make coverage data make sense 💅✨

🌸 NAME 🌸

lcov — lcov documentation.

🌸 NAME, again (yes, it's literally the section name, bestie) 🌸

lcov — Capture and manipulate coverage data from lcov tracefiles or gcov.

🦋 SYNOPSIS 🦋

Bestie, here's the whole menu of ways to run lcov. First up: capture a coverage data tracefile from compiler-generated data. The lcov tracefile (the “.info” file) format is described in geninfo(1) (file://../man/geninfo.1.html).

lcov -c | --capture
    [ -d | --directory *directory* ]
    [ -k | --kernel-directory *directory* ]
    [ -o | --output-file *tracefile* ]
    [ -t | --test-name *testname* ]
    [ -b | --base-directory *directory* ]
    [ --build-directory *directory* ]
    [ --source-directory *directory* ]
    [ -i | --initial ]
    [ --all ]
    [ --gcov-tool *tool* ]
    [ --branch-coverage ]
    [ --mcdc-coverage ]
    [ --demangle-cpp [ *param* ] ]
    [ --checksum ]
    [ --no-checksum ]
    [ --no-recursion ]
    [ -f | --follow ]
    [ --sort-input ]
    [ --compat-libtool ]
    [ --no-compat-libtool ]
    [ --msg-log [ *log_file_name* ] ]
    [ --ignore-errors *errors* ]
    [ --expect-message-count *message_type=expr[,message_type=expr..]* ]
    [ --preserve ]
    [ --to-package *package* ]
    [ --from-package *package* ]
    [ --no-markers ]
    [ --external ]
    [ --no-external ]
    [ --compat *mode*\ =on|off|auto]
    [ --context-script *script_file* ]
    [ --criteria-script *script_file* ]
    [ --history-script *callback* ]
    [ --resolve-script *script_file* ]
    [ --version-script *script_file* ]
    [ --unreachable-script *callback* ]
    [ --comment *comment_string* ]
    [ --large-file *regexp* ]

Generate a tracefile from compiler-generated data with all counter values set to zero — a little reset moment, no cap:

lcov -z | --zerocounters
    [ -d | --directory *directory* ]
    [ --no-recursion ]
    [ -f | --follow ]

Show the coverage counts recorded in previously generated tracefiles:

lcov -l | --list *tracefile*
    [ --list-full-path ]
    [ --no-list-full-path ]

Aggregate multiple coverage tracefiles into one:

lcov -a | --add-tracefile *tracefile_patterns*
    [ -o | --output-file *tracefile* ]
    [ --prune-tests ]
    [ --forget-test-names ]
    [ --map-functions ]
    [ --branch-coverage ]
    [ --mcdc-coverage ]
    [ --checksum ]
    [ --no-checksum ]
    [ --sort-input ]

Depending on your use model, it may not be necessary to create aggregate coverage data files. For example, if your regression tests are split into multiple suites, you may want to keep separate suite data and to compare both per-suite and aggregate results over time. genhtml allows you specify tracefiles via one or more glob patterns — which enables you generate aggregate reports without explicitly generating aggregated trace files. See the genhtml man page.

Generate a new tracefile from an existing tracefile, keeping only data from files matching the pattern:

lcov -e | --extract *tracefile pattern*
    [ -o | --output-file *tracefile* ]
    [ --checksum ]
    [ --no-checksum ]

Generate a new tracefile from an existing tracefile, removing data from files matching the pattern:

lcov -r | --remove *tracefile pattern*
    [ -o | --output-file *tracefile* ]
    [ --checksum ]
    [ --no-checksum ]

Generate a new tracefile from existing tracefiles by performing set operations on coverage data — math but make it coverage 💅:

lcov --intersect *rh_glob_pattern*
    [ -o | --output-file *tracefile* ]
    lh_glob_pattern

The output will reflect:

(union of files matching lh_glob_patterns) intersect (union of files
matching rh_glob_patterns)

such that coverpoints found in both sets are merged (summed) whereas coverpoints found in only one set are dropped. Note that branch blocks are defined to be the same if and only if their block ID and the associated branch expressions list are identical. Functions are defined to be the same if their name and location are identical.

lcov --subtract *rh_glob_pattern*
    [ -o | --output-file *tracefile* ]
    lh_glob_pattern

The output will reflect:

(union of files matching lh_glob_patterns) subtract (union of files
matching rh_glob_patterns)

such that coverpoints found only in the set on the left will be retained and all others are dropped.

Summarize tracefile content:

lcov --summary *tracefile*

Print version or help message and exit:

lcov [ -h | --help ]
    [ --version ]

Common lcov options — supported by all the above use cases, bestie:

lcov [ --keep-going ]
    [ --filter *type* ]
    [ -q | --quiet ]
    [ -v | --verbose ]
    [ --comment *comment_string* ]
    [ --debug ]
    [ --parallel | -j [*integer*] ]
    [ --memory *integer_num_Mb* ]
    [ --tempdir *dirname* ]
    [ --branch-coverage ]
    [ --mcdc-coverage ]
    [ --config-file *config-file* ]
    [ --rc *keyword*\ =\ *value* ]
    [ --profile [ *profile-file* ] ]
    [ --include *glob_pattern* ]
    [ --exclude *glob_pattern* ]
    [ --erase-functions *regexp_pattern* ]
    [ --substitute *regexp_pattern* ]
    [ --omit-lines *regexp_pattern* ]
    [ --fail-under-branches *percentage* ]
    [ --fail-under-lines *percentage* ]

🌈 DESCRIPTION 🌈

lcov is a graphical front-end for GCC's coverage testing tool gcov. It collects line, function and branch coverage data for multiple source files and creates HTML pages containing the source code annotated with coverage information. It also adds overview pages for easy navigation within the file structure.

Use lcov to collect coverage data and genhtml to create HTML pages. Coverage data can either be collected from the currently running Linux kernel or from a user space application. To do this, you have to complete the following preparation steps:

  • For Linux kernel coverage: Follow the setup instructions for the gcov-kernel infrastructure: https://docs.kernel.org/dev-tools/gcov.html
  • For user space application coverage: Compile the application with GCC using the options -fprofile-arcs and -ftest-coverage or --coverage.

Please note that this man page refers to the output format of lcov as “.info file” or “tracefile” and that the output of GCOV is called “.da file”.

Also note that when printing percentages, 0% and 100% are only printed when the values are exactly 0% and 100% respectively. Other values which would conventionally be rounded to 0% or 100% are instead printed as nearest non-boundary value. This behavior is in accordance with that of the gcov(1) tool (file://../man/gcov.1.html).

By default, lcov and related tools generate and collect line and function coverage data. Branch data is not collected or displayed by default; all tools support the --branch-coverage and --mcdc-coverage options to enable branch and MC/DC coverage, respectively — or you can permanently enable branch coverage by adding the appropriate settings to your personal, group, or site lcov configuration file. See man lcovrc(5) (file://../man/lcovrc.5.html) for details.

✨ OPTIONS ✨

In general, (almost) all lcov options can also be specified in a configuration file — see man lcovrc(5) (file://../man/lcovrc.5.html) for details.

  • -a tracefile_patterns, --add-tracefile tracefile_patterns — Add contents of all files matching glob pattern tracefile_patterns. Specify several tracefiles using the -a switch to combine the coverage data contained in these files by adding up execution counts for matching test and filename combinations. The result of the add operation will be written to stdout or the tracefile specified with -o. Only one of -z, -c, -a, -e, -r, -l or --summary may be specified at a time.
  • -b directory, --base-directory directory — Use directory as base directory for relative paths. Use this option to specify the base directory of a build-environment when lcov produces error messages like: ERROR: could not read source file /home/user/project/subdir1/subdir2/subdir1/subdir2/file.c. In this example, use /home/user/project as base directory. This option is required when using lcov on projects built with libtool or similar build environments that work with a base directory, i.e. environments, where the current working directory when invoking the compiler is not the same directory in which the source code file is located. Note that this option will not work in environments where multiple base directories are used. In that case use configuration file setting geninfo_auto_base=1 (see man lcovrc(5) (file://../man/lcovrc.5.html)).
  • --build-directory build_directory — search for .gcno data files from build_directory rather than adjacent to the corresponding .gcda file. See man geninfo(1) (file://../man/geninfo.1.html) for details.
  • --source-directory dirname — Add ‘*dirname*’ to the list of places to look for source files. For relative source file paths listed in e.g. paths found in tracefile, or found in gcov output during --capture — possibly after substitutions have been applied — lcov will first look for the path from ‘cwd’ (where genhtml was invoked) and then from each alternate directory name in the order specified. The first location matching location is used. This option can be specified multiple times, to add more directories to the source search path.
  • -c, --capture — Capture runtime coverage data. By default captures the current kernel execution counts and writes the resulting coverage data to the standard output. Use the --directory option to capture counts for a user space program. The result of the capture operation will be written to stdout or the tracefile specified with -o. When combined with the --all flag, both runtime and compile-time coverage will be extracted in one step. See the description of the --initial flag, below. See man geninfo(1) (file://../man/geninfo.1.html) for more details about the capture process and available options and parameters.

Okay so first up: if your project is big, you can make that capture go brrr with the --parallel option. 💨 How the work gets batched across those forked children — and how a large compilation unit gets its own child process so it doesn’t serialize the tail of the run — is controlled by these entries in lcovrc(5): geninfo_chunk_size, geninfo_dedicate_segment_size, dedicate_segment_threshold, and dedicate_segment_line_estimate. Also peep the --large-file option below, bestie — it handles the related-but-distinct problem of a single file whose memory footprint could exhaust available memory during parallel processing. 😭

⚠️ Real talk: only one of -z, -c, -a, -e, -r, -l, --diff or --summary may be specified at a time.
  • --branch-coverage — Collect and/or retain branch coverage data. ✨ This is literally equivalent to using the option --rc branch_coverage=1; the option was added to better match the genhtml interface.
  • --mcdc-coverage — Collect and retain MC/DC data. This is equivalent to using the option --rc mcdc_coverage=1. MC/DC coverage is supported for GCC versions 14.2 and higher, or LLVM 18.1 and higher. See llvm2lcov --help for details on MC/DC data capture in LLVM. See the MC/DC section of man genhtml(1) for more details.
  • --checksum, --no-checksum — Specify whether to generate checksum data when writing tracefiles and/or to verify matching checksums when combining trace files. Use --checksum to enable checksum generation or --no-checksum to disable it. Checksum generation is disabled by default. When checksum generation is enabled, a checksum will be generated for each source code line and stored along with the coverage data. This checksum will be used to prevent attempts to combine coverage data from different source code versions. If you don’t work with different source code versions, disable this option to speed up coverage data processing and to reduce the size of tracefiles. Note that this option is somewhat subsumed by the --version-script option — which does something similar, but at the ‘whole file’ level. 💅
  • --compat mode=value*[,*mode=value,…] — Set compatibility mode. Use --compat to specify that lcov should enable one or more compatibility modes when capturing coverage data. You can provide a comma-separated list of mode=value pairs to specify the values for multiple modes.

Valid values are:

  • on — Enable compatibility mode.
  • off — Disable compatibility mode.
  • auto — Apply auto-detection to determine if compatibility mode is required. Note that auto-detection is not available for all compatibility modes.

If no value is specified, ‘on’ is assumed as default value.

Valid modes are:

  • libtool — Enable this mode if you are capturing coverage data for a project that was built using the libtool mechanism. See also --compat-libtool. The default value for this setting is ‘on’.
  • hammer — Enable this mode if you are capturing coverage data for a project that was built using a version of GCC 3.3 that contains a modification (hammer patch) of later GCC versions. You can identify a modified GCC 3.3 by checking the build directory of your project for files ending in the extension ‘.bbg’. Unmodified versions of GCC 3.3 name these files ‘.bb’. The default value for this setting is ‘auto’.
  • split_crc — Enable this mode if you are capturing coverage data for a project that was built using a version of GCC 4.6 that contains a modification (split function checksums) of later GCC versions. Typical error messages when running lcov on coverage data produced by such GCC versions are ‘out of memory’ and ‘reached unexpected end of file’. The default value for this setting is ‘auto’.
  • --compat-libtool, --no-compat-libtool — Specify whether to enable libtool compatibility mode. Use --compat-libtool to enable libtool compatibility mode or --no-compat-libtool to disable it. The libtool compatibility mode is enabled by default. When libtool compatibility mode is enabled, lcov will assume that the source code relating to a .da file located in a directory named “.libs” can be found in its parent directory. If you have directories named “.libs” in your build environment but don’t use libtool, disable this option to prevent problems when capturing coverage data. 🫶
  • --config-file config-file — Specify a configuration file to use. See man lcovrc(5) for details of the file format and options. Also see the config_file entry in the same man page for details on how to include one config file into another. When this option is specified, neither the system-wide configuration file /etc/lcovrc, nor the per-user configuration file ~/.lcovrc is read. This option may be useful when there is a need to run several instances of lcov with different configuration file options in parallel. Note that this option must be specified in full — abbreviations are not supported. 🚫
  • --profile [profile-data-file] — Tell the tool to keep track of performance and other configuration data. If the optional profile-data-file is not specified, then the profile data is written to a file named with the same basename as the --output-filename, with suffix “.json” appended. Profile data is useful if you are trying to optimize the lcov implementation (see $LCOV_ROOT/share/lcov/support-scripts/spreadsheet.py), and can also enable faster --parallel execution (see the “--history-script” section of this man page). 🔥
  • --history-script callback — Use callback to predict current runtime cost using observed cost from prior execution. See man genhtml(1) for more information.
⚠️ Again for the people in the back: only one of -z, -c, -a, -e, -r, -l, --diff or --summary may be specified at a time.
  • -d directory, --directory directory — Use .da files in directory instead of kernel. If you want to work on coverage data for a user space program, use this option to specify the location where the program was compiled (that’s where the counter files ending with .da will be stored). Note that you may specify this option more than once. 📁
  • --exclude pattern — Exclude source files matching pattern. Use this switch if you want to exclude coverage data for a particular set of source files matching any of the given patterns. Multiple patterns can be specified by using multiple --exclude command line switches. The patterns will be interpreted as shell wildcard patterns (note that they may need to be escaped accordingly to prevent the shell from expanding them first). 🐚

Note: the pattern must be specified to match the absolute path of each source file. If you specify a pattern which does not seem to be correctly applied — files that you expected to be excluded still appear in the output — you can look for warning messages in the log file. lcov will emit a warning for every pattern which is not applied at least once.

Can be combined with the --include command line switch. If a given file matches both the include pattern and the exclude pattern, the exclude pattern will take precedence. 👑

  • --erase-functions regexp — Exclude coverage data from lines which fall within a function whose name matches the supplied regexp. Note that this is a mangled or demangled name, depending on whether the --demangle-cpp option is used or not. Note that this option requires that you use a gcc version which is new enough to support function begin/end line reports or that you configure the tool to derive the required data — see the derive_function_end_line discussion in man lcovrc(5). 🧠
  • --substitute regexp_pattern — Apply Perl regexp regexp_pattern to source file names found during processing. This is useful, for example, when the path name reported by gcov does not match your source layout and the file is not found, or in more complicated environments where the build directory structure does not match the source code layout or the layout in the project’s revision control system. 🌀

Use this option in situations where geninfo cannot find the correct path to source code files of a project. By providing a regexp_pattern in Perl regular expression format (see man perlre(1)), you can instruct geninfo to remove or change parts of the incorrect source path. Also see the --resolve-script option.

One or more --substitute patterns and/or a --resolve-script may be specified. When multiple patterns are specified, they are applied in the order specified, substitution patterns first followed by the resolve callback. The file search order is:

  1. Look for file name (unmodified). If the file exists: return it.
  2. Apply all substitution patterns in order — the result of the first pattern is used as the input of the second pattern, and so forth. If a file corresponding to the resulting name exists: return it.
  3. Apply the ‘resolve’ callback to the final result of pattern substitutions. If a file corresponding to the resulting name exists: return it.
  4. Otherwise: return original (unmodified) file name. Depending on context, the unresolved file name may or may not result in an error.

Substitutions are used in multiple contexts by lcov/genhtml/geninfo:

  • during --capture, applied to source file names found in gcov-generated coverage data files (see man gcov(1)).
  • during --capture, applied to alternate --build-dir paths, when looking for the .gcno (compile time) data file corresponding to some .gcda (runtime) data file.
  • applied to file names found in lcov data files (“.info” files) — e.g., during lcov data aggregation or HTML and text report generation. For example, substituted names are used to find source files for text-based filtering (see the --filter section, below) and are passed to --version-script, --annotate-script, and -criteria-script callbacks.
  • applied to file names found in the --diff-file passed to genhtml.

Example:

  1. When geninfo reports that it cannot find source file
  /path/to/src/.libs/file.c

but bestie the file is literally sitting in

/path/to/src/file.c

then you hit it with this parameter:

--substitute 's#/.libs##g'

which yeets every /.libs string out of the path. 💅

  1. Say geninfo is whining that it can't find the source file
/tmp/build/file.c

even though it's really chilling in

/usr/src/file.c

then use this parameter instead:

--substitute 's#/tmp/build#/usr/src#g'

and that swaps every /tmp/build string in the path over to /usr/src. slay. ✨

Patterns get applied after the directory separator in a name has been translated to this platform's, so if your pattern is meant to match input captured on the other platform, write it with the separator used here — e.g., --substitute 's#^C:/##' to remove a Windows drive letter. See cross_platform_read in lcovrc(5).

  • --omit-lines regexp — exclude coverage data from lines whose content matches regexp. 🚫

Use this switch if you want to exclude line and branch coverage data for some particular constructs in your code (e.g., some complicated macro). Multiple patterns can be specified by using multiple --omit-lines command line switches. The regexp will be interpreted as perl regular expressions (note that they may need to be escaped accordingly to prevent the shell from expanding them first). If you want the pattern to explicitly match from the start or end of the line, your regexp should start and/or end with ^ and/or $.

Ngl, the lcovrc config file setting lcov_excl_line = regexp is similar to --omit-lines.. --omit-lines is useful if there are multiple teams each of which want to exclude certain patterns. --omit-lines is additive and can be specified across multiple config files whereas each call to lcov_excl_line overrides the previous value — and thus teams must coordinate. 😭 (communication era, fr)
  • --external, --no-external — specify whether to capture coverage data for external source files. 🌍

External source files are files which are not located in one of the directories specified by --directory or --base-directory. Use --external to include coverpoints in external source files while capturing coverage data or --no-external to exclude them. If your --directory or --base-directory path contains a soft link, then actual target directory is not considered to be "internal" unless the --follow option is used.

The --no-external option is somewhat of a blunt instrument; the --exclude and --include options provide finer grained control over which coverage data is and is not included if your project structure is complex and/or --no-external does not do what you want.

Data for external source files is included by default.

  • --forget-test-names — if non-zero, ignore testcase names in .info file — i.e., treat all coverage data as if it came from the same testcase. This may improve performance and reduce memory consumption if user does not need per-testcase coverage summary in coverage reports. 🧠💨

This option can also be configured permanently using the configuration file option forget_testcase_names.

  • --prune-tests — determine list of unique tracefiles. ✂️

Use this option to determine a list of unique tracefiles from the list specified by --add-tracefile. A tracefile is considered to be unique if it is the only tracefile that:

  1. contains data for a specific source file
  2. contains data for a specific test case name
  3. contains non-zero coverage data for a specific line, function or branch
Note that the list of retained files may depend on the order they are processed. For example, if A and B contain identical coverage data, then the first one we see will be retained and the second will be pruned. The file processing order is nondeterministic when the --parallel option is used — implying that the pruned result may differ from one execution to the next in this case. 💀 (chaos, honestly)

--prune-tests must be specified together with --add-tracefile. When specified, lcov will emit the list of unique files rather than combined tracefile data.

  • --map-functions — list tracefiles with non-zero coverage for each function. 🗺️

Use this option to determine the list of tracefiles that contain non-zero coverage data for each function from the list of tracefiles specified by --add-tracefile.

This option must be specified together with --add-tracefile. When specified, lcov will emit the list of functions and associated tracefiles rather than combined tracefile data.

  • --context-script script — use script to collect additional tool execution context information — to aid in infrastructure debugging and/or tracking. 🔍

See the genhtml man page for more details on the context script.

  • --criteria-script script — use script to test for coverage acceptance criteria. ✅

See the genhtml man page for more details on the criteria script. Note that lcov does not keep track of date and owner information (see the --annotate-script entry in the genhtml man page) — so this information is not passed to the lcov callback.

  • --resolve-script script — use script to find the file path for some source file which appears in an input data file if the file is not found after applying --substitute patterns and searching the --source-directory list. This option is equivalent to the resolve_script config file option. See lcovrc(5) for details. 🧭
  • --version-script script — use script to get a source file's version ID from revision control when extracting data and to compare version IDs for the purpose of error checking when merging .info files. 🏷️

See the genhtml man page for more details on the version script.

  • --unreachable-script module — use module to decide whether particular branch expressions and/or MC/DC conditions should be removed from the coverage report. This option is equivalent to the unreachable_script config file option. See lcovrc(5) for details. 🫥
Note that "module" is required to be a Perl module. 🐪

See the genhtml man page for more details.

  • --comment comment_string — append comment_string to list of comments emitted into output result file. This option may be specified multiple times. Comments are printed at the top of the file, in the order they were specified. 💬

Comments may be useful to document the conditions under which the trace file was generated: host, date, environment, etc.

Note that this option has no effect for lcov operations which do not write an output result file: --list --summary, --prune-tests, and --map-functions.

See the geninfo man page for a description of the comment format in the result file.

  • -e tracefile pattern, --extract tracefile pattern — extract data from tracefile. 🎣

Use this switch if you want to extract coverage data for only a particular set of files from a tracefile. Additional command line parameters will be interpreted as shell wildcard patterns (note that they may need to be escaped accordingly to prevent the shell from expanding them first). Every file entry in tracefile which matches at least one of those patterns will be extracted.

Note: The pattern must be specified to match the absolute path of each source file. 📍

The result of the extract operation will be written to stdout or the tracefile specified with -o.

Only one of -z, -c, -a, -e, -r, -l, --diff or --summary may be specified at a time. (pick one, bestie, you can't have it all 💅)

  • -f, --follow — follow links when searching for .da files. 🔗
  • --large-file regexp — see the --large-file section of geninfo(1) for details. 🐘
  • --from-package package — use .da files in package instead of kernel or directory. 📦

Use this option if you have separate machines for build and test and want to perform the .info file creation on the build machine. See --to-package for more information.

  • --sort-input — specify whether to sort file names before capture and/or aggregation. Sorting reduces certain types of processing order-dependent output differences. See the sort_input section in lcovrc(5). 🔤
  • --gcov-tool tool — specify the location of the gcov tool. 🛠️

See the geninfo man page for more details.

  • -h, --help — print a short help text, then exit. 🙋‍♀️
  • --include pattern — include source files matching pattern. 💖

Use this switch if you want to include coverage data for only a particular set of source files matching any of the given patterns. Multiple patterns can be specified by using multiple --include command line switches. The patterns will be interpreted as shell wildcard patterns (note that they may need to be escaped accordingly to prevent the shell from expanding them first).

Note: The pattern must be specified to match the absolute path of each source file. 📍

If you specify a pattern which does not seem to be correctly applied — files that you expected to be included in the output do not appear — lcov will generate an error message of type 'unused'. See the --ignore-errors option for how to make lcov ignore the error or turn it into a warning. 🙈

  • --msg-log [log_file_name] — specify location to store error and warning messages (in addition to writing to STDERR). If log_file_name is not specified, then default location is used. 📝
  • --ignore-errors errors — specify a list of errors after which to continue processing. 🚧

Use this option to specify a list of one or more classes of errors after which lcov should continue processing instead of aborting. Note that the tool will generate a warning (rather than a fatal error) unless you ignore the error two (or more) times:

lcov ... --ignore-errors source,source ...

errors can be a comma-separated list of the following keywords:

  • branch — branch ID (2nd field in the .info file BRDA entry) does not follow expected integer sequence.
  • callback — Version script error.
  • child — child process returned non-zero exit code during --parallel execution. This typically indicates that the child encountered an error: see the log file immediately above this message. In contrast: the parallel error indicates an unexpected/unhandled exception in the child process — not a 'typical' lcov error.

okay so the message-type lore continues, and yes we’re still in --ignore-errors territory, bestie 💅 here’s the rest of the menu:

  • corrupt — corrupt/unreadable file found. 😭
  • count — an excessive number of messages of some class have been reported, so subsequent messages of that type will be suppressed. The limit is controlled by the max_message_count variable. See man lcovrc(5) (file://../man/lcovrc.5.html). 💅
  • deprecated — you are using a deprecated option. This option will be removed in an upcoming release, so you should change your scripts now. ⚠️
  • empty — the .info data file is empty (e.g., because all the code was ‘removed’ or excluded). 🫙
  • excessive — your coverage data contains a suspiciously large ‘hit’ count which is unlikely to be correct, possibly indicating a bug in your toolchain. See the excessive_count_threshold section in man lcovrc(5) (file://../man/lcovrc.5.html) for details. 🚩
  • fork — unable to create child process during --parallel execution. If the message is ignored (--ignore-errors fork), then genhtml will wait a brief period and then retry the failed execution. If you see continued errors, either turn off or reduce parallelism, set a memory limit, or find a larger server to run the task. 🍴
  • format — unexpected syntax or value found in .info file — for example, negative number or zero line number encountered. A count field which is not a legal integer (for example ‘nan’ or ‘inf’) is likewise treated as zero if this message is ignored; a count which is a number but not an integer is truncated toward zero, and one too large to store is saturated to 9223372036854775807 (0x7ffffffffffffff). 😵‍💫
  • gcov — the gcov tool returned with a non-zero return code. 💀
  • graph — the graph file could not be found or is corrupted. 🕸️
  • inconsistent — your coverage data is internally inconsistent: it makes two or more mutually exclusive claims. For example, some expression is marked as both an exception branch and not an exception branch. (See man genhtml(1) (file://../man/genhtml.1.html) for more details.) A warning of this type is also issued when, after all input data has been merged, some source file has data for two or more testcases but one of its coverage types has data for only some of them — for example, both testcases have line coverage data for the file, but only one of them has branch data. This usually means that the tracefiles being combined were captured with different coverage types enabled, and it means that the per-testcase tables for that file are not directly comparable. The message is issued once per source file per coverage type per testcase:
lcov: WARNING: (inconsistent) no branch data for testcase_name in path/to/file.c

The data is used as-is: no coverpoints are added or removed. 🫠

  • internal — internal tool issue detected. Please report this bug along with a testcase. 🐛
  • mismatch — inconsistent entries found in trace file:
    • branch expression (3rd field in the .info file ‘BRDA’ entry) of merge data does not match, or
    • function execution count (FNDA:…) but no function declaration (FN:…). 🧩
  • missing — file does not exist or is not readable. 🫥
  • negative — negative ‘hit’ count found. A negative count is not a legal value for any cover type, so if this message is ignored, the count is treated as zero. Note that negative counts may be caused by a known GCC bug — see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68080 — and try compiling with -fprofile-update=atomic. You will need to recompile, re-run your tests, and re-capture coverage data. 😬
  • package — a required perl package is not installed on your system. In some cases, it is possible to ignore this message and continue — however, certain features will be disabled in that case. 📦
  • parallel — various types of errors related to parallelism — i.e., a child process died due to an error. The corresponding error message appears in the log file immediately before the parallel error. If you see an error related to parallel execution that seems invalid, it may be a good idea to remove the --parallel flag and try again. If removing the flag leads to a different result, please report the issue (along with a testcase) so that the tool can be fixed. 🧵
  • parent — the parent process exited while child was active during --parallel execution. This happens when the parent has encountered a fatal error — e.g. an error in some other child which was not ignored. This child cannot continue working without its parent — and so will exit. 👋
  • range — coverage data refers to a line number which is larger than the number of lines in the source file. This can be caused by a version mismatch or by an issue in the gcov data. 📏
  • source — the source code file for a data set could not be found. 📄
  • unreachable — a coverpoint (line, branch, function, or MC/DC) within an “unreachable” region is executed (hit); either the code, directive placement, or both are wrong. If the error is ignored, the offending coverpoint is retained (not excluded) or not, depending on the value of the retain_unreachable_coverpoints_if_executed configuration parameter. See man lcovrc(5) (file://../man/lcovrc.5.html) and the “Exclusion markers” section of man geninfo(1) (file://../man/geninfo.1.html) for more information. 🚫
  • unsupported — the requested feature is not supported for this tool configuration. For example, function begin/end line range exclusions use some GCOV features that are not available in older GCC releases. 🙅‍♀️
  • unused — the include/exclude/erase/omit/substitute pattern did not match any file pathnames. 🫥
  • usage — unsupported usage detected — e.g. an unsupported option combination. 🧠
  • utility — a tool called during processing returned an error code (e.g., ‘find’ encountered an unreadable directory). 🔧
  • version — revision control IDs of the file which we are trying to merge are not the same — line numbering and other information may be incorrect. 🔢

Also see man lcovrc(5) (file://../man/lcovrc.5.html) for a discussion of the ‘max_message_count’ parameter which can be used to control the number of warnings which are emitted before all subsequent messages are suppressed. This can be used to reduce log file volume. 📉

  • --expect-message-count message_type:expr[,message_type:expr] — give lcov a constraint on the number of messages of one or more types which are expected to be produced during execution. If the constraint is not true, then generate an error of type “count” (see above). See man genhtml(1) (file://../man/genhtml.1.html) for more details about the flag, as well as the “expect_message_count” section in man lcovrc(5) (file://../man/lcovrc.5.html) for a description of the equivalent configuration file option. 🎯
  • --keep-going — do not stop if error occurs: attempt to generate a result, however flawed. This command line option corresponds to the stop_on_error [0|1] lcovrc option. See man lcovrc(5) (file://../man/lcovrc.5.html) for more details. 🚀
  • --preserve — preserve intermediate data files generated by various steps in the tool — e.g., for debugging. By default, these files are deleted. 🧺
  • --filter filters — specify a list of coverpoint filters to apply to input data. See the genhtml man page for details. 🫧
  • --demangle-cpp [param] — demangle C++ function names. See the genhtml man page for details. ✨
  • -i --initial — capture initial zero coverage data — i.e., from the compile-time ‘.gcno’ data files. Also see the --all flag, which tells the tool to capture both compile-time (‘.gcno’) and runtime (‘.gcda’) data at the same time. Run lcov with -c and this option on the directories containing .bb, .bbg or .gcno files before running any test case. The result is a “baseline” coverage data file that contains zero coverage for every instrumented line. Combine this data file (using lcov -a) with coverage data files captured after a test run to ensure that the percentage of total lines covered is correct even when not all source code files were loaded during the test. 🌱

Recommended procedure when capturing data for a test case:

  1. create baseline coverage data file
# lcov -c -i -d appdir -o app_base.info
  1. perform test
# appdir/test
  1. create test coverage data file
# lcov -c -d appdir -o app_test.info
  1. combine baseline and test coverage data
# lcov -a app_base.info -a app_test.info -o app_total.info

The above 4 steps are equivalent to

# lcov --capture --all -o app_total.info -d appdir

The combined compile- and runtime data will produce a different result than capturing runtime data alone if your project contains some compilation units which are not used in any of your testcase executables or shared libraries — that is, there are some ‘.gcno’ (compile time) data files that do not have matching ‘.gcda’ (runtime) data files. In that case, the runtime-only report will not contain any coverpoints from the unused files, whereas those coverpoints will appear (with all zero ‘hit’ counts) in the combined report. 🧠

The --initial flag is ignored except in --capture mode. The --all flag is ignored if the --initial flag is specified. 🫶

  • -k subdirectory --kernel-directory subdirectory — capture kernel coverage data only from subdirectory. Use this option if you don’t want to get coverage data for all of the kernel, but only for specific subdirectories. This option may be specified more than once. Note that you may need to specify the full path to the kernel subdirectory depending on the version of the kernel gcov support. 🐧
  • -l tracefile --list tracefile — list the contents of the tracefile. Only one of -z, -c, -a, -e, -r, -l, --diff or --summary may be specified at a time. 📋
  • --list-full-path --no-list-full-path — specify whether to show full paths during list operation. 🛣️

Okay bestie, real quick on the full-path situation before we keep going: use --list-full-path to show full paths during list operation, or --no-list-full-path to show shortened paths. Paths are shortened by default. ✨

  • --no-markers — use this if you want coverage data without regard to exclusion markers in the source code file. See geninfo(1) for details on exclusion markers. 🫶
  • --no-recursion — use this if you want coverage data for the specified directory only, without processing subdirectories. 💅
  • -o tracefile, --output-file tracefile — write data to tracefile instead of stdout.
    • Specify - as a filename to use the standard output.
    • By convention, lcov-generated coverage data files are called “tracefiles” and should have the filename extension .info. 🎀
  • -v, --verbose — increment informational message verbosity. This is mainly used for script and/or flow debugging — e.g., to figure out which data file are found, where. Also see the --quiet flag.
    • Messages are sent to stdout unless there is no output file (i.e., if the coverage data is written to stdout rather than to a file) and to stderr otherwise. 😭
  • -q, --quiet — decrement informational message verbosity.
    • Decreased verbosity will suppress ‘progress’ messages for example — while error and warning messages will continue to be printed. 💀
  • --debug — increment ‘debug messages’ verbosity. This is useful primarily to developers who want to enhance the lcov tool suite. 🧚
  • --parallel [integer], -j [integer] — specify parallelism to use during processing (maximum number of forked child processes). If the optional integer parallelism parameter is zero or is missing, then use to use up the number of cores on the machine. Default is to use a single process (no parallelism). 🔥
    • Also see the memory, memory_percentage, max_fork_fails and fork_fail_timeout entries in man lcovrc(5).
    • Parallelism is also used when reading coverage data: when several --add-tracefile files are named, each is read in its own child process — and when only one is named, that file is split at section boundaries and the pieces are read (and filtered) by several children at once. See the parallel_parse_min_lines and parallel_parse_chunks_per_worker entries in man lcovrc(5) for the size at which a single file is split, how many pieces are used, and the cases in which it is read serially anyway.
    • A previously generated execution profile may help to enable better utilization and faster parallel execution. See the “--profile” and “--history” sections of this man page. 👑
  • --memory integer — specify the maximum amount of memory to use during parallel processing, in Mb. Effectively, the process will not fork() if this limit would be exceeded. Default is 0 (zero) — which means that there is no limit. 🍓
    • This option may be useful if the compute farm environment imposes strict limits on resource utilization such that the job will be killed if it tries to use too many parallel children — but the user does now know a priori what the permissible maximum is. This option enables the tool to use maximum parallelism — up to the limit imposed by the memory restriction.
    • The configuration file memory_percentage option provided another way to set the maximum memory consumption. See man lcovrc(5) for details. 🌸
  • --rc keyword=value — override a configuration directive.
    • Use this option to specify a keyword=value statement which overrides the corresponding configuration statement in the lcovrc configuration file. You can specify this option more than once to override multiple configuration statements. See man lcovrc(5) for a list of available keywords and their meaning. ✨
  • -r tracefile pattern, --remove tracefile pattern — remove data from tracefile.
    • Use this switch if you want to remove coverage data for a particular set of files from a tracefile. Additional command line parameters will be interpreted as shell wildcard patterns (note that they may need to be escaped accordingly to prevent the shell from expanding them first). Every file entry in tracefile which matches at least one of those patterns will be removed.
    • Note: the pattern must be specified to match the absolute path of each source file. 🚨
    • The result of the remove operation will be written to stdout or the tracefile specified with -o.
    • Only one of -z, -c, -a, -e, -r, -l, --diff or --summary may be specified at a time. 💅
  • --summary tracefile — show summary coverage information for the specified tracefile.
    • Note that you may specify this option more than once.
    • Only one of -z, -c, -a, -e, -r, -l, --diff or --summary may be specified at a time. 🦋
  • --fail-under-branches percentage — tell lcov to exit with a status of 1 if the total branch coverage is less than percentage. 😭
  • --fail-under-lines percentage — tell lcov to exit with a status of 1 if the total line coverage is less than percentage. 😭
  • -t testname, --test-name testname — specify test name to be stored in the tracefile.
    • This name identifies a coverage data set when more than one data set is merged into a combined tracefile (see option -a).
    • Valid test names can consist of letters, decimal digits and the underscore character (_). 🎀
  • --to-package package — store .da files for later processing.
    • Use this option if you have separate machines for build and test and want to perform the .info file creation on the build machine. To do this, follow these steps:
      • On the test machine:
        • run the test
        • run lcov -c [-d directory] --to-package file
        • copy file to the build machine
      • On the build machine:
        • run lcov -c --from-package file [-o and other options]
    • This works for both kernel and user space coverage data. Note that you might have to specify the path to the build directory using -b with either --to-package or --from-package. Note also that the package data must be converted to a .info file before recompiling the program or it will become invalid. 🫶
  • --version — print version number, then exit. 👑
  • -z, --zerocounters — reset all execution counts to zero.
    • By default tries to reset kernel execution counts. Use the --directory option to reset all counters of a user space program.
    • Only one of -z, -c, -a, -e, -r, -l, --diff or --summary may be specified at a time. 💀
  • --tempdir dirname — write temporary and intermediate data under the indicated dirname. Default is the platform temporary directory: $TMPDIR, $TEMP or $TMP if one of them names a writeable directory, otherwise /tmp on Unix or C:\temp on Windows. 🍓
    • A uniquely named subdirectory of dirname is created for the run, and the data is written there — so several runs can share one dirname without colliding. dirname itself is created if it does not exist.
    • Unless --preserve is specified, the generated subdirectory and its contents are removed when lcov exits.
    • This option can also be configured permanently using the configuration file option lcov_tmp_dir. 🌈

🌸 FILES 🌸

  • /etc/lcovrc — the system-wide configuration file.
  • ~/.lcovrc — the per-user configuration file. 🎀

💖 AUTHOR 💖

  • Peter Oberparleiter Peter.Oberparleiter@de.ibm.com
  • Henry Cox henry.cox@mediatek.com — Filtering, error management, parallel execution sections. 🫶

🦋 SEE ALSO 🦋

2024-2026, LCOV Project

And that’s the whole page, bestie — this manual is from LCOV 2.6, dated 2026-10-03. Go forth and cover all the things! 💅✨

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