LLVM-COV(1)

📦
version 14.0.6 · 8 versions
, in ubuntu questing

💖 LLVM-COV(1) — the LLVM manual, section 1 💖

okay bestie, sit down, hydrate, and let me tell you about llvm-cov, because this tool is actually iconic and you're gonna need it.

✨ NAME ✨

llvm-cov — emit coverage information

like, it tells you which lines of your code actually ran. main character energy fr.

🌸 SYNOPSIS 🌸

llvm-cov command [args…]

🦋 DESCRIPTION 🦋

The llvm-cov tool shows code coverage information for programs that are instrumented to emit profile data. no cap, that's the whole vibe. It can be used to work with gcov-style coverage, or with clang's instrumentation based profiling. two lanes, pick your fave.

okay so here's the little plot twist: if the program is invoked with a base name of gcov, it will behave as if the llvm-cov gcov command were called. otherwise, you gotta provide a command. she's not gonna guess, bestie, you have to tell her what you want.

👑 COMMANDS 👑

  • gcov
  • show
  • report
  • export

🎀 GCOV COMMAND 🎀

SYNOPSIS

llvm-cov gcov [options] SOURCEFILE

DESCRIPTION

The llvm-cov gcov tool reads code coverage data files and displays the coverage information for a specified source file. It is compatible with the gcov tool from version 4.2 of GCC, and may also be compatible with some later versions of gcov. so like… it speaks gcov. periodt.

To use llvm-cov gcov, you must first build an instrumented version of your application that collects coverage data as it runs. Compile with the -fprofile-arcs and -ftest-coverage options to add the instrumentation. (Alternatively, you can use the --coverage option, which includes both of those other options — a little two-for-one deal, we love.)

At the time you compile the instrumented code, a .gcno data file will be generated for each object file. These .gcno files contain half of the coverage data. The other half of the data comes from .gcda files that are generated when you run the instrumented program, with a separate .gcda file for each object file. Each time you run the program, the execution counts are summed into any existing .gcda files, so be sure to remove any old files if you do not want their contents to be included. 🚨 yes this is a real warning, the numbers pile up, it's giving "why is my count so high" and the answer is your dusty old .gcda from last tuesday.

By default, the .gcda files are written into the same directory as the object files, but you can override that by setting the GCOV_PREFIX and GCOV_PREFIX_STRIP environment variables. The GCOV_PREFIX_STRIP variable specifies a number of directory components to be removed from the start of the absolute path to the object file directory. After stripping those directories, the prefix from the GCOV_PREFIX variable is added. These environment variables allow you to run the instrumented program on a machine where the original object file directories are not accessible, but you will then need to copy the .gcda files back to the object file directories where llvm-cov gcov expects to find them. it's a little bit of a fetch quest, ngl, but you got this 🫶

Once you have generated the coverage data files, run llvm-cov gcov for each main source file where you want to examine the coverage results. This should be run from the same directory where you previously ran the compiler. The results for the specified source file are written to a file named by appending a .gcov suffix. A separate output file is also created for each file included by the main source file, also with a .gcov suffix added. one for you, one for every header you dragged into this. so generous.

The basic content of an .gcov output file is a copy of the source file with an execution count and line number prepended to every line. The execution count is shown as - if a line does not contain any executable code. If a line contains code but that code was never executed, the count is displayed as #####. 💀 that's the "girl, nobody ran this" marker.

OPTIONS

  • -a, --all-blocks — Display all basic blocks. If there are multiple blocks for a single line of source code, this option causes llvm-cov to show the count for each block instead of just one count for the entire line. per-block receipts, as she deserves.
  • -b, --branch-probabilities — Display conditional branch probabilities and a summary of branch information.
  • -c, --branch-counts — Display branch counts instead of probabilities (requires -b). note the parenthetical bestie, -b is mandatory here.
  • -m, --demangled-names — Demangle function names. because nobody wants to read mangled symbols at 2am.
  • -f, --function-summaries — Show a summary of coverage for each function instead of just one summary for an entire source file.
  • --help — Display available options (--help-hidden for more).
  • -l, --long-file-names — For coverage output of files included from the main source file, add the main file name followed by ## as a prefix to the output file names. This can be combined with the --preserve-paths option to use complete paths for both the main file and the included file. combo move ✨
  • -n, --no-output — Do not output any .gcov files. Summary information is still displayed. like, no files, but she still tells you the tea.
  • -o=<DIR|FILE>, --object-directory=<DIR>, --object-file=<FILE> — Find objects in DIR or based on FILE's path. If you specify a particular object file, the coverage data files are expected to have the same base name with .gcno and .gcda extensions. If you specify a directory, the files are expected in that directory with the same base name as the source file.
  • -p, --preserve-paths — Preserve path components when naming the coverage output files. In addition to the source file name, include the directories from the path to that file. The directories are separate by # characters, with . directories removed and .. directories replaced by ^ characters. When used with the --long-file-names option, this applies to both the main file name and the included file name.
  • -r — Only dump files with relative paths or absolute paths with the prefix specified by -s.
  • -s=<string> — Source prefix to elide.
  • -t, --stdout — Print to stdout instead of producing .gcov files. screen-only, no file crumbs 🧚
  • -u, --unconditional-branches — Include unconditional branches in the output for the --branch-probabilities option.
  • -version — Display the version of llvm-cov.
  • -x, --hash-filenames — Use md5 hash of file name when naming the coverage output files. The source file name will be suffixed by ## followed by MD5 hash calculated for it.

EXIT STATUS

llvm-cov gcov returns 1 if it cannot read input files. Otherwise, it exits with zero.

so 1 = couldn't read your files, 0 = we're so back. simple as that 💅

to be continued, bestie…

✨ SHOW COMMAND ✨

💖 SYNOPSIS 💖

llvm-cov show [options] -instr-profile PROFILE BIN [-object BIN,…]
[[-object BIN]] [SOURCES]

🌸 DESCRIPTION 🌸

Okay so llvm-cov show is the one that shows you line-by-line coverage of the binaries BIN,… using the profile data PROFILE. Bestie, you can optionally filter it so it only shows coverage for the files listed in SOURCES. Chef's kiss. 👑

And like, BIN can be a whole executable, an object file, a dynamic library, or an archive (thin or otherwise). All of them are valid, no cap.

So here's the tea on how to actually use it: you need a program compiled with instrumentation that emits profile and coverage data. To build such a program with clang, use the -fprofile-instr-generate and -fcoverage-mapping flags. And if you're linking with the clang driver, pass -fprofile-instr-generate to the link stage too, so the necessary runtime libraries actually get linked in. Don't skip that part, fr. 💅

The coverage information lives inside the built executable or library itself, and THAT is what you pass to llvm-cov show as a BIN argument. The profile data comes from running this instrumented program normally. When the program exits it writes out a raw profile file — typically called default.profraw — and you can convert that into a format suitable for the PROFILE argument using the llvm-profdata merge tool. 🦋

🎀 OPTIONS 🎀

  • -show-branches=<VIEW> — Shows coverage for branch conditions, either as a count or as a percentage. The supported views are: “count”, “percent”. ✨
  • -show-line-counts — Shows the execution counts for each line. Defaults to true, unless another -show option is used.
  • -show-expansions — Expands inclusions (like preprocessor macros or textual inclusions) inline in the display of the source file. Defaults to false.
  • -show-instantiations — For source regions that get instantiated multiple times (like C++ templates, iykyk), shows each instantiation separately and the combined summary. Defaults to true.
  • -show-regions — Shows the execution counts for each region by displaying a caret that points to the character where the region starts. Defaults to false.
  • -show-line-counts-or-regions — Shows execution counts for each line if there's only one region on that line, but shows the individual regions if there are multiple on the line. Defaults to false.
  • -use-color — Enable or disable color output. By default this is autodetected.
  • -arch=[*NAMES*] — Specify a list of architectures such that the Nth entry in the list corresponds to the Nth specified binary. If the covered object is a universal binary, this specifies the architecture to use. It is an error to specify an architecture that is not included in the universal binary, or to use an architecture that does not match a non-universal binary. 🚨
  • -name=<NAME> — Show code coverage only for functions with the given name.
  • -name-allowlist=<FILE> — Show code coverage only for functions listed in the given file. Each line in the file should start with allowlist_fun:, immediately followed by the name of the function to accept. This name can be a wildcard expression.
  • -name-whitelist=<FILE> — Show code coverage only for functions listed in the given file. Each line in the file should start with whitelist_fun:, immediately followed by the name of the function to accept. This name can be a wildcard expression. This option will be deprecated for -name-allowlist=<FILE> in future releases. 🙈
  • -name-regex=<PATTERN> — Show code coverage only for functions that match the given regular expression.
  • -ignore-filename-regex=<PATTERN> — Skip source code files with file paths that match the given regular expression.
  • -format=<FORMAT> — Use the specified output format. The supported formats are: “text”, “html”.
  • -tab-size=<TABSIZE> — Replace tabs with <TABSIZE> spaces when preparing reports. Currently, this is only supported for the html format.
  • -output-dir=PATH — Specify a directory to write coverage reports into. If the directory does not exist, it is created. When used in function view mode (i.e when -name or -name-regex are used to select specific functions), the report is written to PATH/functions.EXTENSION. When used in file view mode, a report for each file is written to PATH/REL_PATH_TO_FILE.EXTENSION.
  • -Xdemangler=<TOOL>|<TOOL-OPTION> — Specify a symbol demangler. This can be used to make reports more human-readable. This option can be specified multiple times to supply arguments to the demangler (e.g -Xdemangler c++filt -Xdemangler -n for C++). The demangler is expected to read a newline-separated list of symbols from stdin and write a newline-separated list of the same length to stdout. 🧚
  • -num-threads=N, -j=N — Use N threads to write file reports (only applicable when -output-dir is specified). When N=0, llvm-cov auto-detects an appropriate number of threads to use. This is the default.
  • -compilation-dir=<dir> — Directory used as a base for relative coverage mapping paths. Only applicable when binaries have been compiled with one of -fcoverage-prefix-map, -fcoverage-compilation-dir, or -ffile-compilation-dir.
  • -line-coverage-gt=<N> — Show code coverage only for functions with line coverage greater than the given threshold.
  • -line-coverage-lt=<N> — Show code coverage only for functions with line coverage less than the given threshold.
  • -region-coverage-gt=<N> — Show code coverage only for functions with region coverage greater than the given threshold.
  • -region-coverage-lt=<N> — Show code coverage only for functions with region coverage less than the given threshold.
  • -path-equivalence=<from>,<to> — Map the paths in the coverage data to local source file paths. This lets you generate the coverage data on one machine, and then use llvm-cov on a different machine where you have the same files on a different path. 🌈

📊 REPORT COMMAND 📊

💜 SYNOPSIS 💜

llvm-cov report [options] -instr-profile PROFILE BIN [-object BIN,…]
[[-object BIN]] [SOURCES]

🌟 DESCRIPTION 🌟

The llvm-cov report command displays a summary of the coverage of the binaries BIN,… using the profile data PROFILE. And yes, it can optionally be filtered to only show the coverage for the files listed in SOURCES. 💖

BIN may be an executable, object file, dynamic library, or archive (thin or otherwise). Same deal as before, bestie.

If no source files are provided, a summary line is printed for each file in the coverage data. If any files are provided, summaries can be shown for each function in the listed files — but only if the -show-functions option is enabled. ⭐

For information on compiling programs for coverage and generating profile data, see SHOW COMMAND.

🍓 OPTIONS 🍓

  • -use-color[=VALUE] — Enable or disable color output. By default this is autodetected.
  • -arch=<name> — If the covered binary is a universal binary, select the architecture to use. It is an error to specify an architecture that is not included in the universal binary, or to use an architecture that does not match a non-universal binary. 🚨
  • -show-region-summary — Show statistics for all regions. Defaults to true.
  • -show-branch-summary — Show statistics for all branch conditions. Defaults to true.
  • -show-functions — Show coverage summaries for each function. Defaults to false.
  • -show-instantiation-summary — Show statistics for all function instantiations. Defaults to false.
  • -ignore-filename-regex=<PATTERN> — Skip source code files with file paths that match the given regular expression.
  • -compilation-dir=<dir> — Directory used as a base for relative coverage mapping paths. Only applicable when binaries have been compiled with one of -fcoverage-prefix-map, -fcoverage-compilation-dir, or -ffile-compilation-dir.

🔥 EXPORT COMMAND 🔥

💅 SYNOPSIS 💅

llvm-cov export [options] -instr-profile PROFILE BIN [-object BIN,…]
[[-object BIN]] [SOURCES]

🦋 DESCRIPTION 🦋

The llvm-cov export command exports coverage data of the binaries BIN,… using the profile data PROFILE, in either JSON or lcov trace file format. Pick your fighter. ✨

When exporting JSON, the regions, functions, branches, expansions, and summaries of the coverage data will be exported. When exporting an lcov trace file, the line-based coverage, branch coverage, and summaries will be exported. Both are giving data. 👑

The exported data can optionally be filtered to only export the coverage for the files listed in SOURCES.

For information on compiling programs for coverage and generating profile data, see SHOW COMMAND.

🌸 OPTIONS 🌸

  • -arch=<name> — If the covered binary is a universal binary, select the architecture to use. It is an error to specify an architecture that is not included in the universal binary, or to use an architecture that does not match a non-universal binary. 🚨
  • -format=<FORMAT> — Use the specified output format. The supported formats are: “text” (JSON), “lcov”.
  • -summary-only — Export only summary information for each file in the coverage data. This mode will not export coverage information for smaller units such as individual functions or regions. The result will contain the same information as produced by the llvm-cov report command, but presented in JSON or lcov format rather than text.
  • -ignore-filename-regex=<PATTERN> — Skip source code files with file paths that match the given regular expression.
  • -skip-expansions — Skip exporting macro expansion coverage data.
  • -skip-functions — Skip exporting per-function coverage data.
  • -num-threads=N, -j=N — Use N threads to export coverage data. When N=0, llvm-cov auto-detects an appropriate number of threads to use. This is the default.
  • -compilation-dir=<dir> — Directory used as a base for relative coverage mapping paths. Only applicable when binaries have been compiled with one of -fcoverage-prefix-map, -fcoverage-compilation-dir, or -ffile-compilation-dir.

👑 AUTHOR 👑

Maintained by the LLVM Team (https://llvm.org/). Shoutout to the whole squad. 🫶

2003-2025, LLVM Project

And that's a wrap on the whole page, bestie!! This was LLVM-COV(1), the 14th of May 2025 edition — yeah, dated 2025-05-22, slay. Go run your coverage, you've got this. 💜✨🎀
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