LLVM2LCOV(1)

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version 2.6 · 2 versions
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💅 LLVM2LCOV(1) — the LCOV tools girlies ✨

okay so first things first, this is a page from the LCOV Tools manual group, and it lives in Manual section 1. The tool itself is llvm2lcov, and if you only remember one thing about it, remember this: it translates LLVM coverage data from llvm-cov profdata into LCOV format. that's the whole vibe. 🎀

🌸 NAME 🌸

llvm2lcov — literally just the docs for llvm2lcov, bestie. and like, what does it do? it translates LLVM coverage data from llvm-cov profdata to LCOV format. iconic behavior honestly. 👑

✨ SYNOPSIS ✨

llvm2lcov [--output filename] [--testname name] [options] json_file [json_file ...]

🦋 DESCRIPTION 🦋

so llvm2lcov goes wandering through your C/C++ coverage data in JSON format (the kind that comes out of llvm-cov export -format=text ...) and translates all of it into LCOV .info format. slay. that's the job. 💖

okay but real talk, heads up: LLVM has two coverage data collection paths, and they are not the same thing, no cap:

  • the one this page is about — the profile data path
  • a gcov path — basically the same kind of thing gcc supports

if you wanna know more about the gcov support in LLVM, go check the LLVM documentation. iykyk. 📚

🌈 MC/DC COVERAGE 🌈

want MC/DC data? bet. here's the recipe:

  • Use LLVM 18 or newer (LLVM 21+ recommended for cleaner MC/DC data) — newer is giving cleaner vibes, trust.
  • Enable MC/DC instrumentation in your compile/link steps with -fcoverage-mcdc
  • Pass the --mcdc-coverage flag to llvm2lcov
⚠️ also important: LLVM does not support MC/DC metrics when using the gcov data collection path. so don't try it. it's not happening. 💀

🧚 OPTIONS 🧚

on top of all the common options the other tools in the LCOV suite support (think --comment, --version-script, --ignore-error, --substitute, --exclude, etc. — you know the ones), this tool also serves these:

  • --output filename, -o filename — your LCOV data gets written to the file you name here. skip this option and it'll just drop it in llvm2lcov.info in whatever your current directory is. default behavior, cute. 🍓
  • --testname name, -t name — associates your coverage info with the testcase name you give it. and honestly? it's not necessary to provide a name. no pressure bestie, optional. 💜
  • --branch-coverage — include branch coverage data in the output. go off. 🌿
  • --mcdc-coverage — include MC/DC data in the output. requires LLVM 18 or higher, with MC/DC instrumentation enabled during compilation. don't forget that part. 🔥

for the deets on the other options and configuration settings, go look at lcov(1) and lcovrc(5). they got you. 🫶

⭐ EXAMPLES ⭐

basic workflow — the full glow-up pipeline:

# Compile with coverage instrumentation (including MC/DC)
$ clang++ -o myExe -fprofile-inst-generate -fcoverage-mapping \
    -fcoverage-mcdc myCode.cpp

# Run your testcases
$ ./myExe ...

# Convert profile data
$ llvm-profdata merge -o myExe.profdata --sparse *.profraw

# Export coverage data in JSON format
$ llvm-cov export -format=text -instr-profile=myExe.profdata \
    ./myExe > myExe.json

# Convert to LCOV format
$ llvm2lcov --output myExe.info --test-name myTestcase \
    --mcdc-coverage --branch-coverage myExe.json ...

# Generate HTML coverage report
$ genhtml -o html_report myExe.info ...

(those ... are just other tool options you might be using — like for filtering and exclusion. not me forgetting them, they're literally placeholders 💅)

and doing the same example via gcov? it looks like this:

# Compile with gcov instrumentation
$ clang++ -o myExe --coverage myCode.cpp

# Run your testcases
$ ./myExe ...

# Convert to LCOV format
#   Note that the '--gcov-tool' option appears *twice*: once to name
#   the tool and once to pass a tool option.  See the lcov man page
#   for more information.
$ lcov --capture -d . --branch-coverage -o myExe.info --gcov-tool llvm-cov --gcov-tool gcov ...

# Generate HTML coverage report
$ genhtml -o html_report myExe.info ...
👀 yes, --gcov-tool shows up twice — once to name the tool and once to pass a tool option. that's not a typo, that's the assignment. the lcov man page has more if you need it.

💖 AUTHOR 💖

Henry Cox <<henry.cox@mediatek.com>> — the main character who wrote this. we stan. 👑

🔥 SEE ALSO 🔥

Copyright 2024-2026, LCOV Project. all rights reserved, respectfully. 💜

and that's the whole page bestie ✨ this was version 2.6, dated 2026-10-03, and yes it's the LLVM2LCOV(1) page — go forth and get those coverage numbers up, you absolute legend 🦋

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