GCOV-TOOL(1)

📦
version 16.2.0 · 3 versions
, in arch rolling

💅 GCOV-TOOL(1) 💅

okay so this is the gcov-tool page from the GNU manual, section 1, and bestie you're gonna want a snack for this one because she is detailed. no cap. 🍓

✨ NAME ✨

gcov-tool — the offline gcda profile processing tool 🎀

✨ SYNOPSIS ✨


gcov-tool merge [merge-options] directory1 directory2
     [-o|--output directory]
     [-v|--verbose]
     [-w|--weight w1,w2]

gcov-tool merge-stream [merge-stream-options] [file]
     [-v|--verbose]
     [-w|--weight w1,w2]

gcov-tool rewrite [rewrite-options] directory
     [-n|--normalize long_long_value]
     [-o|--output directory]
     [-s|--scale float_or_simple-frac_value]
     [-v|--verbose]

gcov-tool overlap [overlap-options] directory1 directory2
     [-f|--function]
     [-F|--fullname]
     [-h|--hotonly]
     [-o|--object]
     [-t|--hot_threshold] float
     [-v|--verbose]

literally just vibes and flags, iykyk 😌

🌸 DESCRIPTION 🌸

gcov-tool is an offline tool that processes gcc's gcda profile files. she does not need the network, she does not need a compiler, she just sits there and handles profiles. main character energy fr. 👑

right now gcov-tool supports these functionalities:

  • merge two sets of profiles with weights.
  • read a stream of profiles with associated filenames and merge it with a set of profiles with weights.
  • read one set of profile and rewrite profile contents. one can scale or normalize the count values.

and here's where you'd actually use her:

  • collect the profiles for different set of inputs, and use this tool to merge them. one can specify the weight to factor in the relative importance of each input. 🫶
  • collect profiles from target systems without a filesystem (freestanding environments). merge the collected profiles with associated profiles present on the host system. one can specify the weight to factor in the relative importance of each input.
  • rewrite the profile after removing a subset of the gcda files, while maintaining the consistency of the summary and the histogram. iconique. ✨
  • it can also be used to debug or libgcov code as the tools shares the majority code as the runtime library.
🚨 heads up bestie: for the merging operation, this profile generated offline may contain slight different values from the online merged profile. so don't come for her when the numbers don't line up perfectly, okay?

here's a list of typical differences, and yes i'm listing all of them:

  • histogram difference: this offline tool recomputes the histogram after merging the counters. the resulting histogram, therefore, is precise. the online merging does not have this capability -- the histogram is merged from two histograms and the result is an approximation. so like, ours is the accurate one 💅
  • summary checksum difference: summary checksum uses a CRC32 operation. the value depends on the link list order of gcov-info objects. this order is different in gcov-tool from that in the online merge. it's expected to have different summary checksums. it does not really matter as the compiler does not use this checksum anywhere. so breathe, it's giving harmless. 🌈
  • value profile counter values difference: some counter values for value profile are runtime dependent, like heap addresses. it's normal to see some difference in these kind of counters. totally expected, no drama. 😭

💖 OPTIONS 💖

okay this is the part where we go through every single one of them. buckle up. 🎢

  • -h, --help — display help about using gcov-tool (on the standard output), and exit without doing any further processing. she tells you what's up and then she leaves. queen behavior.
  • -v, --version — display the gcov-tool version number (on the standard output), and exit without doing any further processing. same energy, different info.

🦋 merge

merge two profile directories. two profiles walk in, one profile walks out.

  • -o directory, --output directory — set the output profile directory. the default output directory name is merged_profile. (yes that's the default, don't @ me)
  • -v, --verbose — set the verbose mode. she gets chatty. 🗣️
  • -w w1,w2, --weight w1,w2 — set the merge weights of the directory1 and directory2, respectively. the default weights are 1 for both. so like, equal importance unless you say otherwise ⚖️

🧚 merge-stream

collect profiles with associated filenames from a gcfn and gcda data stream. read the stream from the file specified by file or from stdin. merge the profiles with associated profiles in the host filesystem. apply the optional weights while merging profiles. whew, that was a lot, but she ate. 🔥

for the generation of a gcfn and gcda data stream on the target system, please have a look at the __gcov_filename_to_gcfn() and __gcov_info_to_gcda() functions declared in #include <gcov.h>. go read them, i'll wait 💜

  • -v, --verbose — set the verbose mode. (again. she loves to talk.)
  • -w w1,w2, --weight w1,w2 — set the merge weights of the profiles from the gcfn and gcda data stream and the associated profiles in the host filesystem, respectively. the default weights are 1 for both. two things, two weights, in that order, pls don't mix them up 🙈

⭐ rewrite

read the specified profile directory and rewrite to a new directory. glow-up for your profile data. 💅✨

  • -n long_long_value, --normalize <long_long_value> — normalize the profile. the specified value is the max counter value in the new profile.
  • -o directory, --output directory — set the output profile directory. default output name is rewrite_profile. that's the default, fr fr.
  • -s float_or_simple-frac_value, --scale float_or_simple-frac_value — scale the profile counters. the specified value can be in floating point value, or simple fraction value form, such 1, 2, 2/3, and 5/3. yes she accepts fractions, she's flexible like that 🎀
  • -v, --verbose — set the verbose mode. (third time's the charm)

👑 overlap

compute the overlap score between the two specified profile directories. the overlap score is computed based on the arc profiles. it is defined as the sum of min (p1_counter[i] / p1_sum_all, p2_counter[i] / p2_sum_all), for all arc counter i, where p1_counter[i] and p2_counter[i] are two matched counters and p1_sum_all and p2_sum_all are the sum of counter values in profile 1 and profile 2, respectively.

that's the math. i don't make the rules, i just write them down accurately. 🧮

  • -f, --function — print function level overlap score.
  • -F, --fullname — print full gcda filename.
  • -h, --hotonly — only print info for hot objects/functions. 🔥 (note: here -h means hotonly, not help — stay woke)
  • -o, --object — print object level overlap score.
  • -t float, --hot_threshold <float> — set the threshold for hot counter value.
  • -v, --verbose — set the verbose mode. (you knew this was coming)

🌈 SEE ALSO 🌈

gpl(7), gfdl(7), fsf-funding(7), gcc(1), gcov(1) and the Info entry for gcc. go read the whole friend group 💖

Copyright (c) 2014-2026 Free Software Foundation, Inc.

permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being "GNU General Public License" and "Funding Free Software", the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). a copy of the license is included in the gfdl(7) man page.

(a) The FSF's Front-Cover Text is:

     A GNU Manual

(b) The FSF's Back-Cover Text is:

     You have freedom to copy and modify this GNU Manual, like GNU
     software.  Copies published by the Free Software Foundation raise
     funds for GNU development.

and that's the whole page, bestie 🫶 this lil masterpiece is from gcc-16.2.0, dated 2026-08-07 — go forth and merge your profiles responsibly 💜🌸✨

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