doc: add coverage instrumentation hint to libFuzzer quickstart #33536

1. 
   frankomosh commented at 3:57 pm on October 3, 2025: none

   This patch shows how to enable clang source-based coverage instrumentation in the libFuzzer quickstart section. No defaults are changed, and the addition is intended to be optional.

   Fixes silent “no .profraw file” confusion/error when trying to generate coverage data.

2. DrahtBot added the label Docs on Oct 3, 2025
3. 
   DrahtBot commented at 3:57 pm on October 3, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33536.

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   Concept NACK	janb84

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4. frankomosh marked this as ready for review on Oct 3, 2025
5. 
   janb84 commented at 9:47 am on October 6, 2025: contributor

   NACK Developer notes already has an extensive section on generating coverage. Maintaining the same documentation in 2 places is not ideal.
6. in doc/fuzzing.md:27 in 32c0e56c0a

   20@@ -21,6 +21,15 @@ See [further](#run-without-sanitizers-for-increased-throughput) for more informa
   21 There is also a runner script to execute all fuzz targets. Refer to
   22 `./build_fuzz/test/fuzz/test_runner.py --help` for more details.
   23 
   24+If you also want source-based coverage reports, append the instrumentation flags to `cmake --preset=libfuzzer`:
   25+
   26+```sh
   27+$ cmake --preset=libfuzzer \
   

   ---

   ---

   

   maflcko commented at 9:54 am on October 6, 2025:

   not sure about recommending libfuzzer here. It has issues properly counting runs, so coverage will be off. See also https://github.com/bitcoin/bitcoin/blob/a33bd767a37dccf39a094d03c2f62ea81633410f/contrib/devtools/deterministic-fuzz-coverage/src/main.rs#L111-L115

   ---

   

   frankomosh commented at 10:33 am on October 6, 2025:

   thanks. wasn’t aware of the run counting issues with LibFuzzer.

   So I guess the best approach is to build without the fuzzer sanitizer ?

7. 
   frankomosh commented at 10:34 am on October 6, 2025: none

   NACK Developer notes already has an extensive section on generating coverage. Maintaining the same documentation in 2 places is not ideal.

   ok . Would you atleast like to see a reference to the developer notes in this section(assume for someone who lands here first)?

8. 
   janb84 commented at 12:03 pm on October 6, 2025: contributor

   NACK Developer notes already has an extensive section on generating coverage. Maintaining the same documentation in 2 places is not ideal.

   ok . Would you atleast like to see a reference to the developer notes in this section(assume for someone who lands here first)?

   That would be better, imho (although the correct way would be to first read the contributing guide as a developer), but i can understand that one interested in fuzzing would only read the fuzzing readme before the contributing.md.

9. frankomosh force-pushed on Oct 8, 2025
10. doc: mention coverage build in quickstart section

    Points a reader to Developer Notes which explains to compile with llvm source based coverage instrumentation

    df1815e319
11. frankomosh force-pushed on Oct 8, 2025

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frankomosh DrahtBot janb84 maflcko

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