fuzz: doc: add info about afl-system-config for macOS #32175

1. 
   brunoerg commented at 4:17 pm on March 31, 2025: contributor

   afl-system-config adjusts the shared memory segment size limits and configures kernel parameters for better fuzzing performance. Since macOS has more conservative values on shared memory, it’s necessary to run afl-system-config, or manually adjust the values to fuzz with AFL++.

   e.g.:

   0kern.sysv.shmmax: 524288000
   1kern.sysv.shmmin: 1
   2kern.sysv.shmseg: 48
   3kern.sysv.shmall: 131072000
   

2. 
   DrahtBot commented at 4:17 pm on March 31, 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/32175.

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   Type	Reviewers
   ACK	janb84, w0xlt, Crypt-iQ

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3. DrahtBot added the label Tests on Mar 31, 2025
4. in doc/fuzzing.md:190 in 66572c2745 outdated

   186@@ -187,6 +187,8 @@ $ cmake -B build_fuzz \
   187 $ cmake --build build_fuzz
   188 # For macOS you may need to ignore x86 compilation checks when running "cmake --build". If so,
   189 # try compiling using: AFL_NO_X86=1 cmake --build build_fuzz
   190+# Also, it might be required to run afl-system-config to adjust the shared
   

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   janb84 commented at 5:59 pm on April 14, 2025:

   0# Also, it might be required to run "afl-system-config" to adjust the shared
   

   Small nit, to keep it in the same style as line 188

   ---

   

   brunoerg commented at 5:56 pm on April 28, 2025:

   Done. Thanks.
5. 
   janb84 commented at 6:02 pm on April 14, 2025: contributor

   Concept ACK 66572c2

   Small style NIT, to keep the comment in the same style as 2 lines before. Not blocking.

   Overall small addition to the documentation, provides extra valuable information, looks good to me.

6. brunoerg force-pushed on Apr 28, 2025
7. 
   brunoerg commented at 5:56 pm on April 28, 2025: contributor

   Pushed 66572c27454e1464173dc318d62fdfc11d4b7832..6e026606f368d8d1139b266c382076685e76d0b2 to address #32175 (review)
8. 
   janb84 commented at 6:04 pm on April 28, 2025: contributor

   re ACK 6e02660

   Changes sinds last ACK:

   • Minor style change in comments to align with rest of comment style.
9. DrahtBot added the label CI failed on Apr 29, 2025
10. fuzz: doc: add info about `afl-system-config` for macOS 61ea5f348d
11. brunoerg force-pushed on Apr 29, 2025
12. DrahtBot removed the label CI failed on Apr 29, 2025
13. 
    janb84 commented at 6:21 pm on April 29, 2025: contributor

    reACK 61ea5f3

    Changes since last ACK:

    • none, CI related push
14. 
    w0xlt commented at 11:13 pm on May 8, 2025: contributor

    ACK https://github.com/bitcoin/bitcoin/pull/32175/commits/61ea5f348da71b886807c0492587835dd7e57499

    Good clarification.

15. 
    Crypt-iQ commented at 8:57 pm on May 21, 2025: contributor

    ACK 61ea5f3

    I noticed that a couple lines above, the link to “selecting the best AFL compiler…” is invalid and has instead moved to https://github.com/AFLplusplus/AFLplusplus/blob/stable/docs/fuzzing_in_depth.md#a-selecting-the-best-afl-compiler-for-instrumenting-the-target. I can open a PR to fix the doc link.

16. 
    brunoerg commented at 12:51 pm on May 22, 2025: contributor

    I noticed that a couple lines above, the link to “selecting the best AFL compiler…” is invalid and has instead moved to https://github.com/AFLplusplus/AFLplusplus/blob/stable/docs/fuzzing_in_depth.md#a-selecting-the-best-afl-compiler-for-instrumenting-the-target. I can open a PR to fix the doc link.

    Cool, go ahead.

17. 
    brunoerg commented at 11:41 am on June 13, 2025: contributor

    rfm?
18. 
    fanquake commented at 12:59 pm on June 13, 2025: member

    I think we just need to make sure we don’t start recreating all the AFL docs, in our own docs, especially not for macOS, given fuzzing is not well supported/seems to be constantly having issues there. IIRC the note about afl-system-config is also output by afl itself, so it’s not clear that repeating it here is needed?
19. fanquake merged this on Jun 13, 2025
20. fanquake closed this on Jun 13, 2025

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Contributors
brunoerg DrahtBot janb84 w0xlt Crypt-iQ fanquake

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