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I'm mindful of CI availability and note this adds three slow, ~23-28 minute jobs:

Is there any caching that can be used to speed them up?

Should we restrict these jobs to only trigger when C files change, and not Python/other support files?

And, if we've already run this on PRs, do we also need to run on main after merge?

And, if we've already run this on PRs, do we also need to run on main after merge?

I'd second this, especially if given OSS Fuzz's runs (per the comment at the top of the new job).

A

I'm mindful of CI availability and note this adds three slow, ~23-28 minute jobs:

Is there any caching that can be used to speed them up?

I agree, but it seems that CIFuzz does not support any settings for caching and Python compilation happens in its Docker containers.

There is a fuzz-seconds: 600 setting, I used the default (and the recommended minimum) 10-minute value because it makes the tests run for roughly the same amount of time as "Windows (x86)".

Should we restrict these jobs to only trigger when C files change, and not Python/other support files?

This sounds like a good idea!

And, if we've already run this on PRs, do we also need to run on main after merge?

Running on PR updates should be enough.

I don't understand well which Python is tested. Does the job builds Python and run the fuzzer on the freshly built Python?

CIFuzz (address) pass but it see a log with an error:

=================================================================
==83==ERROR: AddressSanitizer: ABRT on unknown address 0x000000000053 (pc 0x7f4f5cf8600b bp 0x7fffccb9f100 sp 0x7fffccb9ee80 T0)
SCARINESS: 10 (signal)
    #0 0x7f4f5cf8600b in raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b) (BuildId: 1878e6b475720c7c51969e69ab2d276fae6d1dee)
    #1 0x7f4f5cf65858 in abort (/lib/x86_64-linux-gnu/libc.so.6+0x22858) (BuildId: 1878e6b475720c7c51969e69ab2d276fae6d1dee)
    #2 0x586744 in LLVMFuzzerTestOneInput /src/cpython3/Modules/_xxtestfuzz/fuzzer.c
    #3 0x4578d3 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:611:15
    #4 0x4570ba in fuzzer::Fuzzer::RunOne(unsigned char const*, unsigned long, bool, fuzzer::InputInfo*, bool, bool*) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:514:3
    #5 0x458f24 in fuzzer::Fuzzer::ReadAndExecuteSeedCorpora(std::__Fuzzer::vector<fuzzer::SizedFile, std::__Fuzzer::allocator<fuzzer::SizedFile> >&) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:826:7
    #6 0x459159 in fuzzer::Fuzzer::Loop(std::__Fuzzer::vector<fuzzer::SizedFile, std::__Fuzzer::allocator<fuzzer::SizedFile> >&) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:857:3
    #7 0x4487bf in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerDriver.cpp:912:6
    #8 0x471e12 in main /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerMain.cpp:20:10
    #9 0x7f4f5cf67082 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24082) (BuildId: 1878e6b475720c7c51969e69ab2d276fae6d1dee)
    #10 0x4391fd in _start (build-out/fuzz_ast_literal_eval+0x4391fd)

DEDUP_TOKEN: raise--abort--LLVMFuzzerTestOneInput
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: ABRT (/lib/x86_64-linux-gnu/libc.so.6+0x4300b) (BuildId: 1878e6b475720c7c51969e69ab2d276fae6d1dee) in raise
==83==ABORTING

@vstinner please check "How it works".

It builds CPython from the source at a particular pull request, and it does not report crashes that occurred on older OSS-Fuzz builds. You can find that particular error in the list of known issues here.

Could CIFuzz be run as a buildbot instead of on CI? There's been a concerted effort to reduce CI times as of late, and I do worry that this PR adds a substantial amount of work for little apparent benefit, given that OSS Fuzz runs anyway on actual commits.

If we could do a "test with fuzz buildbots" label, that might be a compromise?

A

There's been a concerted effort to reduce CI times as of late, and I do worry that this PR adds a substantial amount of work for little apparent benefit, given that OSS Fuzz runs anyway on actual commits.

If the CI job is not mandatory and doesn't prevent to merge a PR, I think that it's acceptable to use GHA resources.

If we could do a "test with fuzz buildbots" label, that might be a compromise?

I am not sure how often the label will be set, it is pretty likely that this approach will not solve the problem of OSS-Fuzz builds being left broken from time to time

@ezio-melotti @hugovk is there anything I can do here to make this PR ready for merging?

@illia-v It's the core dev sprint next week, I'll bring it up for discussion then. I think fuzzing can be extremely valuable, and we need to balance how long it runs so we're not waiting too long for PRs to complete.

It seems @15r10nk found several issues that OSS-Fuzz missed, I assume using a different approach. If we're to adopt fuzzing, perhaps we should try his mechanism that seems to find more (release-blocking!) issues?

A

Is there a doc somewhere explaining how to handle a CIFuzz failure? Or this CI never fails? :-)

I just would like to know who I should contact if it goes wrong. @hugovk if I understood correctly :-)

If/when it fails, let's open an issue and figure it out :)

We've been seeing CIFuzz failures on otherwise good PRs not related to the PR change at hand of late with the build failing:

./Programs/_freeze_module importlib._bootstrap_external ./Lib/importlib/_bootstrap_external.py Python/frozen_modules/importlib._bootstrap_external.h
Segmentation fault (core dumped)
make: *** [Makefile:1660: Python/frozen_modules/importlib._bootstrap_external.h] Error 139

these are understandably confusing people.

We've been seeing CIFuzz failures on otherwise good PRs not related to the PR change at hand of late with the build failing:
./Programs/_freeze_module importlib._bootstrap_external ./Lib/importlib/_bootstrap_external.py Python/frozen_modules/importlib._bootstrap_external.h
Segmentation fault (core dumped)

@gpshead created issue #116886.