Looks like a false positive. Not sure why it broke all of a sudden..

UBSan build was broken for a while, so it's hard to say at which point this has started to occur :/

But all the code in the stacktrace doesn't seem to be updated recently, it's like super old:

https://chromium.googlesource.com/external/github.com/google/re2/+/44c5d168e6e92bbdf3e81c1031e56e8081ed9f44

https://chromium.googlesource.com/external/github.com/google/re2/+/bfa5864478949b19e345fc8da15e681ee0326dac

Uploaded this to OSS-Fuzz: https://oss-fuzz.com/v2/testcase-detail/4806351671787520

I guess it will not crash

ClusterFuzz has detected this issue as fixed in range 508791:508824.

Detailed report: https://clusterfuzz.com/testcase?key=6452250875789312

Fuzzer: libFuzzer_third_party_re2_fuzzer
Job Type: libfuzzer_chrome_ubsan
Platform Id: linux

Crash Type: Incorrect-function-pointer-type
Crash Address: 
Crash State:
  Test
  _start
  
Sanitizer: undefined (UBSAN)

Recommended Security Severity: Medium

Regressed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=506298:506317
Fixed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=508791:508824

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=6452250875789312

See https://chromium.googlesource.com/chromium/src/+/master/testing/libfuzzer/reproducing.md for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.

ClusterFuzz testcase 6452250875789312 is verified as fixed, so closing issue as verified.

If this is incorrect, please add ClusterFuzz-Wrong label and re-open the issue.