[UBSAN] Undefined behavior in DataFormats/FEDRawData

[mrodozov]

The UBSAN IB reports undefined behavior in 1 file, with example relval and step they appear in:

11603.0 step2
DataFormats/FEDRawData/src/FEDHeader.cc:37:24: runtime error: left shift of 65535 by 20 places cannot be represented in type 'int'

check the relval logs in here for the examples:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/ubsan_logs/relvals/11603.0_SingleElectronPt1000+2021+SingleElectronPt1000_pythia8_GenSimINPUT+Digi+Reco+HARVEST+ALCA/step2_SingleElectronPt1000+2021+SingleElectronPt1000_pythia8_GenSimINPUT+Digi+Reco+HARVEST+ALCA.log

[cmsbuild]

A new Issue was created by @mrodozov Mircho Rodozov.

@Dr15Jones, @perrotta, @dpiparo, @makortel, @smuzaffar, @qliphy can you please review it and eventually sign/assign? Thanks.

cms-bot commands are listed here

[mrodozov]

assign daq

[cmsbuild]

New categories assigned: daq

@emeschi,@smorovic you have been requested to review this Pull request/Issue and eventually sign? Thanks

[smorovic]

This is caused by (bxID << FED_BXID_SHIFT).
However, bunch crossing ID is always smaller than 4096, it's using only 12-bits when packed.

From DataFormats/FEDRawData/src/fed_header.h:

#define FED_BXID_WIDTH 0x00000fff
#define FED_BXID_SHIFT 20

So, instead of (bxID << FED_BXID_SHIFT), having ((bxID & FED_BXID_WIDTH) << FED_BXID_SHIFT) should (hopefully?) silence the checker.
I will prepare a PR.

[smorovic]

+1

[cmsbuild]

This issue is fully signed and ready to be closed.

[mrodozov]

@smorovic when you make the PR we can test it against the UBSAN IB, and you can type in the description of the pr
Fixes: #35035
which will close this issue as well
Link it to this issue I'll run it against the UBSAN

[smorovic]

Thanks, I edited the PR and included "Fixes: #35035"