[tor-bugs] #19079 [Core Tor/Tor]: clang -m32 -ftrapv seems buggy with 64-bit signed integer multiply

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#19079: clang -m32 -ftrapv seems buggy with 64-bit signed integer multiply
------------------------------+--------------------------------
     Reporter:  nickm         |      Owner:
         Type:  defect        |     Status:  new
     Priority:  High          |  Milestone:  Tor: 0.2.9.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
------------------------------+--------------------------------
 If you try building with clang -m32 -ftrapv, you get a bunch of these
 warnings:
 {{{
 12:39:59 /home/jenkins/workspace/tor-ci-linux-master-
 clang/ARCHITECTURE/i386/SUITE/sid/src/or/dirvote.c:828: undefined
 reference to `__mulodi4'
 12:39:59 /home/jenkins/workspace/tor-ci-linux-master-
 clang/ARCHITECTURE/i386/SUITE/sid/src/or/dirvote.c:828: undefined
 reference to `__mulodi4'
 12:39:59 /home/jenkins/workspace/tor-ci-linux-master-
 clang/ARCHITECTURE/i386/SUITE/sid/src/or/dirvote.c:855: undefined
 reference to `__mulodi4'
 12:39:59 /home/jenkins/workspace/tor-ci-linux-master-
 clang/ARCHITECTURE/i386/SUITE/sid/src/or/dirvote.c:930: undefined
 reference to `__mulodi4'
 12:39:59 /home/jenkins/workspace/tor-ci-linux-master-
 clang/ARCHITECTURE/i386/SUITE/sid/src/or/dirvote.c:930: undefined
 reference to `__mulodi4'
 12:39:59 src/or/libtor-testing.a(src_or_libtor_testing_a-
 dirvote.o):/home/jenkins/workspace/tor-ci-linux-master-
 clang/ARCHITECTURE/i386/SUITE/sid/src/or/dirvote.c:834: more undefined
 references to `__mulodi4' follow
 }}}

 Since -ftrapv is now on by default, that's a problem!

 Others have seen errors like this before; for example see:
   https://bugs.chromium.org/p/chromium/issues/detail?id=503229
 and
   https://llvm.org/bugs/show_bug.cgi?id=14469

 I'm calling this must-fix-for-029, since otherwise we just broke 32-bit
 clang.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/19079>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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