--- layout: fc_discuss_archives title: Message 4 from Frama-C-discuss on January 2020 ---
Thanks, Iâll update it right away! This makes me wonder though.. How do I know if I get another false positive again? Should I always check that the opposite of what Iâm trying to prove is false? Or how do you guys handle issues like this? // Nauck > On 10 Jan 2020, at 09:49, Loïc Correnson <loic.correnson at cea.fr> wrote: > > Hi, > Actually, there was probably a bug in 19.1 regarding right-shift, which has been fixed in 20.0 ; > Indeed, you shall upgrade to the new version. > Debugging z3 output is not _yet_ available, since we need some extra support from why3 for doing so. > You can however get the prover output with `-wp-msg-key prover` and have the why3 task for each prover logged down with `-wp-out <dir>`. > Regards, > L. > > >> Le 9 janv. 2020 à 22:47, Benjamin Nauck <benjamin at nauck.se> a écrit : >> >> Hi, >> I know v20 is out and I should probably update but I've got some questions about the behaviour of v19.1 that I would like to have the answer to. >> >> The problem is that I get some strange result when using frama-c v19.1 with why3 v1.2.1 and z3 v4.8.6 (running on macos 10.14.1). >> It seems to starts when I have bit shift in the code I'm trying to verify, as seen in the following example: >> >> $ cat test.c >> //@ ensures \result == 0; ensures \result != 0; >> unsigned test(unsigned value) { >> return value >> 1; >> } >> $ frama-c -wp -wp-prover=z3 test.c >> [kernel] Parsing test.c (with preprocessing) >> [wp] Warning: Missing RTE guards >> [wp] 2 goals scheduled >> [wp] Proved goals: 2 / 2 >> Qed: 0 (0.38ms-0.82ms) >> Z3: 2 (140ms) >> >> 1. Maybe I'm missing something, but to me, \result should neither be always 0 nor never 0 and it should especially not be both at the same time, right? >> >> 2. Any idea what could be causing this? >> >> 3. Is there a way to read the output of why3 and z3 to try to debug what is happening without diving into the source code of frama-c or the configuration files of why3? >> >> I've put off upgrading to v20 as I need to verify quite a lot of bit manipulation of integers and I've got the impression that the new version is a bit buggy when it comes to that (even though workarounds seems to exist). >> 4. Should I upgrade to v20 anyway or am I better off with 19.1 for that? >> >> Regards, >> Benjamin Nauck >> _______________________________________________ >> Frama-c-discuss mailing list >> Frama-c-discuss at lists.gforge.inria.fr >> https://lists.gforge.inria.fr/mailman/listinfo/frama-c-discuss > > _______________________________________________ > Frama-c-discuss mailing list > Frama-c-discuss at lists.gforge.inria.fr > https://lists.gforge.inria.fr/mailman/listinfo/frama-c-discuss