--- layout: fc_discuss_archives title: Message 3 from Frama-C-discuss on January 2020 ---
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