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Closed
Open
Issue created Feb 01, 2018 by Jochen Burghardt@burghardt

alt-ergo goals generated directly / via why3 differ in provability

ID0002353: This issue was created automatically from Mantis Issue 2353. Further discussion may take place here.


Id Project Category View Due Date Updated
ID0002353 Frama-C Plug-in > wp public 2018-02-01 2019-10-17
Reporter Jochen Assigned To correnson Resolution no change required
Priority normal Severity minor Reproducibility always
Platform Sulfur-20171101 OS - OS Version Ubuntu 17.04
Product Version Frama-C 16-Sulfur Target Version - Fixed in Version -

Description :

I generated an Alt-Ergo proof obligation for the ensures clause "xxx" (line 1140) of the attached program "search_n_standalone.c" (which was obtained from "search_n" in "Acsl by example" by "gcc -E -C"). When I did this directly (see attached script "fd"), it was proven without problems. However, when I did this via Why3 (see script "fw"), Alt-Ergo responded "Don't know" after 0.1 seconds.

In order to compare both mlw files given to Alt-Ergo, I moved the goal of the via-Why3 file into the direct file; it became provable there. Removing as many axioms and definitions as possible while keeping the (non-)provability, I obtained the files "xxx_direct.mlw" and "xxx_via_why3.mlw". It seems that the former defines and uses "shift_sint32", while the latter does not (it uses "shift" instead). Probably, this is the reason for the different outcomes of Alt-Ergo.

Although the observed issue may not be bug (both mlw files may be semanically equivalent), it might be desirable to unify the proof obligations given to Alt-Ergo on different pathways.

Attachments

  • search_n_standalone.c
  • fd
  • fw
  • xxx_direct.mlw
  • xxx_via_why3.mlw
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