Frama-C Bug Tracking System - Frama-C
View Issue Details
0002353Frama-CPlug-in > wppublic2018-02-01 13:272019-10-17 18:01
closedno change required 
Sulfur-20171101Ubuntu 17.04
Frama-C 16-Sulfur 
0002353: alt-ergo goals generated directly / via why3 differ in provability
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.
No tags attached.
c search_n_standalone.c (35,513) 2018-02-01 13:27
? fd (382) 2018-02-01 13:27
? fw (602) 2018-02-01 13:28
? xxx_direct.mlw (3,871) 2018-02-01 13:28
? xxx_via_why3.mlw (3,589) 2018-02-01 13:28
Issue History
2018-02-01 13:27JochenNew Issue
2018-02-01 13:27JochenStatusnew => assigned
2018-02-01 13:27JochenAssigned To => correnson
2018-02-01 13:27JochenFile Added: search_n_standalone.c
2018-02-01 13:27JochenFile Added: fd
2018-02-01 13:28JochenFile Added: fw
2018-02-01 13:28JochenFile Added: xxx_direct.mlw
2018-02-01 13:28JochenFile Added: xxx_via_why3.mlw
2018-02-01 13:31JochenNote Added: 0006516
2019-10-17 17:13corrensonNote Added: 0006904
2019-10-17 17:13corrensonStatusassigned => resolved
2019-10-17 17:13corrensonResolutionopen => no change required
2019-10-17 18:01signolesStatusresolved => closed

2018-02-01 13:31   
I changed some layout and capitalization in the mlw files to reduce their differences found by "diff"; this shouldn't have affected their semantics.
2019-10-17 17:13   
Actually, the wp-native output for alt-ergo differs from the why3 output for alt-ergo. The second one is now the default, and the former one will be deprecated.