goto-symex: assumed pointer equalities must update value set#8494
Open
tautschnig wants to merge 1 commit intodiffblue:developfrom
Open
goto-symex: assumed pointer equalities must update value set#8494tautschnig wants to merge 1 commit intodiffblue:developfrom
tautschnig wants to merge 1 commit intodiffblue:developfrom
Conversation
Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## develop #8494 +/- ##
===========================================
- Coverage 78.90% 78.89% -0.01%
===========================================
Files 1727 1727
Lines 198425 198452 +27
Branches 18523 18499 -24
===========================================
+ Hits 156561 156568 +7
- Misses 41864 41884 +20 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
|
Value sets and constant propagation are our only sources of points-to information when resolving dereferences in goto-symex. Therefore, assuming or branching on equalities of pointer-typed variables must have us consider both of their value sets to be equal. Else we may end up with spurious counterexamples as seen with the enclosed regression test (where we previously did not have any known value for `a`). Fixes: diffblue#8492
tautschnig
force-pushed
the
bugfixes/8492-value-set
branch
from
7834dd5 to
2a27074
Compare
Comment on lines
+130
to
+132
| // We have a condition a == b. Make both a's and b's value sets the | ||
| // union of their previous value sets (the last "true" argument makes | ||
| // sure we add rather than replace value sets). |
Collaborator
There was a problem hiding this comment.
What would happen in a situation like this ?
p = malloc(4);// o1
q = malloc(4);// o2
__CPROVER_assume(p == q);
// now p and q have both &o1 and &o2 in their value sets
*p = 1; // what happens here ?
*q = 2; // what happens here ?
Collaborator
|
This is problematic, and needs a deeper discussion. I appreciate this is meant as a fix for #8492, but I'd advise to do a contract-specific fix. |
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Value sets and constant propagation are our only sources of points-to information when resolving dereferences in goto-symex. Therefore, assuming or branching on equalities of pointer-typed variables must have us consider both of their value sets to be equal. Else we may end up with spurious counterexamples as seen with the enclosed regression test (where we previously did not have any known value for
a).Fixes: #8492