Overview Queries

An Overview Query queries a BSim database for the number of matches to each function in an executable. The matching functions themselves are not returned. Similarity and Confidence thresholds can be set for an Overview Query, but there is no “Matches per Function” bound and no filters can be applied.

To perform an Overview Query, select BSim -> Perform Overview… from the Code Browser.

Exercise: Hit Counts and Self-Significance

  1. Perform an Overview query on postgres using the default query thresholds. You should see the following result: overview window
  2. Sort the table by the “Hit Count” column in ascending order. Typically, the functions with the largest hit counts will have low self-significance. Verify that that is the case for this table.
  3. Q: Examine the functions with the highest hit count. Why are there so many matches for these functions?
    Answer: These are all instances of PostgreSQL statistics-reporting functions. Their bodies are quite similar and they have identical BSim signatures.

Exercise: Selections and Queries

Using the hit count column, it is possible to exclude functions with large numbers of matches.

  1. In the Overview Table, select all functions whose hit count is 2 or less.
  2. Right-click on the selection and perform the Search Selected Functions action. Sort the query results by descending Function Count and verify that demangler_gnu_v2_41 is far down the list.

Exercise: Vector Hashes

Suppose foo and bar have the same number of hits in the Overview table. There are two possibilities:

  1. foo and bar have distinct feature vectors which happen to have the same number of matches.
  2. foo and bar have the same feature vector.

An optional column, Vector Hash, can be used to distinguish between these two cases.

  1. Enable the Vector Hash Column in the Overview Table.
  2. Find two functions with the same vector hash.
  3. Select the two corresponding rows in the table and then transfer the selection to the Listing using the make selection icon icon in the BSim Overview toolbar.
  4. In the Listing, press Shift-C or right-click and perform the Compare Selected Functions action.
  5. In the resulting Function Comparison window, convince yourself that these two functions should have the same BSim signature.

Next Section: Queries and Filters