Update EXP39-C to use the new dataflow library by MichaelRFairhurst · Pull Request #1201 · github/codeql-coding-standards · GitHub
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Update EXP39-C to use the new dataflow library - #1201

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michaelrfairhurst/use-new-dataflow-exp39-c

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@MichaelRFairhurst

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Description

Update EXP39-C to use the new dataflow library.

This query has other issues I decided not to immediately address -- see #1200. The query actually makes all sources sinks in order to report casts from A* to B* (though this doesn't technically cause UB or violate the rule), only truly requiring dataflow to handle the realloc case.

Updating to the new dataflow began reporting both x and &x in (T*) &x. To continue reporting the issue at the sink, and to exclude T, I check that the node.asExpr() satisfies the expression's sink conditions, that it's either a cast or a dereference.

This query is very slow, partly because its design essentially disables forward/reverse pruning. Roughly timing it on my system indicates that this slowness isn't affected by the dataflow update, so its not something I worried about addressing here.

Change request type

  • Release or process automation (GitHub workflows, internal scripts)
  • Internal documentation
  • External documentation
  • Query files (.ql, .qll, .qls or unit tests)
  • External scripts (analysis report or other code shipped as part of a release)

Rules with added or modified queries

  • No rules added
  • Queries have been added for the following rules:
    • rule number here
  • Queries have been modified for the following rules:
    • EXP39-C

Release change checklist

A change note (development_handbook.md#change-notes) is required for any pull request which modifies:

  • The structure or layout of the release artifacts.
  • The evaluation performance (memory, execution time) of an existing query.
  • The results of an existing query in any circumstance.

If you are only adding new rule queries, a change note is not required.

Author: Is a change note required?

  • Yes
  • No

🚨🚨🚨
Reviewer: Confirm that format of shared queries (not the .qll file, the
.ql file that imports it) is valid by running them within VS Code.

  • Confirmed

Reviewer: Confirm that either a change note is not required or the change note is required and has been added.

  • Confirmed

Query development review checklist

For PRs that add new queries or modify existing queries, the following checklist should be completed by both the author and reviewer:

Author

  • Have all the relevant rule package description files been checked in?
  • Have you verified that the metadata properties of each new query is set appropriately?
  • Do all the unit tests contain both "COMPLIANT" and "NON_COMPLIANT" cases?
  • Are the alert messages properly formatted and consistent with the style guide?
  • Have you run the queries on OpenPilot and verified that the performance and results are acceptable?
    As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.
  • Does the query have an appropriate level of in-query comments/documentation?
  • Have you considered/identified possible edge cases?
  • Does the query not reinvent features in the standard library?
  • Can the query be simplified further (not golfed!)

Reviewer

  • Have all the relevant rule package description files been checked in?
  • Have you verified that the metadata properties of each new query is set appropriately?
  • Do all the unit tests contain both "COMPLIANT" and "NON_COMPLIANT" cases?
  • Are the alert messages properly formatted and consistent with the style guide?
  • Have you run the queries on OpenPilot and verified that the performance and results are acceptable?
    As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.
  • Does the query have an appropriate level of in-query comments/documentation?
  • Have you considered/identified possible edge cases?
  • Does the query not reinvent features in the standard library?
  • Can the query be simplified further (not golfed!)

Copilot AI balanced review requested due to automatic review settings September 20, 2026 20:51

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Copilot review overview

🟡 Changes recommended

Mandatory QLDoc, line-length, and change-note clarity issues remain.

Get a fresh assessment by requesting another Copilot review.

Review effort: Balanced
Findings: 3 Low severity

Open (3)
What changed in this PR

Migrates EXP39-C from the deprecated data-flow library to the new CodeQL data-flow API while preserving reported alerts.

Changes:

  • Updates data-flow configuration and sink filtering.
  • Refreshes expected path-graph output.
  • Adds the required change note.
  • Manual VS Code validation remains unconfirmed.
File Description
change_notes/​2026-09-20-update-exp39-c-to-use-new-dataflow.md Documents the migration.
c/​cert/​src/​rules/​EXP39-C/​DoNotAccessVariableViaPointerOfIncompatibleType.ql Migrates the query to new data flow.
c/​cert/​test/​rules/​EXP39-C/​DoNotAccessVariableViaPointerOfIncompatibleType.expected Updates expected paths and locations.

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class IndirectCastAnalysisUnconvertedCastExpr extends Expr {
IndirectCastAnalysisUnconvertedCastExpr() { this = any(Cast c).getUnconverted() }
class CastedExpr extends Expr {
where
not isExcluded(sink.getNode().asExpr(),
Pointers3Package::doNotAccessVariableViaPointerOfIncompatibleTypeQuery()) and
not isExcluded(sinkExpr, Pointers3Package::doNotAccessVariableViaPointerOfIncompatibleTypeQuery()) and
Comment on lines +2 to +3
- Updated the underlying dataflow library to use the new dataflow from the deprecated old data flow. This may cause behavioral changes in some analyses, usually with improved results and performance.
- Some refactoring required to accommodate functional changes in how dataflow nodes attach to the AST. No functional changes to the analysis from this are expected. No newline at end of file
@MichaelRFairhurst

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/test-performance

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🏁 Beep Boop! Performance testing for this PR has been initiated. Please check back later for results. Note that the query package generation step must complete before testing will start so it might be a minute.

💡 If you do not hear back from me please check my status! I will report even if I fail!

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2 participants