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C/C++ overlay: use new discard strategy

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idrissrio
2026-03-04 15:28:37 +01:00
parent 44de113376
commit 2ca7d8cb6d
1 changed files with 13 additions and 34 deletions
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47
cpp/ql/lib/semmle/code/cpp/internal/Overlay.qll
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@@ -1,20 +1,7 @@
/**
* Defines entity discard predicates for C++ overlay analysis.
*
* The discard strategy is based on TRAP file and tag tracking rather than
* source locations. The extractor records which TRAP file or tag each element
* is defined in (`in_trap_or_tag`), which source files use which TRAP files
* (`source_file_uses_trap`), and which TRAP files use which tags
* (`trap_uses_tag`). These relations allow us to precisely determine whether
* a base element should be discarded or retained in the combined database.
*/
private import OverlayXml
/**
* Holds always for the overlay variant and never for the base variant.
* This local predicate is used to define local predicates that behave
* differently for the base and overlay variant.
*/
overlay[local]
predicate isOverlay() { databaseMetadata("isOverlay", "true") }
@@ -22,16 +9,11 @@ predicate isOverlay() { databaseMetadata("isOverlay", "true") }
/**
* Holds if TRAP file or tag `t` is reachable from a source file named
* `source_file` in the given variant (base or overlay).
*
* A TRAP file is directly reachable from its source file. A tag is reachable
* if the TRAP file that uses it is reachable.
*/
overlay[local]
private predicate locallyReachableTrapOrTag(
boolean isOverlayVariant, string source_file, @trap_or_tag t
) {
private predicate locally_reachable_trap_or_tag(boolean is_overlay, string source_file, @trap_or_tag t) {
exists(@source_file sf, string source_file_raw, @trap trap |
(if isOverlay() then isOverlayVariant = true else isOverlayVariant = false) and
(if isOverlay() then is_overlay = true else is_overlay = false) and
source_file_uses_trap(sf, trap) and
source_file_name(sf, source_file_raw) and
source_file = source_file_raw.replaceAll("\\", "/") and
@@ -44,28 +26,25 @@ private predicate locallyReachableTrapOrTag(
* variant (base or overlay).
*/
overlay[local]
private predicate locallyInTrapOrTag(boolean isOverlayVariant, @element e, @trap_or_tag t) {
(if isOverlay() then isOverlayVariant = true else isOverlayVariant = false) and
private predicate locally_in_trap_or_tag(boolean is_overlay, @element e, @trap_or_tag t) {
(if isOverlay() then is_overlay = true else is_overlay = false) and
in_trap_or_tag(e, t)
}
/**
* Discards an element from the base variant if:
* - It is known to be in a base TRAP file or tag, and
* - It is not reachable from any overlay source file, and
* - Every base source file that reaches it has either changed or had its TRAP
* file redefined by the overlay.
* Holds if element `e` from the base variant should be discarded because
* it has been redefined or is no longer reachable in the overlay.
*/
overlay[discard_entity]
private predicate discardElement(@element e) {
private predicate discard_element(@element e) {
// If we don't have any knowledge about what TRAP file something
// is in, then we don't want to discard it, so we only consider
// entities that are known to be in a base TRAP file.
locallyInTrapOrTag(false, e, _) and
locally_in_trap_or_tag(false, e, _) and
// Anything that is reachable from an overlay source file should
// not be discarded.
not exists(@trap_or_tag t | locallyInTrapOrTag(true, e, t) |
locallyReachableTrapOrTag(true, _, t)
not exists(@trap_or_tag t | locally_in_trap_or_tag(true, e, t) |
locally_reachable_trap_or_tag(true, _, t)
) and
// Finally, we have to make sure that base shouldn't retain it.
// If it is reachable from a base source file, then that is
@@ -73,10 +52,10 @@ private predicate discardElement(@element e) {
// particular, been deleted) or the overlay has redefined the TRAP
// file it is in.
forall(@trap_or_tag t, string source_file |
locallyInTrapOrTag(false, e, t) and
locallyReachableTrapOrTag(false, source_file, t)
locally_in_trap_or_tag(false, e, t) and
locally_reachable_trap_or_tag(false, source_file, t)
|
overlayChangedFiles(source_file) or
locallyReachableTrapOrTag(true, _, t)
locally_reachable_trap_or_tag(true, _, t)
)
}