diff --git a/cpp/ql/lib/change-notes/2023-12-22-unique-function.md b/cpp/ql/lib/change-notes/2023-12-22-unique-function.md
new file mode 100644
index 000000000000..bd5d84132abf
--- /dev/null
+++ b/cpp/ql/lib/change-notes/2023-12-22-unique-function.md
@@ -0,0 +1,4 @@
+---
+category: fix
+---
+* Under certain circumstances a function declaration that is not also a definition could be associated with a `Function` that did not have the definition as a `FunctionDeclarationEntry`. This is now fixed when only one definition exists, and a unique `Function` will exist that has both the declaration and the definition as a `FunctionDeclarationEntry`.
\ No newline at end of file
diff --git a/cpp/ql/lib/semmle/code/cpp/Element.qll b/cpp/ql/lib/semmle/code/cpp/Element.qll
index 79df774d80f1..98b5da60c1c5 100644
--- a/cpp/ql/lib/semmle/code/cpp/Element.qll
+++ b/cpp/ql/lib/semmle/code/cpp/Element.qll
@@ -7,6 +7,7 @@ import semmle.code.cpp.Location
private import semmle.code.cpp.Enclosing
private import semmle.code.cpp.internal.ResolveClass
private import semmle.code.cpp.internal.ResolveGlobalVariable
+private import semmle.code.cpp.internal.ResolveFunction
/**
* Get the `Element` that represents this `@element`.
@@ -30,11 +31,14 @@ pragma[inline]
@element unresolveElement(Element e) {
not result instanceof @usertype and
not result instanceof @variable and
+ not result instanceof @function and
result = e
or
e = resolveClass(result)
or
e = resolveGlobalVariable(result)
+ or
+ e = resolveFunction(result)
}
/**
diff --git a/cpp/ql/lib/semmle/code/cpp/Function.qll b/cpp/ql/lib/semmle/code/cpp/Function.qll
index db6f1c487e74..92134dca31d9 100644
--- a/cpp/ql/lib/semmle/code/cpp/Function.qll
+++ b/cpp/ql/lib/semmle/code/cpp/Function.qll
@@ -9,6 +9,7 @@ import semmle.code.cpp.exprs.Call
import semmle.code.cpp.metrics.MetricFunction
import semmle.code.cpp.Linkage
private import semmle.code.cpp.internal.ResolveClass
+private import semmle.code.cpp.internal.ResolveFunction
/**
* A C/C++ function [N4140 8.3.5]. Both member functions and non-member
@@ -25,6 +26,8 @@ private import semmle.code.cpp.internal.ResolveClass
* in more detail in `Declaration.qll`.
*/
class Function extends Declaration, ControlFlowNode, AccessHolder, @function {
+ Function() { isFunction(underlyingElement(this)) }
+
override string getName() { functions(underlyingElement(this), result, _) }
/**
diff --git a/cpp/ql/lib/semmle/code/cpp/controlflow/internal/ConstantExprs.qll b/cpp/ql/lib/semmle/code/cpp/controlflow/internal/ConstantExprs.qll
index dfb5782238bc..84e96fa9c468 100644
--- a/cpp/ql/lib/semmle/code/cpp/controlflow/internal/ConstantExprs.qll
+++ b/cpp/ql/lib/semmle/code/cpp/controlflow/internal/ConstantExprs.qll
@@ -110,8 +110,8 @@ private predicate loopConditionAlwaysUponEntry(ControlFlowNode loop, Expr condit
* should be in this relation.
*/
pragma[noinline]
-private predicate isFunction(Element el) {
- el instanceof Function
+private predicate isFunction(@element el) {
+ el instanceof @function
or
el.(Expr).getParent() = el
}
@@ -122,7 +122,7 @@ private predicate isFunction(Element el) {
*/
pragma[noopt]
private predicate callHasNoTarget(@funbindexpr fc) {
- exists(Function f |
+ exists(@function f |
funbind(fc, f) and
not isFunction(f)
)
diff --git a/cpp/ql/lib/semmle/code/cpp/internal/ResolveFunction.qll b/cpp/ql/lib/semmle/code/cpp/internal/ResolveFunction.qll
new file mode 100644
index 000000000000..95cd28068568
--- /dev/null
+++ b/cpp/ql/lib/semmle/code/cpp/internal/ResolveFunction.qll
@@ -0,0 +1,57 @@
+private predicate hasDefinition(@function f) {
+ exists(@fun_decl fd | fun_decls(fd, f, _, _, _) | fun_def(fd))
+}
+
+private predicate onlyOneCompleteFunctionExistsWithMangledName(@mangledname name) {
+ strictcount(@function f | hasDefinition(f) and mangled_name(f, name)) = 1
+}
+
+/** Holds if `f` is a unique function with a definition named `name`. */
+private predicate isFunctionWithMangledNameAndWithDefinition(@mangledname name, @function f) {
+ hasDefinition(f) and
+ mangled_name(f, name) and
+ onlyOneCompleteFunctionExistsWithMangledName(name)
+}
+
+/** Holds if `f` is a function without a definition named `name`. */
+private predicate isFunctionWithMangledNameAndWithoutDefinition(@mangledname name, @function f) {
+ not hasDefinition(f) and
+ mangled_name(f, name)
+}
+
+/**
+ * Holds if `incomplete` is a function without a definition, and there exists
+ * a unique function `complete` with the same name that does have a definition.
+ */
+private predicate hasTwinWithDefinition(@function incomplete, @function complete) {
+ not function_instantiation(incomplete, complete) and
+ (
+ not compgenerated(incomplete) or
+ not compgenerated(complete)
+ ) and
+ exists(@mangledname name |
+ isFunctionWithMangledNameAndWithoutDefinition(name, incomplete) and
+ isFunctionWithMangledNameAndWithDefinition(name, complete)
+ )
+}
+
+import Cached
+
+cached
+private module Cached {
+ /**
+ * If `f` is a function without a definition, and there exists a unique
+ * function with the same name that does have a definition, then the
+ * result is that unique function. Otherwise, the result is `f`.
+ */
+ cached
+ @function resolveFunction(@function f) {
+ hasTwinWithDefinition(f, result)
+ or
+ not hasTwinWithDefinition(f, _) and
+ result = f
+ }
+
+ cached
+ predicate isFunction(@function f) { f = resolveFunction(_) }
+}
diff --git a/cpp/ql/lib/semmle/code/cpp/internal/ResolveGlobalVariable.qll b/cpp/ql/lib/semmle/code/cpp/internal/ResolveGlobalVariable.qll
index c11e1457dae7..3727a1aaa00c 100644
--- a/cpp/ql/lib/semmle/code/cpp/internal/ResolveGlobalVariable.qll
+++ b/cpp/ql/lib/semmle/code/cpp/internal/ResolveGlobalVariable.qll
@@ -24,8 +24,8 @@ private predicate isGlobalWithMangledNameAndWithoutDefinition(@mangledname name,
* a unique global variable `complete` with the same name that does have a definition.
*/
private predicate hasTwinWithDefinition(@globalvariable incomplete, @globalvariable complete) {
+ not variable_instantiation(incomplete, complete) and
exists(@mangledname name |
- not variable_instantiation(incomplete, complete) and
isGlobalWithMangledNameAndWithoutDefinition(name, incomplete) and
isGlobalWithMangledNameAndWithDefinition(name, complete)
)
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