C++: Improve function pointer resolution

cpp/ql/lib/change-notes/2024-10-16-function-pointer-resolution.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* The function call target resolution algorithm has been improved to resolve more calls through function pointers. As a result, dataflow queries may have more results.

cpp/ql/lib/change-notes/2024-10-16-new-api-for-call-target-resolution.md

@@ -0,0 +1,4 @@
+---
+category: feature
+---
+* Added a new predicate `DataFlow::getARuntimeTarget` for getting a function that may be invoked by a `Call` expression. Unlike `Call.getTarget` this new predicate may also resolve function pointers.

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowPrivate.qll

@@ -1328,7 +1328,10 @@ predicate lambdaCreation(Node creation, LambdaCallKind kind, DataFlowCallable c)
 
 /** Holds if `call` is a lambda call of kind `kind` where `receiver` is the lambda expression. */
 predicate lambdaCall(DataFlowCall call, LambdaCallKind kind, Node receiver) {
-  call.(SummaryCall).getReceiver() = receiver.(FlowSummaryNode).getSummaryNode() and
+  (
+    call.(SummaryCall).getReceiver() = receiver.(FlowSummaryNode).getSummaryNode() or
+    call.asCallInstruction().getCallTargetOperand() = receiver.asOperand()
+  ) and
   exists(kind)
 }
 

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowUtil.qll

@@ -17,6 +17,7 @@ private import SsaInternals as Ssa
 private import DataFlowImplCommon as DataFlowImplCommon
 private import codeql.util.Unit
 private import Node0ToString
+private import DataFlowDispatch as DataFlowDispatch
 import ExprNodes
 
 /**
@@ -2497,3 +2498,16 @@ class AdditionalCallTarget extends Unit {
    */
   abstract Declaration viableTarget(Call call);
 }
+
+/**
+ * Gets a function that may be called by `call`.
+ *
+ * Note that `call` may be a call to a function pointer expression.
+ */
+Function getARuntimeTarget(Call call) {
+  exists(DataFlowCall dfCall | dfCall.asCallInstruction().getUnconvertedResultExpression() = call |
+    result = DataFlowDispatch::viableCallable(dfCall).asSourceCallable()
+    or
+    result = DataFlowImplCommon::viableCallableLambda(dfCall, _).asSourceCallable()
+  )
+}

cpp/ql/test/library-tests/dataflow/dataflow-tests/dataflow-consistency.expected

@@ -3,6 +3,9 @@ uniqueEnclosingCallable
 | test.cpp:864:47:864:54 | call to source | Node should have one enclosing callable but has 0. |
 | test.cpp:872:46:872:51 | call to source | Node should have one enclosing callable but has 0. |
 | test.cpp:872:53:872:56 | 1 | Node should have one enclosing callable but has 0. |
+| test.cpp:1126:33:1129:1 | {...} | Node should have one enclosing callable but has 0. |
+| test.cpp:1127:3:1127:13 | reads_input | Node should have one enclosing callable but has 0. |
+| test.cpp:1128:3:1128:21 | not_does_read_input | Node should have one enclosing callable but has 0. |
 uniqueCallEnclosingCallable
 | test.cpp:864:47:864:54 | call to source | Call should have one enclosing callable but has 0. |
 | test.cpp:872:46:872:51 | call to source | Call should have one enclosing callable but has 0. |

cpp/ql/test/library-tests/dataflow/dataflow-tests/test-source-sink.expected

@@ -323,6 +323,7 @@ irFlow
 | test.cpp:1069:9:1069:14 | call to source | test.cpp:1074:10:1074:10 | i |
 | test.cpp:1069:9:1069:14 | call to source | test.cpp:1081:10:1081:10 | i |
 | test.cpp:1117:27:1117:34 | call to source | test.cpp:1117:27:1117:34 | call to source |
+| test.cpp:1132:11:1132:16 | call to source | test.cpp:1121:8:1121:8 | x |
 | true_upon_entry.cpp:9:11:9:16 | call to source | true_upon_entry.cpp:13:8:13:8 | x |
 | true_upon_entry.cpp:17:11:17:16 | call to source | true_upon_entry.cpp:21:8:21:8 | x |
 | true_upon_entry.cpp:27:9:27:14 | call to source | true_upon_entry.cpp:29:8:29:8 | x |

cpp/ql/test/library-tests/dataflow/dataflow-tests/test.cpp

@@ -1115,4 +1115,20 @@ void indirect_sink_const_ref(const T&);
 
 void test_temp_with_conversion_from_materialization() {
   indirect_sink_const_ref(source()); // $ ir MISSING: ast
+}
+
+void reads_input(int x) {
+  sink(x); // $ ir MISSING: ast
+}
+
+void not_does_read_input(int x);
+
+void (*dispatch_table[])(int) = {
+  reads_input,
+  not_does_read_input
+};
+
+void test_dispatch_table(int i) {
+  int x = source();
+  dispatch_table[i](x);
 }