C++: Override toString on argument indirections

Without this override, end users would see the string
`BufferReadSideEffect` in path explanations.

Author: jbj

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

@@ -387,6 +387,20 @@ class DefinitionByReferenceNode extends InstructionNode {
   }
 }
 
+/**
+ * A node representing the memory pointed to by a function argument.
+ *
+ * This class exists only in order to override `toString`, which would
+ * otherwise be the default implementation inherited from `InstructionNode`.
+ */
+private class ArgumentIndirectionNode extends InstructionNode {
+  override ReadSideEffectInstruction instr;
+
+  override string toString() {
+    result = "Argument " + instr.getIndex() + " indirection"
+  }
+}
+
 /**
  * A `Node` corresponding to a variable in the program, as opposed to the
  * value of that variable at some particular point. This can be used for

cpp/ql/test/library-tests/dataflow/fields/ir-path-flow.expected

@@ -1,8 +1,8 @@
 edges
 | A.cpp:98:12:98:18 | new | A.cpp:100:5:100:13 | Store |
-| A.cpp:100:5:100:13 | Chi [a] | A.cpp:101:8:101:9 | BufferReadSideEffect [a] |
+| A.cpp:100:5:100:13 | Chi [a] | A.cpp:101:8:101:9 | Argument 0 indirection [a] |
 | A.cpp:100:5:100:13 | Store | A.cpp:100:5:100:13 | Chi [a] |
-| A.cpp:101:8:101:9 | BufferReadSideEffect [a] | A.cpp:103:14:103:14 | *c [a] |
+| A.cpp:101:8:101:9 | Argument 0 indirection [a] | A.cpp:103:14:103:14 | *c [a] |
 | A.cpp:103:14:103:14 | *c [a] | A.cpp:107:16:107:16 | a |
 | A.cpp:103:14:103:14 | *c [a] | A.cpp:107:16:107:16 | a |
 | A.cpp:107:16:107:16 | a | A.cpp:107:12:107:16 | (void *)... |
@@ -32,9 +32,9 @@ edges
 | aliasing.cpp:79:11:79:20 | call to user_input | aliasing.cpp:80:12:80:13 | m1 |
 | aliasing.cpp:86:10:86:19 | call to user_input | aliasing.cpp:87:12:87:13 | m1 |
 | aliasing.cpp:92:12:92:21 | call to user_input | aliasing.cpp:93:12:93:13 | m1 |
-| by_reference.cpp:68:17:68:18 | nonMemberSetA output argument [a] | by_reference.cpp:69:22:69:23 | BufferReadSideEffect [a] |
+| by_reference.cpp:68:17:68:18 | nonMemberSetA output argument [a] | by_reference.cpp:69:22:69:23 | Argument 0 indirection [a] |
 | by_reference.cpp:68:21:68:30 | call to user_input | by_reference.cpp:68:17:68:18 | nonMemberSetA output argument [a] |
-| by_reference.cpp:69:22:69:23 | BufferReadSideEffect [a] | by_reference.cpp:69:8:69:20 | call to nonMemberGetA |
+| by_reference.cpp:69:22:69:23 | Argument 0 indirection [a] | by_reference.cpp:69:8:69:20 | call to nonMemberGetA |
 | by_reference.cpp:84:3:84:25 | Chi [a] | by_reference.cpp:102:21:102:39 | taint_inner_a_ptr output argument [a] |
 | by_reference.cpp:84:3:84:25 | Chi [a] | by_reference.cpp:106:21:106:41 | taint_inner_a_ptr output argument [a] |
 | by_reference.cpp:84:3:84:25 | Store | by_reference.cpp:84:3:84:25 | Chi [a] |
@@ -54,26 +54,26 @@ edges
 | simple.cpp:65:5:65:22 | Store [i] | simple.cpp:66:12:66:12 | Store [i] |
 | simple.cpp:65:11:65:20 | call to user_input | simple.cpp:65:5:65:22 | Store [i] |
 | simple.cpp:66:12:66:12 | Store [i] | simple.cpp:67:13:67:13 | i |
-| simple.cpp:83:9:83:28 | Chi [f1] | simple.cpp:84:14:84:20 | BufferReadSideEffect [f1] |
+| simple.cpp:83:9:83:28 | Chi [f1] | simple.cpp:84:14:84:20 | Argument -1 indirection [f1] |
 | simple.cpp:83:9:83:28 | Store | simple.cpp:83:9:83:28 | Chi [f1] |
 | simple.cpp:83:17:83:26 | call to user_input | simple.cpp:83:9:83:28 | Store |
-| simple.cpp:84:14:84:20 | BufferReadSideEffect [f1] | simple.cpp:84:14:84:20 | call to getf2f1 |
+| simple.cpp:84:14:84:20 | Argument -1 indirection [f1] | simple.cpp:84:14:84:20 | call to getf2f1 |
 | struct_init.c:14:24:14:25 | *ab [a] | struct_init.c:15:12:15:12 | a |
-| struct_init.c:20:20:20:29 | Chi [a] | struct_init.c:24:10:24:12 | BufferReadSideEffect [a] |
+| struct_init.c:20:20:20:29 | Chi [a] | struct_init.c:24:10:24:12 | Argument 0 indirection [a] |
 | struct_init.c:20:20:20:29 | Store | struct_init.c:20:20:20:29 | Chi [a] |
 | struct_init.c:20:20:20:29 | call to user_input | struct_init.c:20:20:20:29 | Store |
 | struct_init.c:20:20:20:29 | call to user_input | struct_init.c:22:11:22:11 | a |
-| struct_init.c:24:10:24:12 | BufferReadSideEffect [a] | struct_init.c:14:24:14:25 | *ab [a] |
-| struct_init.c:27:7:27:16 | Chi [a] | struct_init.c:36:10:36:24 | BufferReadSideEffect [a] |
+| struct_init.c:24:10:24:12 | Argument 0 indirection [a] | struct_init.c:14:24:14:25 | *ab [a] |
+| struct_init.c:27:7:27:16 | Chi [a] | struct_init.c:36:10:36:24 | Argument 0 indirection [a] |
 | struct_init.c:27:7:27:16 | Store | struct_init.c:27:7:27:16 | Chi [a] |
 | struct_init.c:27:7:27:16 | call to user_input | struct_init.c:27:7:27:16 | Store |
 | struct_init.c:27:7:27:16 | call to user_input | struct_init.c:31:23:31:23 | a |
-| struct_init.c:36:10:36:24 | BufferReadSideEffect [a] | struct_init.c:14:24:14:25 | *ab [a] |
+| struct_init.c:36:10:36:24 | Argument 0 indirection [a] | struct_init.c:14:24:14:25 | *ab [a] |
 nodes
 | A.cpp:98:12:98:18 | new | semmle.label | new |
 | A.cpp:100:5:100:13 | Chi [a] | semmle.label | Chi [a] |
 | A.cpp:100:5:100:13 | Store | semmle.label | Store |
-| A.cpp:101:8:101:9 | BufferReadSideEffect [a] | semmle.label | BufferReadSideEffect [a] |
+| A.cpp:101:8:101:9 | Argument 0 indirection [a] | semmle.label | Argument 0 indirection [a] |
 | A.cpp:103:14:103:14 | *c [a] | semmle.label | *c [a] |
 | A.cpp:107:12:107:16 | (void *)... | semmle.label | (void *)... |
 | A.cpp:107:16:107:16 | a | semmle.label | a |
@@ -116,7 +116,7 @@ nodes
 | by_reference.cpp:68:17:68:18 | nonMemberSetA output argument [a] | semmle.label | nonMemberSetA output argument [a] |
 | by_reference.cpp:68:21:68:30 | call to user_input | semmle.label | call to user_input |
 | by_reference.cpp:69:8:69:20 | call to nonMemberGetA | semmle.label | call to nonMemberGetA |
-| by_reference.cpp:69:22:69:23 | BufferReadSideEffect [a] | semmle.label | BufferReadSideEffect [a] |
+| by_reference.cpp:69:22:69:23 | Argument 0 indirection [a] | semmle.label | Argument 0 indirection [a] |
 | by_reference.cpp:84:3:84:25 | Chi [a] | semmle.label | Chi [a] |
 | by_reference.cpp:84:3:84:25 | Store | semmle.label | Store |
 | by_reference.cpp:84:14:84:23 | call to user_input | semmle.label | call to user_input |
@@ -142,20 +142,20 @@ nodes
 | simple.cpp:83:9:83:28 | Chi [f1] | semmle.label | Chi [f1] |
 | simple.cpp:83:9:83:28 | Store | semmle.label | Store |
 | simple.cpp:83:17:83:26 | call to user_input | semmle.label | call to user_input |
-| simple.cpp:84:14:84:20 | BufferReadSideEffect [f1] | semmle.label | BufferReadSideEffect [f1] |
+| simple.cpp:84:14:84:20 | Argument -1 indirection [f1] | semmle.label | Argument -1 indirection [f1] |
 | simple.cpp:84:14:84:20 | call to getf2f1 | semmle.label | call to getf2f1 |
 | struct_init.c:14:24:14:25 | *ab [a] | semmle.label | *ab [a] |
 | struct_init.c:15:12:15:12 | a | semmle.label | a |
 | struct_init.c:20:20:20:29 | Chi [a] | semmle.label | Chi [a] |
 | struct_init.c:20:20:20:29 | Store | semmle.label | Store |
 | struct_init.c:20:20:20:29 | call to user_input | semmle.label | call to user_input |
 | struct_init.c:22:11:22:11 | a | semmle.label | a |
-| struct_init.c:24:10:24:12 | BufferReadSideEffect [a] | semmle.label | BufferReadSideEffect [a] |
+| struct_init.c:24:10:24:12 | Argument 0 indirection [a] | semmle.label | Argument 0 indirection [a] |
 | struct_init.c:27:7:27:16 | Chi [a] | semmle.label | Chi [a] |
 | struct_init.c:27:7:27:16 | Store | semmle.label | Store |
 | struct_init.c:27:7:27:16 | call to user_input | semmle.label | call to user_input |
 | struct_init.c:31:23:31:23 | a | semmle.label | a |
-| struct_init.c:36:10:36:24 | BufferReadSideEffect [a] | semmle.label | BufferReadSideEffect [a] |
+| struct_init.c:36:10:36:24 | Argument 0 indirection [a] | semmle.label | Argument 0 indirection [a] |
 #select
 | A.cpp:107:12:107:16 | (void *)... | A.cpp:98:12:98:18 | new | A.cpp:107:12:107:16 | (void *)... | (void *)... flows from $@ | A.cpp:98:12:98:18 | new | new |
 | A.cpp:107:16:107:16 | a | A.cpp:98:12:98:18 | new | A.cpp:107:16:107:16 | a | a flows from $@ | A.cpp:98:12:98:18 | new | new |