CPP: Fix FPs.

cpp/ql/src/semmle/code/cpp/commons/Printf.qll

@@ -169,7 +169,12 @@ class FormattingFunctionCall extends Expr {
    * Gets the number of arguments to this call that are parameters to the
    * format string.
    */
-  int getNumFormatArgument() { result = count(this.getFormatArgument(_)) }
+  int getNumFormatArgument() {
+  	result = count(this.getFormatArgument(_)) and
+
+  	// format arguments must be known
+  	exists(getTarget().(FormattingFunction).getFirstFormatArgumentIndex())
+ }
 }
 
 /**

cpp/ql/src/semmle/code/cpp/models/interfaces/FormattingFunction.qll

@@ -115,7 +115,20 @@ abstract class FormattingFunction extends Function {
    * Gets the position of the first format argument, corresponding with
    * the first format specifier in the format string.
    */
-  int getFirstFormatArgumentIndex() { result = getNumberOfParameters() }
+  int getFirstFormatArgumentIndex() {
+  	result = getNumberOfParameters()
+  	and
+    // the formatting function either has a definition in the snapshot, or all
+    // `DeclarationEntry`s agree on the number of parameters (otherwise we don't
+    // really know the correct number)
+    (
+      hasDefinition() or
+      forall(FunctionDeclarationEntry fde |
+        fde = getADeclarationEntry() |
+        result = fde.getNumberOfParameters()
+      )
+    )
+  }
 
   /**
    * Gets the position of the buffer size argument, if any.

cpp/ql/test/query-tests/Likely Bugs/Format/WrongNumberOfFormatArguments/TooManyFormatArguments.expected

@@ -1,9 +1,6 @@
 | a.c:14:3:14:25 | call to myMultiplyDefinedPrintf | Format expects 1 arguments but given 2 |
-| a.c:17:3:17:26 | call to myMultiplyDefinedPrintf2 | Format expects 1 arguments but given 2 |
 | b.c:11:3:11:25 | call to myMultiplyDefinedPrintf | Format expects 1 arguments but given 2 |
-| b.c:14:3:14:26 | call to myMultiplyDefinedPrintf2 | Format expects 1 arguments but given 2 |
 | c.c:7:3:7:25 | call to myMultiplyDefinedPrintf | Format expects 1 arguments but given 2 |
-| c.c:10:3:10:26 | call to myMultiplyDefinedPrintf2 | Format expects 1 arguments but given 2 |
 | custom_printf.cpp:31:5:31:12 | call to myPrintf | Format expects 2 arguments but given 3 |
 | macros.cpp:12:2:12:31 | call to printf | Format expects 2 arguments but given 3 |
 | macros.cpp:16:2:16:30 | call to printf | Format expects 2 arguments but given 3 |

cpp/ql/test/query-tests/Likely Bugs/Format/WrongNumberOfFormatArguments/WrongNumberOfFormatArguments.expected

@@ -1,9 +1,6 @@
 | a.c:12:3:12:25 | call to myMultiplyDefinedPrintf | Format expects 1 arguments but given 0 |
-| a.c:15:3:15:26 | call to myMultiplyDefinedPrintf2 | Format expects 1 arguments but given 0 |
 | b.c:9:3:9:25 | call to myMultiplyDefinedPrintf | Format expects 1 arguments but given 0 |
-| b.c:12:3:12:26 | call to myMultiplyDefinedPrintf2 | Format expects 1 arguments but given 0 |
 | c.c:5:3:5:25 | call to myMultiplyDefinedPrintf | Format expects 1 arguments but given 0 |
-| c.c:8:3:8:26 | call to myMultiplyDefinedPrintf2 | Format expects 1 arguments but given 0 |
 | custom_printf.cpp:29:5:29:12 | call to myPrintf | Format expects 2 arguments but given 1 |
 | macros.cpp:14:2:14:37 | call to printf | Format expects 4 arguments but given 3 |
 | macros.cpp:21:2:21:36 | call to printf | Format expects 4 arguments but given 3 |

cpp/ql/test/query-tests/Likely Bugs/Format/WrongNumberOfFormatArguments/a.c

@@ -12,7 +12,7 @@ void test_custom_printf1()
   myMultiplyDefinedPrintf("%i", 0); // BAD (too few format arguments)
   myMultiplyDefinedPrintf("%i", 0, 1); // GOOD
   myMultiplyDefinedPrintf("%i", 0, 1, 2); // BAD (too many format arguments)
-  myMultiplyDefinedPrintf2("%i", 0); // GOOD (we can't tell which definition is correct so we have to assume this is OK) [FALSE POSITIVE]
+  myMultiplyDefinedPrintf2("%i", 0); // GOOD (we can't tell which definition is correct so we have to assume this is OK)
   myMultiplyDefinedPrintf2("%i", 0, 1); // GOOD (we can't tell which definition is correct so we have to assume this is OK)
-  myMultiplyDefinedPrintf2("%i", 0, 1, 2); // GOOD (we can't tell which definition is correct so we have to assume this is OK) [FALSE POSITIVE]
+  myMultiplyDefinedPrintf2("%i", 0, 1, 2); // GOOD (we can't tell which definition is correct so we have to assume this is OK)
 }

cpp/ql/test/query-tests/Likely Bugs/Format/WrongNumberOfFormatArguments/b.c

@@ -9,7 +9,7 @@ void test_custom_printf2()
   myMultiplyDefinedPrintf("%i", 0); // BAD (too few format arguments)
   myMultiplyDefinedPrintf("%i", 0, 1); // GOOD
   myMultiplyDefinedPrintf("%i", 0, 1, 2); // BAD (too many format arguments)
-  myMultiplyDefinedPrintf2("%i", 0); // GOOD (we can't tell which definition is correct so we have to assume this is OK) [FALSE POSITIVE]
+  myMultiplyDefinedPrintf2("%i", 0); // GOOD (we can't tell which definition is correct so we have to assume this is OK)
   myMultiplyDefinedPrintf2("%i", 0, 1); // GOOD (we can't tell which definition is correct so we have to assume this is OK)
-  myMultiplyDefinedPrintf2("%i", 0, 1, 2); // GOOD (we can't tell which definition is correct so we have to assume this is OK) [FALSE POSITIVE]
+  myMultiplyDefinedPrintf2("%i", 0, 1, 2); // GOOD (we can't tell which definition is correct so we have to assume this is OK)
 }

cpp/ql/test/query-tests/Likely Bugs/Format/WrongNumberOfFormatArguments/c.c

@@ -5,7 +5,7 @@ void test_custom_printf2()
   myMultiplyDefinedPrintf("%i", 0); // BAD (too few format arguments)
   myMultiplyDefinedPrintf("%i", 0, 1); // GOOD
   myMultiplyDefinedPrintf("%i", 0, 1, 2); // BAD (too many format arguments)
-  myMultiplyDefinedPrintf2("%i", 0); // GOOD (we can't tell which definition is correct so we have to assume this is OK) [FALSE POSITIVE]
+  myMultiplyDefinedPrintf2("%i", 0); // GOOD (we can't tell which definition is correct so we have to assume this is OK)
   myMultiplyDefinedPrintf2("%i", 0, 1); // GOOD (we can't tell which definition is correct so we have to assume this is OK)
-  myMultiplyDefinedPrintf2("%i", 0, 1, 2); // GOOD (we can't tell which definition is correct so we have to assume this is OK) [FALSE POSITIVE]
+  myMultiplyDefinedPrintf2("%i", 0, 1, 2); // GOOD (we can't tell which definition is correct so we have to assume this is OK)
 }