Handling function pointers in contracts instrumentation

During instrumentation for enforcing/replacing function contracts,
all calls to function pointers were not handled. We now consider
that a function call might be a dereference and properly handle it
during instrumentation.

Signed-off-by: Felipe R. Monteiro <[email protected]>

Author: feliperodri

regression/contracts/function-calls-05/main.c

@@ -0,0 +1,25 @@
+#include <assert.h>
+#include <stdlib.h>
+
+static int add_operator(const int *a, const int *b)
+{
+  return (*a + *b);
+}
+
+// clang-format off
+int foo(int *x, int *y)
+  __CPROVER_requires(x != NULL &&  y != NULL)
+  __CPROVER_ensures(__CPROVER_return_value == 10)
+// clang-format on
+{
+  int (*sum)(const int *, const int *) = add_operator;
+  return sum(x, y);
+}
+
+int main()
+{
+  int x = 5;
+  int y = 5;
+  assert(foo(&x, &y) == 10);
+  return 0;
+}

regression/contracts/function-calls-05/test.desc

@@ -0,0 +1,12 @@
+CORE
+main.c
+--enforce-all-contracts
+^EXIT=0$
+^SIGNAL=0$
+\[postcondition.\d+\] file main.c line \d+ Check ensures clause: SUCCESS
+\[foo.\d+\] line \d+ Check that sum is assignable: SUCCESS
+\[main.assertion.\d+\] line \d+ assertion foo\(\&x, \&y\) \=\= 10: SUCCESS
+^VERIFICATION SUCCESSFUL$
+--
+--
+Checks whether function contracts are properly propagated to function pointers.

src/goto-instrument/code_contracts.cpp

@@ -649,8 +649,16 @@ void code_contractst::instrument_call_statement(
     "a function call");
 
   code_function_callt call = instruction_iterator->get_function_call();
-  const irep_idt &called_name =
-    to_symbol_expr(call.function()).get_identifier();
+  irep_idt called_name;
+  if(call.function().id() == ID_dereference)
+  {
+    called_name = to_symbol_expr(to_dereference_expr(call.function()).pointer())
+                    .get_identifier();
+  }
+  else
+  {
+    called_name = to_symbol_expr(call.function()).get_identifier();
+  }
 
   if(called_name == "malloc")
   {
@@ -699,12 +707,15 @@ void code_contractst::instrument_call_statement(
     ++instruction_iterator;
   }
 
-  PRECONDITION(call.function().id() == ID_symbol);
   const symbolt &called_symbol = ns.lookup(called_name);
-  const code_typet &called_type = to_code_type(called_symbol.type);
-
+  // Called symbol might be a function pointer.
+  const typet &called_symbol_type = (called_symbol.type.id() == ID_pointer)
+                                      ? called_symbol.type.subtype()
+                                      : called_symbol.type;
   exprt called_assigns =
-    to_code_with_contract_type(called_symbol.type).assigns();
+    to_code_with_contract_type(called_symbol_type).assigns();
+  const code_typet &called_type = to_code_type(called_symbol_type);
+
   if(called_assigns.is_not_nil())
   {
     replace_symbolt replace_formal_params;
@@ -753,8 +764,17 @@ bool code_contractst::check_for_looped_mallocs(const goto_programt &program)
     if(instruction.is_function_call())
     {
       code_function_callt call = instruction.get_function_call();
-      const irep_idt &called_name =
-        to_symbol_expr(call.function()).get_identifier();
+      irep_idt called_name;
+      if(call.function().id() == ID_dereference)
+      {
+        called_name =
+          to_symbol_expr(to_dereference_expr(call.function()).pointer())
+            .get_identifier();
+      }
+      else
+      {
+        called_name = to_symbol_expr(call.function()).get_identifier();
+      }
 
       if(called_name == "malloc")
       {