CONTRACTS: support bounded user defined memory-predicates

Author: Remi Delmas

regression/contracts-dfcc/user-defined-memory-predicates/main.c

@@ -0,0 +1,77 @@
+#include <assert.h>
+#include <stdbool.h>
+#include <stdlib.h>
+typedef struct list_t
+{
+  int value;
+  struct list_t *next;
+} list_t;
+
+// true iff list of len max_len with values in [-10,10]
+bool is_list(list_t *l, size_t len)
+{
+  if(len == 0)
+    return l == NULL;
+  else
+    return __CPROVER_is_fresh(l, sizeof(*l)) &&
+           (-10 <= l->value && l->value <= 10) && is_list(l->next, len - 1);
+}
+
+typedef struct buffer_t
+{
+  size_t size;
+  char *arr;
+  char *cursor;
+} buffer_t;
+
+typedef struct double_buffer_t
+{
+  buffer_t *first;
+  buffer_t *second;
+} double_buffer_t;
+
+bool is_sized_array(char *arr, size_t size)
+{
+  return __CPROVER_is_fresh(arr, size);
+}
+
+bool is_ranged_cursor(char *cursor, char *arr, size_t size)
+{
+  void *lb = arr;
+  void *ub = arr + size;
+  __CPROVER_pointer_in_range_dfcc(lb, cursor, ub);
+}
+
+bool is_buffer(buffer_t *b)
+{
+  return __CPROVER_is_fresh(b, sizeof(*b)) && (0 < b->size && b->size <= 10) &&
+         is_sized_array(b->arr, b->size) &&
+         is_ranged_cursor(b->cursor, b->arr, b->size);
+}
+
+bool is_double_buffer(double_buffer_t *b)
+{
+  return __CPROVER_is_fresh(b, sizeof(*b)) && is_buffer(b->first) &&
+         is_buffer(b->second);
+}
+
+int foo(list_t *l, double_buffer_t *b)
+  // clang-format off
+  __CPROVER_requires(is_list(l, 3))
+  __CPROVER_requires(is_double_buffer(b))
+  __CPROVER_ensures(-28 <= __CPROVER_return_value &&
+                    __CPROVER_return_value <= 50)
+// clang-format on
+{
+  // access the assumed data structure
+  return l->value + l->next->value + l->next->next->value + b->first->size +
+         b->second->size;
+}
+
+int main()
+{
+  list_t *l;
+  double_buffer_t *b;
+  int return_value = foo(l, b);
+  assert(-28 <= return_value && return_value <= 50);
+}

regression/contracts-dfcc/user-defined-memory-predicates/test.desc

@@ -0,0 +1,9 @@
+CORE
+main.c
+--dfcc main --enforce-contract foo _ --pointer-check
+^EXIT=0$
+^SIGNAL=0$
+^VERIFICATION SUCCESSFUL$
+--
+--
+Checks if user-defined predicates work;

src/ansi-c/c_typecheck_expr.cpp

@@ -2342,6 +2342,17 @@ exprt c_typecheck_baset::do_special_functions(
     // returning nil leaves the call expression in place
     return nil_exprt();
   }
+  else if(identifier == CPROVER_PREFIX "pointer_in_range_dfcc")
+  {
+    // experimental feature for DFCC contracts encodings -- do not use
+    if(expr.arguments().size() != 3)
+    {
+      error().source_location = f_op.source_location();
+      error() << "pointer_in_range_dfcc expects three arguments" << eom;
+      throw 0;
+    }
+    return nil_exprt();
+  }
   else if(identifier == CPROVER_PREFIX "same_object")
   {
     if(expr.arguments().size()!=2)

src/ansi-c/cprover_builtin_headers.h

@@ -50,6 +50,8 @@ __CPROVER_bool __CPROVER_is_freeable(const void *mem);
 __CPROVER_bool __CPROVER_was_freed(const void *mem);
 __CPROVER_bool __CPROVER_is_fresh(const void *mem, __CPROVER_size_t size);
 __CPROVER_bool __CPROVER_obeys_contract(void (*)(void), void (*)(void));
+// same as pointer_in_range with experimental support in contracts
+__CPROVER_bool __CPROVER_pointer_in_range_dfcc(void *lb, void *ptr, void *ub);
 void __CPROVER_old(const void *);
 void __CPROVER_loop_entry(const void *);
 

src/ansi-c/library/cprover_contracts.c

@@ -1283,6 +1283,57 @@ __CPROVER_HIDE:;
   }
 }
 
+__CPROVER_size_t __VERIFIER_nondet_size();
+
+__CPROVER_bool __CPROVER_contracts_pointer_in_range_dfcc(
+  void *lb,
+  void **ptr,
+  void *ub,
+  __CPROVER_contracts_write_set_ptr_t write_set)
+{
+__CPROVER_HIDE:;
+  __CPROVER_assert(
+    (write_set != 0) & ((write_set->assume_requires_ctx == 1) |
+                        (write_set->assert_requires_ctx == 1) |
+                        (write_set->assume_ensures_ctx == 1) |
+                        (write_set->assert_ensures_ctx == 1)),
+    "__CPROVER_pointer_in_range_dfcc is used only in requires or ensures "
+    "clauses");
+  __CPROVER_assert(__CPROVER_r_ok(lb, 0), "lb pointer must be valid");
+  __CPROVER_assert(__CPROVER_r_ok(ub, 0), "ub pointer must be valid");
+  __CPROVER_assert(
+    __CPROVER_same_object(lb, ub),
+    "lb and ub pointers must have the same object");
+  __CPROVER_ssize_t lb_offset = __CPROVER_POINTER_OFFSET(lb);
+  __CPROVER_ssize_t ub_offset = __CPROVER_POINTER_OFFSET(ub);
+  __CPROVER_assert(
+    lb_offset <= ub_offset, "lb and ub pointers must be ordered");
+  if(write_set->assume_requires_ctx | write_set->assume_ensures_ctx)
+  {
+    if(__VERIFIER_nondet_CPROVER_bool())
+    {
+      // add nondet offset
+      __CPROVER_size_t offset = __VERIFIER_nondet_size();
+
+      // this cast is safe because we prove that ub and lb are ordered
+      __CPROVER_size_t max_offset = (__CPROVER_size_t)(ub_offset - lb_offset);
+      __CPROVER_assume(offset <= max_offset);
+      *ptr = (char *)lb + offset;
+      return 1;
+    }
+    else
+    {
+      return 0;
+    }
+  }
+  else /* write_set->assert_requires_ctx | write_set->assert_ensures_ctx */
+  {
+    __CPROVER_ssize_t offset = __CPROVER_POINTER_OFFSET(ptr);
+    return __CPROVER_same_object(lb, ptr) && lb_offset <= offset &&
+           offset <= ub_offset;
+  }
+}
+
 /// \brief Returns the start address of the conditional address range found at
 /// index \p idx in  \p set->contract_assigns.
 void *__CPROVER_contracts_write_set_havoc_get_assignable_target(

src/goto-instrument/Makefile

@@ -22,12 +22,14 @@ SRC = accelerate/accelerate.cpp \
       contracts/dynamic-frames/dfcc_is_fresh.cpp \
       contracts/dynamic-frames/dfcc_is_freeable.cpp \
       contracts/dynamic-frames/dfcc_obeys_contract.cpp \
+      contracts/dynamic-frames/dfcc_lift_memory_predicates.cpp \
       contracts/dynamic-frames/dfcc_instrument.cpp \
       contracts/dynamic-frames/dfcc_spec_functions.cpp \
       contracts/dynamic-frames/dfcc_contract_functions.cpp \
       contracts/dynamic-frames/dfcc_wrapper_program.cpp \
       contracts/dynamic-frames/dfcc_contract_handler.cpp \
       contracts/dynamic-frames/dfcc_swap_and_wrap.cpp \
+      contracts/dynamic-frames/dfcc_pointer_in_range.cpp \
       contracts/dynamic-frames/dfcc.cpp \
       contracts/havoc_assigns_clause_targets.cpp \
       contracts/instrument_spec_assigns.cpp \

src/goto-instrument/contracts/doc/developer/contracts-dev-arch.md

@@ -28,6 +28,8 @@ Each of these translation passes is implemented in a specific class:
  :-------------------------------|:---------------------------------------
  @ref dfcc_instrumentt           | Implements @ref contracts-dev-spec-dfcc for @ref goto_functiont, @ref goto_programt, or subsequences of instructions of @ref goto_programt
  @ref dfcc_is_fresht             | Implements @ref contracts-dev-spec-is-fresh
+ @ref dfcc_pointer_in_ranget     | Implements @ref contracts-dev-spec-pointer-in-range
+ @ref dfcc_lift_memory_predicatest | Implements @ref contracts-dev-spec-memory-predicates-rewriting
  @ref dfcc_is_freeablet          | Implements @ref contracts-dev-spec-is-freeable
  @ref dfcc_obeys_contractt       | Implements @ref contracts-dev-spec-obeys-contract
  @ref dfcc_spec_functionst       | Implements @ref contracts-dev-spec-spec-rewriting

src/goto-instrument/contracts/doc/developer/contracts-dev-spec-dfcc-instrument.md

@@ -162,12 +162,17 @@ skip_target: SKIP;
 CALL __CPROVER_deallocate(ptr);
 ```
 
-Calls to `__CPROVER_was_freed` or `__CPROVER_is_freeable` are rewritten as described
-in @subpage contracts-dev-spec-is-freeable
+Calls to `__CPROVER_was_freed` or `__CPROVER_is_freeable` are rewritten as
+described in @subpage contracts-dev-spec-is-freeable
 
-Calls to `__CPROVER_is_fresh` are rewritten as described in @subpage contracts-dev-spec-is-fresh
+Calls to `__CPROVER_is_fresh` are rewritten as described in
+@subpage contracts-dev-spec-is-fresh
 
-Calls to `__CPROVER_obeys_contract` are rewritten as described in @subpage contracts-dev-spec-obeys-contract
+Calls to `__CPROVER_obeys_contract` are rewritten as described in
+@subpage contracts-dev-spec-obeys-contract
+
+Calls to `__CPROVER_pointer_in_range_dfcc` are rewritten as described in
+@subpage contracts-dev-spec-pointer-in-range
 
 For all other function or function pointer calls, we proceed as follows.