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py/obj: Add static safety checks to mp_obj_is_type().

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Commit d96cfd13e3 introduced a regression by breaking existing
users of mp_obj_is_type(.., &mp_obj_bool).  This function (and associated
helpers like mp_obj_is_int()) have some specific nuances, and mistakes like
this one can happen again.

This commit adds mp_obj_is_exact_type() which behaves like the the old
mp_obj_is_type().  The new mp_obj_is_type() has the same prototype but it
attempts to statically assert that it's not called with types which should
be checked using mp_obj_is_type().  If called with any of these types: int,
str, bool, NoneType - it will cause a compilation error.  Additional
checked types (e.g function types) can be added in the future.

Existing users of mp_obj_is_type() with the now "invalid" types, were
translated to use mp_obj_is_exact_type().

The use of MP_STATIC_ASSERT() is not bulletproof - usually GCC (and other
compilers) can't statically check conditions that are only known during
link-time (like variables' addresses comparison).  However, in this case,
GCC is able to statically detect these conditions, probably because it's
the exact same object - `&mp_type_int == &mp_type_int` is detected.
Misuses of this function with runtime-chosen types (e.g:
`mp_obj_type_t *x = ...; mp_obj_is_type(..., x);` won't be detected.  MSC
is unable to detect this, so we use MP_STATIC_ASSERT_NOT_MSC().

Compiling with this commit and without the fix for d96cfd13e3 shows
that it detects the problem.

Signed-off-by: Yonatan Goldschmidt <yon.goldschmidt@gmail.com>
This commit is contained in:
Yonatan Goldschmidt
2020-01-22 13:34:19 +01:00
committed by Damien George
parent 6670281472
commit 2a6ba47110
10 changed files with 38 additions and 24 deletions
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22
py/obj.h
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@@ -743,15 +743,29 @@ void *mp_obj_malloc_helper(size_t num_bytes, const mp_obj_type_t *type);
// check for more specific object types.
// Note: these are kept as macros because inline functions sometimes use much
// more code space than the equivalent macros, depending on the compiler.
#define mp_obj_is_type(o, t) (mp_obj_is_obj(o) && (((mp_obj_base_t *)MP_OBJ_TO_PTR(o))->type == (t))) // this does not work for checking int, str or fun; use below macros for that
// don't use mp_obj_is_exact_type directly; use mp_obj_is_type which provides additional safety checks.
// use the former only if you need to bypass these checks (because you've already checked everything else)
#define mp_obj_is_exact_type(o, t) (mp_obj_is_obj(o) && (((mp_obj_base_t *)MP_OBJ_TO_PTR(o))->type == (t)))
// Type checks are split to a separate, constant result macro. This is so it doesn't hinder the compilers's
// optimizations (other tricks like using ({ expr; exper; }) or (exp, expr, expr) in mp_obj_is_type() result
// in missed optimizations)
#define mp_type_assert_not_bool_int_str_nonetype(t) ( \
MP_STATIC_ASSERT_NOT_MSC((t) != &mp_type_bool), \
MP_STATIC_ASSERT_NOT_MSC((t) != &mp_type_int), \
MP_STATIC_ASSERT_NOT_MSC((t) != &mp_type_str), \
MP_STATIC_ASSERT_NOT_MSC((t) != &mp_type_NoneType), \
1)
#define mp_obj_is_type(o, t) (mp_type_assert_not_bool_int_str_nonetype(t) && mp_obj_is_exact_type(o, t))
#if MICROPY_OBJ_IMMEDIATE_OBJS
// bool's are immediates, not real objects, so test for the 2 possible values.
#define mp_obj_is_bool(o) ((o) == mp_const_false || (o) == mp_const_true)
#else
#define mp_obj_is_bool(o) mp_obj_is_type(o, &mp_type_bool)
#define mp_obj_is_bool(o) mp_obj_is_exact_type(o, &mp_type_bool)
#endif
#define mp_obj_is_int(o) (mp_obj_is_small_int(o) || mp_obj_is_type(o, &mp_type_int))
#define mp_obj_is_str(o) (mp_obj_is_qstr(o) || mp_obj_is_type(o, &mp_type_str))
#define mp_obj_is_int(o) (mp_obj_is_small_int(o) || mp_obj_is_exact_type(o, &mp_type_int))
#define mp_obj_is_str(o) (mp_obj_is_qstr(o) || mp_obj_is_exact_type(o, &mp_type_str))
#define mp_obj_is_str_or_bytes(o) (mp_obj_is_qstr(o) || (mp_obj_is_obj(o) && ((mp_obj_base_t *)MP_OBJ_TO_PTR(o))->type->binary_op == mp_obj_str_binary_op))
#define mp_obj_is_dict_or_ordereddict(o) (mp_obj_is_obj(o) && ((mp_obj_base_t *)MP_OBJ_TO_PTR(o))->type->make_new == mp_obj_dict_make_new)
#define mp_obj_is_fun(o) (mp_obj_is_obj(o) && (((mp_obj_base_t *)MP_OBJ_TO_PTR(o))->type->name == MP_QSTR_function))