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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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4
py/binary.c
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@@ -334,7 +334,7 @@ void mp_binary_set_val(char struct_type, char val_type, mp_obj_t val_in, byte *p
#endif
default:
#if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
if (mp_obj_is_type(val_in, &mp_type_int)) {
if (mp_obj_is_exact_type(val_in, &mp_type_int)) {
mp_obj_int_to_bytes_impl(val_in, struct_type == '>', size, p);
return;
}
@@ -371,7 +371,7 @@ void mp_binary_set_val_array(char typecode, void *p, size_t index, mp_obj_t val_
break;
default:
#if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
if (mp_obj_is_type(val_in, &mp_type_int)) {
if (mp_obj_is_exact_type(val_in, &mp_type_int)) {
size_t size = mp_binary_get_size('@', typecode, NULL);
mp_obj_int_to_bytes_impl(val_in, MP_ENDIANNESS_BIG,
size, (uint8_t *)p + index * size);