MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_B

[jickster]

Code: Select all

// A MicroPython object is a machine word having the following form:
//  - xxxx...xx01 : a small int, bits 2 and above are the value
//  - xxxx...xx11 : a qstr, bits 2 and above are the value
//  - xxxx...xxx0 : a pointer to an mp_obj_base_t (unless a fake object)
#define MICROPY_OBJ_REPR_B (1)

Does this mean pointers must have 2-byte alignment?

[dhylands]

Pointers to micropython objects always have at least 4-byte alignment. Note that this representation is not for pointers in general, just pointers to micropython objects.

[jickster]

Pointers to micropython objects always have at least 4-byte alignment. Note that this representation is not for pointers in general, just pointers to micropython objects.

I don’t see how this is enforced. The REPR macros are not used in any of allocation functions

[dhylands]

For the pyboard, the heap is aligned to 4 byte boundary, and the blocks are 16-bytes each. This causes all allocated objects to automatically have 4-byte alignment.

In C, any structure which contains a pointer is also pointer-size aligned. Since all python objects declared in C have an mp_obj_type_t object as their first member and it contains a pointer, this ensures that all C declared python objects have 4-byte alignment.

The stack is also setup to have 4-byte alignment.