QUERY · ISSUE
uctypes: Element assignment through PTR silently fails
bug
Port, board and/or hardware
unix port, longlong build
MicroPython version
MicroPython v1.26.0-preview.391.gba3f9cacf0.dirty
Reproduction
import uctypes
# Find the size corresponding to a pointer
ptr_size = uctypes.sizeof((uctypes.PTR, uctypes.INT8))
assert ptr_size in (4, 8)
UINTPTR = uctypes.UINT64 if ptr_size == 8 else uctypes.UINT32
# This descriptor lets us store an address via val then dereference it via ptr
descr = {
'ptr': (uctypes.PTR | 0, uctypes.INT8),
'val': UINTPTR | 0
}
# Build the data. `x.ptr` points at b2.
b1 = bytearray(uctypes.sizeof(descr))
b2 = bytearray(8)
x = uctypes.struct(uctypes.addressof(b1), descr)
x.val = uctypes.addressof(b2)
# Optimization: avoid rebuilding the `x.ptr` struct object
# (this has no influence over the bug)
ptr = x.ptr
# Access the data...
print("Setting via uctypes ptr, reading via bytearray")
for i in range(8):
ptr[i] = i
for i in range(8):
print(b2[i], end=" ")
#assert ptr[i] == i ## Assertion fails!
print()
print("Setting via bytearray, reading via ptr")
for i in range(8):
b2[i] = 10 + i
for i in range(8):
print(ptr[i], end=" ")
assert ptr[i] == 10 + i
print()
Expected behaviour
The first line printed should say 0 1 2 3 4 5 6 7 (the values assigned by ptr[i] = i)
Observed behaviour
Instead, it says 0 0 0 0 0 0 0 , because the element assignment is silently ignored.
Additional Information
over in m68k-micropython I'm using this change:
} else if (agg_type == PTR) {
byte *p = *(void **)self->addr;
if (mp_obj_is_small_int(t->items[1])) {
uint val_type = GET_TYPE(MP_OBJ_SMALL_INT_VALUE(t->items[1]), VAL_TYPE_BITS);
- return get_aligned(val_type, p, index);
+ if (value == MP_OBJ_SENTINEL) {
+ return get_aligned(val_type, p, index);
+ } else {
+ set_aligned(val_type, p, index, value);
+ return value; // just !MP_OBJ_NULL
+ }
I can submit this as a PR, but I wanted to make sure the functionality wasn't intentionally missing for some reason I wasn't aware of.
Code of Conduct
Yes, I agree
CANDIDATE · ISSUE
uctypes.bytes_at() accepts out-of-range (non-canonical) address and segfaults
bug
Port, board and/or hardware
Unix port
MicroPython version
MicroPython v1.27.0-preview.107.gd1607598f on 2025-09-09; linux [GCC 14.2.0] version
Reproduction
A Python-level exception when the address is obviously invalid, e.g.:
- ValueError/OverflowError for negative/out-of-range addresses, or
- OSError if the runtime chooses to probe and detect unreadable memory on the unix port.
At minimum, reject negative addresses and detect addr + size overflow to avoid trivial VM crashes.
Expected behaviour
import uctypes
ptr = 1 << 48
arr = uctypes.bytes_at(ptr, 8)
print('READ', arr)
Observed behaviour
Program received signal SIGSEGV, Segmentation fault.
#0 qstr_compute_hash(data=0x1000000000000, len=0x8)
#1 mp_obj_new_str_copy(type=mp_type_bytes, data=0x1000000000000, len=0x8)
#2 mp_obj_new_bytes(...)
#3 uctypes_struct_bytes_at(ptr=0x1000000000000, size=0x8)
#4 fun_builtin_2_call(...)
#5 mp_call_function_n_kw(...)
#6 mp_execute_bytecode(...)
...
Additional Information
No, I've provided everything above.
Code of Conduct
Yes, I agree