Segmentation fault in array sorting with GC interaction #17941
Description
Port, board and/or hardware
unix port
MicroPython version
v1.26.0-46-g1588c455c on 2025-08-17
Reproduction
- Create a comparison class that modifies the array being sorted
- Call gc.collect() within the comparison function
- Attempt to sort the array
import gc
class check:
def __init__(self, arr1, arr2):
self.arr1 = arr1
self.arr2 = arr2
def __lt__(self, other):
# Clear one array, modify another
self.arr1.clear()
self.arr2.extend([777] * 5)
gc.collect()
self.arr2.clear()
return True
d1 = []
d2 = []
contaminators = [check(d1, d2) for _ in range(3)]
d1.extend(contaminators)
d2.extend(contaminators)
d1.sort()Expected behaviour
The code should either:
- Raise a Python exception (e.g., RuntimeError, ValueError)
- Handle the edge case gracefully without crashing
Observed behaviour
MicroPython crashes with a segmentation fault when array.clear() and gc.collect() are called within comparison functions during array sorting operations. This appears to be caused by a NULL pointer dereference in py/obj.c at line 61.
AddressSanitizer:DEADLYSIGNAL
=================================================================
==1758094==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x64c7a2bd4b4b bp 0x000000000000 sp 0x7fffd2494c90 T0)
==1758094==The signal is caused by a READ memory access.
==1758094==Hint: address points to the zero page.
#0 0x64c7a2bd4b4b in mp_obj_get_type ../../py/obj.c:61
#1 0x64c7a2bccdac in mp_binary_op ../../py/runtime.c:640
#2 0x64c7a2bf012d in mp_quicksort ../../py/objlist.c:288
#3 0x64c7a2bf0405 in mp_obj_list_sort ../../py/objlist.c:330
#4 0x64c7a2be8192 in fun_builtin_var_call ../../py/objfun.c:118
#5 0x64c7a2bc6984 in mp_call_function_n_kw ../../py/runtime.c:727
#6 0x64c7a2bc7547 in mp_call_method_n_kw ../../py/runtime.c:743
#7 0x64c7a2c2b5cd in mp_execute_bytecode ../../py/vm.c:1069
#8 0x64c7a2be85a9 in fun_bc_call ../../py/objfun.c:295
#9 0x64c7a2bc6984 in mp_call_function_n_kw ../../py/runtime.c:727
#10 0x64c7a2bcadb3 in mp_call_function_0 ../../py/runtime.c:701
#11 0x64c7a2d4adc6 in execute_from_lexer /home/kai/project/hypothesmith/micropython/ports/unix/main.c:162
#12 0x64c7a2d4aedc in do_file /home/kai/project/hypothesmith/micropython/ports/unix/main.c:311
#13 0x64c7a2d4c825 in main_ /home/kai/project/hypothesmith/micropython/ports/unix/main.c:728
#14 0x64c7a2d4ce63 in main /home/kai/project/hypothesmith/micropython/ports/unix/main.c:494
#15 0x7b69f7c2a3b7 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
#16 0x7b69f7c2a47a in __libc_start_main_impl ../csu/libc-start.c:360
#17 0x64c7a2b69734 in _start (micropython/ports/unix/build-coverage/micropython+0x1a8734) (BuildId: bb66085681e6f5a07b78002d60ef2779d5eae802)The AddressSanitizer output shows a NULL pointer dereference at address 0x000000000000. The call stack reveals:
mp_quicksort (objlist.c:288) - Sorting algorithm in progress
mp_binary_op (runtime.c:640) - Calls comparison operation
mp_obj_get_type (obj.c:61) - CRASH HERE - Dereferencing NULL pointer
Additional Information
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Code of Conduct
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