FA-90596 / Garbage collector invariants / Open access
Stack maps: reference bitmask read most-significant bit first · case 01
Integer slots are relocated as pointers while real reference slots keep stale addresses.
ROOT CAUSE
Slot i is tested against bit (len - 1 - i) instead of bit i.
VERIFIED REPAIR
Bit i of the mask describes slot i.
Unsuccessful approach: Testing bit i + 1 is shifted by one slot.
Case contract
Relocate frame slots after a moving collection. Each frame has a safepoint pc and a slot list; maps[pc] gives a reference bitmask (bit i set means slot i holds a reference; bit 0 is slot 0) and derived pointers [derived_slot, base_slot], which hold base + offset and are not in the mask. moves maps old object addresses to new ones (unmoved objects are absent or map to themselves). Reference slots are relocated, derived slots become new base + (old derived - old base), and every other slot is left untouched. A pc without a map returns ["no-stackmap", pc].
Why this case matters
Precise collectors rely on stack maps; misreading them corrupts registers or keeps stale pointers.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(frames, maps, moves):
out = []
for f in frames:
key = f['pc']
if key not in maps:
return ['no-stackmap', key]
m = maps[key]
old = list(f['slots'])
slots = list(old)
for i in range(len(slots)):
if m['refs'] >> (len(slots) - 1 - i) & 1 and old[i] is not None:
slots[i] = moves.get(old[i], old[i])
for dslot, bslot in m['derived']:
base = old[bslot]
slots[dslot] = moves.get(base, base) + (old[dslot] - base)
out.append(slots)
return out
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 8, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[5016, 8, 2400, 5032, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3001]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[2000, 5016, 3001]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1989]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[None, 2400, 2389]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3005]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5016, 3000, 3005]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 12, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
['no-stackmap', 12]),
('control: null reference slots',
([{'pc': 20, 'slots': [1, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[1, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 9, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[5032, 9, 2400, 5048, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3002]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[2000, 5032, 3002]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1988]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[None, 2400, 2388]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3006]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5032, 3000, 3006]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 13, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
['no-stackmap', 13]),
('control: null reference slots',
([{'pc': 20, 'slots': [2, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[2, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 10, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[5048, 10, 2400, 5064, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3003]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[2000, 5048, 3003]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1987]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[None, 2400, 2387]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3007]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5048, 3000, 3007]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 14, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
['no-stackmap', 14]),
('control: null reference slots',
([{'pc': 20, 'slots': [3, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[3, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 11, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[5064, 11, 2400, 5080, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3004]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[2000, 5064, 3004]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1986]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[None, 2400, 2386]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3008]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5064, 3000, 3008]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 15, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
['no-stackmap', 15]),
('control: null reference slots',
([{'pc': 20, 'slots': [4, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[4, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 12, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[5080, 12, 2400, 5096, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3005]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[2000, 5080, 3005]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1985]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[None, 2400, 2385]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3009]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5080, 3000, 3009]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 16, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
['no-stackmap', 16]),
('control: null reference slots',
([{'pc': 20, 'slots': [5, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[5, None, 0]])]]
for label, args, expected in cases[N - 1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| regression: references, integers and derived pointers | [[1000, 8, 2000, 5032, 1000, 2392]] | [[5016, 8, 2400, 5032, 1000, 2392]] | Failed |
| integer that looks like a moved address | [[2000, 5016, 3001]] | [[2000, 5016, 3001]] | Passed |
| derived pointer below its base | [[None, 2400, 2389]] | [[None, 2400, 2389]] | Passed |
| several frames | [[5, 2400, 9], [1000, 3000, 3005]] | [[5, 2400, 9], [5016, 3000, 3005]] | Failed |
| missing stack map | ['no-stackmap', 12] | ['no-stackmap', 12] | Passed |
| control: null reference slots | [[1, None, 0]] | [[1, None, 0]] | Passed |
SHA-256 / 99df0d368fb742fc1029be5711069daa0a65ef2d419268f4068caa4455bd8aac
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(frames, maps, moves):
out = []
for f in frames:
key = f['pc']
if key not in maps:
return ['no-stackmap', key]
m = maps[key]
old = list(f['slots'])
slots = list(old)
for i in range(len(slots)):
if m['refs'] & (1 << i + 1) and old[i] is not None:
slots[i] = moves.get(old[i], old[i])
for dslot, bslot in m['derived']:
base = old[bslot]
slots[dslot] = moves.get(base, base) + (old[dslot] - base)
out.append(slots)
return out
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 8, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[5016, 8, 2400, 5032, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3001]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[2000, 5016, 3001]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1989]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[None, 2400, 2389]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3005]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5016, 3000, 3005]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 12, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
['no-stackmap', 12]),
('control: null reference slots',
([{'pc': 20, 'slots': [1, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[1, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 9, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[5032, 9, 2400, 5048, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3002]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[2000, 5032, 3002]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1988]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[None, 2400, 2388]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3006]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5032, 3000, 3006]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 13, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
['no-stackmap', 13]),
('control: null reference slots',
([{'pc': 20, 'slots': [2, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[2, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 10, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[5048, 10, 2400, 5064, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3003]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[2000, 5048, 3003]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1987]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[None, 2400, 2387]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3007]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5048, 3000, 3007]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 14, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
['no-stackmap', 14]),
('control: null reference slots',
([{'pc': 20, 'slots': [3, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[3, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 11, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[5064, 11, 2400, 5080, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3004]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[2000, 5064, 3004]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1986]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[None, 2400, 2386]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3008]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5064, 3000, 3008]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 15, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
['no-stackmap', 15]),
('control: null reference slots',
([{'pc': 20, 'slots': [4, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[4, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 12, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[5080, 12, 2400, 5096, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3005]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[2000, 5080, 3005]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1985]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[None, 2400, 2385]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3009]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5080, 3000, 3009]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 16, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
['no-stackmap', 16]),
('control: null reference slots',
([{'pc': 20, 'slots': [5, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[5, None, 0]])]]
for label, args, expected in cases[N - 1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| regression: references, integers and derived pointers | [[1000, 8, 2000, 5032, 1000, 2392]] | [[5016, 8, 2400, 5032, 1000, 2392]] | Failed |
| integer that looks like a moved address | [[2400, 1000, 3001]] | [[2000, 5016, 3001]] | Failed |
| derived pointer below its base | [[None, 2000, 2389]] | [[None, 2400, 2389]] | Failed |
| several frames | [[5, 2000, 9], [5016, 3000, 3005]] | [[5, 2400, 9], [5016, 3000, 3005]] | Failed |
| missing stack map | ['no-stackmap', 12] | ['no-stackmap', 12] | Passed |
| control: null reference slots | [[1, None, 0]] | [[1, None, 0]] | Passed |
SHA-256 / 1bb98601e1c1743d014dd55d7c9d337457c338dd1257b7b886b7efc75f51dac9
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(frames, maps, moves):
out = []
for f in frames:
key = f['pc']
if key not in maps:
return ['no-stackmap', key]
m = maps[key]
old = list(f['slots'])
slots = list(old)
for i in range(len(slots)):
if m['refs'] >> i & 1 and old[i] is not None:
slots[i] = moves.get(old[i], old[i])
for dslot, bslot in m['derived']:
base = old[bslot]
slots[dslot] = moves.get(base, base) + (old[dslot] - base)
out.append(slots)
return out
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 8, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[5016, 8, 2400, 5032, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3001]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[2000, 5016, 3001]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1989]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[None, 2400, 2389]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3005]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5016, 3000, 3005]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 12, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
['no-stackmap', 12]),
('control: null reference slots',
([{'pc': 20, 'slots': [1, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5016, 2000: 2400, 3000: 3000}),
[[1, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 9, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[5032, 9, 2400, 5048, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3002]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[2000, 5032, 3002]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1988]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[None, 2400, 2388]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3006]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5032, 3000, 3006]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 13, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
['no-stackmap', 13]),
('control: null reference slots',
([{'pc': 20, 'slots': [2, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5032, 2000: 2400, 3000: 3000}),
[[2, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 10, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[5048, 10, 2400, 5064, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3003]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[2000, 5048, 3003]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1987]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[None, 2400, 2387]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3007]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5048, 3000, 3007]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 14, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
['no-stackmap', 14]),
('control: null reference slots',
([{'pc': 20, 'slots': [3, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5048, 2000: 2400, 3000: 3000}),
[[3, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 11, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[5064, 11, 2400, 5080, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3004]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[2000, 5064, 3004]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1986]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[None, 2400, 2386]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3008]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5064, 3000, 3008]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 15, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
['no-stackmap', 15]),
('control: null reference slots',
([{'pc': 20, 'slots': [4, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5064, 2000: 2400, 3000: 3000}),
[[4, None, 0]])],
[('regression: references, integers and derived pointers',
([{'pc': 10, 'slots': [1000, 12, 2000, 1016, 1000, 1992]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[5080, 12, 2400, 5096, 1000, 2392]]),
('integer that looks like a moved address',
([{'pc': 20, 'slots': [2000, 1000, 3005]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[2000, 5080, 3005]]),
('derived pointer below its base',
([{'pc': 30, 'slots': [None, 2000, 1985]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[None, 2400, 2385]]),
('several frames',
([{'pc': 20, 'slots': [5, 2000, 9]}, {'pc': 30, 'slots': [1000, 3000, 3009]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[5, 2400, 9], [5080, 3000, 3009]]),
('missing stack map',
([{'pc': 20, 'slots': [1, 2, 3]}, {'pc': 16, 'slots': []}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
['no-stackmap', 16]),
('control: null reference slots',
([{'pc': 20, 'slots': [5, None, 0]}],
{10: {'derived': [[3, 0], [5, 2]], 'refs': 5},
20: {'derived': [], 'refs': 2},
30: {'derived': [[2, 1]], 'refs': 3}},
{1000: 5080, 2000: 2400, 3000: 3000}),
[[5, None, 0]])]]
for label, args, expected in cases[N - 1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| regression: references, integers and derived pointers | [[5016, 8, 2400, 5032, 1000, 2392]] | [[5016, 8, 2400, 5032, 1000, 2392]] | Passed |
| integer that looks like a moved address | [[2000, 5016, 3001]] | [[2000, 5016, 3001]] | Passed |
| derived pointer below its base | [[None, 2400, 2389]] | [[None, 2400, 2389]] | Passed |
| several frames | [[5, 2400, 9], [5016, 3000, 3005]] | [[5, 2400, 9], [5016, 3000, 3005]] | Passed |
| missing stack map | ['no-stackmap', 12] | ['no-stackmap', 12] | Passed |
| control: null reference slots | [[1, None, 0]] | [[1, None, 0]] | Passed |
SHA-256 / 6ae4e2a6c84cc691ad46a6e4823658781ff8fc819798e0ff12df2a4e7056dd98
Verification & scope
A deterministic, bounded teaching model of one garbage-collector mechanism with stipulated rules; it is not a production collector and claims no conformance to any particular runtime. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.
Observations recorded using Python 3.12.14 at 2026-09-29T14:51:28.313553+00:00.
Case digest / 0673b4bf0eca6d6eeacb76626884f04cb10e647ab2ffaef4c4b17168f537bb4d