FA-90611 / Garbage collector invariants / Open access
Stack maps: derived pointer offset dropped · case 01
Derived pointers are reset to the object start after a move.
ROOT CAUSE
The derived slot is set to the relocated base without adding its offset.
THE FAILURE
The derived slot is set to the relocated base without adding its offset.
Unsuccessful approach: Taking the absolute offset breaks derived pointers that point below their base.
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'] >> 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)
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, 5016, 1000, 2400]] | [[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, 2400]] | [[None, 2400, 2389]] | Failed |
| several frames | [[5, 2400, 9], [5016, 3000, 3000]] | [[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 / 54efb8f48f84ba450f4585e6c5970622796183521c6c48eb272754079720043b
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'] >> 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) + abs(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, 2408]] | [[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, 2411]] | [[None, 2400, 2389]] | Failed |
| 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 / e59552134478c7ce32ef07686203c72c2d579c279158802626ffe5027895986c
HELD IN THE MEMBER ARCHIVE
The verified repair and its recorded checks are member-only.
This mechanism has 6 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.
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Sign in to the archive ↗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 2026-09-29T14:51:28.357418+00:00.
Case digest / 74f36fa1b8297d41c3f541d3d55f6da70b3bdf2e98d1196f1980194827327bd4