FA-90601 / Garbage collector invariants / Open access
Stack maps: derived pointers rebased on the already-relocated base · case 01
Interior pointers into moved objects end up offset by the distance the object moved.
ROOT CAUSE
The derived computation reads the base slot after it has been relocated.
THE FAILURE
The derived computation reads the base slot after it has been relocated.
Unsuccessful approach: Using the derived value itself as the base treats it as an exact object pointer.
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 = slots[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, 1016, 1000, 1992]] | [[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, 1989]] | [[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 / f5243bd109ce037dda3f81a89ed7d95b79794ebb3fd50054488f9defbee717d9
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[dslot]
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, 1016, 1000, 1992]] | [[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, 1989]] | [[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 / 6e7425046cbc958aabeb576846444e38162491203f5ca45252c2296cf1e8a53c
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.
Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.
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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 / 02e564c69386712e169814e7a43f172a5836bc3ef42f977483fc5fb5bb89b385