FA-90316 / Bytecode virtual machines / Open access

Stack map frames: one-item frame delta not rebased · case 01

same_locals_1_stack_item frames land 64 bytes too far.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The frame type is used as the delta without subtracting 64.

VERIFIED REPAIR

Subtract 64 from the type to get the delta.

Unsuccessful approach: Subtracting 63 is one byte off.

Case contract

Expand compressed stack map frames. Types: 0-63 same (delta = type), 64-127 same_locals_1_stack_item (delta = type - 64, one stack item), 128-246 reserved (["ClassFormatError", index]), 247 extended one item [247, delta, item], 248-250 chop 251-type locals [t, delta], 251 same extended [251, delta], 252-254 append type-251 locals [t, delta, items...], 255 full [255, delta, locals, stack]. The first frame's offset is its delta; each later offset is previous + delta + 1. Chopping more locals than exist is an error. Return [offset, locals, stack] for every frame; each frame's locals are an independent snapshot.

Why this case matters

Verifiers reconstruct per-offset types from this compressed encoding; any slip mistypes locals.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(initial, frames):
    locals_ = list(initial)
    out = []
    offset = 0
    for idx, fr in enumerate(frames):
        t = fr[0]
        stack = []
        if t <= 63:
            delta = t
        elif t <= 127:
            delta = t
            stack = [fr[1]]
        elif t < 247:
            return ['ClassFormatError', idx]
        elif t == 247:
            delta = fr[1]
            stack = [fr[2]]
        elif t <= 250:
            delta = fr[1]
            k = 251 - t
            if k > len(locals_):
                return ['ClassFormatError', idx]
            locals_ = locals_[:len(locals_) - k]
        elif t == 251:
            delta = fr[1]
        elif t <= 254:
            delta = fr[1]
            locals_ = locals_ + list(fr[2:2 + t - 251])
        else:
            delta = fr[1]
            locals_ = list(fr[2])
            stack = list(fr[3])
        offset = delta if idx == 0 else offset + delta + 1
        out.append([offset, locals_, stack])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [71, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [13, ['I', 'Object'], ['I']],
    [17, ['I', 'Object', 'F'], []],
    [20, ['I'], []],
    [321, ['I'], []],
    [323, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[11], [3]]),
   [[11, ['I', 'Object'], []], [15, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[65, 'Object'], [64, 'I']]),
   [[1, ['I', 'Object'], ['Object']], [2, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 5, 'Object']]),
   [[5, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 1], [251, 0]]), [[1, [], []], [2, [], []]]),
  ('chop more locals than exist', ([], [[250, 1]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 1, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [2, ['I', 'Object', 'I', 'I', 'F'], []],
    [3, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 1, ['Object'], []], [2]]),
   [[1, ['Object'], []], [4, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [72, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [14, ['I', 'Object'], ['I']],
    [18, ['I', 'Object', 'F'], []],
    [21, ['I'], []],
    [322, ['I'], []],
    [324, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[12], [3]]),
   [[12, ['I', 'Object'], []], [16, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[66, 'Object'], [64, 'I']]),
   [[2, ['I', 'Object'], ['Object']], [3, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 6, 'Object']]),
   [[6, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 2], [251, 0]]), [[2, [], []], [3, [], []]]),
  ('chop more locals than exist', ([], [[250, 2]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 2, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [3, ['I', 'Object', 'I', 'I', 'F'], []],
    [4, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 2, ['Object'], []], [2]]),
   [[2, ['Object'], []], [5, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [73, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [15, ['I', 'Object'], ['I']],
    [19, ['I', 'Object', 'F'], []],
    [22, ['I'], []],
    [323, ['I'], []],
    [325, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[13], [3]]),
   [[13, ['I', 'Object'], []], [17, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[67, 'Object'], [64, 'I']]),
   [[3, ['I', 'Object'], ['Object']], [4, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 7, 'Object']]),
   [[7, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 3], [251, 0]]), [[3, [], []], [4, [], []]]),
  ('chop more locals than exist', ([], [[250, 3]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 3, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [4, ['I', 'Object', 'I', 'I', 'F'], []],
    [5, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 3, ['Object'], []], [2]]),
   [[3, ['Object'], []], [6, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [74, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [16, ['I', 'Object'], ['I']],
    [20, ['I', 'Object', 'F'], []],
    [23, ['I'], []],
    [324, ['I'], []],
    [326, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[14], [3]]),
   [[14, ['I', 'Object'], []], [18, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[68, 'Object'], [64, 'I']]),
   [[4, ['I', 'Object'], ['Object']], [5, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 8, 'Object']]),
   [[8, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 4], [251, 0]]), [[4, [], []], [5, [], []]]),
  ('chop more locals than exist', ([], [[250, 4]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 4, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [5, ['I', 'Object', 'I', 'I', 'F'], []],
    [6, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 4, ['Object'], []], [2]]),
   [[4, ['Object'], []], [7, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [75, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [17, ['I', 'Object'], ['I']],
    [21, ['I', 'Object', 'F'], []],
    [24, ['I'], []],
    [325, ['I'], []],
    [327, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[15], [3]]),
   [[15, ['I', 'Object'], []], [19, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[69, 'Object'], [64, 'I']]),
   [[5, ['I', 'Object'], ['Object']], [6, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 9, 'Object']]),
   [[9, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 5], [251, 0]]), [[5, [], []], [6, [], []]]),
  ('chop more locals than exist', ([], [[250, 5]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 5, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [6, ['I', 'Object', 'I', 'I', 'F'], []],
    [7, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 5, ['Object'], []], [2]]),
   [[5, ['Object'], []], [8, ['Object'], []]])]]
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: every compressed frame kind	`[[5, ['I', 'Object'], []], [77, ['I', 'Object'], ['I']], [81, ['I', 'Object', 'F'], []], [84, ['I'], []], [385, ['I'], []], [387, ['I'], ['Object', 'J']]]`	`[[5, ['I', 'Object'], []], [13, ['I', 'Object'], ['I']], [17, ['I', 'Object', 'F'], []], [20, ['I'], []], [321, ['I'], []], [323, ['I'], ['Object', 'J']]]`	Failed
first frame offset is its delta	`[[11, ['I', 'Object'], []], [15, ['I', 'Object'], []]]`	`[[11, ['I', 'Object'], []], [15, ['I', 'Object'], []]]`	Passed
same_locals_1_stack_item delta	`[[65, ['I', 'Object'], ['Object']], [130, ['I', 'Object'], ['I']]]`	`[[1, ['I', 'Object'], ['Object']], [2, ['I', 'Object'], ['I']]]`	Failed
reserved frame type	`['ClassFormatError', 1]`	`['ClassFormatError', 1]`	Passed
extended one-item frame type	`[[5, ['I', 'Object'], ['Object']]]`	`[[5, ['I', 'Object'], ['Object']]]`	Passed
chop three locals	`[[1, [], []], [2, [], []]]`	`[[1, [], []], [2, [], []]]`	Passed
chop more locals than exist	`['ClassFormatError', 0]`	`['ClassFormatError', 0]`	Passed
append three locals then snapshot	`[[0, ['I', 'Object'], []], [2, ['I', 'Object', 'I', 'I', 'F'], []], [3, ['I', 'Object', 'I', 'I', 'F'], []]]`	`[[0, ['I', 'Object'], []], [2, ['I', 'Object', 'I', 'I', 'F'], []], [3, ['I', 'Object', 'I', 'I', 'F'], []]]`	Passed
control: full frame replaces locals	`[[1, ['Object'], []], [4, ['Object'], []]]`	`[[1, ['Object'], []], [4, ['Object'], []]]`	Passed

SHA-256 / eac92535b7c4d96389aeaa29f5a2f9c52fbd9c549263e5bb00581a30549212a9

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(initial, frames):
    locals_ = list(initial)
    out = []
    offset = 0
    for idx, fr in enumerate(frames):
        t = fr[0]
        stack = []
        if t <= 63:
            delta = t
        elif t <= 127:
            delta = t - 63
            stack = [fr[1]]
        elif t < 247:
            return ['ClassFormatError', idx]
        elif t == 247:
            delta = fr[1]
            stack = [fr[2]]
        elif t <= 250:
            delta = fr[1]
            k = 251 - t
            if k > len(locals_):
                return ['ClassFormatError', idx]
            locals_ = locals_[:len(locals_) - k]
        elif t == 251:
            delta = fr[1]
        elif t <= 254:
            delta = fr[1]
            locals_ = locals_ + list(fr[2:2 + t - 251])
        else:
            delta = fr[1]
            locals_ = list(fr[2])
            stack = list(fr[3])
        offset = delta if idx == 0 else offset + delta + 1
        out.append([offset, locals_, stack])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [71, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [13, ['I', 'Object'], ['I']],
    [17, ['I', 'Object', 'F'], []],
    [20, ['I'], []],
    [321, ['I'], []],
    [323, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[11], [3]]),
   [[11, ['I', 'Object'], []], [15, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[65, 'Object'], [64, 'I']]),
   [[1, ['I', 'Object'], ['Object']], [2, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 5, 'Object']]),
   [[5, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 1], [251, 0]]), [[1, [], []], [2, [], []]]),
  ('chop more locals than exist', ([], [[250, 1]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 1, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [2, ['I', 'Object', 'I', 'I', 'F'], []],
    [3, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 1, ['Object'], []], [2]]),
   [[1, ['Object'], []], [4, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [72, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [14, ['I', 'Object'], ['I']],
    [18, ['I', 'Object', 'F'], []],
    [21, ['I'], []],
    [322, ['I'], []],
    [324, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[12], [3]]),
   [[12, ['I', 'Object'], []], [16, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[66, 'Object'], [64, 'I']]),
   [[2, ['I', 'Object'], ['Object']], [3, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 6, 'Object']]),
   [[6, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 2], [251, 0]]), [[2, [], []], [3, [], []]]),
  ('chop more locals than exist', ([], [[250, 2]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 2, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [3, ['I', 'Object', 'I', 'I', 'F'], []],
    [4, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 2, ['Object'], []], [2]]),
   [[2, ['Object'], []], [5, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [73, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [15, ['I', 'Object'], ['I']],
    [19, ['I', 'Object', 'F'], []],
    [22, ['I'], []],
    [323, ['I'], []],
    [325, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[13], [3]]),
   [[13, ['I', 'Object'], []], [17, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[67, 'Object'], [64, 'I']]),
   [[3, ['I', 'Object'], ['Object']], [4, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 7, 'Object']]),
   [[7, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 3], [251, 0]]), [[3, [], []], [4, [], []]]),
  ('chop more locals than exist', ([], [[250, 3]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 3, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [4, ['I', 'Object', 'I', 'I', 'F'], []],
    [5, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 3, ['Object'], []], [2]]),
   [[3, ['Object'], []], [6, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [74, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [16, ['I', 'Object'], ['I']],
    [20, ['I', 'Object', 'F'], []],
    [23, ['I'], []],
    [324, ['I'], []],
    [326, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[14], [3]]),
   [[14, ['I', 'Object'], []], [18, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[68, 'Object'], [64, 'I']]),
   [[4, ['I', 'Object'], ['Object']], [5, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 8, 'Object']]),
   [[8, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 4], [251, 0]]), [[4, [], []], [5, [], []]]),
  ('chop more locals than exist', ([], [[250, 4]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 4, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [5, ['I', 'Object', 'I', 'I', 'F'], []],
    [6, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 4, ['Object'], []], [2]]),
   [[4, ['Object'], []], [7, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [75, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [17, ['I', 'Object'], ['I']],
    [21, ['I', 'Object', 'F'], []],
    [24, ['I'], []],
    [325, ['I'], []],
    [327, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[15], [3]]),
   [[15, ['I', 'Object'], []], [19, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[69, 'Object'], [64, 'I']]),
   [[5, ['I', 'Object'], ['Object']], [6, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 9, 'Object']]),
   [[9, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 5], [251, 0]]), [[5, [], []], [6, [], []]]),
  ('chop more locals than exist', ([], [[250, 5]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 5, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [6, ['I', 'Object', 'I', 'I', 'F'], []],
    [7, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 5, ['Object'], []], [2]]),
   [[5, ['Object'], []], [8, ['Object'], []]])]]
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: every compressed frame kind	`[[5, ['I', 'Object'], []], [14, ['I', 'Object'], ['I']], [18, ['I', 'Object', 'F'], []], [21, ['I'], []], [322, ['I'], []], [324, ['I'], ['Object', 'J']]]`	`[[5, ['I', 'Object'], []], [13, ['I', 'Object'], ['I']], [17, ['I', 'Object', 'F'], []], [20, ['I'], []], [321, ['I'], []], [323, ['I'], ['Object', 'J']]]`	Failed
first frame offset is its delta	`[[11, ['I', 'Object'], []], [15, ['I', 'Object'], []]]`	`[[11, ['I', 'Object'], []], [15, ['I', 'Object'], []]]`	Passed
same_locals_1_stack_item delta	`[[2, ['I', 'Object'], ['Object']], [4, ['I', 'Object'], ['I']]]`	`[[1, ['I', 'Object'], ['Object']], [2, ['I', 'Object'], ['I']]]`	Failed
reserved frame type	`['ClassFormatError', 1]`	`['ClassFormatError', 1]`	Passed
extended one-item frame type	`[[5, ['I', 'Object'], ['Object']]]`	`[[5, ['I', 'Object'], ['Object']]]`	Passed
chop three locals	`[[1, [], []], [2, [], []]]`	`[[1, [], []], [2, [], []]]`	Passed
chop more locals than exist	`['ClassFormatError', 0]`	`['ClassFormatError', 0]`	Passed
append three locals then snapshot	`[[0, ['I', 'Object'], []], [2, ['I', 'Object', 'I', 'I', 'F'], []], [3, ['I', 'Object', 'I', 'I', 'F'], []]]`	`[[0, ['I', 'Object'], []], [2, ['I', 'Object', 'I', 'I', 'F'], []], [3, ['I', 'Object', 'I', 'I', 'F'], []]]`	Passed
control: full frame replaces locals	`[[1, ['Object'], []], [4, ['Object'], []]]`	`[[1, ['Object'], []], [4, ['Object'], []]]`	Passed

SHA-256 / 0e2328a334ed2def889d0f90f1af0342f0eddad7f8d4f9d0f496f6fd08074ddc

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(initial, frames):
    locals_ = list(initial)
    out = []
    offset = 0
    for idx, fr in enumerate(frames):
        t = fr[0]
        stack = []
        if t <= 63:
            delta = t
        elif t <= 127:
            delta = t - 64
            stack = [fr[1]]
        elif t < 247:
            return ['ClassFormatError', idx]
        elif t == 247:
            delta = fr[1]
            stack = [fr[2]]
        elif t <= 250:
            delta = fr[1]
            k = 251 - t
            if k > len(locals_):
                return ['ClassFormatError', idx]
            locals_ = locals_[:len(locals_) - k]
        elif t == 251:
            delta = fr[1]
        elif t <= 254:
            delta = fr[1]
            locals_ = locals_ + list(fr[2:2 + t - 251])
        else:
            delta = fr[1]
            locals_ = list(fr[2])
            stack = list(fr[3])
        offset = delta if idx == 0 else offset + delta + 1
        out.append([offset, locals_, stack])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [71, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [13, ['I', 'Object'], ['I']],
    [17, ['I', 'Object', 'F'], []],
    [20, ['I'], []],
    [321, ['I'], []],
    [323, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[11], [3]]),
   [[11, ['I', 'Object'], []], [15, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[65, 'Object'], [64, 'I']]),
   [[1, ['I', 'Object'], ['Object']], [2, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 5, 'Object']]),
   [[5, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 1], [251, 0]]), [[1, [], []], [2, [], []]]),
  ('chop more locals than exist', ([], [[250, 1]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 1, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [2, ['I', 'Object', 'I', 'I', 'F'], []],
    [3, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 1, ['Object'], []], [2]]),
   [[1, ['Object'], []], [4, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [72, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [14, ['I', 'Object'], ['I']],
    [18, ['I', 'Object', 'F'], []],
    [21, ['I'], []],
    [322, ['I'], []],
    [324, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[12], [3]]),
   [[12, ['I', 'Object'], []], [16, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[66, 'Object'], [64, 'I']]),
   [[2, ['I', 'Object'], ['Object']], [3, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 6, 'Object']]),
   [[6, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 2], [251, 0]]), [[2, [], []], [3, [], []]]),
  ('chop more locals than exist', ([], [[250, 2]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 2, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [3, ['I', 'Object', 'I', 'I', 'F'], []],
    [4, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 2, ['Object'], []], [2]]),
   [[2, ['Object'], []], [5, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [73, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [15, ['I', 'Object'], ['I']],
    [19, ['I', 'Object', 'F'], []],
    [22, ['I'], []],
    [323, ['I'], []],
    [325, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[13], [3]]),
   [[13, ['I', 'Object'], []], [17, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[67, 'Object'], [64, 'I']]),
   [[3, ['I', 'Object'], ['Object']], [4, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 7, 'Object']]),
   [[7, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 3], [251, 0]]), [[3, [], []], [4, [], []]]),
  ('chop more locals than exist', ([], [[250, 3]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 3, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [4, ['I', 'Object', 'I', 'I', 'F'], []],
    [5, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 3, ['Object'], []], [2]]),
   [[3, ['Object'], []], [6, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [74, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [16, ['I', 'Object'], ['I']],
    [20, ['I', 'Object', 'F'], []],
    [23, ['I'], []],
    [324, ['I'], []],
    [326, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[14], [3]]),
   [[14, ['I', 'Object'], []], [18, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[68, 'Object'], [64, 'I']]),
   [[4, ['I', 'Object'], ['Object']], [5, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 8, 'Object']]),
   [[8, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 4], [251, 0]]), [[4, [], []], [5, [], []]]),
  ('chop more locals than exist', ([], [[250, 4]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 4, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [5, ['I', 'Object', 'I', 'I', 'F'], []],
    [6, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 4, ['Object'], []], [2]]),
   [[4, ['Object'], []], [7, ['Object'], []]])],
 [('regression: every compressed frame kind',
   (['I', 'Object'], [[5], [75, 'I'], [252, 3, 'F'], [249, 2], [251, 300], [255, 1, ['I'], ['Object', 'J']]]),
   [[5, ['I', 'Object'], []],
    [17, ['I', 'Object'], ['I']],
    [21, ['I', 'Object', 'F'], []],
    [24, ['I'], []],
    [325, ['I'], []],
    [327, ['I'], ['Object', 'J']]]),
  ('first frame offset is its delta',
   (['I', 'Object'], [[15], [3]]),
   [[15, ['I', 'Object'], []], [19, ['I', 'Object'], []]]),
  ('same_locals_1_stack_item delta',
   (['I', 'Object'], [[69, 'Object'], [64, 'I']]),
   [[5, ['I', 'Object'], ['Object']], [6, ['I', 'Object'], ['I']]]),
  ('reserved frame type', (['I', 'I', 'J', 'F', 'Object', 'D'], [[1], [246, 0]]), ['ClassFormatError', 1]),
  ('extended one-item frame type',
   (['I', 'Object'], [[247, 9, 'Object']]),
   [[9, ['I', 'Object'], ['Object']]]),
  ('chop three locals', (['I', 'J', 'F'], [[248, 5], [251, 0]]), [[5, [], []], [6, [], []]]),
  ('chop more locals than exist', ([], [[250, 5]]), ['ClassFormatError', 0]),
  ('append three locals then snapshot',
   (['I', 'Object'], [[0], [254, 5, 'I', 'I', 'F'], [0]]),
   [[0, ['I', 'Object'], []],
    [6, ['I', 'Object', 'I', 'I', 'F'], []],
    [7, ['I', 'Object', 'I', 'I', 'F'], []]]),
  ('control: full frame replaces locals',
   (['I', 'Object'], [[255, 5, ['Object'], []], [2]]),
   [[5, ['Object'], []], [8, ['Object'], []]])]]
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: every compressed frame kind	`[[5, ['I', 'Object'], []], [13, ['I', 'Object'], ['I']], [17, ['I', 'Object', 'F'], []], [20, ['I'], []], [321, ['I'], []], [323, ['I'], ['Object', 'J']]]`	`[[5, ['I', 'Object'], []], [13, ['I', 'Object'], ['I']], [17, ['I', 'Object', 'F'], []], [20, ['I'], []], [321, ['I'], []], [323, ['I'], ['Object', 'J']]]`	Passed
first frame offset is its delta	`[[11, ['I', 'Object'], []], [15, ['I', 'Object'], []]]`	`[[11, ['I', 'Object'], []], [15, ['I', 'Object'], []]]`	Passed
same_locals_1_stack_item delta	`[[1, ['I', 'Object'], ['Object']], [2, ['I', 'Object'], ['I']]]`	`[[1, ['I', 'Object'], ['Object']], [2, ['I', 'Object'], ['I']]]`	Passed
reserved frame type	`['ClassFormatError', 1]`	`['ClassFormatError', 1]`	Passed
extended one-item frame type	`[[5, ['I', 'Object'], ['Object']]]`	`[[5, ['I', 'Object'], ['Object']]]`	Passed
chop three locals	`[[1, [], []], [2, [], []]]`	`[[1, [], []], [2, [], []]]`	Passed
chop more locals than exist	`['ClassFormatError', 0]`	`['ClassFormatError', 0]`	Passed
append three locals then snapshot	`[[0, ['I', 'Object'], []], [2, ['I', 'Object', 'I', 'I', 'F'], []], [3, ['I', 'Object', 'I', 'I', 'F'], []]]`	`[[0, ['I', 'Object'], []], [2, ['I', 'Object', 'I', 'I', 'F'], []], [3, ['I', 'Object', 'I', 'I', 'F'], []]]`	Passed
control: full frame replaces locals	`[[1, ['Object'], []], [4, ['Object'], []]]`	`[[1, ['Object'], []], [4, ['Object'], []]]`	Passed

SHA-256 / a1e4f2597be70b86de5251cdab6fe6ae3a4f73edc84db53cdecc2e859bfe058a

Verification & scope

A deterministic, bounded teaching model of one bytecode virtual machine mechanism with a stipulated instruction encoding; it is not a production VM and claims no conformance to any real specification. 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 2026-09-29T14:51:25.678675+00:00.

Case digest / 8ae4805c6d8f2bec735402304aba1f5e2d842ee4ddbbb17899139b76f3f96f76