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FA-90311 / Bytecode virtual machines / Open access

Stack map frames: first frame offset shifted by one · case 01

Every frame is attached to the instruction after the one it describes.

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

ROOT CAUSE

The +1 separator is applied to the first frame as well.

VERIFIED REPAIR

Use delta for the first frame and previous + delta + 1 afterwards.

Unsuccessful approach: Dropping the +1 for later frames collapses consecutive frames onto the wrong offsets.

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 - 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 = 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 fixtureActualExpectedOutcome
regression: every compressed frame kind[[6, ['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[[12, ['I', 'Object'], []], [16, ['I', 'Object'], []]][[11, ['I', 'Object'], []], [15, ['I', 'Object'], []]]Failed
same_locals_1_stack_item delta[[2, ['I', 'Object'], ['Object']], [3, ['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[[6, ['I', 'Object'], ['Object']]][[5, ['I', 'Object'], ['Object']]]Failed
chop three locals[[2, [], []], [3, [], []]][[1, [], []], [2, [], []]]Failed
chop more locals than exist['ClassFormatError', 0]['ClassFormatError', 0]Passed
append three locals then snapshot[[1, ['I', 'Object'], []], [3, ['I', 'Object', 'I', 'I', 'F'], []], [4, ['I', 'Object', 'I', 'I', 'F'], []]][[0, ['I', 'Object'], []], [2, ['I', 'Object', 'I', 'I', 'F'], []], [3, ['I', 'Object', 'I', 'I', 'F'], []]]Failed
control: full frame replaces locals[[2, ['Object'], []], [5, ['Object'], []]][[1, ['Object'], []], [4, ['Object'], []]]Failed

SHA-256 / b490c5e6f14b1e85d751f19c43fdac15bd243fd4738c9e1ed7f0d82233a51ace

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 - 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
        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 fixtureActualExpectedOutcome
regression: every compressed frame kind[[5, ['I', 'Object'], []], [12, ['I', 'Object'], ['I']], [15, ['I', 'Object', 'F'], []], [17, ['I'], []], [317, ['I'], []], [318, ['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'], []], [14, ['I', 'Object'], []]][[11, ['I', 'Object'], []], [15, ['I', 'Object'], []]]Failed
same_locals_1_stack_item delta[[1, ['I', 'Object'], ['Object']], [1, ['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, [], []], [1, [], []]][[1, [], []], [2, [], []]]Failed
chop more locals than exist['ClassFormatError', 0]['ClassFormatError', 0]Passed
append three locals then snapshot[[0, ['I', 'Object'], []], [1, ['I', 'Object', 'I', 'I', 'F'], []], [1, ['I', 'Object', 'I', 'I', 'F'], []]][[0, ['I', 'Object'], []], [2, ['I', 'Object', 'I', 'I', 'F'], []], [3, ['I', 'Object', 'I', 'I', 'F'], []]]Failed
control: full frame replaces locals[[1, ['Object'], []], [3, ['Object'], []]][[1, ['Object'], []], [4, ['Object'], []]]Failed

SHA-256 / ae52960b83fb699083b689894231d910008d0f4486e4a0257c591d4883f841b0

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 fixtureActualExpectedOutcome
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 2026-09-29T14:51:25.501821+00:00.

Case digest / 0b7a0950d34771e8e7884e917b79afa5845a37618b53fe6ff0670106234fd721