FA-90323 / Bytecode virtual machines / Member archive

Stack map frames: extended one-item frame rejected as reserved · case 03

Methods using frame type 247 fail verification.

Member previewVariant 3 · 3 implementations · 9 checks per implementation

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.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
extended one-item frame type	`["ClassFormatError", 0]`	`[[7, ["I", "Object"], ["Object"]]]`	Failed

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