gimli-rs / gimli / 27444837970

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Handle bare S CFI augmentation (#887)

.debug_frame CIEs may use augmentation string "S" as a DWARF signal-frame
marker without the GNU "z" augmentation prefix. The "z" prefix is what
indicates z-style augmentation data, where the CIE and associated FDEs
carry augmentation payloads with a uleb128 length prefix.

Gimli treated any non-empty parsed CIE augmentation as if it used that
z-style format. When parsing an FDE for a bare "S" .debug_frame CIE,
it unconditionally tried to read an FDE augmentation-data length and
failed with UnexpectedEof because no such data exists.

Track whether the CIE augmentation actually used the z-style format,
and only parse FDE augmentation data for z-style augmentations. Bare "S"
still marks the FDE as a signal trampoline without consuming nonexistent
per-FDE augmentation data.

Add a regression test for the .debug_frame bare-S case.

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