The fault-time SSE4a fallback was Windows-only because the POSIX signal
bridge never carried XMM state: the CONTEXT scratch buffer only held the
17 general-purpose registers, so emulating EXTRQ/INSERTQ there would
have computed results from zeroed bytes and discarded the write. Bridge
the XMM registers on Linux by copying them between the mcontext's
FXSAVE image (kernel sigcontext ABI, libc-independent) and the CONTEXT
FltSave slots on capture and write-back, and gate the recovery on that
bridge instead of on Windows. Darwin still declines: its XMM area
remains unbridged.
With this, guest EXTRQ/INSERTQ on Linux hosts without SSE4a (any Intel
CPU) resumes with correct register state instead of dying on an
unrecovered SIGILL (#328).
Handle immediate EXTRQ and INSERTQ as well as MONITORX and MWAITX when the host raises illegal-instruction faults. Add unit coverage for SSE4a bit-field semantics and preserve existing load-time patching.
Co-authored-by: zocomputer <help@zocomputer.com>
999sian