fix(cpu): decode wide extend-and-add (UXTAH/UXTAB/SXTAH/SXTAB)#331
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Follow-up to the wide register-extend decode: that change only handled the
plain extends (Rn=0xF). The extend-and-add variants {S,U}XTA{B,H}.W
(Rn != 0xF, e.g. UXTAH = 0xFA1n) still fell through to Unknown32 and were
skipped, leaving the destination register stale.
clang emits `uxtah r6, r3, r0` (FA13 F680) for `4 + (val & 0xFFFF)` — a udslib
RequestFileTransfer (0x38) handler uses exactly this for its `4 + path_len`
length check. With the insn skipped, r6 kept a stale value and the check
wrongly rejected valid requests (NRC 0x13). Broadens the decode to the whole
extend family and adds Rn to the executor (add Rn when Rn != 0xF). Adds a
UXTAH regression case; full labwired-core lib suite green (1342).
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Summary
Follow-up to the wide register-extend decode. That change covered only the
plain extends (
{S,U}XT{B,H}.W,Rn=0xF). The extend-and-add variants{S,U}XTA{B,H}.W(Rn != 0xF, e.g.UXTAH=0xFA1n) still fell through toUnknown32and were silently skipped, leaving the destination register stale.clang emits
uxtah r6, r3, r0(FA13 F680) for4 + (val & 0xFFFF). A udslibRequestFileTransfer(0x38) handler uses exactly this for its4 + path_lenlength check — with the instruction skipped,
r6kept a stale value and thecheck wrongly rejected valid requests (NRC
0x13). (A debugprintf"fixed"it by perturbing register allocation — the tell that this was an emulator
instruction gap, not firmware.)
Fix
Broaden the wide-extend decode to the whole family (
0xFA00..0xFA5F), captureRn, and in the executor addRnwhenRn != 0xF(the extend-and-add form).Test
Adds a
UXTAHcase (extend-and-add with a stale-register overwrite check) tothe wide-extend regression test. Full
labwired-corelib suite green (1399).