Hi, On Tue, May 05, 2015 at 02:34:38PM +0200, Nicholas Mc Guire wrote: > > Hi ! > > Not sure if this is a bug or maybe a placeholder for > something... so patch - but maybe someone that knows this code can > give it a look. > > arch/mips/kvm/emulate.c:emulation_result kvm_mips_complete_mmio_load() > <snip> > 2414 case 2: > 2415 if (vcpu->mmio_needed == 2) > 2416 *gpr = *(int16_t *) run->mmio.data; > 2417 else > 2418 *gpr = *(int16_t *) run->mmio.data; > 2419 > 2420 break; > <snip> > > either the if/else is not needed or one of the branches is wrong > or it is a place-holder for somethign that did not get > done - in which case a few lines explaining this would be > nice (e.g. like in arch/sh/kernel/traps_64.c line 59) > > line numbers refer to 4.1-rc2 mmio_needed encodes whether the MMIO load is a signed (2) or unsigned (1) load. E.g. the len == 1 case just below casts the pointer to u8 vs int8_t to control sign extension. So it appears the else branch (line 2418 in your quote) should be uint16_t (or u16) to prevent the MMIO value loaded by a lhu (load halfword unsigned) being sign extended to the full width of the registers. Nice catch! Feel free to send a patch to fix. Otherwise I'm happy to do it. Thanks! James
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