On Tue, 05 May 2015, James Hogan wrote: > 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! > thanks for the clarification - will send the patch out shortly. This was found by a trivial coccinelle scanner <snip> virtual context virtual org virtual report @cond@ position p; statement S1; @@ <+... * if@p (...) S1 else S1 ...+> @script:python@ p << cond.p; @@ print "%s:%s WARNING: condition with no effect (if branch == else)" % (p[0].file,p[0].line) <snip>
