Hi Avi Kivity:
> EFLAGS.ZF needs to be checked after each iteration, not before.
>
> Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
> ---
> arch/x86/kvm/emulate.c | 38 ++++++++++++++++++--------------------
> 1 files changed, 18 insertions(+), 20 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 729853a..d15a746 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -2782,28 +2782,10 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
> ctxt->restart = true;
> /* All REP prefixes have the same first termination condition */
> if (address_mask(c, c->regs[VCPU_REGS_RCX]) == 0) {
> - string_done:
> ctxt->restart = false;
> ctxt->eip = c->eip;
> goto done;
> }
> - /* The second termination condition only applies for REPE
> - * and REPNE. Test if the repeat string operation prefix is
> - * REPE/REPZ or REPNE/REPNZ and if it's the case it tests the
> - * corresponding termination condition according to:
> - * - if REPE/REPZ and ZF = 0 then done
> - * - if REPNE/REPNZ and ZF = 1 then done
> - */
> - if ((c->b == 0xa6) || (c->b == 0xa7) ||
> - (c->b == 0xae) || (c->b == 0xaf)) {
> - if ((c->rep_prefix == REPE_PREFIX) &&
> - ((ctxt->eflags & EFLG_ZF) == 0))
> - goto string_done;
> - if ((c->rep_prefix == REPNE_PREFIX) &&
> - ((ctxt->eflags & EFLG_ZF) == EFLG_ZF))
> - goto string_done;
> - }
> - c->eip = ctxt->eip;
>
It seems that you cannot remove the above line, the assign for eip is need.
remove it will break FreeDOS livecd. Not sure why need this.
> }
>
> if ((c->src.type == OP_MEM) && !(c->d & NoAccess)) {
> @@ -3230,13 +3212,29 @@ writeback:
> if (c->rep_prefix && (c->d & String)) {
> struct read_cache *rc = &ctxt->decode.io_read;
> register_address_increment(c, &c->regs[VCPU_REGS_RCX], -1);
> + /* The second termination condition only applies for REPE
> + * and REPNE. Test if the repeat string operation prefix is
> + * REPE/REPZ or REPNE/REPNZ and if it's the case it tests the
> + * corresponding termination condition according to:
> + * - if REPE/REPZ and ZF = 0 then done
> + * - if REPNE/REPNZ and ZF = 1 then done
> + */
> + if (((c->b == 0xa6) || (c->b == 0xa7) ||
> + (c->b == 0xae) || (c->b == 0xaf))
> + && (((c->rep_prefix == REPE_PREFIX) &&
> + ((ctxt->eflags & EFLG_ZF) == 0))
> + || ((c->rep_prefix == REPNE_PREFIX) &&
> + ((ctxt->eflags & EFLG_ZF) == EFLG_ZF))))
> + ctxt->restart = false;
> /*
> * Re-enter guest when pio read ahead buffer is empty or,
> * if it is not used, after each 1024 iteration.
> */
> - if ((rc->end == 0 && !(c->regs[VCPU_REGS_RCX] & 0x3ff)) ||
> - (rc->end != 0 && rc->end == rc->pos))
> + else if ((rc->end == 0 && !(c->regs[VCPU_REGS_RCX] & 0x3ff)) ||
> + (rc->end != 0 && rc->end == rc->pos)) {
> ctxt->restart = false;
> + c->eip = ctxt->eip;
> + }
> }
> /*
> * reset read cache here in case string instruction is restared
>
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