Re: [PATCH v2 19/23] target/i386: Use gen_jmp_rel for gen_jcc

[Paolo Bonzini]

On Sat, Oct 1, 2022 at 3:04 AM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 9/21/22 06:09, Paolo Bonzini wrote:
> > On Tue, Sep 6, 2022 at 12:09 PM Richard Henderson
> > <richard.henderson@linaro.org> wrote:
> > > +    gen_jcc1(s, b, l1);
> > > +    gen_jmp_rel(s, ot, 0, 1);
> > > +    gen_set_label(l1);
> > > +    gen_jmp_rel(s, ot, diff, 0);
> >
> > Might be worth a comment that jumps with 16-bit operand size truncate
> > EIP even if the jump is not taken.
>
> Hmm.  But is that correct?  That's not reflected by the pseudocode for Jcc.

No, it's not:

int main() {
        asm("clc; data16 jc 1f; 1:");
}

does not crash (it does with stc) on real hardware, but it does with
this series applied.  So the various occurrences of gen_jmp_rel(s, ot,
0, 1) or gen_jmp_rel(s, MO_32, 0, 1) should stay as gen_jmp_tb(s,
s->pc - s->cs_base, 1).

Paolo