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

[Richard Henderson]

On 10/1/22 00:03, Paolo Bonzini wrote:
> 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).

Nice test.  I had an idea this would be the case, so I had already added a helper to 
perform the jump with truncation to the "current code size".  It turned out that I needed 
that in other places too, like rep.

New patch set coming up.


r~