Re: tcg: pointer size warning on x32 arch

[Richard Henderson]

On 9/11/21 2:46 PM, Philippe Mathieu-Daudé wrote:
> On 9/11/21 11:06 PM, Philippe Mathieu-Daudé wrote:
> > On 9/11/21 7:50 PM, Michael Tokarev wrote:
> > > Hi.
> > >
> > > The following warning is reported by the C compiler when compiling
> > > tcg code on x32 architecture:
> > >
> > > In file included from ../../tcg/tcg.c:429:
> > > tcg/i386/tcg-target.c.inc: In function ‘tcg_out_movi_int’:
> > > tcg/i386/tcg-target.c.inc:959:30: warning: cast to pointer from integer
> > > of different size [-Wint-to-pointer-cast]
> > >    959 |     diff = tcg_pcrel_diff(s, (const void *)arg) - 7;
> >
> > Likely fixed by:
> >
> > ---
> > diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc
> > index 98d924b91a8..0895f5670a1 100644
> > --- a/tcg/i386/tcg-target.c.inc
> > +++ b/tcg/i386/tcg-target.c.inc
> > @@ -956,7 +956,7 @@ static void tcg_out_movi_int(TCGContext *s, TCGType
> > type,
> >       }
> >
> >       /* Try a 7 byte pc-relative lea before the 10 byte movq.  */
> > -    diff = tcg_pcrel_diff(s, (const void *)arg) - 7;
> > +    diff = tcg_pcrel_diff(s, (const void *)(uintptr_t)arg) - 7;
>
> Hmm not quite. At this point tcg_out_movi_int() already checked 'arg'
> does not fit into a 32-bit value... And on x32 we have sizeof(void*) = 4
> so we can't cast a >32-bit value that way.
>
> But tcg_out_movi_int() is called by tcg_out_movi(), and all 'arg' values
> are either 0, 1 or a host address (often casted as uintptr_t).

That's false -- 'arg' is an arbitrary 64-bit constant here, for x32. But you're right that 
no x32 pointers will arrive here, because TCG_TYPE_PTR == TCG_TYPE_I32 for that case and 
we'll use the 5-byte mov immediate insn.

> +    assert(sizeof(uintptr_t) > sizeof(uint32_t));
> +
>       /* Try a 7 byte pc-relative lea before the 10 byte movq.  */
>       diff = tcg_pcrel_diff(s, (const void *)arg) - 7;
>       if (diff == (int32_t)diff) {

We may need something like

    if (sizeof(void *) == 8) {
        diff = tcg_pcrel_diff(s, (const void *)(uintptr_t)arg) - 7;
        ...
    }

I wonder if I still have an x32 vmm hanging about.


r~