Re: [Qemu-devel] [PULL 18/76] optionrom: add new PVH option rom

[Stefano Garzarella]

On Fri, Mar 19, 2021 at 06:03:59PM +0100, Paolo Bonzini wrote:
> On 19/03/21 15:06, Philippe Mathieu-Daudé wrote:
> > > +
> > > +/* Search RSDP signature. */
> > > +static uintptr_t search_rsdp(uint32_t start_addr, uint32_t end_addr)
> > > +{
> > > +    uint64_t *rsdp_p;
> > > +
> > > +    /* RSDP signature is always on a 16 byte boundary */
> > > +    for (rsdp_p = (uint64_t *)start_addr; rsdp_p < (uint64_t *)end_addr;
> > > +         rsdp_p += 2) {
> > > +        if (*rsdp_p == RSDP_SIGNATURE) {
> > > +            return (uintptr_t)rsdp_p;
> > > +        }
> > > +    }
> > > +
> > > +    return 0;
> > > +}
> > gcc 10.2.1 "cc (Alpine 10.2.1_pre2) 10.2.1 20210313" reports:
> >
> > pc-bios/optionrom/pvh_main.c: In function 'search_rsdp':
> > pc-bios/optionrom/pvh_main.c:61:21: warning: comparison is always false
> > due to limited range of data type [-Wtype-limits]
> >    61 |         if (*rsdp_p == RSDP_SIGNATURE) {
> >       |                     ^~
>
> This is probably a different bug, but I'll also add that uint64_t is 
> supposed to be aligned to 64 bits, so you need either 
> __attribute__((packed)), or use char* and memcmp.  If you go for the 
> latter, it would fix the issue that Philippe is reporting.

Yes, memcmp maybe is also more readable, but being baremetal, I have to 
implement it right?

Thanks,
Stefano