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

[Paolo Bonzini]

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.

Paolo