Re: [Qemu-devel] [Qemu-arm] [PATCH v4 5/6] loader: Implement .hex file loader

[Stefan Hajnoczi]

On Wed, Aug 15, 2018 at 3:18 PM Philippe Mathieu-Daudé <address@hidden> wrote:
> On 08/13/2018 12:56 PM, Stefan Hajnoczi wrote:
> > On Fri, Aug 10, 2018 at 02:00:44AM -0300, Philippe Mathieu-Daudé wrote:
> >> On 08/03/2018 11:47 AM, Stefan Hajnoczi wrote:
> >>> +        parser->rom_start_address = parser->next_address_to_write;
> >>> +        parser->current_rom_index = 0;
> >>> +        break;
> >>> +
> >>> +    case START_SEG_ADDR_RECORD:
> >>> +        if (line->byte_count != 4 && line->address != 0) {
> >>> +            return -1;
> >>> +        }
> >>> +
> >>> +        /* x86 16-bit CS:IP segmented addressing */
> >>> +        *(parser->start_addr) = (((line->data[0] << 8) | line->data[1]) 
> >>> << 4) |
> >>> +                                (line->data[2] << 8) | line->data[3];
> >>
> >> Can you add a qtest for this case?
> >> For the HEX loader I understand the specs as this is the same parsing as
> >> the START_LINEAR_ADDR_RECORD case; so I disagree with data[0] and
> >> data[1] shifts.
> >
> > x86 real-mode CS:IP addressing means (CS << 4) + IP.  It produces 24-bit
> > addresses on 80286 and later.  This is not the same as
> > START_LINEAR_ADDR_RECORD.
>
> OK!
>
> >
> > GNU bfd implements it as follows:
> >
> >   abfd->start_address += (HEX4 (buf) << 4) + HEX4 (buf + 4);
>
> Hmm any idea why they use +4 ?

buf is char* and HEX4("0123") produces 0x0123.  So this line evaluates
ASCII hex input buf="XXXXYYYY" to (0xXXXX << 4) + 0xYYYY.