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

[Stefan Hajnoczi <stefanha@redhat.com>]

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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.

GNU bfd implements it as follows:

  abfd->start_address += (HEX4 (buf) << 4) + HEX4 (buf + 4);

https://sourceware.org/git/?p=binutils.git;a=blob;f=bfd/ihex.c;h=09f756a1c2c11e57c5da15a6ff96491275575b86;hb=HEAD#l415

Thanks for commenting on this, I had written (CS << 4) | IP instead of
(CS << 4) + IP.  This will be fixed in the next revision.

> This is different for the consumer (i386 expects 2 16-bit registers but
> HexParser->start_addr is a hwaddr, used as a single (at least) 32-bit
> register.

I think you're saying that on x86 the guest CS:IP registers should be
set.  This loader is never called from hw/i386/ so it doesn't matter at
this time.

GNU bfd uses START_SEG_ADDR_RECORD records on non-x86 architectures
where there are no segment registers and that's where we've encountered
them.

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