Re: [Qemu-devel] [PATCH 2/4] multiboot: load any machine type of ELF

[Anatol Pomozov]

Hi

On Mon, Jan 15, 2018 at 6:52 AM, Kevin Wolf <address@hidden> wrote:
> Am 16.10.2017 um 20:38 hat Anatol Pomozov geschrieben:
>> Hi
>>
>> On Mon, Oct 16, 2017 at 1:27 AM, Kevin Wolf <address@hidden> wrote:
>> > Am 14.10.2017 um 15:41 hat Peter Maydell geschrieben:
>> >> On 14 October 2017 at 00:21, Eduardo Habkost <address@hidden> wrote:
>> >> > I don't believe the spec restricts that, but I don't see why it
>> >> > would be useful to load an ELF file that doesn't match the target
>> >> > architecture (e.g. loading non-x86 ELF files on a x86 machine
>> >> > like PC).
>>
>> I see what do you mean Eduardo. Yes it makes sense to restrict ELF to
>> the currently emulated platform.
>>
>> On a second thought adding multiboot support for non x86 needs to go
>> with other changes, e.g. multiboot.c should be moved out of hw/i386 to
>> some platform-independent location. It probably worth to postpone this
>> change until after Qemu gets multiboot2 support that explicitly states
>> MIPS support, thus it will be easier to test this codepath on multiple
>> platforms.
>>
>> So if you don't mind I'll remove this patch from the current patch
>> series and put it into later one.
>
> I can't find a new version of this patch series with this patch dropped.
> Are you still planning to send one?

Yes I dropped it. It belongs to future multiboot refactoring patch series.

> The spec isn't really explicit about it being a requirement, but it does
> say that its target are 32-bit OSes on PCs, and it defines the boot
> state in terms of i386 registers, so it doesn't make sense for non-x86.

>From my reading of multiboot specification it says that boot state is
32-bit. Thus OS image should make sure its entry point is 32bit code.
But specification does not say that ELF should not contain 64bit code.
GRUB project, the reference multiboot implementation, supports 64bit
ELF.

> From my interpretation of the spec, even support for 64-bit ELFs seems
> to be (implicitly) out of spec (there is one place where it even says
> "refer to the i386 ELF documentation for details"), but if GRUB
> implements it...

Yes, GRUB supports it from its early days. One reason why I sent this
patch is to make QEMU multiboot functionality compatible with GRUB. So
the same binary can work in emulator and at real hardware.