[Xen-devel] Re: [PATCH 04/10] i386: clean up bzImage generation

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

H. Peter Anvin wrote:
> Jeremy Fitzhardinge wrote:
>   
>> H. Peter Anvin wrote:
>>     
>>> Jeremy Fitzhardinge wrote:
>>>   
>>>       
>>>> -setup_move_size: .word  0x8000            # size to move, when setup is 
>>>> not
>>>> +setup_move_size: .word  _setup_size       # size to move, when setup is 
>>>> not
>>>>                                    # loaded at 0x90000. We will move setup
>>>>                                    # to 0x90000 then just before jumping
>>>>                                    # into the kernel. However, only the
>>>>     
>>>>         
>>> This is WRONG and will break 2.00 protocol bootloaders, if any still
>>> exist, and quite possibly some 2.01 protocol bootloaders.  There are
>>> definitiely bootloaders in the field that rely on this implicit value.   
>>>       
>> Ah, I see.  I didn't see any documentation saying that this must be
>> 0x8000.  Or does _setup_size just have to be <= 0x8000?
>>
>>     
>
> The default for unaware bootloaders has been 0x8000 since the boot
> protocol was created, and bootloaders are known to (improperly) rely on
> it.  _setup_size does have to be <= 0x8000, but that's another issue.
>   

Hm, so the worst that could happen is that an old bootloader will
over-copy 0x8000 bytes rather than the specified amount?  How would that
break anything?

> I said it probably wouldn't hurt to drop it.  I don't believe you ever
> actually explained why you wanted it dropped.

Well, I don't specifically care for Xen; I don't really mind either way
in general.  I'll break it into a separate patch and we can handle it
that way.

    J

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