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

["H. Peter Anvin" <hpa@xxxxxxxxx>]

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.

>>> @@ -246,7 +246,6 @@ setup2:
>>>     jnz     1f
>>>     movw    $0xfffc, %sp    # Make sure we're not zero
>>>  1: movzwl  %sp, %esp       # Clear upper half of %esp
>>> -   sti
>>>     
>> Motivation, please?
>>   
> 
> We talked about this, and you said it was a mistake.  It needn't be in
> this patch; it could be separate, or just dropped as far as I'm concerned.
> 

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

        -hpa

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