On 01/09/2013 02:05 PM, H. Peter Anvin wrote:
> On 01/09/2013 02:02 PM, Jordan Justen wrote:
>> On Wed, Jan 9, 2013 at 11:12 AM, David Woodhouse <dw...@infradead.org> wrote:
>>> We're supposed to zero everything in the kernel bootparams that we don't
>>> explicitly initialise, other than the setup_header from 0x1f1 onwards
>>> for a precisely defined length, which is copied from the bzImage.
>>>
>>> We're *not* supposed to just pass the garbage that we happened to find
>>> in the bzImage file surrounding the setup_header.
>>
>> In which case might this be garbage? A PE/COFF based image?
>>
>
> For all kernels. For non-EFI-stub kernels there will be a dummy boot
> sector there; there is also garbage *after* the initialized header.
>
>> For non-PE/COFF kernels, will be potentially be zero'ing out valuable
>> config information built into the image?
>>
>
> No.
>
As a clarification: what the spec specifies -- and the 16-bit BIOS stub
built into the kernel implements nowadays -- is to take a 4K long page
of bss memory and zero it, then copy the specific initialized structure
starting at 0x1f1 and with the length given by the byte at 0x201. This
is of course equivalent to copying the first 4K of the file and zeroing
out the head and tail, but it might be more intuitive to think about.
-hpa
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