Eric W. Biederman wrote:
> Jeremy Fitzhardinge <[email protected]> writes:
>
>
>> When the paravirt dispatcher gets run immediately on entry to
>> startup_32, the bss isn't cleared. This happens to work if the
>> hypervisor's domain builder loaded the complete kernel image and
>> cleared the bss for us, but this may not always be true (for example,
>> if we're running out of a decompressed bzImage).
>>
>> Change head.S so that it unconditionally clears the bss before doing
>> the paravirt dispatch or continuing on to normal native boot.
>>
>> There are a couple of points to note:
>> - We can't, in general, load the segment registers before paravirt
>> dispatch, because we could be running with a non-standard gdt and
>> segment selectors. In practice though, all code which ends up
>> jumping into startup_32 will have already set the segment registers
>> up to sane values, so we don't need to do it again.
>> - Paging may or may not be enabled, and if enabled we may or may not
>> be mapped to the proper kernel virtual address. To deal with this,
>> we compare the kernel's linked address with where we're actually
>> running, and use that to offset the bss pointer.
>>
BTW, I should have marked this as an RFC comment, rather than an actual
submission. We don't need it for .22.
> NAK.
>
> Skipping the segment register load is likely fine.
> Supporting V!=P at startup_32 is not.
>
Why?
> Assuming that we have a stack at startup_32 is not.
>
> If you want to figure out where the kernel is loaded you can do
> (from arch/i386/boot/head.S)
>
Yes, that's more or less the same code, aside from using 0x40(%esi) as a
stack. Would that be OK here?
J
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