Re: [Xen-devel] [RFC v1 4/8] x86/init: add linker table support

["Luis R. Rodriguez" <mcgrof@xxxxxxxxxxxxxxxx>]

On Thu, Jan 21, 2016 at 11:50 AM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>> The PV init code would kick in early and could parse the
>> boot_params.hdr.hardware_subarch_data pointer as it sees fit.
>>
>
> Right... we already do that.
>
> I don't even think you need to initialize any tables.

The init above is for the sorting. Its not needed unless your
subsystem uses it, its the same sort as with the IOMMU stuff only with
stronger semantics. In theory one would *not* need to do this so
early, it could wait, provided you at least are confident the linker
order suffices for all routines called early. To be clear, the struct
proposed defines a set of callbacks for calling feature's callbacks at
different levels of the x86 init path. As this patch series is
concerned it had one for x86_64_start_reservations(). This could
easily be extended to also include one to be called for instance at
setup_arch(). If we were able to solve the ability to make use of
subarch so early as of we could then have a callback for
x86_64_start_kernel(), then one at x86_64_start_reservations() and
perhaps one at setup_arch() later -- Kasan is an example that could
fit this example in the future. What I mean is that we could avoid the
sort or wait for the run time sort later until
x86_64_start_reservations() or even setup_arch() provided the deafult
linker order suffices for the series of previous callbacks. Its up to
us but I'm taken care to be pedantic about semantics here.

> At least on i386,
> we have to do this in assembly code.

Neat! How is that order kept?

> However, it is just a simple table walk.  :)

 Luis

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