Re: [Xen-devel] Starting to port xen on beagleboard-x15 (GSoC 2019 project)

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 6/19/19 10:51 PM, Denis Obrezkov wrote:
> Hi,
>
> On 6/19/19 5:32 PM, Julien Grall wrote:
> > Hi,
> >
> > On 19/06/2019 16:27, Andrii Anisov wrote:
> > > On 19.06.19 18:06, Julien Grall wrote:
> > > > Lastly, please clean-up the code and send the patch on xen-devel. I
> > > > will have a closer look at that time. Feel free to ping me on IRC if
> > > > you have any doubt how to proceed.
> > > About the code: I think omap5_init_secondary() must be moved to the
> > > platform code (omap5.c).
> > Well omap5.c is C code... You can't call C in the boot process at least
> > until the MMU is on and we fully setup the processor.
> I don't understand this since init_secondary is installed in C code,
> isn't it? (in omap5.c:omap5_smp_init())
init_secondary is installed by the boot CPU. But init_secondary is
executed on the secondary CPU.

You can't execute C code that early for a few reasons:
   1) You don't know the state of the registers. So you need to set 
them up in a sane state.
   2) Xen is compiled position depend so far. This means some of the C 
code use hardcoded address to access data or jump to other function. The 
hardcoded address are virtual. In most of the cases, Xen will not be 
loaded at at virtual address == physical address. So you need to setup 
the MMU first.
Cheers,

--
Julien Grall

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