Re: [Xen-devel] [PATCH v2] xen/tools: Introduce QNX IFS loader

[Oleksandr Tyshchenko <oleksandr.tyshchenko@xxxxxxxxxxxxxxx>]

Hi Ian

On Mon, Sep 22, 2014 at 4:03 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Fri, 2014-09-19 at 19:45 +0300, Oleksandr Tyshchenko wrote:
>
>> > Is it possible to make QNX position independent?
>> Unfortunately, I was trying but I couldn't make.
>>
>> More detailed:
>> we have base address of the image: [image=0x80008000]
>> startup_vaddr is based on "base address"
>> domainbuilder: detail: xc_dom_probe_qnx_ifs: startup_vaddr: 0x800085bc
>>
>> I dropped base address from IFS buildfile:
>> domainbuilder: detail: xc_dom_probe_qnx_ifs: startup_vaddr: 0x000005bc
>> and tried to do next thing:
>> dom->parms.virt_entry = v_start + startup_hdr->startup_vaddr;
>> But this didn't work. QNX didn't boot.
>
> There's more to making something position independent than just dropping
> the base address, it needs the code in question to be carefully
> written/compiled to be position independent, at least up to the point
> where it controls its own virtual address space mappings.
>
> e.g. Xen on ARM is very careful throughout xen/arch/arm/*/head.S to
> handle this, once we hit C we are running on our page tables and can
> assume a 2MB base address.
>
> I'd not be especially surprised if qnx, which is targeting the embedded
> space, had no support for being built as a position independent binary.
>
> The upshot of that is that I expect you would need to do a bunch of core
> QNX work to make it position independent, or more likely you would
> accept that a given QNX binary may only run on one version of Xen and
> upgrading Xen would have knock on affects on your guest VMs (given your
> market I don't expect you will be upgrading Xen in the field, so perhaps
> you are fine with this).
It is clear. For now, I OK with it. The loader must to throw an error
if QNX IFS has wrong hardcoded address.

>
> Ian.
>



-- 

Oleksandr Tyshchenko | Embedded Dev
GlobalLogic
www.globallogic.com

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