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Re: [Qemu-devel] [RFC PATCH 2/2] spapr: -kernel: allow linking with spec

From: Andrew Jones
Subject: Re: [Qemu-devel] [RFC PATCH 2/2] spapr: -kernel: allow linking with specified addr
Date: Tue, 21 Jul 2015 09:07:30 +0200
User-agent: Mutt/ (2014-03-12)

On Fri, Jul 17, 2015 at 01:56:40PM +0200, Andrew Jones wrote:
> I've started playing with adding ppc support to kvm-unit-tests,
> using spapr for the machine model. I wanted to link the unit test
> at 0x400000 to match qemu's load address, making the unit test
> startup code simpler, but ended up with 0x800000 instead, due to
> how translate_kernel_address works. The translation makes sense
> for how Linux kernels are linked (always at 0xc0000000 or
> 0xc000000000000000), but for the unit test case we need to avoid
> adding the offset.
> Signed-off-by: Andrew Jones <address@hidden>
> ---
> Big RFC because I don't know if the "always at 0xc..." statement
> is 100% true for Linux, nor if this patch would break other stuff...
>  hw/ppc/spapr.c | 3 +++
>  1 file changed, 3 insertions(+)
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index c1cbf3387ae0c..4f1548f5168db 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -832,6 +832,9 @@ static void spapr_finalize_fdt(sPAPRMachineState *spapr,
>  static uint64_t translate_kernel_address(void *opaque, uint64_t addr)
>  {
> +    if ((addr & 0x0fffffff) == addr) {
> +        return addr;
> +    }
>      return (addr & 0x0fffffff) + KERNEL_LOAD_ADDR;
>  }

OK, while I'm still not sure if this is a bad idea or not, and I do think
it would be nice to give users more control over the kernel's linked VMAs,
I've decided it would probably be harder to prove this patch is safe, than
to add reloc support to kvm-unit-tests/powerpc. So I added the support
yesterday, at least enough for now, and this patch is no longer necessary.


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