[RFC PATCH 7/8] ARM: vmlinux.lds: Setup physical load address not virtual

[Michal Simek]

2012/6/18 Nicolas Pitre <nicolas.pitre at linaro.org>

> On Mon, 18 Jun 2012, Michal Simek wrote:
>
> > On 06/18/2012 09:02 PM, Nicolas Pitre wrote:
> > > On Mon, 18 Jun 2012, Michal Simek wrote:
> > >
> > > > 2012/6/18 Nicolas Pitre<nicolas.pitre at linaro.org>
> > > >
> > > > > On Mon, 18 Jun 2012, Michal Simek wrote:
> > > > >
> > > > > > Setup correct virtual and physical address in ELF LOAD section.
> > > > >
> > > > > We are moving to a single kernel binary for multiple targets,
> including
> > > > > targets with different physical load addresses.  The kernel code
> figures
> > > > > out at run time what the actual physical address is when
> > > > > CONFIG_ARM_PATCH_PHYS_VIRT is set which is the default these days.
>  In
> > > > > other words, we don't know the physical offset at build time in
> that
> > > > > case and CONFIG_PHYS_OFFSET is simply not defined.
> > > > >
> > > >
> > > > ok. good to know and nice features. In that case I expect that you
> are
> > > > using any binary format and you copy it to memory and run it. Code
> > > > find out where it runs and based on that setup things.
> > >
> > > Exact.
> >
> > ok. One more question about this feature. What is the alignment for
> > it? I mean I have done the similar feature for Xilinx ppc440 and
> > alignment depends on MMU TLB size.
>
> Currently the alignment is 16MB as this is the granularity that a single
> add or sub instruction can cover with an immediate argument.  This is
> highly specific to the ARM instruction set.  At some point we needed 2MB
> alignment which required two adds or subs, but that requirement has now
> been removed.
>

ok.


>
> > > If you want to use the ELF image, then you need to hardcode the
> physical
> > > memory location in its header, and that's something we want to get away
> > > from because it prevents a single kernel binary image from being used
> on
> > > different targets with different memory layouts.  Same issue with
> > > u-Boot's legacy uImage format.
> >
> > And are you able to get these information away from ELF? Or you just
> > need to set it up to any default value. I would expect to 0x0.
>
> We just don't use the ELF image format with bootloaders.
>


ok


>
> > > > I haven't played with CONFIG_ARM_PATCH_PHYS_VIRT option but what is
> elf
> > > > entry point for this case?
> > >
> > > For the kernel image itself it is the kernel virtual address.
> >
> > Is it used somewhere? Or is it just setup to virtual address and no
> > code use it? I mean that kernel virtual entry point.
>
> Nothing uses it.  The official ARM kernel image format is a binary image
> and its entry point is the very beginning of it.
>

ok.


>
> > I expect that if CONFIG_ARM_PATCH_PHYS_VIRT=y then CONFIG_PHYS_OFFSET
> > is not setup Then LOAD_OFFSET should be equal to CONFIG_PAGE_OFFSET.
>
> No. CONFIG_PAGE_OFFSET is the virtual address that the kernel uses for
> the beginning of its memory view.  That is not where the kernel is
> loaded.
>
>
ok. Correct. For ARM_PATCH_PHYS_VIRT default value should be used.

Thanks,
Michal
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