[PATCH 1/1] image: usage of value ~0UL for intrd_high

[Tom Rini <trini@konsulko.com>]

On Sat, Jan 09, 2021 at 08:59:01PM +0100, Heinrich Schuchardt wrote:
> Am 9. Januar 2021 20:40:04 MEZ schrieb Tom Rini <trini@konsulko.com>:
> >On Sat, Jan 09, 2021 at 08:33:40PM +0100, Heinrich Schuchardt wrote:
> >> On 1/9/21 7:58 PM, Tom Rini wrote:
> >> > On Sat, Jan 09, 2021 at 08:47:07PM +0200, Andy Shevchenko wrote:
> >> > > On Sat, Jan 9, 2021 at 8:06 PM Heinrich Schuchardt
> ><xypron.glpk@gmx.de> wrote:
> >> > > > 
> >> > > > The comment for initrd_high in the coding and in README were
> >contradicting
> >> > > > and neither fully described what the coding does.
> >> > > > 
> >> > > > Clarify the usage of the special value ~0UL for the environment
> >variable
> >> > > > initrd_high.
> >> > > 
> >> > > All those F:s are hard to read in the comments and documentation
> >and
> >> > > typo prone. I would prefer to rephrase like "all 1:s value in 32-
> >or
> >> > > 64-bit format" or alike.
> >> > 
> >> > If we're going to improve this we should also note it's discouraged
> >> > unless you know for certain there will be no overlap and it's
> >strongly
> >> > discouraged in default environments.
> >> 
> >> What exactly is discouraged?
> >> 
> >> * setting initrd_high to a value != ~0? Here I would agree.
> >> * setting intird_high to ~0? Why should we copy initrd to a
> >>   different place? Is it for some outdated Linux release?
> >
> >We should always default to allowing the initrd to be relocated because
> >we can see (in many cases) overlap that will lead to failure to boot
> >but
> >this forces us to ignore that.  Having good default load values means
> >we
> >don't have a problem here.
> 
> We have an initrd that is already in memory. What could it overlap
> with that is not already overwritten?

Having the kernel and initrd too close in memory has the kernel BSS
overwrite the initrd.  This has happened time and time again before
I went around making some platforms have reasonable (ie kernel early,
ramdisk in lowmem but beyond where a kernel+bss can be, etc) defaults
and pushing others to do the same.

> Can you provide the text you want to see here?

Off-hand, it should look more like the big comment block in
include/configs/ti_armv7_common.h and reference the Linux booting on
arm/arm64 documents while noting that other architectures have the same
fundamental issues and their exact limits may or may not be as well
documented.

-- 
Tom
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