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

[Heinrich Schuchardt]

Am 9. Januar 2021 22:23:01 MEZ schrieb Tom Rini <trini at 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 at 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 at 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.


Who would understand that? 

All 1s that is 111111111?

We need something a non-developer will grasp. Copying the exact value from the readme is the easiest thing to do and the least typo prone.

Best regards

Heinrich

>> >> > 
>> >> > 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 Is it for some outdated Linux release?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.