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

[Heinrich Schuchardt]

On 1/9/21 10:23 PM, Tom Rini wrote:
> 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.
>>>>>
>>>>> 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 Is it for some outdated Linux release?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.
>

There is nothing in the include/configs/ti_armv7_common.h comments
requiring to relocate initrd.

Best regards

Heinrich