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

[Adam Ford]

On Sat, Jan 9, 2021 at 5:23 PM Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> 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.

What about -1?

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 Is it for some outdated Linux release?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