[U-Boot] [PATCH] board_f: save "malloc_base" from zeroing in case of CONFIG_SYS_MALLOC_F_LEN

[Alexey Brodkin]

Hi Albert,

On Tue, 2015-01-20 at 08:07 +0100, Albert ARIBAUD wrote:
> Hello Alexey,
> 
> On Mon, 19 Jan 2015 20:55:03 +0300, Alexey Brodkin
> <Alexey.Brodkin at synopsys.com> wrote:
> > In case of CONFIG_SYS_MALLOC_F_LEN "malloc_base" is used for early
> > start-up code and is set very early, typically in "start.S" or "crt1.S".
> 
> There is no "crt1.S" in U-Boot. Did you mean "crt0.S"?

Indeed I meant "crt0.S"

> > In current implementation in case of CONFIG_SYS_GENERIC_GLOBAL_DATA all
> > global data gets zeroed on "board_init_f" entry. But by that time
> > "malloc_base" could have been set already, which means it will be zeroed
> > and subsequent C-code will be executed improperly (if executed at all -
> > if there's no memory mapped to 0 or it is read-only then on some arches
> > there will be an exception and others will quetly die).
> > 
> > To work-around described situation we just need to make sure
> > "malloc_base" is saved prior zeroing global data and recovered
> > afterwards.
> 
> Keeping data from being zeroed etc is usually done through GD. Could
> malloc_base be placed there instead of creating a specific exemption
> for it?

Unfortunately I didn't understand your suggestion here.
"malloc_base" is already in global data structure.

But the point is global data structure also requires zeroing sometime on
early start-up. This is required to make sure we don't have any garbage
in GD (for example left-overs from lower-level bootloader or previously
executed kernel etc).

So other option is to zero GD earlier in start-up code. This is
essentially doable but it will be done on per-architecture or even
per-CPU basis in their "start.S" - which means we'll have duplication of
the same functionality and maintenance will be difficult then.

Probably I just didn't get you point so then could you please clarify
what did you mean.

-Alexey