Zeroing Unused Memory in U-Boot

[Simon Glass]

Hi Friedrich,

On Thu, 7 Nov 2024 at 14:53, Friedrich Doku
<friedrichdoku2030 at u.northwestern.edu> wrote:
>
> Hi,
>
> I hope this email finds you well. I am currently working on a project
> involving U-Boot, and I have a question regarding memory management.
> Specifically, I would like to understand the best approach to zero all
> memory that is not currently in use.
>
> I am considering using memset to achieve this, but I am unsure about the
> most efficient and safe way to determine which regions of memory are not in
> use and can be safely zeroed out. Could you please provide guidance on:
>
> 1. Identifying unused memory regions in U-Boot during runtime.
> 2. Using memset or any other recommended method to zero these regions
> without interfering with critical data structures or operational stability.
> 3. Any potential risks or best practices I should be aware of when
> performing such operations in U-Boot.
>
> I would greatly appreciate any insights, examples, or documentation you
> could share on this topic. Thank you for your time and for all the
> incredible work you do to maintain and enhance U-Boot.
>
> Looking forward to your response.

After relocation, before images are loaded, you can zero from the
start of memory to the bottom of the U-Boot stack. The 'meminfo'
command[1] shows this mapping.

Unfortunately a recent change has make the EFI_LOADER use memory
outside the U-Boot region. I am still hoping we can correct this
design error before it causes too many problems. For now you can
disable CONFIG_EFI_LOADER to avoid this, so long as you don't need to
load/run EFI apps.

Regards,
Simon

[1] https://docs.u-boot.org/en/latest/usage/cmd/meminfo.html